Journal
Journalof
ofCoastal
CoastalResearch
Research
SI 64
pg -- pg
412
416
ICS2011
ICS2011 (Proceedings)
Poland
ISSN 0749-0208
Influence of abiotic environmental conditions on spatial distribution
of charophytes in the coastal waters of West Estonian Archipelago,
Baltic Sea
A. Kovtun, K. Torn, G. Martin, T. Kullas, J. Kotta and Ü. Suursaar
Estonian Marine Institute,
University of Tartu, Mäealuse 14,
Tallinn, 12618 Estonia
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
ABSTRACT
Kovtun, A., Torn, K., Martin, G., Kullas, T., Kotta J. and Suursaar Ü., 2011. Influence of abiotic environmental
conditions on spatial distribution of charophytes in the coastal waters of West Estonian Archipelago, Baltic Sea.
Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), Szczecin, Poland, ISSN 0749-0208
Charophytes are submerged macroalgae with well-developed thallus and complex morphology, which can be
found in fresh and brackish water bodies. The order Charales includes over 300 species worldwide of which 7
are found in the Estonian coastal sea. The sheltered, soft-bottom and shallow environment in the Gulf of Riga
and the highly indented West Estonian Archipelago Sea (Väinameri) offer suitable substrate, shelter, depth, and
salinity range for their growth. Their spatial distribution depends mostly on light conditions (via depth and
substrate properties), waves (via exposure, depth and slope), and bottom substrate. Preferring clay-sandy bottoms
and sheltered brackish-water bays, Chara aspera, Tolypella nidifica and Chara canescens are the most abundant
species. In the future, higher storm surges, increased storm wave height and turbidity may cause changes in the
composition and spatial patterns of macrophyte communities. As environmental variability increases, the species
with narrow tolerance ranges will probably suffer.
ADDITIONAL INDEX WORDS: Macroalgae, Coastal ecosystems, Currents, Waves, Climate change.
INTRODUCTION
Charophytes are submerged macroalgae with a well-developed
complex thallus and morphology, which can be found in fresh and
brackish water bodies, but not in areas of high salinity (SoulieMärche, 2008). Believed to be the closest relatives of the green
land plants, the order Charales includes over 300 species
worldwide. Although freshwater charophytes are relatively wellstudied, information on brackish water species and their
environmental preferences is rather scarce. To date only single
aspects of charophyte ecology have been studied (Schubert and
Blindow, 2003; Torn et al., 2004; Kovtun et al., 2009) and there is
still a lack of knowledge on what abiotic factors influence their
distribution in brackish conditions.
To date only 7 species have been reported in the Estonian
coastal sea (Torn et al., 2004; 2006). The sheltered, soft-bottom
archipelago environment found especially in Western Estonia
(Figure 1) is an excellent habitat for charophytes. Particularly, the
Gulf of Riga and the highly indented West Estonian Archipelago
Sea (Väinameri) offer suitable substrate, shelter, depth, and
salinity range for their growth. Charophyte communities are an
important habitat for a number of invertebrate and macrophyte
species and they provide feeding and nursery areas for several
species of fish and birds. They are also considered the first
colonizing pioneers in water bodies after a disturbance event and
supposedly may improve the management and restoration of more
or less degraded aquatic ecosystems (Hollerbach and Krasavina,
1983). Although it is generally known that charophytes mostly
inhabit sheltered soft-bottom areas, and the distribution is believed
to be controlled mostly by exposure (to wind-waves) and sediment
type (e.g. according to Schubert and Blindow, 2003), there are
also a number of other factors, such as light, temperature and
salinity, which are potentially important ecological variables
influencing charophyte growth (Shteinman et al., 1999; Schwarz
et al., 2004). However, their combined influence has only been
poorly analysed. Moreover, most of the mentioned factors are
subjected to climate-change induced variations.
The aim of the paper is to give an overview of current
knowledge of charophytes in the Estonian coastal sea (Figure 1),
to investigate the spatial distribution of different species from the
main limiting factors (i.e., bottom substrate, salinity, light and
seasonal ice conditions, movements of water), and to discuss the
possible future developments in the macrophyte communities in
relation to manifestations of climate change (such as increasing
storminess and wave-generated turbidity, decreased ice cover, and
increased range of water level fluctuations).
MATERIAL AND METHODS
The material for the study was collected in 2001–2008 and is
based on the results of the Estonian National Monitoring
Programme and local scale studies carried out in the Estonian
Marine Institute (EMI). Also a number of special surveys aimed at
mapping of the charophyte communities have been carried out.
Altogether 2397 locations were visited (Figure 2a).
Sampling has been predominantly performed by SCUBA diving
from a boat or directly from the shore. For each locality, its GPS
position, depth and sediment type were recorded. The total cover
of benthic vegetation and the cover of each macrophyte species
were estimated and quantitative samples were collected using a
metal frame (20x20 cm) or an Ekman-type grab sampler (15x15
Journal of Coastal Research, Special Issue 64, 2011
412
Charophytes in the West Estonian coastal sea
Figure 1. Map of the Baltic Sea with the study area indicated by
the rectangle.
cm) placed randomly inside the community in order to properly
identify the species at each station. The collected macrophytes
were packed and frozen until sorting and determination. In the
laboratory, species were determined and biomass (dry weight) of
charophytes and other species were measured.
The abiotic conditions in the studied areas are discussed on the
basis of hydrological data, which were recorded simultaneously
during the sampling expeditions, as well as on inquiries on the
long-term regimes from the monitoring database of the EMI. The
phytobenthos sub-base was matched with data sets on
hydrography, hydrology and hydrochemistry (Kovtun et al.,
2009). The inclination of the coastal slope was calculated for each
station at 100 m resolution using the Spatial Analyst tool of
ArcInfo software. Hydrological data (e.g. salinity, water velocity,
temperature) were computed in a resolution of 5 days using the
COHERENCE model (Bendtsen et al., 2009). Averages of the
one-month period prior to sampling were used. A simplified wave
model (Isæus, 2004) and the SMB-type wave model were used to
calculate the wave exposure for mean wind conditions (Suursaar
and Kullas, 2009). Hydrodynamic conditions were studied on the
basis of episodical in situ flow measurements, as well as on the
results of wave hindcast and hydrodynamic modelling
experiments with the shallow sea 2D model (see Suursaar and
Kullas, 2006; 2009 for more details and applications). Multivariate
data analysis (Spearman Rank Correlation analysis) was
performed by the statistical program PRIMER version 6.1.5 to
relate the environmental variables to the patterns of phytobenthic
communities.
RESULTS
The larger part of the West Estonian coasts have been covered
by the phytobenthos monitoring studies (Figure 2). Out of 2397
sampled locations, charophyte species were present in 532
locations representing ca 22% of studied stations (Figure 2a).
Vegetation occurred in 83% of cases, but only in well sheltered
and relatively shallow areas, charophytes dominated among the
bottom vegetation. In the phytobenthos database, the depth ranged
between 0.1 and 35 m. Still mostly shallow, the maximum depth
in the Väinameri Sea (2243 km2) is 22 m, it is up to 52 m in the
Gulf of Riga (17 913 km2), and the 50 m isobath runs typically
within 10 km of the shore along the west coasts of Saaremaa and
Hiiumaa Islands. Including several straits and channels, the
practically tideless Gulf of Riga and the Väinameri Sea are
hydrodynamically highly dynamic water bodies (Figure 3), where
wind-driven currents may reach up to 1.5 m/s and the historical
range of sea level variations is 3–4 m (Suursaar et al., 2006).
Although limited by restricted fetch, waves can be up to 4–5 m
high. Due to the existence of numerous shallow bays and banks
within the study area, there are still a number of suitable habitats
for charophytes, which require good light conditions, and need to
be relatively well sheltered from physical disturbances.
Chara aspera (258 locations; Figure 2c), Tolypella nidifica (226
locations; Figure 2d) and Chara canescens (112 locations; Figure
2e) are the most abundant species among the charophytes in the
West Estonian coastal sea, followed by Chara connivens (110
locations), Chara baltica (69 locations; Figure 2f) and Chara
tomentosa (27 findings). The seventh species, Chara horrida, is
extremely rare, presented in just a few findings in the brackish
Estonian coastal waters. Communities dominated by charophytes
with high coverage values (80–100%; Figure 2b) could be found
scattered over the area. In over 60% of cases, charophytes occur in
low densities and with spatial coverages of less than 10%. The
maximum biomass values (over 1000 g/m2 dry weight) were
recorded from sheltered bays of Saaremaa Island. The majority of
biomass values remained below 100 g/m2 dry weight.
ANALYSIS AND DISCUSSION
Spatial distribution of different species in relation
to abiotic environmental factors
Charophytes are fast growing species with high growth rates in
summer and the site specific variables have a stronger effect on
their distribution compared to time-dependent variables (Torn et
al., 2006). The coverage and biomass of charophytes is mostly
influenced by depth, exposure, sediment type and slope (Table 1,
Figure 2). They prefer shallow water, the majority of findings
(94% of localities) were found above 4 m isobath. Depth
influences benthic macrophytes indirectly, mainly as a function of
light intensity (Schwarz et al., 2002).
It appeared from the surveys that C. aspera (Figure 2c, Table 1),
the most frequent plant species of the group, can be found in the
coastal zone of the Gulf of Riga and the Väinameri, but also in
several bays of the Gulf of Finland and Baltic Proper. It occurs at
depths of up to 4 m, prefers silty and sandy bottoms, and tolerates
both fresh and brackish water. However, the main reason for such
a wide spread is its relatively high tolerance of waves, currents,
ice scratch and water level fluctuations. C. canescens (Figure 2e)
tolerates salinities in relatively wide range between 1 and 20, but
is sensitive to water movements. C. baltica (Figure 2f) and C.
connivens usually dwell in small abundances. They are sensitive to
eutrophication and turbidity-related diminishing of light
conditions. C. tomentosa is currently restricted to the silty (Table
1) bays of western Estonia. In locations with larger depth, slope
and exposure values only T. nidifica occurs (Figure 2d), which can
obviously tolerate wider range of environmental variables
compared to genus Chara species.
In previous studies, genus Chara species were found up to 3 m
depth and T. nidifica till 5 m in the Estonian coastal sea (Torn et
al., 2004).
Journal of Coastal Research, Special Issue 64, 2011
413
Kovtun et al.
Figure 2. Distribution of various charophyte species in the study area (a; filled markers – charophytes found, empty markers – no
findings) and coverages of charophytes (b; starting from 1%). Findings of selected taxa (c–f) in the West Estonian coastal sea in 2001–
2008. Species drawings (in c–f) from Hollerbach and Krasavina (1983).
Journal of Coastal Research, Special Issue 64, 2011
414
Wave height (m) .
Charophytes in the West Estonian coastal sea
4
10 m
5m
2
2m
1
1m
0
Wave height (m) .
0
5
According to the current study, Chara species were found in low
abundance up to 6 m depth and specimens of T. nidifica down to 8
meters. The survey-time salinity range for higher biomass and
coverage values was 5–7, and 11–21°C for temperature. The
linkage between the distribution of benthos and bottom substrate
can be related to bottom slope, granulometric composition of
particles and wave activity (Shteinman et al., 1999). As it was also
confirmed by our results, charophytes are sensitive not only to
substrate quality but also to mean grain size within soft substrate
(Selig et al., 2007). Large particles floating along with water
movements may bring additional stress to plant. Charophytes
prefer soft bottom types with fine sediment particles and mixture
of silt-clay or silt with organic debris.
Hydrodynamic variability is connected to the “exposure”,
“depth”, and “average speed” factor (Table 1). Potentially, wave
heights, independent of wind speed, depend on the depth of a
location and fetch (Figure 4). In shallow water (up to 1–2 m),
waves cannot be high and the corresponding water movements
(orbital velocities) are generally of acceptable magnitude for
charophytes. Owing to their large thalluses, strong water
movements may rip them out of the substrate. In deeper locations
(2–10 m), much higher waves can physically occur, but starting
from about 10–15 m, the bottom orbital velocities are damped
(Figure 4c). Light availability limits charophytes in this zone.
Thus, charophytes require a certain combination of depth and
exposure values. For windy locations, either depth or maximumwind fetch distance should be small enough, which occurs in
sheltered bays (Figure 2). In contrast to waves, currents can be fast
in the narrow straits of Väinameri (Figure 3), but in shallow bays
(e.g. Matsalu and Haapsalu) with large bottom friction they do not
appear to limit charophytes growth. According to our simulations,
in large areas of the Väinameri, wind-driven currents never exceed
40 cm/s (Suursaar and Kullas, 2006, Figure 3).
In most cases, waves and turbidity-connected light availability
remains the most important hydrodynamic factors for charophytes.
In Table 1, the magnitude of correlations somewhat depends on
abundances of particular species and the values are not strictly
comparable to each other. Also, the importance of a factor
Orbital velocity (cm/s)
10
15
20
25
30
35
1.8
50 km
b) Depth 5 m
20 km
1.2
10 km
5 km
0.6
2 km
1 km
0
0
Figure 3. A snapshot of modelled currents in the West Estonian
coastal sea in 14 m/s SSW wind conditions.
20 m
a) Fetch 50 km
3
120
5
10
15
20
25
35
Depth 2,
fetch 100
Depth 2,
fetch 10
Depth 2,
fetch 2
Depth 15,
fetch 100
c)
80
40
0
0
30
5
10
15
20
Wind speed (m/s)
25
Figure 4. Modelled with SMB model dependences between
significant wave height and wind speeds in different depths (m)
considering the fetch of 50 km (a); in different fetches (km)
considering the depth of 5 m (b); dependence between wind
speed and near-bottom orbital velocities (c).
depends on the used input data range. For instance, “salinity” does
not include the whole possible range, but just the values between
ca 1–7, as they appear in the Estonian coastal sea. Temperature
essentially includes the moment in a seasonal course. Many
factors are correlated to each other, which number could be further
reduced in multivariate analysis. Wave action is represented by
“exposure”, “depth” and “slope”. However, average current speed
seems indeed unimportant in our practically tideless study area, as
the values roughly between 3 and 20 cm/s are much smaller than
the orbital velocities of waves. Still, the currents can be up to 1
m/s during storm surges, when sea level in some westerly exposed
bays (Haapsalu, Matsalu and Pärnu) can rise and fall for about 2 m
within a single day. Such infrequent catastrophic events (Suursaar
et al., 2006) cannot be taken into account in average state analyses
(e.g. Table 1). However, accompanied by strong wave activity
once in a couple of years, they may physically destroy charophyte
habitats. According to experimental findings (Yanez et al., 2008;
Torn et al., 2010), the habitat may recover to a nearly equal level
in the subsequent season. It is, however, very likely if such a
destruction or burying under redistributed sediment layer becomes
too frequent the whole habitat starts to decline.
Possible future changes
Compared to the earlier surveys by T. Trei between 1960 and
the 1980s, some changes in the charophyte distribution have
already occurred in the bays of Matsalu (rise of C. connivens and
decline of C. aspera) and Rame, but no significant changes were
found in the Haapsalu Bay. In the future, climate change induced
shifts in water temperature and salinity will likely affect
macrophyte species distribution and community structure
Journal of Coastal Research, Special Issue 64, 2011
415
Kovtun et al.
Table 1: Results of Spearman Rank Correlation analysis on the effect of selected environmental variables on the biomass of
the selected charophyte taxa. Statistically insignificant (p<0.05) correlations are given in parentheses.
Factor
all Chara
C. aspera
T. nidifica
C. canescens C. connivens
C. baltica
C. tomentosa
Depth
-0.41
-0.34
-0.17
-0.22
-0.14
-0.12
-0.11
Exposure
-0.33
-0.28
-0.11
-0.15
-0.18
-0.13
-0.10
Slope
-0.20
-0.16
-0.07
-0.08
-0.13
-0.10
-0.08
Bottom: silt
0.24
0.15
0.04
0.09
0.20
0.10
0.18
Fine sand
0.12
(0.03)
0.13
0.05
0.06
0.04
(0.01)
Coarse sand
0.08
0.08
0.05
0.04
(-0.01)
0.05
(-0.02)
Gravel
(0.01)
0.04
(0.01)
(0.01)
-0.03
(0.02)
(-0.03)
Salinity
-0.18
-0.12
-0.10
-0.09
-0.05
0.03
-0.04
Temperature
0.19
0.12
0.11
0.08
0.06
0.06
0.08
Av. current
0.07
(0.03)
0.05
(0.03)
(0.03)
(-0.03)
0.05
(Eriksson et al., 2002). Higher storm surges, lengthening of icefree periods in winter and increased turbidity may cause changes
as well. Increasing storminess and wave-generated turbidity is
supposed to force stoneworts out to deeper water. On the one
hand, increasing resuspension and decreasing water transparency
also sets limits for that. As environmental variability increases, the
species with narrow tolerance ranges will suffer. It is possible that
the already observed shifts in storm wind directions (decrease in
northerly and southerly storms and increase in westerly storms:
e.g. Suursaar and Kullas, 2009) make, depending on their
orientation and exposure, some of the bays more and others less
suitable for charophytes. The populations are more likely to
survive in well sheltered bays. In the Estonian coastal sea,
conditions in some northerly exposed bays probably become more
tolerable than they were a few decades ago.
CONCLUSIONS
Although only seven species of charophytes occur in the
Estonian coastal sea, they are important group of plants which
spatial distribution depends on light conditions (via depth and
substrate properties), waves (via exposure, depth and slope), and
bottom substrate. Preferring clay-sandy bottoms and sheltered
brackish-water bays, C. aspera, T. nidifica and C. canescens were
the most abundant species. In the future, higher storm surges,
increased storm wave height and turbidity may cause changes in
compositions and spatial patterns of macrophytes communities.
LITERATURE CITED
Bendtsen, J.; Gustafsson, K.E.; Söderkvist, J., and Hansen, J.L.S.,
2009. Ventilation of bottom water in the North Sea–Baltic Sea
transition zone. Journal of Marine Systems, 75(1–2), 138–149.
Eriksson, B.K.; Johansson, G., and Snoeijs, P., 2002. Long-term
changes in the macroalgal vegetation of the inner Gullmar
Fjord, Swedish Skagerrak coast. Journal of Phycology, 38(2),
284–296.
Hollerbach, M.M. and Krasavina, L.K., 1983. Freshwater algae of
the USSR. Charales – Charophyta. St. Petersburg: Nauka, 190
p.
Isæus, M., 2004. Factors structuring Fucus communities at open
and complex coastlines in the Baltic Sea. Sweden: Stockholm
University, Ph.D. Thesis, 40 p.
Kovtun, A.; Torn, K., and Kotta J., 2009. Long-term changes in a
northern Baltic macrophyte community. Estonian Journal of
Ecology, 58(4), 270–285.
Schubert, H. and Blindow, I., (eds.), 2003. Charophytes of the
Baltic Sea. Gantner Verlag, 332 p.
Schwarz, A.M.; de Winton, M., and Hawes, I., 2002. Speciesspecific depth zonation in New Zealand charophytes as a
function of light availability. Aquatic Botany, 72(3–4), 209–
217.
Selig, U.; Schubert, M.; Eggert, A.; Steinhardt, T.; Sagert, S., and
Schubert, H., 2007. The influence of sediments on soft bottom
vegetation in inner coastal waters of MecklenburgVorpommern (Germany). Estuarine, Coastal and Shelf
Science, 71(1–2), 241–249.
Soulie-Märsche, I., 2008. Charophytes, indicators for low salinity
phases in North African sebkhet. Journal of African Earth
Sciences, 51(2), 69–76.
Shteinman, B.; Kamenir, Y., and Gophen, M., 1999. Effect of
hydrodynamic factors on benthic communities in Lake
Kinneret. Hydrobiologia, 408/409, 211–216.
Suursaar, Ü. and Kullas, T., 2006. Influence of wind climate
changes on the mean sea level and current regime in the
coastal waters of west Estonia, Baltic Sea. Oceanologia,
48(3), 361–383.
Suursaar, Ü. and Kullas, T., 2009. Decadal variations in wave
heights off Cape Kelba, Saaremaa Island, and their
relationships with changes in wind climate. Oceanologia,
51(1), 39–61.
Suursaar, Ü.; Kullas, T.; Otsmann, M.; Saaremäe, I.; Kuik, J., and
Merilain, M., 2006. Cyclone Gudrun in January 2005 and
modelling its hydrodynamic consequences in the Estonian
coastal waters. Boreal Environment Research, 11(2), 143–159.
Torn, K.; Martin, G.; Kotta, J., and Kupp, M., 2010. Effects of
different types of mechanical disturbances on a charophyte
dominated macrophyte community. Estuarine, Coastal and
Shelf Science, 87(1), 27–32.
Torn, K.; Martin, G.; Kukk, H., and Trei, T., 2004. Distribution of
charophyte species in Estonian coastal water (NE Baltic Sea).
Scientia Marina, 68(S1), 129–136.
Torn, K.; Martin, G., and Paalme, T., 2006. Seasonal changes in
biomass, elongation growth and primary production rate of
Chara tomentosa in the NE Baltic Sea. Annales Botanici
Fennici, 43(4), 276–283.
Yáñez, B.; Carballo, J.L.; Olabarria, C., and Barrón, J., 2008.
Recovery
of
macrobenthic
assamblages
following
experimental sand burial. Oceanologia, 50(3), 391–420.
ACKNOWLEDGEMENT
The study was supported by the ESF grants No.7609 and
No.8254 and Estonian target financed themes SF0180104s08 and
SF0180013s08.
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