Literature Review
Introduction
Water temperature and pH are key abiotic factors in freshwater environments,
governing the distribution, behaviour and possibly abundance of the
organisms within them (Brönmark and Hansson, 2005). They fluctuate on
both temporal and spatial scales with the degree of fluctuation dependant on
several criteria including the size and depth of the water body, the speed of its
flow (Maitland, 1990) and seasonality (Berezina, 2001). Water temperature is
also inextricably linked with seasonal change. In lakes, the strength and depth
of solar penetration and wind generated currents regulate temperature. Most
lakes with an average depth of over approximately 3 metres exhibit thermal
stratification during winter and summer (Dobson and Frid, 1998). In shallower
lakes and around the littoral zones, thermal stratification does not necessarily
occur, as solar radiation penetrates through the water column and reaches
the lake floor, provided the water column is not overly turbid (ibid.); however
there is obviously still seasonal difference in water temperature. Freshwater
invertebrates are poikilothermic and therefore their internal temperature is
governed by the surrounding water temperature. As water temperature
fluctuates, enzyme activity involved in vital physiological functions will be
compromised either side of the optimal temperature (Campbell and Reece,
2002). Therefore, those with a wider temperature range (eurytherms) may be
present all year round whilst those with a narrower temperature range
(stenotherms) may be absent at the more extreme seasonal temperature
shifts (Brönmark and Hansson, 2005). Another factor to bear in mind, which is
affected by changes in water temperature, is oxygen concentration; the
capacity of water to hold oxygen decreases as temperature increases (ibid.).
Many complex interactions exist between numerous abiotic and biotic
components of a freshwater system (Macan and Worthington, 1974) but this
study is focused on water temperature and pH. It is acknowledged that other
water chemistry, such as oxygen, carbon dioxide and nutrient levels interplay
with water temperature and pH in defining the community structure of a
freshwater ecosystem, but these other factors are beyond the scope of this
study.
1
Water pH fluctuates both diurnally and seasonally, heavily influenced by the
photosynthesis and respiration of aquatic organisms and therefore, the
vegetated shallow, littoral edges of lakes are more prone to pH fluctuation
than deeper water (Brönmark and Hansson, 2005). The majority of lakes
worldwide have a pH value of between 6.0 and 9.0 and although originally
governed by the surrounding geology, water pH can be altered by high plant
productivity, high precipitation and the addition of acidifying material (ibid.;
Camargo and Alonso, 2006). High plant productivity can be caused by
nutrient enrichment from sources such as agricultural runoff and sewage
diffusion (Maitland and Morgan, 1997). The increase in the rate of
photosynthesis elevates pH by decreasing the amount of H+ ions and CO2 in
the water (Brönmark and Hansson, 2005). High precipitation can serve to
‘dilute’ the effects of high productivity by increasing through-flow in systems
with an inflow and outflow. However, in areas of high industrialisation, high
precipitation may have an acidifying effect on the pH of a freshwater system
(Maitland and Morgan, 1997). As with water temperature, pH fluctuation has
an effect on the physiological processes of an organism, as enzyme function
has a specific optimum pH level too. The more the surrounding water pH
differs from the pH of the cell plasma, the more detrimental the change is on
the organism (Lampert and Sommer, 1997).
Effects on freshwater organisms
Relatively few studies exist on the effects of seasonal change in water
temperature on the invertebrate community of a freshwater lake. This may be
because seasonal change in water temperature is relatively predictable in
temperate regions and the effects of it are well known (MacArthur and Baillie,
1929; Macan, 1974; Macan and Worthington, 1974). Water temperature
fluctuation appears more frequently in studies concerned with the effects of
climate change on freshwater communities, which is not the basis of the
present study. Water pH fluctuation, however, can be less predictable and
there is a greater body of work available on its effects on the invertebrate
community and the structure of freshwater ecosystems in general. Studies
carried out on the effects of fluctuation in water temperature and pH, range
2
from individual species to the community as a whole and from a variety of lotic
(running) and lentic (standing) freshwater habitats ranging from springs and
rivers to vast lakes. Their effects on macrophytes and fish are briefly
considered here to provide a wider context, as all the components of
freshwater systems ultimately influence one another, affecting both plant and
animal.
Macrophytes are the basis of any freshwater community, being the primary
producers. In shallow lakes, their populations are affected by, amongst other
things, algal blooms caused by certain species of phytoplankton and pH
fluctuation. Under the right conditions, algal blooms occur in nutrient-rich,
eutrophic freshwater and their biomass can increase turbidity which reduces
the ability of submerged macrophytes to photosynthesise. In addition, the
increase in photosynthetic activity by the phytoplankton causes a rise in the
water pH, which further exacerbates the problems for macrophytes and other
aquatic organisms (Sand-Jensen and Borum, 1990; Scheffer et al., 1993).
Balls et al. (1989) acknowledge that in shallow eutrophic lakes, submerged
macrophyte populations can be replaced by dense phytoplankton blooms and
that this can, in turn, increase pH. To further investigate this process they set
up an experiment in the shallow lakes of the Norfolk Broads. They found that,
with the addition of extra nutrients, phytoplankton biomass did not increase to
predicted levels if the submerged macrophyte communities were fully intact.
This may be because phytoplankton biomass is nutrient limited (Sand-Jensen
and Borum, 1990) so if dense macrophyte beds were present they could act
as a sink thereby limiting the availability of nutrients for an algal bloom to
occur. The focus of the present study is an area that has suffered losses to its
macrophyte populations.
Rooney and Kalff (2000) compared inter-annual temperature fluctuations in
their study of macrophyte biomass and distribution in Quebec, Canada.
Temperatures in 1998 were generally warmer than in 1997 and this was
shown to have an impact on the macrophyte communities with an average
74% increase in macrophyte cover. The warmer temperatures allowed
establishment of macrophyte populations earlier in the season and at a
3
greater depth than in the previous, cooler year. Barko et al. (1982) also report
that increasing temperature, up to 28°C, leads to an increase in macrophyte
biomass. However, Rooney and Kalff (2000) noted a positive relationship
between macrophyte and phytoplankton populations which appears to
contradict the general consensus. This is explained by a difference in lake
depth, the former study being of a shallow lake and the latter of deeper lakes.
The relationship between phytoplankton and macrophytes can vary under
different circumstances (Beklio lu and Moss, 1996). Various species of
phytoplankton respond in different ways to elevated temperature and pH
(Alam et al., 2001) and not all cause blooms detrimental to macrophytes.
Indeed, some phytoplankton are controlled by high macrophyte biomass
(Fitzgerald, 1969).
Macrophyte populations can have a direct impact on the invertebrate fauna.
McKee et al. (2003), state that increasing macrophyte biomass generally
precedes an increase in invertebrate biomass and diversity. This is supported
by Schriver et al. (1995) who found a low zooplankton biomass was
associated with an absence of macrophytes. This is proposed to be due to
macrophytes offering refugia to invertebrates from predation. Therefore a loss
of macroinvertebrate diversity should follow if a significant reduction in the
macrophyte population occurs, whether it is as a result of an algal bloom
increasing turbidity or the associated rise in pH.
At the other end of the trophic scale are fish, generally considered a
secondary consumer in freshwater communities. Fish predate a variety of
invertebrate species and so a change in abundance or distribution of fish
species could have an impact on the macroinvertebrate community structure.
Serafy and Harrell (1993) mention a number of laboratory based studies that
show fish begin to avoid areas once the pH reaches 9.0 and in their own
laboratory based investigation, avoidance occurred at pH 9.5. However, under
circumstances where pH was elevated naturally by photosynthesis in dense
macrophyte beds and dissolved oxygen was high, fish did not avoid these
areas of elevated pH nor did they necessarily seek out areas of a lower pH. In
Slapton Ley, the same lake in which the present study was undertaken, Scott
4
et al. (2005) examined the effects of elevated pH on perch (Perca fluvatilis),
pike (Esox lucius) and roach (Rutilus rutilus). Behaviourally, they found that
the fish did not move to areas of lower pH, although available. There
appeared to be a predation risk associated with moving to these areas,
offering an explanation as to why they would choose to remain in an area
despite it being physiologically stressful. Therefore, an organism may risk
‘waiting-out’ the period of elevated pH in a trade-off between physiological
stress and reducing predation risk or remaining in an area with plentiful
resources.
At the interface between the previous two trophic groups are the
invertebrates. Friday (1987) shows that invertebrate diversity in ponds
increases with pH increase (Fig. 1) but this only considers the limited range of
pH 3.8 to pH 7.5. Similarly, Townsend et al. (1983) note that the number of
invertebrate species in streams increases alongside increasing pH but this is
again only looking at a limited range of pH 3.8 to pH 7.8. It would appear that
a movement towards an alkaline pH supports a greater diversity of freshwater
invertebrate fauna than an acid pH (Collier and Winterbourn, 1987) but is
there a point at which the increase in pH becomes prohibitive?
100
90
Invertebrate taxa
Number of taxa
80
70
60
50
40
30
20
10
0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
pH
Figure 1. Data on the macroinvertebrate taxa from 16 ponds in the Isle of Purbeck, Dorset;
with trend line. (Friday, 1987).
5
Crustacea feature as the focus for many studies, particularly Cladocera and
Copepoda. Beklio lu and Moss (1995) comment on previous studies that
show high pH to be detrimental to certain Cladocera species. Their own study
concurred showing a decrease in numbers of Polyphemus pediculus,
Bosmina longirostris, Ceriodaphnia spp. and also Cyclops spp. at elevated pH
levels. The crucial pH in their study of a shallow, eutrophic lake in Cheshire
was pH 11.0; Daphnia hyalina actually increased in numbers at pH 10.0 but
numbers collapsed on reaching pH 11.0. In a study of eight small (approx.
0.10ha) nutrient enriched ponds in New York State, O’Brien and De Noyelles
(1972) showed a direct link between increased pH and the decline of
Ceriodaphnia reticulate in ponds, most markedly between pH 10.5 and pH
11.0. The high pH was attributed to the primary productivity of high levels of
phytoplankton. Hansen et al. (1991), again with Cladocera and Copepoda
species, observed significant decreases in the abundance of Daphnia
longispina, Bosmina longirostris and Chydorus sphaericus upon reaching pH
10.6 in enclosures in Lake Søbygård, Denmark. However, once the pH
dropped below 10.5, D. longispina began to increase in abundance. Three
species though, Daphnia magna and two Cyclops species, showed no signs
of being adversely affected. It would appear that the threshold for these
particular Crustacea invertebrates is between pH 10.5 and pH 11.0.
Monitoring of the effects of seasonal change on the Crustacean community of
an alkaline lake in Iceland (Ingvason et al, 2003) showed wide variation in
densities which closely followed seasonal water temperature fluctuation.
During summer when water temperature reached a maximum of 16°C,
crustacean density was at its highest whilst during the winter months when
maximum water temperature was 4°C, densities dropped considerably. Also,
during the growth period of May to September, pH was at its highest; over pH
9.0. As this high pH coincides with the period of highest density, it would
suggest the crustaceans present have a tolerance to high pH.
Under experimental conditions, Berezina (2001) found that a pH of between
4.09 and 8.65 supported the highest general invertebrate species diversity;
diversity decreased both above pH 9.0 and below pH 4.0. At pH 4.0 to 5.0,
Mollusca diversity dropped and Oligochaetes (worms) were absent. Below pH
6
4.0, communities were only formed by a few insect species and within this
group, the Chironomidae (non-biting midge larvae) were the most tolerant of
changes in pH. This latter observation is supported by Collier and
Winterbourn (1987), whose study of the faunal and chemical dynamics in both
acid and alkaline streams in New Zealand, found Chironomidae dominated
the benthic fauna at most sites, regardless of pH. Both water temperature and
pH tolerance were examined in the hatching and survival of the water mite
Unionicola foili (Edwards, 2004). Eggs, larvae and adults were exposed to
four pH levels (pH 4.1, 5.2, 7.0 and 7.8) and three different temperatures
(25°C, 33°C and 38°C); larvae survival was significantly reduced at pH 5.2
and adults suffered a higher mortality at pH 4.1. At 33°C, survivorship of the
larvae was significantly reduced and adults showed increasing mortality with
increasing temperature. The eggs were unaffected at all levels of pH and
temperature. These temperatures are however in excess of anything likely to
be experienced in temperate freshwaters. In his qualitative paper on the
habitats of freshwater Molluscs in Britain, Boycott (1936) states that Molluscs
tend to be absent from acidic water with a pH of less than 6.0 but he observed
a concomitant rise in diversity as pH increases up to approximately pH 8.5.
This would appear reasonable as a low pH would damage a calcium based
shell.
Seasonal change in water temperature probably has the most profound effect
on insect macroinvertebrates as it is strongly linked to reproduction, growth
and emergence (Newbold et al., 1994; Vannote and Sweeny, 1980). In a
study of Ephemeroptera in streams in New Zealand, Huryn (1996) found that
any variation in larval growth rate was a direct result of temperature
differences; December had the highest growth rates coinciding with the
warmest temperatures. He also predicted that eggs hatched before the middle
of February (end of the Southern Hemisphere summer) would emerge as
adults before May but eggs hatched later than the middle of February would
not emerge until the following year due to reduced growth rates during the
colder winter months.
7
Overwhelmingly, these studies concur that fluctuations in water temperature
and/or water pH do in some way affect the behaviour and community
structure of these organisms. It appears the most extreme pH fluctuation is
driven by high primary productivity which is of particular interest to the present
study as it is concerned with a nutrient-enriched eutrophic lake. If pH
increases over a certain value, approximately pH 10.5, there is either
immigration to another area with lower pH or more likely, high mortality of
species which will ultimately alters the community structure. On the other
hand, seasonal increase in water temperature, at least at the present latitude,
serves only to increase species diversity; with a loss of diversity occurring as
the water temperature drops.
Most studies are concerned with the effects of acidification or with pH
increase over 10.0. As Beklio lu and Moss (1995) rightly highlight, freshwater
ecosystems with a water pH between 6.0 and 10.0 have not received as much
attention, considering the majority of the Earth’s freshwater lakes are within
this pH range. Presumably, this is because they are considered species rich
and relatively stable ecosystems and therefore not as noteworthy for
discussion. The focus of this study is a freshwater lake with recorded lowest
and highest pH values of 6.17 and 10.57 respectively within the last 25 years.
Slapton Ley
The study site is Slapton Ley, a large naturally eutrophic freshwater lake in
the South Hams, Devon (Fig. 1). It consists of two sections, the Higher and
Lower Leys, connected by a narrow channel at Slapton Bridge. The Higher
Ley is largely silted up and vegetated but has several deep pools and the
Lower Ley is a large expanse of relatively shallow, open water. Together they
form part of a nationally important area of wetland. It has four lotic inputs, the
largest being the River Gara at the northern end, which empties into the
Higher Ley and Slapton, Start and Stokeley Streams, which empty into the
Lower Ley at various locations (Mercer, 1966). Together, these inputs make
Slapton Ley a slow-moving water body with an outflow at Torcross, at the
most southerly end of the Ley, controlled by a sluice gate.
8
Figure 2. Map of Slapton Ley, South Devon, UK.
Although the Ley is naturally eutrophic, excess nutrients leach in further up
the catchment due to agricultural fertiliser use. Water pH can fluctuate
considerably depending on rainfall, speed of through-flow and algal bloom
coverage. In hot, dry summers the Lower Ley can experience extensive algal
blooms as a result of nutrient enrichment, during which the increased
photosynthesis results in an increase in pH (O’Brien and De Noyelles, 1972).
Along with sediment deposition, the effects of the algal bloom cause a
decrease
in
the
macrophytic
populations
(N.
Stewart,
personal
communication, 2006) and this may in turn affect macroinvertebrate (Friday,
9
1987), fish and bird populations (B. Whitehall, personal communication,
2006). There is quite large intra-lake variability in pH; the pH at Torcross can
be 2 to 3 values higher than at Slapton Bridge whilst the pH of the Higher Ley
shows less fluctuation and variability. Due to its shallow depth - the Lower Ley
has an average depth of 1.55m and a maximum depth of 2.8m and the Higher
Ley is assumed to be no deeper than 4m (van Vlymen, 1979) - thermal
stratification rarely occurs and if it does, it only stays stratified for a very short
period (Morey, 1976). The Lower Ley has an open water area of
approximately 72ha (Mercer, 1966). In areas permanently shaded by
vegetation, water temperature can be several degrees below that of areas
exposed to sunlight.
Slapton Ley currently has a high deposition of sediment from its catchment
which has led to the ‘marshing-up’ of the Higher Ley. In addition to deposition,
efforts to significantly decrease nutrient input have not been effective enough
and the lag-effect of nutrients in the ground will continue to cause problems
(T. Burt, personal communication, 2007). To maintain the Lower Ley as an
expanse of open water together with its particular assemblage of
macrophytes, a suggested future management option may include a seasonal
re-directing of the River Gara. This may have implications for the pH through
the reduction in the flushing effect of the through-flow and a reduced nutrient
input from the catchment runoff and for water temperature from a possible
increase
in
depth.
An
examination
of
the
relationship
between
macroinvertebrates, water temperature and pH may offer some insight as to
the possible future effects on community structure.
As highly diverse ecosystems (Verbeck et al., 2005), it is important to
understand how freshwater habitats function on a variety of scales.
Furthermore, in an area of such recognised natural importance, it is essential
to maintain longitudinal data so that trends can be observed to aid
understanding of interactions between different aspects of a system, both
biotic and abiotic.
10
Aim and Objectives
The overall aim of this study is to investigate the impact seasonal change in
water temperature and pH has on the species composition and community
structure of the freshwater macroinvertebrates in Slapton Ley. A secondary
aspect to the study is to examine the changes at two spatial scales – the
microhabitat (each sample station) level and the water body as a whole.
Objectives
Analyse how distribution and abundance of macroinvertebrates
changes throughout the course of 12 months.
Investigate if any observed changes relate to water temperature and
pH fluctuation both temporally and spatially.
11
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environmental factors on the seasonally change of phytoplankton populations in a
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Balls, H., Moss, B. and Irvine, K. 1989. The loss of submerged plants with
eutrophication I. Experimental design, water chemistry, aquatic plant and
phytoplankton biomass in experiments carried out in ponds in the Norfolk Broadland.
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Barko, J.W., Hardin, D.G. and Matthews, M.S. 1982. Growth and morphology of
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Beklio lu, M. and Moss, B. 1995. The impact of pH on interactions among
phytoplankton algae, zooplankton and perch (Perca fluviatilis) in a shallow, fertile
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Beklio lu, M. and Moss, B. 1996. Mesocosm experiments on the interaction of
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phytoplankton and zooplankton communities. Freshwater Biology, 36 (2), 315–325.
Berezina, N.A. 2001. Influence of Ambient pH on Freshwater Invertebrates under
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Indiana Academy of Science, 113 (1), 26-32.
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12
Hansen, A.M., Christensen, J.V. and Sortkjær, O. 1991. Effect of high pH on
zooplankton and nutrients in fish-free enclosures. Archiv f r Hydrobiologie, 123 (2),
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Wilson, D. and Moss, B. 2003. Response of freshwater microcosm communities to
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14
Title:
Effects of annual fluctuation in water
temperature and pH on the diversity of the
freshwater macroinvertebrate fauna of
Slapton Ley
Advisor: Dr Stephen Burchett
Name: Maxine Chavner
Course: BSc Wildlife Conservation
Year: 4th year, 2007 – 2008
15
Effects of annual fluctuation in water temperature and
pH on the diversity of the freshwater
macroinvertebrate fauna of Slapton Ley
MAXINE A. CHAVNER
SUMMARY
1. Slapton Ley is a eutrophic lake that has recorded lowest and
highest water pH values of 6.17 and 10.57 respectively within the
last 25 years.
2. To assess whether pH had an effect on the macroinvertebrate
populations of the Ley, a study was undertaken investigating water
temperature and pH fluctuation over a 12 month period.
3. Macroinvertebrate
samples,
water
temperature
and
pH
measurements were taken at 11 stations around the Ley every
month between September 2006 and August 2007.
4. The species data was used to generate an MDS plot and diversity
indices and one-way and balanced ANOVAs were carried out on
the water temperature, pH and diversity indices data.
5. Water temperature and pH changed significantly in the Ley
throughout the year.
6. Overall, the diversity of the macroinvertebrate fauna in Slapton Ley
did not change significantly throughout the year but there was
significant intra-lake variability in macroinvertebrate diversity.
7. Intra-lake variability in pH may be a factor in determining species
composition at various locations around the Ley.
8. It would appear that water temperature and pH are not as important
in determining species composition and diversity as spatial habitat
heterogeneity.
Keywords: freshwater macroinvertebrates, water temperature, water
pH, species diversity, habitat heterogeneity.
16
Introduction
Water temperature and pH are key abiotic factors in freshwater environments,
governing the distribution, behaviour and possibly abundance of the
organisms within them (Brönmark and Hansson, 2005). They fluctuate on
both temporal and spatial scales with the degree of fluctuation dependant on
several criteria including the size and depth of the water body, the speed of its
flow (Maitland, 1990) and seasonality (Berezina, 2001). Water temperature is
inextricably linked with seasonal change. In lakes, the strength and depth of
solar penetration and wind generated currents regulate temperature. Most
lakes with an average depth of over approximately 3 metres exhibit thermal
stratification during winter and summer (Dobson and Frid, 1998). In shallower
lakes and around the sub-littoral zones, thermal stratification does not
necessarily occur, as solar radiation penetrates through the water column and
reaches the lake floor, provided the water column is not overly turbid (ibid.);
however there is obviously still seasonal difference in water temperature.
Freshwater invertebrates are poikilothermic and therefore their internal
temperature is governed by the surrounding water temperature. As water
temperature fluctuates, enzyme activity involved in vital physiological
functions will be compromised either side of the optimal temperature
(Campbell and Reece, 2002). Therefore, those with a wider temperature
range (eurytherms) may be present all year round whilst those with a
narrower temperature range (stenotherms) may be absent at the more
extreme seasonal temperature shifts (Brönmark and Hansson, 2005). Another
factor to bear in mind, which is affected by changes in water temperature, is
oxygen concentration; the capacity of water to hold oxygen decreases as
temperature increases (ibid.). Many complex interactions exist between
numerous abiotic and biotic components of a freshwater system (Macan and
Worthington, 1974) but this study is focused on water temperature and pH.
Water pH fluctuates both diurnally and seasonally, heavily influenced by the
photosynthesis and respiration of aquatic organisms and therefore, the
vegetated shallow, sub-littoral edges of lakes are more prone to pH fluctuation
than deeper water (Brönmark and Hansson, 2005). The majority of lakes
worldwide have a pH value of between 6.0 and 9.0 and although originally
17
governed by the surrounding geology, water pH can be altered by high plant
productivity, high precipitation and the addition of acidifying material (ibid.;
Camargo and Alonso, 2006). High plant productivity can be caused by
nutrient enrichment from sources such as agricultural runoff and effluent
diffusion (Maitland and Morgan, 1997). The increase in the rate of
photosynthesis elevates pH by decreasing the amount of H+ ions and CO2 in
the water (Brönmark and Hansson, 2005). High precipitation can serve to
‘dilute’ the effects of high productivity by increasing through-flow in systems
with an inflow and outflow. However, in areas of high industrialisation, high
precipitation may have an acidifying effect on the pH of a freshwater system
(Maitland and Morgan, 1997). As with water temperature, pH fluctuation has
an effect on the physiological processes of an organism, as enzyme function
has a specific optimum pH level too. The more the surrounding water pH
differs from the pH of the cell plasma, the more detrimental the change is on
the organism (Lampert and Sommer, 1997).
Effects on freshwater invertebrates
Friday (1987) shows that invertebrate diversity in ponds increases with pH
increase (Fig. 1) but this only considers the limited range of pH 3.8 to pH 7.5.
Similarly, Townsend et al. (1983) note that the number of invertebrate species
in streams increases alongside increasing pH but this is again only looking at
a limited range of pH 3.8 to pH 7.8. It would appear that a movement towards
an alkaline pH supports a greater diversity of freshwater invertebrate fauna
than an acid pH (Collier and Winterbourn, 1987) but is there a point at which
the increase in pH becomes prohibitive?
The work of several studies of Cladocera and Copepoda species in eutrophic
water bodies have shown a pH level of between 10.5 and 11.0 to be
detrimental (Beklio lu and Moss, 1995; O’Brien and De Noyelles, 1972;
Hansen et al., 1991) and so it would appear that this is the threshold for these
particular Crustacea invertebrates. Monitoring of the effects of seasonal
change on the Crustacean community of an alkaline lake in Iceland (Ingvason
et al, 2003) showed wide variation in densities which closely followed
seasonal water temperature fluctuation. During summer when water
18
temperature reached a maximum of 16°C, Crustacea density was at its
highest whilst during the winter months when maximum water temperature
was 4°C, densities dropped considerably. Also, during the growth period of
May to September, pH was at its highest; over pH 9.0. As this high pH
coincides with the period of highest density, it would suggest the Crustacea
present have a tolerance of high pH.
100
90
Invertebrate taxa
Number of taxa
80
70
60
50
40
30
20
10
0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
pH
Figure 3. Data on the macroinvertebrate taxa from 16 ponds in the Isle of Purbeck, Dorset;
with trend line. (Friday, 1987).
Under experimental conditions, Berezina (2001) found that a pH range of pH
4.09 to 8.65 supported the highest general invertebrate species diversity;
diversity decreased both above pH 9.0 and below pH 4.0. Both water
temperature and pH tolerance were examined in the hatching and survival of
the water mite Unionicola foili (Edwards, 2004). Larvae survival was
significantly reduced at pH 5.2 and adults suffered a higher mortality at pH
4.1. At 33°C, survivorship of the larvae was significantly reduced and adults
showed increasing mortality with increasing temperature. The eggs were
unaffected at all levels of pH and temperature. These temperatures are
however in excess of anything likely to be experienced in temperate
freshwaters. Mollusca tend to be absent from acidic water with a pH of less
than 6.0 but diversity increases up to approximately pH 8.5. (Boycott, 1936).
Seasonal change in water temperature probably has the most profound effect
19
on insect macroinvertebrates as it is strongly linked to reproduction, growth
and emergence (Newbold et al., 1994; Vannote and Sweeny, 1980).
Overwhelmingly, studies concur that fluctuations in water temperature and/or
water pH do in some way affect the behaviour and community structure of
aquatic invertebrates. It appears the most extreme pH fluctuation is driven by
high primary productivity which is of particular interest to the present study as
it is concerned with a nutrient-enriched eutrophic lake. If pH increases over a
certain value, approximately pH 10.5, there is either emigration to another
area with lower pH or more likely, high mortality of species which will
ultimately alter the community structure. On the other hand, seasonal
increase in water temperature, at least at the present latitude, serves only to
increase species diversity with a loss of diversity occurring as the water
temperature drops.
Most studies of freshwater invertebrates are concerned with the effects of
acidification or with pH increase over 10.0. As Beklio lu and Moss (1995)
rightly highlight, freshwater ecosystems with a water pH between 6.0 and 10.0
have not received as much attention, considering the majority of the Earth’s
freshwater lakes are within this pH range. Presumably, this is because they
are considered species rich and relatively stable ecosystems and therefore
not as noteworthy for discussion. The focus of this study is a freshwater lake
with recorded lowest and highest pH values of 6.17 and 10.57 respectively
within the last 25 years.
Slapton Ley NNR
The study site is Slapton Ley, a large naturally eutrophic freshwater lake in
the South Hams, Devon (Fig. 2). It consists of two basins, the Higher and
Lower Leys, connected by a narrow channel at Slapton Bridge. The Higher
Ley is largely silted up and vegetated but has several deep pools and the
Lower Ley is a large expanse of relatively shallow, open water. Together they
form part of a nationally important area of wetland; it is a designated National
Nature Reserve (NNR), Site of Special Scientific Interest (SSSI) and is within
the South Devon Area of Outstanding Natural Beauty (AONB). It has four lotic
20
inputs, the largest being the River Gara at the northern end, which empties
into the Higher Ley and Slapton Wood, Start and Stokeley Barton Streams,
which empty into the Lower Ley at various locations (Mercer, 1966). Together,
these inputs make Slapton Ley a slow-moving water body with an outflow at
Torcross, at the most southerly end of the Ley, controlled by a sluice gate.
Although the Ley is naturally eutrophic, excess nutrients leach in further up
the catchment due to agricultural fertiliser use. Water pH can fluctuate
considerably depending on rainfall, speed of through-flow and algal bloom
coverage. In hot, dry summers the Lower Ley can experience extensive algal
blooms as a result of nutrient enrichment, during which the increased
photosynthesis results in an increase in pH (O’Brien and De Noyelles, 1972).
Along with sediment deposition, the effects of the algal bloom cause a
decrease
in
the
macrophytic
populations
(N.
Stewart,
personal
communication, 2006) and this may in turn affect macroinvertebrate (Friday,
1987), fish and bird populations (B. Whitehall, personal communication,
2006). There is quite large intra-lake variability in pH; the pH at Torcross can
be 2 to 3 values higher than at Slapton Bridge whilst the pH of the Higher Ley
shows less fluctuation and variability. Due to its shallow depth - the Lower Ley
has an average depth of 1.55m and a maximum depth of 2.8m and the Higher
Ley is assumed to be no deeper than 4m (van Vlymen, 1979) - thermal
stratification rarely occurs and if it does, it only stays stratified for a very short
period (Morey, 1976). The Lower Ley has an open water area of
approximately 77ha (van Vlymen, 1979; Scott, 2005). In areas permanently
shaded by vegetation, water temperature can be several degrees below that
of areas exposed to sunlight.
Slapton Ley currently has a high deposition of sediment from its catchment
which has led to the ‘marshing-up’ of the Higher Ley. In addition to deposition,
efforts to significantly decrease nutrient input have not been effective enough
and the lag-effect of nutrients in the ground will continue to cause problems
(T. Burt, personal communication, 2007). To maintain the Lower Ley as an
expanse of open water together with its particular assemblage of
macrophytes, a suggested future management option may include a seasonal
21
re-directing of the River Gara. This may have implications for the pH through
the reduction in the flushing effect of the through-flow and a reduced nutrient
input from the catchment runoff and for water temperature from a possible
increase in depth through reduced silt deposition. An examination of the
relationship between macroinvertebrates, water temperature and pH may
offer some insight as to the possible future effects on species composition
and community structure.
Figure 4. Map of Slapton Ley, South Devon, UK.
As highly diverse ecosystems (Verbeck et al., 2005), it is important to
understand how freshwater habitats function on a variety of scales.
Furthermore, in an area of such recognised natural importance, it is essential
to maintain longitudinal data so that trends can be observed to aid
22
understanding of interactions between different aspects of a system, both
biotic and abiotic.
Aim
The overall aim of this study is to investigate the impact annual change in
water temperature and pH has on the species composition and community
structure (diversity) of the freshwater macroinvertebrates in Slapton Ley. A
secondary aspect to the study is to examine the changes at two spatial scales
– the microhabitat (each sample station) level and the water body as a whole.
Objectives
Analyse how distribution and abundance of macroinvertebrates
changes throughout the course of 12 months.
Investigate if any observed changes relate to water temperature and
pH fluctuation both temporally and spatially.
Methods
Sample stations
Eight sample stations were chosen around the sub-littoral zone of the Lower
Ley and three stations in the channel of the Higher Ley (Fig. 3). They were
chosen primarily due to ease of access and offered different microhabitats. A
full description of each station and an aerial photo (Plate 1) can be found in
Appendix 1.
Equipment
The following equipment and materials were used:
1mm mesh hand net, 0.3m bag, 250mm diameter, 1.48m handle; white
polypropylene sampling tray 417mm x 315mm x 90mm; Hanna HI-991001
portable pH meter and thermometer; Garmin etrex 12 channel GPS device; x8
and x15 hand lens; 1m rule; pipettes with various sized nozzles; specimen
pots; waders; data recording sheets; pencil; identification books (Appendix 2);
boat.
23
Figure 5. Maps of the Higher and Lower Leys showing the location of sampling stations.
Sampling methods
Each station was sampled once a month from September 2006 to August
2007, resulting in 132 data sets. At each sampling station the following
parameters were recorded: station number; time and date; water temperature
and pH; algal bloom extent; substrate size and type; associated vegetation;
weather conditions; water depth at which sample was taken; GPS reading.
The water temperature and pH readings were taken prior to the kick sample
being performed as the disturbed water may have caused an inaccurate
reading. The pH meter was recalibrated at the start of each new sampling
period. This was done using 4.01pH and 7.01pH buffer solutions to perform a
two-point calibration. The electrode was kept moist in between use.
All of the stations in the Lower Ley and station 9 in the Higher Ley were kick
sampled. This involved disturbing the substrate with the feet working in
approximately a 1.5m2 for 15 seconds then sweeping the net through the
water column in the area just kicked to retrieve the disturbed benthic and free
swimming fauna. Stations 10 and 11 in the Higher Ley were too deep to
24
disturb the substrate sufficiently and so a net sweep through the water column
and up through the vegetation was performed instead. The netted organisms
were transferred to a white plastic tray half filled with water. The net was then
thoroughly rinsed in the Ley to allow any microscopic or otherwise unseen
fauna to return to the water. The less abundant organisms were then removed
from the tray and grouped in different pots for identification and counting, after
which the organisms were returned to where they were netted.
When organisms of certain species were too numerous to be counted
individually, an estimation was achieved thus: the tray was divided into
quarters, the organisms in one quarter counted and multiplied by four. In an
attempt to increase accuracy of the estimate, the water was then disturbed
and allowed to settle, the tray divided into two and the organisms in one half
counted and multiplied by two. The figure from the first estimate was added to
the figure from the second estimate and divide by two.
Vegetation and substrate
The dominant vegetation of the wetland area of Slapton Ley NNR is common
reed (Phragmites australis). It creates substantial stands in the Higher Ley
and is present around almost the entire periphery of the Lower Ley. The most
abundant vegetation present within a 1 metre radius of the sample point at
each of the sample stations was also recorded. However, some sites had no
associated vegetation. The particle size of the substrate at each sample
station around the sub-littoral zone of the Ley was classified using the
Wentworth-Udden Particle Scale (Appendix 3) and ranged from silt to boulder.
The substrate type is primarily sedimentary shales, apart from at stations 7
and 8 where the substrate types are gravels washed over from the shingle
ridge.
Identification and taxonomy
Identification of organisms was assisted by the use of several specialist keys
(Appendix 2) as well as some general keys. Identification to species level was
always attempted but was problematic with Trombidiformes, Corixidae
nymphs and organisms in first and second instars. However, all organisms
25
were identified to at least family level. No organisms were killed for the
purpose of identification and the highest magnification used was x15. This
proved adequate magnification to deal with macroinvertebrates.
Statistical analyses
Analysis of the species data was carried out at the family taxa level using
PRIMER version 5 (Plymouth Routines In Multivariate Ecological Research) to
generate a similarity group clustering (CLUSTER), a multi-dimensional scaling
(MDS) plot and diversity indices data. One way ANOVAs were carried out on
the water temperature, pH and diversity data using Minitab version 15.
Results
First, it needs to be clarified that June has been omitted from all statistical
analyses and graph data. This is because sampling could not be carried out at
all stations due to bad weather throughout this month. Secondly, as Table 1
illustrates, there is a need to clarify what the diversity indices used actually
measure as there is some inconsistency in the diversity ranking of each
sample station between indices. Margalef’s Index (d) is specifically a measure
of weighted species richness rather than an actual measure of diversity.
Simpson’s Index (1- ) measures the eveness of a community; the probability
that two individuals randomly selected from a sample will belong to different
families. Shannon’s Index (H’) is generally accepted as a measure of species
diversity within a community (Washington, 1984).
Table 1. Mean diversity ranking of each sample station.
Least diverse station
Most diverse station
d
4
3
5
10
2
7
8
1
9
6
11
H’
4
2
3
10
5
8
1
7
6
9
11
14
2
3
5
8
1
10
9
7
6
11
26
Temporal fluctuation in water temperature, pH and species diversity
The Ley undergoes a significant change in water temperature (F10,110=35.37,
p<0.001) and pH (F10,110=14.76, p<0.001) throughout the year and their
fluctuations are closely linked to one another (Fig. 4). Whilst the changes in
the patterns of diversity (Fig. 5) do follow the fluctuation in water temperature
and pH (most pronounced with the Margalef diversity index), there is not a
significant change in diversity throughout the water body during the year.
Figure 6. Monthly mean for water temperature and pH across all sample stations.
3
d
H
1-
2.5
Index
2
1.5
1
0.5
0
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
July
Aug
Figure 7. Mean changing pattern of diversity across the Ley throughout the year across all
sample stations (d = Margalef; H’ = Shannon; 1- = Simpsons).
27
Spatial fluctuation in water temperature, pH and species diversity
There is no significant intra-lake difference in water temperature between the
sample stations but there is a significant intra-lake difference in pH between
the sample stations (F10,110=3.45, p=0.001). The mean yearly water
temperature and pH are highest at station 4 (Fig. 6) and this corresponds with
the lowest mean diversity (Fig. 7). Station 11, which has the highest mean
diversity, has the 3rd lowest mean water temperature and pH. The two stations
with the lowest mean water temperature and pH are station 1 (12.9°C; pH
6.93) and station 9 (12.4°C; pH 6.95) and the mean diversity at these two
stations is still relatively high. Although the species diversity did not change
significantly in the Ley throughout the year, there was a significant difference
(Shannon: F10,110=5.48, p<0.001; Simpsons: F10,110=4.91, p<0.001; Margalef:
F10,110=4.59, p<0.001) in the diversity between sample stations (Tables 2, 3
and 4). This difference cannot be due to water temperature as there is no
significant difference in temperature between stations but could be as a result
of intra-lake pH variability and heterogeneity of these microhabitats.
Figure 8. Mean water temperature and pH at each sample station from Sep ‘06 to Aug ’07.
The difference in the yearly maximum and minimum water pH is highest at
station 6 and lowest at station 11 (Table 5). Station 11 is the most diverse
station according to all 3 indices (Table 1) and this may be due to the more
stable pH here. However, station 6 also has a high diversity ranking.
28
d
3
H
1-
2.5
Index
2
1.5
1
0.5
0
1
2
3
4
5
6
7
8
9
10
11
Sample station
Figure 9. Mean diversity at each sample station from Sep ’06 to Aug ‘07 (d = Margalef; H’ =
Shannon; 1- = Simpsons).
Table 2. ANOVA table: Shannon diversity versus sample station
Source of variation
df
SS
MS
F
Station
10
8.2942
0.8294
5.48
Error
110
16.6498
0.1514
Total
120
24.9440
Table 3. ANOVA table: Simpsons diversity versus sample station
Source of variation
df
SS
MS
F
Station
10
1.09085
0.10909
4.91
Error
110
2.44560
0.02223
Total
120
3.53645
Table 4. ANOVA table: Margalef diversity versus sample station
Source of variation
df
SS
MS
F
Station
10
15.9880
1.5988
4.59
Error
110
38.3480
0.3486
Total
120
54.3360
p
0.000
p
0.000
p
0.000
Table 5. Yearly maxima and minima of water temperature and pH at each station
Station Max. °C Min. °C Difference Max. pH
Min. pH Difference
1
19.2
8.7
10.5
8.19
6.49
1.70
2
21.1
8.7
12.4
9.32
7.02
2.30
3
19.9
8.3
11.6
9.23
7.00
2.23
4
22.7
9.5
13.2
9.42
7.19
2.23
5
21.2
9.4
11.8
9.36
7.09
2.27
6
21.2
8.9
12.3
9.39
7.01
2.38
7
20.0
8.8
11.2
9.32
7.05
2.27
8
20.3
9.4
10.9
9.22
7.12
2.10
9
16.9
9.2
7.7
8.05
6.50
1.55
10
18.4
6.5
11.9
8.30
6.90
1.40
11
18.7
6.7
12.0
8.14
6.91
1.23
29
CLUSTER and MDS analysis
CLUSTER analysis grouped the 121 samples based on the similarity of their
species composition. The main cluster groups were then marked out on an
MDS plot. These clusters occur by station (Fig. 8) more coherently than by
month (Fig. 9), further indicating that species composition in the whole Ley
was homogeneous throughout the year but different between stations. It is
also worth noting that many of the samples taken from stations 1 and 9 are
positioned on the right side of the MDS plot along with stations 10 and 11,
suggesting that the Higher Ley and the channel connecting the two basins are
more similar to each other than to the rest of the Ley. In addition, stations 4
and 5, which have very similar physicochemical properties and both lack of
vegetation, are also grouped together.
Figure 8. MDS plot showing the main similarity CLUSTER groups with sample stations colour
coordinated.
30
Figure 9. MDS plot showing the main similarity CLUSTER groups with sample months colour
coordinated.
Discussion
Annual fluctuation of water temperature and pH
Although the water temperature and pH in this study did change significantly
through the year and ranged from 6.5°C and pH 6.49 during the colder
months to 22.7°C and pH 9.42 in August, the seasonal fluctuation had no
significant effect on the community structure and composition of the
macroinvertebrates in the Ley. Whilst no significant change in community
structure was recorded over the course of the year, the sample stations are
significantly different from each other, even though the species diversity still
did not necessarily change temporally at each station. The intra-lake
31
variability in water temperature had no significant effect on this spatial
diversity but pH may have.
Effects of pH at the spatial scale
Stations with submerged or emergent vegetation would be expected to have a
higher pH than those devoid of vegetation due to the effects of photosynthesis
(Brönmark and Hansson, 2005). However, stations 3, 4 and 5 had either none
or very sparse submerged vegetation and no emergent herbaceous
vegetation yet had the three highest mean pH values. The decomposition of
vegetation during winter releases H+ ions and CO2 back into the water
therefore decreasing pH (ibid.). Lack of vegetation would mean decomposition
would not be a factor in decreasing pH at these stations during winter, so this
may be why they maintain a higher mean pH than other stations. Berezina
(2001) states pH as the most important environmental factor in governing
species composition and diversity in freshwater. Stations 3, 4 and 5 were
amongst the least diverse (Table 1) and had mean pH values of 7.95, 7.99
and 7.89 respectively. Stations 6, 9 and 11 were among the most diverse
(Table 1) and had mean pH values of 7.74, 6.95 and 7.22 respectively.
According to Berezina, many of the species which are ubiquitous in Slapton
Ley (Dugesia tigrina, Tubifex tubifex, Lumbriculus variegatus, Erpobdella
octoculata,
Glossiphonia
complanata,
Helobdella
stagnalis,
Bithynia
tentaculata, Planorbis sp., Pisidiidae, Asellus aquaticus, Caenis sp.,
Limnephilus sp., Chironomidae) are tolerant of a pH range inclusive of all the
aforementioned values. So it would appear that it is the heterogeneity of
Slapton Ley, represented by the microhabitats of each sample station, which
accounts for the spatial diversity rather than explicitly the pH.
Heino (2000) investigated the claim that water chemistry was more important
in determining the community structure of
littoral macroinvertebrate
assemblages than spatial heterogeneity of habitats. It was found that habitat
heterogeneity was significantly correlated to species richness and that
patterns in species richness were more closely linked to intra-lake habitat
variables than to water chemistry, specifically in a water body where
extremities of water chemistry were absent. The sample stations in the
32
present study offer a variety of microhabitats that are occupied by different
assemblages of species. For example, densely vegetated areas offer refugia
from predation and consequently may harbour a higher diversity than those
sparsely vegetated areas (Gilinsky, 1984) and it would be expected that
Odonata, Hemiptera and Coleoptera species would be found close to
vegetation as this is where they hunt, feed and lay their eggs (Fitter and
Manuel, 1986). In a review of 85 publications on the subject of (terrestrial)
habitat heterogeneity and species diversity, Tews et al. (2004) found the
majority of studies established a positive correlation between habitat
heterogeneity and animal species diversity. The idea that more diverse
habitats will support higher species diversity is known as the ‘habitat
heterogeneity hypothesis’ and it is the plant communities that determine the
physical structure of a particular habitat or microhabitat (ibid.). Therefore, it
would seem reasonable to suppose that the low species diversity at unvegetated stations is a result of their lack of vegetation rather than their pH.
Implications of any proposed management strategies
One of the more radical, but not necessarily viable suggestions for managing
the nutrient loading into Slapton Ley from diffuse pollution in its catchment is a
seasonal re-routing of the River Gara so that it flows directly out to sea rather
than via the Ley (S. Lambert, Slapton Research Seminar, 2007). This could
also reduce silt deposition into the Ley which could have two effects – (1) the
Higher Ley appears to have an assemblage of species distinct from that of the
Lower Ley; continued silt deposition could lead to complete terrestrialisation of
the Higher Ley resulting in the loss of these assemblages and so, reduced silt
deposition could be beneficial in the Higher Ley, (2) reduced silt deposition in
the Lower Ley could lead to increased depth and seasonal stratification, which
could have implications for the macroinvertebrate fauna. Considering annual
water temperature fluctuation does not appear to have a significant effect on
the community structure of macroinvertebrates in Slapton Ley it could mean
that they would be more susceptible to any major temperature fluctuation. The
minimum and maximum water temperatures recorded in the Ley during Sept
2006 – Aug 2007 were 6.5°C and 22.7°C respectively. There were
undoubtedly taxa present in the warmer months that were not recorded in the
33
colder months (Appendix 4) but a more drastic change could compromise
those taxa that are currently present all year round.
Strapwort (Corrigiola litoralis) is a critically endangered plant in the UK found
only at Slapton Ley. The management of Strapwort requires vegetated
shoreline to be manually cleared to provide germination gaps; it will not
germinate or will die before reaching maturity if competing with faster growing
or denser vegetation (McHugh, unpublished). Therefore, the management
strategy for Strapwort could have an effect on the macroinvertebrate
assemblages at sites where emergent vegetation is cleared.
Impacts of agriculture in the future.
The Slapton Ley catchment is 48km2 and predominantly mixed agriculture
land. The Slapton Cycleau Project was an initiative that ran for 3 years, 2004
to 2006, and assisted farms in the Slapton Ley catchment to apply for grants
to improve areas of their farms responsible for diffuse pollution. It also
encouraged farmers to join Stewardship Schemes and prepare them for the
introduction of the Catchment Sensitive Farming Initiative. However, Burt and
Worrall (2007) suggest that the soils at Slapton are nitrogen saturated and a
lag effect of nutrients in the substrate may continue to have an impact on the
eutrophication of Slapton Ley for some time. The measures taken by farmers
through the Cycleau Project and future measures taken as a result of the
Catchment Sensitive Farming Initiative may help to negate these lag effects,
leading to an eventual decrease and stabilisation of pH.
Problems with the experimental design
The lack of a significant result for fluctuating water temperature and pH having
an effect on the overall species diversity of the Ley could be attributed to the
taxonomic level at which statistical analyses were carried out. Guerold (2000)
found that richness was drastically underestimated when calculated at family
level and that “Shannon and Margalef indices showed lower values when
calculated at higher taxonomic level” and was more pronounced in Margalef’s
Index. In the present study, the majority of organisms were identified to genus
or species level but as these levels could not be achieved for all organisms, it
34
was decided to use the taxonomic level of family for analyses so all the data
could be included. Choosing to calculate diversity at the genus or species
level or indeed carrying out any of the analyses at genus or species level
would have meant omitting some of the data; for this study it was deemed
family was an acceptable taxonomic level to use.
Another parameter to consider is water depth. Initially all kick samples were to
be carried out in water less than 50cm deep. During the wetter winter months
and because of the unusually wet summer, the water depth at the precise
location of each kick sample station regularly rose above this preferred depth.
This could enable easier dispersal for disturbed fauna and therefore
compromise the number of individuals and/or taxa represented in the sample.
However, at the outset, the decision was made to remain as true to the
precise location as possible rather than vary the location according to water
depth.
One aspect of the study that was expected to have an influence on the
macroinvertebrate populations were the effects of a dense algal bloom. The
year the sampling period covered was exceptional in that the unusually wet
summer did not allow any algal blooms to occur. A sampling period covering
the same time span and having summer algal blooms occurring may generate
different results.
Conclusions
There are many studies to support that fluctuating water temperature and pH
has an effect on macroinvertebrate diversity and composition in freshwater
lakes. Equally, there are many studies expressing habitat heterogeneity as
the major force in determining diversity and composition. Although in the
present study water temperature and pH did change significantly throughout
the year, they did not fluctuate to the extremities that would cause a
significant change in the species composition and diversity. At a spatial level,
pH may have a role in determining the species composition and community
35
structure but the microhabitats offered by the heterogeneity of Slapton Ley
have an important role in the distribution of diversity as well.
Acknowledgements
I would like to thank all the staff at the Slapton FSC and NNR Field Centre,
especially Barrie Whitehall, Nick Binnie, Rhona Davies and Steve Edmonds
who offered time, knowledge, equipment and permits to carry out work. I
would also like to thank Dr Natasha de Vere and Dave Ellacott of the Whitley
Wildlife Conservation Trust for equipment and their assistance with this
project, Charlotte McHugh for her assistance with counting invertebrates, Dr
Stephen Burchett for his help with statistical analyses and Nicola Synnott and
Robin Callaway for ongoing support.
36
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39
Appendices
40
Appendix 1: Full sample station descriptions
Station 1
Location: Lower Ley – Southgrounds Shore. The north-west of Southgrounds
Shore where the boats are moored, close to Slapton Bridge in the narrow
channel of the Lower Ley. Relatively sheltered from prevailing winds. Steep
drop from the shore therefore very affected by water level rise.
GPS: N50° 17’ 14.2”, W003° 38’ 48.3”
Associated vegetation: Dense submerged macrophytes, Phragmites australis,
Mentha aquatica and Iris pseudacorus.
Substrate size: Silt, sand, gravel and pebble.
Substrate type: Shale
Station 2
Location: Lower Ley – Southgrounds Shore (Compartment E2). Where FSC
staff take pond dip groups.
GPS: N50° 17’ 10.5”, W003° 38’ 53.5”
Associated vegetation: Phragmites australis.
Substrate size: Silt, sand, gravel and pebble.
Substrate type: Silt and shale.
Station 3
Location: Lower Ley – Southgrounds Shore (Compartment E2). Near the
Pillbox at the mouth of Ireland Bay.
GPS: N50° 17’ 06.1”, W003° 39’ 05.8”
Associated vegetation: None.
Substrate size: Sand, gravel and boulder.
Substrate type: Shale and rocky.
Station 4
Location: Lower Ley – Inner Shore (Compartment E4), Hartshorn.
GPS: N50° 16’ 52.0”, W003° 39’ 05.4”
Associated vegetation: Very sparse submerged macrophytes.
Substrate size: Silt, sand, gravel.
Substrate type: Silt and shale.
41
Station 5
Location: Lower Ley – Inner Shore (Compartment E4). Near the end of
America Road.
GPS: N50° 16’ 45.6”, W003° 39’ 10.6”
Associated vegetation: Salix caprea.
Substrate size: Silt, sand, gravel, pebble and cobble.
Substrate type: Silt and shale.
Station 6
Location: Lower Ley – Torcross Weir Shore (Compartment E6). On the southwest side of the Ley between Stokeley Bay and Torcross. Accessed directly
from the side of the road (A379).
GPS: N50° 16’ 14.3”, W003° 39’ 24.0”
Associated vegetation: Salix caprea and Phragmites australis.
Substrate size: Silt, sand, gravel and pebble.
Substrate type: Silt and shale.
Station 7
Location: Lower Ley – Outer Shore (Compartment E1). Torcross. Popular site
for the public to feed the water birds and so always has birds present in
numbers. Close to sluice. Sheltered from the prevailing winds. Relatively
shallow drop from the shore but still affected by water level rise.
GPS: N50° 15’ 59.7”, W003° 39’ 11.5”
Associated vegetation: Phragmites australis and Typha spp.
Substrate size: Silt, sand, gravel and pebble.
Substrate type: Shingle and gravel.
Station 8
Location: Lower Ley – Outer Shore (Compartment E1). Opposite Hartshorn.
GPS: N50° 16’ 53.9”, W003° 38’ 56.1”
Associated vegetation: Phragmites australis.
Substrate size: Silt, sand, gravel and pebble.
Substrate type: Shingle and gravel.
42
Station 9
Location: Higher Ley – Slapton Bridge. In the narrow channel, accessed near
the bird ringers hut.
GPS: N50° 17’ 15.9”, W003° 38’ 47.0”
Associated vegetation: Overhanging Salix caprea, Sambucus nigra and
Hedera helix.
Substrate size: Silt, sand, gravel and pebble.
Substrate type: Mud and shale.
Station 10
Location: Higher Ley – floating islands (Compartment D3). Accessed by boat
from the cattle drinking area.
GPS: N50° 17’ 19.4”, W003° 38’ 44.1”
Associated vegetation: Phragmites australis, Mentha aquatica, Rumex
hydrolapathum, Iris pseudacorus, Solanum dulcamara and Lemna sp.
Substrate size: Silt and sand.
Substrate type: Silt.
Sampling technique: Vegetation/water column sweep.
Station 11
Location: Higher Ley – floating islands (Compartment D3). Accessed by boat
from the cattle drinking area.
GPS: N50° 17’ 22.4”, W003° 38’ 44.0”
Associated vegetation: Tussock sedge (Carex sp.), Phragmites australis,
Rumex hydrolapathum, Mentha aquatica and Myosotis scorpioides.
Substrate size: Silt and sand.
Substrate type: Silt.
Sampling technique: Vegetation/water column sweep.
43
Plate 1. Aerial photo of Slapton Ley showing the location of sample stations (Google maps,
2008)
44
Appendix 2: Identification Guides
Brooks, S. and Lewington, R. 2004. Field Guide to the Dragonflies and
Damselflies of Great Britain and Ireland. (Rev. Ed.). Hampshire: British
Wildlife Publishing.
Croft, P.S. 1986. A Key to the Major Groups of Freshwater Invertebrates.
Shrewsbury: Field Studies Council Publications
Elliott, J.M. 1996. British Freshwater Megaloptera and Neuroptera: A Key with
Ecological Notes. Cumbria: Freshwater Biological Association.
Fitter, R and Manuel, R. 1986. Collins Field Guide to Freshwater Life. London:
Collins.
Friday, L.E. 1988. A Key to the Adults of British Water Beetles. Field Studies,
7 (1), 1-152.
Fryer, G. 1982. The Parasitic Copepoda and Branchiura of British Freshwater
Fishes: A Handbook and Key. Cumbria: Freshwater Biological Association.
Gledhill, T. and Sutcliffe, D.W. 1976. Key to British Freshwater Crustacea:
Malacostraca. Cumbria: Freshwater Biological Association.
Harker, J. 1989. Mayflies. Slough: Richmond Publishing Co. Ltd.
Macan, T.T. 1977. A Key to the British Fresh- and Brackish-water Gastropods
with Notes on their Ecology. (4th ed.). Cumbria: Freshwater Biological
Association.
Mann, K.H. 1964. A Key to the British Freshwater Leeches with Notes on their
Ecology. (2nd ed.). Cumbria: Freshwater Biological Association.
Olsen, L.H., Pedersen, B.V and Sunesen, J. 2001. Small Freshwater
Creatures. Oxford: Oxford University Press.
Reynoldson, T.B. 1967. A Key to the British Species of Freshwater Triclads.
Cumbria: Freshwater Biological Association.
Savage, A.A. 1990. A Key to the Adults of British Lesser Water Boatmen
(Corixidae). Field Studies, 7 (3), 485-515.
Wallace, I. 2006. Simple Key to Caddis Larvae. Shrewsbury: Field Studies
Council Publications.
45
Appendix 3: Wentworth-Udden Particle Scale
For use with grains in a rock or sediment.
DIMENSION
NAME
greater than 256mm
Boulder
64mm – 256mm
Cobble
4mm – 64mm
Pebble
2mm – 4mm
Gravel
1
Sand
/16 – 2mm
1
1
Silt
1
Clay
/16 mm – /256 mm
less than /256 mm
If the grains can be distinguished then it is at least silt grade; if it does not feel
gritty on the teeth, then it is clay.
[Taken from: Walker, P.M.B. (ed.) 1999. Chambers Dictionary of Science and
Technology. Edinburgh: Chambers Harrap Publishers Ltd.]
46
Appendix 4
Table 6. All taxa represented each season with seasonal mean for water temperature and pH
Autumn: 15.2°C, 7.34pH
Winter: 10.46°C, 6.99pH
Spring: 14.85°C, 7.89pH
Summer: 17.7°C, 8.44pH
Aeshnidae
Glossiphoniidae
Asellidae
Hydrometridae
Argulidae
Hydrobiidae
Aeshnidae
Haliplidae
Argulidae
Haliplidae
Caenidae
Asellidae
Hydrometridae
Argulidae
Hydrobiidae
Asellidae
Leptoceridae
Chironomidae
Hygrobiidae
Leptoceridae
Baetidae
Hygrobiidae
Asellidae
Hydrometridae
Baetidae
Libellulidae
Chydoridae
Limnephilidae
Bithyniidae
Laccophilinae
Baetidae
Hydroptilidae
Bithyniidae
Limnephilidae
Coenagrionidae
Limnesiidae
Caenidae
Bithyniidae
Hygrobiidae
Caenidae
Limnesiidae
Corixidae
Lumbriculidae
Chaoboridae
Leptoceridae
Libellulidae
Caenidae
Laccophilinae
Chaoboridae
Lumbriculidae
Crangonyctidae
Nepidae
Chironomidae
Limnephilidae
Chaoboridae
Chironomidae
Lycosidae
Dixidae
Ostrocoda
Chydoridae
Limnesiidae
Chironomidae
Leptoceridae
Libellulidae
Chydoridae
Lymnaeidae
Dugesiidae
Physidae
Coenagrionidae
Lumbriculidae
Chydoridae
Limnephilidae
Coenagrionidae
Naucoridae
Dytiscidae
Piscicolidae
Crangonyctidae
Lycosidae
Coenagrionidae
Limnesiidae
Corixidae
Nepidae
Ecnomidae
Cyclopidae
Lymnaeidae
Corixidae
Crangonyctidae
Ostrocoda
Elmidae
Pisidiidae
Planorbidae
Daphniidae
Microturbellaria
Crangonyctidae
Lumbricidae
Lumbriculidae
Cyclopidae
Physidae
Erpobdellidae
Dixidae
Lymnaeidae
Pionidae
Gammaridae
Notonectidae
Ostrocoda
Cyclopidae
Daphniidae
Polycentropodidae
Psychomyiidae
Daphniidae
Naucoridae
Dixidae
Planorbidae
Glossiphoniidae
Sialidae
Dytiscidae
Dixidae
Dugesiidae
Psychomyiidae
Gyrinidae
Tipulidae
Ecnomidae
Piscicolidae
Psychomyiidae
Dugesiidae
Notonectidae
Ostrocoda
Dytiscidae
Sialidae
Haliplidae
Tubificidae
Elmidae
Sialidae
Dytiscidae
Physidae
Ecnomidae
Sisyridae
Hydrobiidae
Unionicolidae
Erpobdellidae
Tipulidae
Ecnomidae
Planariidae
Elmidae
Tabanidae
Glossiphoniidae
Tubificidae
Elmidae
Erpobdellidae
Tipulidae
Gyrinidae
Unionicolidae
Erpobdellidae
Planorbidae
Psychomyiidae
Gammaridae
Tubificidae
Haliplidae
Gammaridae
Sialidae
Gerridae
Unionicolidae
Gerridae
Tipulidae
Glossiphoniidae
Tubificidae
Gyrinidae
Unionicolidae
44 families
36 families
Dugesiidae
41 families
48 families
47
Appendix 5: Full species list
Microturbellaria
Dalyellidae?
Tricladida
Polycelis nigra
Polycelis tenuis
Dugesia tigrina
Dugesia lugubris
Annelida
Tubifex tubifex
Lumbriculus variegatus
Eiseniella tetraedra
Hirudinea
Piscicola geometra
Glossiphonia complanata
Glossiphonia heteroclita
Glossiphonia concolor
Helobdella stagnalis
Theromyzon tessulatum
Erpobdella octoculata
Erpobdella testacea
Gastropoda
Potamopyrgus jenkinsi
Bithynia tentaculata
Bithynia leachii
Lymnaea palustris
Lymnaea stagnalis
Lymnaea peregra
Physa fontinalis
Planorbis albus
Planorbis sp.
Cyclops sp.
Argulus foliaceus
Gammarus pulex
Crangonyx pseudogracilis
Asellus aquaticus
Insecta
Ephemeroptera (nymphs)
Caenis sp.
Procloeon bifidum
Odonata (nymphs)
Anax imperator
Orthetrum cancellatum
Coenagrion puella
Ischnura elegans
Pyrrhosoma nymphula
Hemiptera
Hydrometra stagnorum
Gerris lacustris
Ranatra linearis
Ilyocoris cimicoides
Notonecta glauca
Corixa sp.
Sigara sp.
Callicorixa sp.
Megaloptera
Sialis lutaria (larvae)
Neuroptera
Sisyra sp. (larvae)
Arachnida
Pirata piraticus
Limnesia sp.
Piona sp.
Unionicolidae
Trichoptera (larvae)
Polycentropodidae
Tinodes waeneri
Ecnomus tenellus
Agraylea sp.
Limnephilus flavicornis
Limnephilus lunatus
Limnephilus rhombicus
Mystacides longicornis
Crustacea
Eurycercus lamellatus
Daphnia sp.
Ostrocoda (3 spp.)
Diptera (larvae)
Tipula sp.
Dixa sp.
Chaoborus sp.
Bivalvia
Pisidiidae
48
Ceratopogonidae
Chironomus spp.
Tabanidae
Coleoptera
Gyrinus sp.
Haliplus varius
Haliplus obliquus
Haliplus confinis
Haliplus sp.
Hygrobia hermanni
Laccophilus hyalinus
Noterus/Ilybius?
Potamonectes depressus elegans
Hyphydrus ovatus
Hygrotus versicolor
Oulimnius sp.
49