MGM 164 Science Report
Marine Conservation Project
Science Report, Phase 164
Euan Mackenzie (Principal Investigator)
And
Ellen Vlaminck (Assistant Research Officer)
MGM 164 Science Report
List of Field Staff
Name
Position
Euan Mackenzie
Principal Investigator
Georgia Campbell-Harris
Dive Officer
Anastasia Harris
Assistant Research Officer
Ellen Vlaminck
Assistant Research Officer
Tali Nachoom
Assistant Research Officer
MGM 164 Science Report
Contents
Contents .................................................................................................................................................. 3
1
General Introduction....................................................................................................................... 4
1.1
Study areas.............................................................................................................................. 5
2 Long term biomonitoring - Comparisons of fish assemblages on varying coral reef quality
habitats. .................................................................................................................................................. 7
2.1
2.1 Introduction ...................................................................................................................... 7
2.2
Survey methodology ............................................................................................................... 7
2.3
Results ..................................................................................................................................... 8
2.4
Discussion................................................................................................................................ 9
3 Long term biomonitoring - Comparison of echinoderm, holothurian and asteroidean abundance
and diversity between sites with varying coral quality........................................................................... 9
3.1
3.1 Introduction .................................................................................................................... 10
3.2
3.2 Methods .......................................................................................................................... 11
3.2.1 Study location ...................................................................................................................... 11
3.2.2 Survey methods ................................................................................................................... 12
4
3.3
Results ................................................................................................................................... 12
3.4
Discussion.............................................................................................................................. 14
Collection and analysis of marine debris from coastal areas proximal to Nosy Be base camp .... 16
4.1
Introduction .......................................................................................................................... 16
4.2
Methods ................................................................................................................................ 16
4.3
Results ................................................................................................................................... 16
4.4
Discussion.............................................................................................................................. 18
MGM 164 Science Report
1 General Introduction
Coral reefs, which globally span ~527,072 km2, maintain the highest levels of diversity among marine
ecosystems containing thousands of fish, macro- and micro-invertebrate, megafauna, scleractinian
corals and octocorals (Veron et al., 2009; Mora et al., 2005). Many of these immense and fragile
ecosystems are in decline due to increasing environmental stressors, including rising ocean water
temperatures, runoff and sedimentation, ocean acidification, overfishing and pollution (Hughes et
al., 2003; Jackson et al., 2001). Such pressures change the structure of reefs, causing them to shift
from a scleractinian- dominated state to an algal, seaweed, and sponge dominated state (Bellwood
et al., 2004; Bell et al., 2013). Long- term ecological impacts of phase- shifts include loss of
invertebrate, fish, and coral diversity and abundance (Jackson et al., 2001; Hughes, 1994; Bellwood
et al., 2004), which in turn destabilises the coral reef ecosystems relied upon by many for
subsistence and income (Costanza et al., 1997).
Madagascar, the fourth largest island in the world with over 5,000 km of coastline, supports
extensive fringing reef systems, brackish and freshwater habitats, and shallow marine and pelagic
environments (Cooke et al., 2003). Around 3,500 km of the coastline is fringed with scleractinian
coral reefs, which are highly productive, dynamic and fragile ecosystems. With 55% of the
population of Madagascar living on the coast, over half of the nation is reliant on fisheries, both for
subsistence and income (Harris, 2011; Le Manach et al., 2012). Following a military backed coup in
2009, foreign aid was withdrawn and fish catch has largely gone unregulated and underreported by
an estimated 40%, leading to poorly managed fish and invertebrate stocks and the continuing
depletion of commercially important species, such as certain Holothurians (sea cucumbers) and large
fish species (Narozanski et al,. 2011; Le Manach et al., 2012). However, with a new president
elected in January 2014, there is hope that conservation and protection of reef ecosystems will
become an issue of importance. There are two fully decreed marine protected areas (MPA’s) in
Madagascar and multiple locally managed marine areas (LMMA’s), however only 2% of the country’s
coral reefs are located within protected zones and the majority of fisheries are regarded as
unsustainable (Harris, 2011). Even with imposed area and fishing restrictions, there is little
enforcement and the exploitation of many marine invertebrate and fish species continues to occur,
leading to increased levels of bio- eroders such as sea urchins that contribute to overall reef decline
(Bigot et al., 2003). Presently, much of Madagascar’s marine resources are depleted, leaving a legacy
of reduced fisheries catch, and a continuing decline toward an unstable level of overall species
abundance and diversity.
To further understand any anthropogenic effects on marine ecosystems, as well as to implement
successful conservation measures, baseline data is required on a wide range of ecological and
biological parameters. Detailed scientific data regarding fish assemblages, influential invertebrate
species abundances, and coverage of benthic substrata are needed to understand processes of how
all these organisms interact with each other and the ecosystem in which they survive. Frontier is a
conservation NGO based in the United Kingdom that has worked out of the village of Ambalahonko
on the island of Nosy Be in Northwest Madagascar since 2010. Trained scientists as well as volunteer
research assistants have used baseline surveys to accumulate extensive data on fish and macro
invertebrate assembles, as well as a preliminary assessment of seagrass diversity at sites within the
Nosy Vorona Bight. As such this report aims to characterise adult and juvenile fish assemblages of
MGM 164 Science Report
specific marine biotopes, examine abundance of echinoderms and opisthobranchs across different
habitats, and quantify marine debris in beach areas surrounding Ambalahonko base camp.
1.1 Study areas
During Phase 164, fish and invertebrate assemblages were examined at several sites within the Nosy
Vorona Bight in Northwest Madagascar (Table 1). Each site contained between one and two habitat
types, and each habitat fell into three broad categories according the dominate substrate type
present. Namely, coral, seagrass and sponge dominated. Coral dominated areas were further
categorised into one of two groups (live or degraded coral) according to health status and benthic
complexity/diversity giving a total of four distinct habitat types. This division was based on the
results of Toor (2015), who previously assessed coral complexity and diversity at several sites within
the region.
N
Figure 1. Location map of sites surveyed off Nosy Be and Nosy Komba during Phase 164. NV = Nosy Vorona,
TB = Three Brothers, TT = Turtle Towers, BP = Blue Pillars, DO = Doany, A51 = Area 51, BR = Black Rocks. Only
sites used in the phase are included.
MGM 164 Science Report
Table 1: Description of the study sites surveyed and known sites in Phase 164: LC, healthiest reef
classification; DC, degraded coral reef; Sg, seagrass- dominated; Sp, sponge- dominated habitat. *No
longer surveyed **Not surveyed due to degraded nature ***Currently not known to present staff
members –re-assess **** Currently not known to present staff members –re-assess ****
Site
GPS
Description
Nosy Vorona (LC)
13°25’30” S,
48°21’46” E
Three brothers (LC)
13°25’53” S,
48°21’50” E
Turtle Towers (LC)
13°26’48” S
48°20’09” E
Home Reef (DC)*
13°24’25” S,
48°20’22” E
Mad Hatters (DC)**
13°24’45” S,
48°20’10” E
Ampasipohy***
13°22’54” S,
48°20’59” E
Doany (LC, Sg)
13°23’59” S
48°21’19” E
Blue Pillars (LC,Sg)
13°27’06” S,
48°19’39” E
13°24’40” S,
48°21’34’' E
Fringing patchy reef formed around a small island.
Moderate live coral cover with extensive coral
rubble and patchy seagrass beds. Little terrestrial
influence, strong current, artisanal fishing pressure.
Temperature range 27°-31°C.
Fringing mix of continuous and patchy reef formed
around three distinct outcrops. Moderate live coral
cover, little terrestrial influence, moderate fishing
pressure. Temperature range 27°-31°C.
Large continuous reef with moderate live fringed
coral reef. Adjacent to MRCI camp. A small scale
MPA has been placed over this area to prevent
fishing and anchor damage. Temperature range
27°-31°C.
Previously a degraded coral reef. Site is now very
difficult to locate consisting of only patches of coral
rubble. Reef completely depleted.
Small degraded patchy reef. High fishing pressure
with high levels of sedimentation. Temperature
range 27°-31°C.
Dense seagrass bed proximal to small coral reef,
dominant species Thalassondendron ciliatum.
Temperature range 27°-31°C.
Patchy seagrass bed, shallow zone exposed at low
tide. Healthy coral patches recently observed to
begin surveying.
Large live and healthy coral reef. Extensive,dense
seagrass beds. Temperature range 27°-31°C.
Large shallow degraded coral reef close to human
settlement. Expansive Acropora beds with large
patches of dead coral, tops of coral can be exposed
and extreme low tides. High artisanal fishing
pressure, temperature range 27°-31°C.
Moderate sized, shallow degraded coral reef with
poor complexity in most parts. High fishing
pressure, occasionally exposed to high current.
Large live coral and sponge site in the middle of the
Vorona Bight. Strong currents and often high
sedimentation. Temperature range 27°-31°C.
Antafondro (DC)****
Black Rocks (DC)
13°24’52”S,
48°20’21”E
Area 51 (LC,Sp)
13°25’27”S,
48°20’71”E
MGM 164 Science Report
2 Long term biomonitoring - Comparisons of fish assemblages on
varying coral reef quality habitats.
2.1 2.1 Introduction
To understand the dynamics of coral reef fish assemblages, it is vital to examine interconnectivity
and relationships between proximal habitats in many coral reef environments. (Wilson et al., 2010;
Aguilar et al., 2014). Habitat selectivity and specificity is documented within many species and is
shaped by a variety of processes such as responses to predation, foraging efficiency and
reproduction (Sutherland, 1996; Wilson et al., 2010). Species of fish within the Lutjanidae, Scaridae
and Lethrinidae families, for example, have been shown in various locations to recruit to mangrove
or seagrass ecosystems, undergoing ontogenic phase shifts where they migrate to coral reefs as subadults or adults (Bell and Westoby, 1986; Lecchini and Galzin, 2005; Nagelkerken et al., 2002; Wilson
et al., 2010). In addition, the adults of many fish species, which are not directly associated with live
coral, still spend part of their early life history closely associated with corals (Jones et al., 2004).
Considering the decline of coral reefs and near shore habitats worldwide, this is a cause for concern;
the knock on effects of coral loss or mangrove removal will undoubtedly affect species that have
habitat specific recruitment, directly utilise these habitats as adults or depend on those that do
(Bellwood et al,. 2002; Honda et al., 2013). Given the rate of environmental deterioration
worldwide, coupled with unregulated fishing practices in developed and developing countries, it is
not surprising that our marine ecosystems are experiencing unprecedented stress (Harris, 2011;
Honda et al., 2013).
Previous studies have focused on the local interconnectivity of coral, algal, rubble and/or seagrass
habitats and their importance at different scales (Dorensbosch et al., 2004; Wilson et al., 2010;
Berkstrom et al., 2013). It is often suggested that the proximity of ‘nursery’ habitats to adjacent coral
reefs plays a role in determining the species diversity and assemblages that are present (Baelde,
1990; Nagelkerken et al., 2002). While it was beyond the scope of this study to examine the complex
ecological relationships and interconnectivity of habitats, the primary aim of this study was to
examine the differences in adult composition across a number of proximal habitats in Nosy Be,
Madagascar. Furthermore, understanding the reliance of fish species on certain habitats is vital to
ensure appropriate management and protection of marine resources (Wilson et al., 2010) This is
especially true in developing countries such as Madagascar, where reliance on natural resource
extraction is in some places the only means of survival (Le Manach et al., 2012). Thus, the
importance of coral habitat type for specific adult fish species or families was assessed.
2.2 Survey methodology
In order to examine the richness, diversity, and abundance of the different fish species and make a
comparison between sites, Baseline Survey Protocols (BSPs) were undertaken at five different sites
(Table 1). In each site, a minimum of six replicate surveys were performed to ensure accurate
statistical analysis. No distinction could be made between habitats in this phase since the
categorisation (live coral, dead coral, sponge habitat or sea grass) of the different investigated dive
sites needed to be reevaluated with actual benthic data,.
Baseline Survey Protocol (BSP)
MGM 164 Science Report
In each baseline survey there were five different research roles: physical surveyor, benthic surveyor,
invertebrate surveyor, territorial fish surveyor and schooling fish surveyor. When there were not
enough researchers to perform all the different tasks, it was made sure that at least one
invertebrate surveyor, one territorial fish surveyor and one schooling fish surveyor were always
present.
All surveys were done using SCUBA, except for surveys conducted at Black Rocks where snorkeling
gear was used. At each survey site, the visibility was measured or estimated by the physical
surveyor, who also placed the start of the transect line and measured out a line of 50m. Within a
5m2 box (2,5m on either side and 5m above the line) along this transect the other surveyors noted
down the abundances of all the inverts, schooling or territorial fish and the benthic surveyor noted
down all the changes in benthic cover. At the end of the survey the line was recovered.
All surveys were conducted within two hours either side of high tide to standardise the conditions
for the presence of fish. The schooling fish surveyor always went first along the line, as schooling fish
are more easily disturbed.
2.3 Results
A total of 7697 fish were observed over a 3-month period from September to December 2016,
representing 17 different families and 71 species. There was little variation in the number of families
between the different dive sites, with the lowest number of families found in Area 51 (N = 11) and
the highest at Turtle Towers (N = 16) (Table 1). The total number of species found at the different
dive sites varied from 31 species in Area 51 to 61 species in Nosy Vorona. This pattern was also
reflected in the Shannon diversity indices, as the lowest diversity (0.556) was present in Area 51 and
the highest diversity (2.775) in Nosy Vorona (Table 1, Figure 1)
Table 1. The total number of fish species and the total number of families recorded in each of the different dive sites
during phase 164 and the Shannon-Wiener Diversity index for all fish species in the different sites.
N° species
N° families
Shannon-diversity
Area 51
Blue Pillars
Nosy Vorona
31
11
0.556
53
12
2.482
61
13
2.775
Three
Brothers
55
12
2.710
Turtle Towers
50
16
2.159
The average fish abundance per survey varied greatly between the different sites, with a
minimum of 22 species per transect in Area 51 and a maximum of 265 species per transect in
Turtle Towers (Fig. 1).
MGM 164 Science Report
Average abundance / survey
350
300
250
200
150
100
50
0
Area 51
Blue pillars
Nosy Vorona
Three
brothers
Turtle towers
Figure 1. Average fish abundance per survey in the different investigated sites.
2.4 Discussion
Area 51 scores very low in all investigated parameters (n° fish species, n° fish families, ShannonWiener diversity and average fish abundance), compared with the other sites. From personal
observations, we can state that Area 51 has a larger portion of sponge habitat, relative to coral
habitat, than the other sites. In previous phases the same pattern was found, where the lowest
diversity of fish species and families was found in sponge habitats. This is likely explained by a high
abundance of coral associated species, including those in the Pomacentridae, Chaetodontidae and
Labridae families. Furthermore, many species within these families rely on scleractinian corals,
particularly branching corals, for shelter, protection, and as a food source (Cole et al., 2008; Reese,
1981; Bozec et al., 2005). Many wrasse feed upon small bivalves, decapods, gastropods and algae;
most of which are often in high abundances on many coral reefs and seagrass beds (Deady and Fives,
1995). These food sources are less abundant in sponge habitat, which may explain the low fish
diversity and abundance in Area 51.
The differences between the number of fish species and families and the Shannon diversity indices
are less evident between the other investigated sites. This may likely be explained by the close
proximity of many of the reefs, making them subject to the same biotic and abiotic influences.
Although the sites will differ in their exposure to environmental stressors, depending on the distance
from terrestrial environmental parameters to reef system, all sites occupy the same body of water,
thus receiving similar flushing times and nutrient turnover.
3 Long term biomonitoring - Comparison of echinoderm,
holothurian and asteroidean abundance and diversity between
sites with varying coral quality
MGM 164 Science Report
3.1 3.1 Introduction
Macroinvertebrates can play a vital role in the food webs of marine ecosystems, as well as
contributing to bioturbation and bioerosion of coral reefs, the latter of which can have an effect on
successful coral settlement (Bak, 1993). The phylum Echinodermata consists of the classes
Echinoidea (sea urchins), Asteroidea (sea stars), and Holothuroidea (sea cucumbers), as well as
Crinoidea (feather stars) and Ophiuroidea (brittle stars) with over 6,000 reef dwelling species critical
in the functionality and stability of coral reef ecosystems (Stella et al., 2010). The symbiotic
relationships of these invertebrate families with scleractinian corals, sponge, soft coral, sand, algae
and seagrass directly and indirectly affect the overall health of reefs. In fact, 51 species of
echinoderms are known to associate with scleractinian corals through direct consumption, as a
habitat to live on or inside of, or for mating (Stella et al., 2010). This causes a negative feedback loop
with the loss of scleractinian corals, which increases the competition between echinoderms for
resources, degrading the scleractinian corals even further (Stella et al. 2010; Dumas, 2007). Only 12
echinoderm species are known corallivores; however, with outbreaks of highly destructive species
such as the asteroidean, Acanthaster planci (crown of thorns starfish), the damage can still be
expansive (Stella et al., 2010).
The structural complexity of marine habitats depends on the species that live within microhabitats.
Sessile animals that form the substrata of different biotopes compete with each other for space,
largely based on life form, colonial or solitary, with different phyla of animals gaining success in
certain areas (Jackson, 1997). Colonial species, including scleractinian corals, tend to dominate reef
space, excluding solitary growth forms such as many sponge species, forcing them to colonise areas
off of the reef crest (Jackson, 1997). In sponge-dominated habitats, usually at greater depths than
scleractinian corals, species are able to exclude most colonial corals even without direct contact by
excreting allelochemical defences (Porter and Targett, 1988; Stella et al., 2010). With climate change
affecting sea-water temperatures and consequently many marine flora and fauna, it is possible that
reef structure may change irreversibly, shifting towards more sponge dominated reefs (Bell et al.,
2013). Warmer water temperatures, causing a higher acidity level and an increase in dissolved
inorganic carbon, prevent the growth of calcifying organisms including scleractinian corals, crustose
coralline algae, and some invertebrates (Caldeira & Wickett, 2003; Raven et al., 2005; Schneider and
Erez, 2006; Anthony et al., 2008; Jokiel et al., 2008). Historical evidence suggests that many sponge
species, while still affected by climate change, are more resilient to warmer water temperatures and
ocean acidification (Bell et al., 2013). With the current state of coral reefs and continuing
degradation, it is possible that sponge dominated reefs may once again emerge (Bell et al., 2013).
Distinct from both scleractinian coral and sponge-dominated biotopes, seagrass beds provide a
unique habitat and are regarded as ecologically important nurseries for many macroinvertebrate
species (Boström et al., 2006). Seagrass beds with high levels of biomass provide shelter and
different nutrient sources through the consumption of leaf tissue and of epiphytes that cover the
leaves of many seagrass species that macroinvertebrates are unable to find in other marine
microhabitats (Boström and Mattila, 1999; Attrill, et al. 2000). The difference in structure between
these biotopes promotes a difference in echinoderm diversity due to different spatial niches and
food resources and possibly less interspecific competition (Pante et al., 2006).
MGM 164 Science Report
Opisthobranchs, from the subclass Opisthobranchia, are gastropods with internal shells, external
shells, or no shell, that largely feed on sponges and macro algae, both of which can be distributed
across multiple marine biotopes (Faulkner and Ghiselin, 1983; Bell et al., 2013). As opisthobranchs
may consume coral and/or sponges, they are able to influence coral reef structure and, in turn,
could be largely affected globally by coral reef loss and degradation through bleaching events and
anthropogenic effects (Ziegler et al., 2014). They largely rely on chemoreceptors (rhinophores) that
are highly sensitive to source food and mates, (Puyana, 2002) and many species leave chemically rich
slime trails that are used to find prey as well as avoid predators (Puyana, 2002). Many chemicals that
are used by opisthobranchs as a defence mechanism are sourced from other organisms upon
consumption (Puyana, 2002). Due to sensitivity in chemoreceptors to changes in water quality,
opisthobranchs are regarded as influential indicators of reef health according to their diversity and
abundance.
This study aimed to examine echinoderm and opisthobranch abundance, species richness and
diversity between biotopes. With many echinoderms playing influential roles in the stability or
degradation of many coral reef ecosystems, it is key to assess the prevalence of destructive species
and their potential impacts on reefs in the area. This study was carried out through the use of
underwater visual censuses (UVC) to record the total number of Asteroidea, Echinoidea,
Holothuroidea and Opisthobranchs, in live coral, degraded coral, sponge, and seagrass habitats.
3.2 3.2 Methods
3.2.1 Study location
In this phase, sampling effort was focused primarily on healthy coral sites to establish differences
between them. Sampling effort is shown in table 5. Fishing pressure around the island is high,
although only from artisanal fishers and spear fishers who also collect sea cucumbers.
Table 5. Number of transects completed at each site during Phase 164. NV = Nosy Vorona, BP = Blue Pillars,
TB = Three Brothers, And = Andrekareka, and A51 = Area 51.
Live Coral
Site
# Trans.
NV
12
BP
2
TB
13
And
8
A51
15
MGM 164 Science Report
3.2.2 Survey methods
To examine the species richness, diversity and abundances of echinoids and opisthobranchs, a 25 m
transect line was laid parallel to the shore at a constant depth. After the transect line was laid, the
first observer slowly swam back to the beginning, recording any echinoids, holothurians and
asteroids that were observed within 1 m either side of the transect line. At the same time, the
second observer would follow behind and survey for opisthobranchs, again searching 1 m either side
of the line. When possible, a photograph was taken of each opisthobranch to aid identification at a
later stage. If this was not possible, a detailed description of the animal was recorded. To maintain
consistency in search effort, each survey typically lasted between 15 – 20 min. The total number of
combined transects for each site is listed in Table 5.
To examine differences in the abundance of species for each class of organism across live coral,
degraded coral, sponge, and seagrass habitats, an analysis of variance (ANOVA) was performed using
R. Prior to analysis data was square root transformed to normalise the data and increase the
importance of rare species. Homoscedasticity was checked using Levene’s test for homogeneity of
variances. Following this, Tukey’s HSD test was used for pair wise comparisons to separate
significance. Due to the overabundance of the echinoderm, D. setosum, recordings of this species
were removed for a comparative analysis. Furthermore, biodiversity was determined using the
Shannon-Wiener Diversity Index for classes separately, and all species combined for each habitat
type.
3.3 Results
A total of 4496 echinoderms, 23 holothurians and 22 asteroideans were recorded over a three
month period during phase 164. Of the 4496 echinoids recorded, 4087 individuals were the echinoid
Diadema setosum, while the remaining individuals were comprised of 4 separate species. Mean
abundances of families across sites are shown in table 6. Evenness of abundance is an important
factor to consider for interpretation of echinoid diversity, as the overabundance of D. setosum had a
large influence on the result. As such, this species was removed from the analysis for comparative
purposes.
Table 6. Mean abundance of invertebrate families across 5 surveys sites around Nosy Be and Nosy Komba.
Echinoids with and without D. setosum are included due to the significant abundances of this species.
Vorona
0
0
1.5
17.85
D. setosum
73.13
146.25
84
110
77.87
Holothurians
14.33
1.33
1
0.35
0.13
Asteroids
1.07
1.08
0
0.42
0.38
Echinoids,
setosum
minus
D.
Blue pillars
Three brothers
Turtle Towers
A51
19.5
MGM 164 Science Report
Shannon diversity indices (Fig 2) show the relative estimate diversity against survey effort. Levels of
diversity were considered as 1 being low and 5 being high. As standard, results <2.0 were considered
very poor diversity (Gering et al. 2002). All sites showed very low levels of invertebrate diversity.
Fig.2 shows the Shannon-diversity indices for sites in the phase. Area 51 showed the highest
diversity (0.57) and Nosy Vorona showed the lowest (0.11).
0.6
0.5
0.4
0.3
Diversity index
0.2
0.1
0
Area51
Vorona
Blue pillars
Three brothers Turtle towers
Survey Site
Fig 2. Shannon-Diversity indices for five dive survey sites.
Species richness estimates were also drawn to compare with diversity indices. Nosy Vorona was
found to have the lowest diversity index but consequently to have the second greatest species
richness.
12
10
8
Echinoids
Number of species 6
Holothurians
Asteroidea
4
Total
2
0
Area 51
Nosy Blue Pillars Three
Verona
brothers
Turtle
Towers
MGM 164 Science Report
Fig 3. Species richness across survey sites including total species richness.
3.4 Discussion
Consistent with results from previous phases, the urchin, D. setosum was very abundant in all areas.
This is likely the result of multiple influences, including low abundance of sea urchin predators on
the reef, particularly balistids, and an abundance of food sources including algae and sponge (Vance,
1979). While some triggerfish were sighted in the LC habitats, they were at such a low abundance
that it’s unlikely that they are able to keep D. setosum numbers balanced. Studies conducted in
Kenya (McClanahan and Shafir, 1990) found similar results with high urchin abundance, specifically
D. setosum, and D. savignyi, on reef in the absence of finfish predators. Furthermore, McClanahan
and Shafir (1990) found that the urchin Echinometra mathaei exhibited dominance over the larger
Diadema species, and excludes them in the absence of predators. This is contrary to the findings of
this study, with D. setosum appearing to be the dominant species and E. mathaei not being recorded
this phase where it has been previously. A later study conducted (McClanahan, 1998) found that E.
mathaei is the most susceptible to predation compared to other Indo-Pacific sea urchin species. The
low number of E. mathaei observed suggests either that they may have been over predated or out
competed by other holothurians. The low survey effort could also have caused this, with not enough
surveys being conducted in areas where E. mathaei resides. Variation of species dominance has
been seen to vary among reefs (McClanahan, 1997; McClanahan, 1998), and the reason for the
dominance of D. setosum on this particular reef and others in the area requires further exploration.
A high abundance of sea urchins on reefs can be productive for coral settlement as many sea urchins
are herbivorous grazers, removing algae from the reef, and simultaneously creating space for coral
recruits to settle (Smith et al., 2009). In fact, urchin abundance is usually higher on over-fished reefs
where predators and herbivorous competitors are scarce (Hay, 1984; McClanahan, 1990). In a study
conducted by Smith (2009), the presence of herbivores was required for coral settlement, and while
sea urchins contribute to algal grazing when herbivorous fish (largely parrotfish and surgeonfish) are
removed, an overabundance of urchins may induce a phase shift to urchin dominated reefs, which
could alter the entire reef structure (Hay, 1984; Smith et al., 2009). Different herbivorous species
target different types of algae and exhibit different methods of grazing the reef, and the variety of
which can be productive for coral growth and the limiting of which can be damaging (Smith et al.,
2009). Many sea urchins are considered bioeroders as they burrow into the framework of the reef
and can erode coral skeletons that they inhabit. Studies have attributed up to 75% of all bioerosion
on reefs to sea urchins, weakening the structure of scleractinian coral and the stability of coral reef
ecosystems (Bak, 1993; McClanahan and Shafir, 1990). Whether this is a process occurring on reefs
in the Nosy Be area remains to be quantified. This demonstrates the importance of maintaining
diversity of fish and invertebrates on coral reefs. Overfishing and other human induced effects of
removing large, predatory fish from reef have long lasting, top down effects on the rest of the
species that inhabit coral reefs.
Comparisons between diversity indices and species richness estimates reveal a large disparity
between predicated diversity. While it is considered that diversity was low across all sites, observed
and predicted diversity did not match with low predicted diversity in sites such as Nosy Vorona but
observed richness being significantly higher than other sites. This suggests that in areas such as
Vorona, sampling effort has revealed the richness equivalency point suggesting extra survey effort
MGM 164 Science Report
will only reveal minimal additional diversity. Future research should look to expand survey effort in
areas with a higher level of predicted diversity to find the equivalency points across all sites.
MGM 164 Science Report
4 Collection and analysis of marine debris from coastal areas
proximal to Nosy Be base camp
4.1 Introduction
Marine debris, especially plastic debris, have become ubiquitous in marine environments and are a
source of global concern due to their longevity and impact on marine organisms (Derraik, 2002). An
extensive review of published research has shown that between 60 - 80% of all marine debris is
plastic, and sources of plastic pollution are varied, but include equipment from fishers/fishing fleets,
other ship traffic, including container ships, deliberate littering or careless handling of waste
(Derraik, 2002). Proximity to industrialised areas, suburban areas and river mouths, and our overreliance on ‘disposable’ products are also significant contributing factors to the amount of marine
debris observed in a given area (Derraik, 2002).
Impacts from marine debris are varied, but affect many species globally. Direct deleterious effects
may be caused by macro or micro plastics, and may occur as a result of ingestion, exposure to toxic
substances adsorbed to plastic surfaces, or entanglement (Derraik, 2002; Wright et al., 2013). As
such, discarded or accidently released fishing equipment, such as nets that continue to ‘ghost fish’
and indiscriminately kill organisms for an extended period of time are also of ecological concern.
Indirect ecological consequences have also been documented, through the introduction of foreign or
invasive species attached to drifting debris (Derraik, 2002).
Collection of marine debris is one of the most effective ways to have a meaningful positive
environmental impact, and assess potential sources of environmental pollution so that management
strategies can be implemented that aim to curb input of non-biodegradable items. As such, Frontier
Madagascar regularly undertake beach cleans, and the following is a summary of items collected, a
discussion of potential sources of marine debris, and suggestions for management strategies that
may reduce the amount of marine debris in the area surrounding Ambalahonko.
4.2 Methods
Beach cleans were typically undertaken twice per week, approximately one hour either side of low
tide. Volunteers and staff would venture to the right of camp, passing Ambalahonko village and a
small stream, or left to Black Rocks, collecting debris as they go between the water and tree line.
For each piece of debris, the type and zone (sand, mangrove, tree line) in which it was collected was
recorded. Upon collection, debris was sorted into flammable and non-flammable items for burning,
or storage respectively. During Phase 164, a total of 5 collections took place to the left, and 8 took
place to the right of base camp.
4.3 Results
During phase 164, a total of 1821 pieces of marine debris were collected from sand, mangrove and
tree areas along the coastline proximal to Ambalahonko base camp. 948 pieces were collected from
mangrove areas, 805 from sandy areas and 62 pieces from the treeline furthest from the water.
Plastic (unidentifiable plastic objects, plastic bottles and plastic bags) accounts for more than 50% of
the total amount of debris found. The most common other items found throughout the phase were
metals, fabrics, clothing and paper (figure 4. All debris with an abundance value below 1.00% are
brought together into the category: Others.
MGM 164 Science Report
2% 2% 2% 2% 1%
3%
Plastic Other
2%
Fabric/Clothing
Metal
4%
Paper/cardboard
Plastic Bottle
5%
Glass
5%
50%
Batteries
Others
6%
Fishing Line/rope
7%
Shoes
9%
Plastic Bag
Polystrene
Figure 4. Composition of the debris collected during beach cleans to the left and right of Ambalahonko base
camp.
25
20
15
10
5
Left of camp
0
Right of camp
Plastic Bag
Plastic Bottle
Sweet Wrappers
Rice Bag
Fishing Line/rope
Lobster Pot
Metal
Shoes
Fabric/Clothing
Glass
China/Crockery
Batteries
Mosquito Net
Eletricals
Nappies
Lighters
Polystrene
Paper/cardboard
Cigarette pack
Other
Mean count per beachclean
Beach cleans on the right side of camp resulted in a significantly higher amount of collected debris
compared to the left side (62.2% and 37.8% respectively). Especially the amount of metals, fabrics,
glass and batteries found on the right side are higher. Unidentifiable plastic objects (Plastic Other)
were also recorded but were removed from the dataset as these recorded objects were significantly
higher than all other materials in both left (n = 324) and right (n = 548) of beach camp.
Marine debris material
Figure 5. Total number of pieces collected for each debris type during beach cleans to either the left or right
of Ambalahonko base camp.
MGM 164 Science Report
4.4 Discussion
Consistent with previously published works, plastic items were the most common type of debris
collected, and many were smaller fragments of unidentifiable origin and unknown age (Derraik,
2002; Santos et al., 2008). The significantly higher amount of debris collected on the right side of
camp may be explained by the location of the Ambalahonko village. Beach cleans on the right side
include the beach area in front of the village; this is also the area where the highest amount of
debris is collected. This knowledge allows us to believe that the origin of a great portion of the
debris is most likely local. Incidence of this type of debris may have been high due to a variety of
contributing factors. For example, a lack of education about the impacts of marine debris, a lack of
litter collection and processing facilities, and a current lack of alternatives to the use of such items.
As such, Environmental Awareness Days that focus the impacts of marine debris, the introduction of
waste bags and containers that are frequently collected and disposed of in the most environmentally
safe way possible (for a developing country where resources are limited), involvement of local
communities in beach cleans, and a discussion about possible alternatives to the use of plastic
products may be an excellent starting point for raising awareness and eventually reducing marine
debris of this nature. For the longer term, like most countries, a general move away from reliance on
single use plastic items is absolutely essential. This also holds true for batteries, which were
frequently collected and are especially toxic. Some progress could be made if funding was available
to buy small solar panels that could then in turn charge reusable batteries.
Of less ecological concern are other items collected such as paper/cardboard, organics and metals.
For the most part, these substances will degrade over time, and most are not especially harmful
when ingested. For this reason future work on reducing marine debris should primarily focus on
plastic items.
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