The Effects of Human Impact, from Invertebrate Fishery, on the Seagrass Meadows O F of Halodule Sp

The effects of human impact, from invertebrate fishery, on the seagrass meadows o f of Halodule sp. at Inhaca Island Mozambique

Emma Järperud

Degree project in biology, Master of science (1 year), 2006 Examensarbete i biologi 30 hp till magisterexamen, 2006 Biology Education Centre and Departement of animal ecology, Uppsala University Supervisors: Prof. Anders Berglund and Dr. Martin Gullström and Dr. Salomão Bandeira

Abstract

Exploitation by humans is known to have a negative impact on the exposed environment. This study investigated habitat characteristics and associated invertebrate faunal assemblages in intertidal seagrass communities mainly composed of Halodule sp. at Inhaca Island, Mozambique. Three areas, two exploited and one unexploited where surveyed. The study showed that there are differences in seagrass characteristics and fauna between the two exploited sites and the unexploited site, but invertebrate collecting by humans is most likely not the main reason for this. Still, it is of great importance to perform more studies in the vulnerable coastal areas to get a better knowledge of the impacts from anthropogenic activities.

Introduction

Seagrass meadows are found all around the world and most of these habitats and ranges of seagrass species has been described (Mukai, 1993). However, there are areas that are not well described, especially in the southern hemisphere including the East African coast and the islands of the western Indian Ocean (Green and Short, 2003).

Seagrass meadows are of great ecological importance and have a high biodiversity and production of both plants and animals. They are important as both fish and invertebrates use these habitats for foraging, for protection against predators and as nursery grounds. In addition, seagrass meadows are important for stabilization of sediment bottoms and water quality (Fonseca and Fisher, 1986; Terrados and Duarte, 2000). Due to the high productivity and other important ecological services they are also of great economical value (Costanza et al., 1997). Furthermore, seagrass may also have a biological value as medicine and fertilizers (de la Torre-Castro and Rönnbäck, 2004).

Seagrass meadows play an important role in the coastal environment since they, among other things, function as a link between mangroves and coral reefs. These three ecosystems are depending on each other; for example, many of the animals are utilizing mangrove and seagrass habitats during early life stages and when large enough to escape predators they migrate to coral reefs where they live as adults (Dorenbosch et al., 2005). The three ecological systems also together constitute a great protection from coastal erosion (Orth et al., 2006) and natural catastrophes such as storms and tsunamis (Conservation International, 2008).

In a worldwide perspective, seagrass habitats are rapidly decreasing due to anthropogenic activity as overexploitation and devastation from for example nutrient enrichment and sediment overloading (Green and Short, 2003). Changes in food webs (due to e.g. overfishing), mechanical damages such as dredging as well as weather and climate changes are also serious threats to seagrass ecosystems (Short and Wyllie-Echeverria, 1996; Duarte, 2002). In addition, an increased pressure from tourism may be harmful for this environment. As a result of the fast decrease of seagrass habitat, this valuable ecosystem was already in the early 1990s classified as a threatened biotope in the Rio convention (1992/93:13). Since then a progressive number of reports of seagrass die-off

1 have highlighted the great need of management and conservation efforts (Short and Wyllie-Echeverria, 1996; Green and Short, 2003; Walker et al., 2006). Because of their high primary production and a complex habitat structure the seagrass meadows can support a large variety of faunal and floral species (Gullström et al., 2002). As fishing areas, seagrass meadows are considered an important habitat by the fishermen themselves, and sometimes even more important than adjacent mangrove and coral reef habitats (Torre-Castro and Rönnbäck, 2004). Many of the species found in seagrass meadows are of commercial value; therefore these habitats are highly exploited by the human population in many areas. Around the coastal zones in the western Indian Ocean they are mainly exploited either by fishing or collection of invertebrates (Gullström et al., 2002).

Seagrass meadows are often inhabited by a large and diverse invertebrate fauna compared to other bottom types such as unvegetated bottoms (Boström and Bonsdorff, 1997), and the seagrass biomass seems to be one important factor contributing to structural complexity (Heck and Wetstone, 1977). There may be a relationship between macroinvertebrate community structure and seagrass biomass. In line with this, Atrill et al. (2000) found that a higher amount of seagrass plants available gives a greater macroinvertebrate biodiversity. Moreover, greater survival in seagrass meadows compared to unvegetated bottoms has been shown for vertebrates and invertebrates (reviewed by Orth et al., 1984).

One of the most abundant groups of invertebrates in shallow coastal waters is suspension- feeding bivalves, which are commonly associated with seagrass. Field experiments have shown positive effects on seagrass from interactions with suspension feeders (e.g. Peterson and Heck, 2001).

In the western Indian Ocean region studies on seagrass and animal interactions are relatively scarce (Gullström et al., 2002). Increasing the knowledge of such interactions is of great importance for the human livelihood, which depends on the food source (i.e. animals) provided by seagrass meadows.

The overall aim of this study was to investigate if invertebrate collectors affect the invertebrate fauna in seagrass meadows composed of Halodule sp. at Inhaca Island, Mozambique.

The specific objectives were to: - Determine if there is a difference in seagrass characteristics between three localities with different degree of exploitation. - Determine if there is a difference in fauna between three localities with different degree of exploitation. - Investigate which animals that are collected.

Figure 1a. The study area of Inhaca Island, Mozambique

Figure 1b. A satellite image of Inhaca Island with the three sampling localities (Exploited 1; Exploited 2 and Unexploited site) marked. The image is a subscene from the Landsat ETM, 2001- 05-07, band 5, 4, 3 as RGB (revised by Prof. Bengt Lundén at the Department of Physical Geography and Quaternary Geology at Stockholm University)

Study area

The study was conducted from October 2005 through January 2006 at Inhaca Island, 32 km east of Maputo, Mozambique (25° 58′ – 26° 05′ S, 32° 55′ – 33° 00′ E, Figure 1a and 1b). It is a relatively small but quite crowded island. Most of the population is either directly or indirectly depending on the marine environment for their daily livelihood, e.g. many of the women, with some help from children, collect invertebrates in the intertidal seagrass meadows (de Boer et al., 2002).

The eastern side of the island is exposed to the open sea and the conditions are rough, whereas the western side of the island is facing the more shallow and sheltered Maputo Bay. Kalk (1995) has described the environment thoroughly. In the northern as well as the southern parts of Inhaca there are large bays formed because of the island shape. In these areas wide-ranging tidal flats are found and through which tidal channels are passing. The channels connect with the ocean in both north and south and separate the island from the mainland. At extreme low tides it is possible to walk across the channels among different banks that appear (Macnae and Kalk, 1962). The tide at the island is semi-diurnal with an average of 3.3 m for spring tide and 1.5 m for neap tide (Tabela de Mares do Porto de Maputo).

Seagrass can be found in intertidal and shallow subtidal areas off the island and the diversity is higher than usually expected for such a small area. In fact, nine species can be found around the island, i.e. Cymodocea rotundata Ehrenb. et Hempr. Ex Aschers, Cymodocea serrulata (R. Br.) Aschers. et Magnus, Halodule sp.(Forsk.) Aschers. in Bossier (Halodule uninervis and Halodule wrightii), Halophila ovalis (R. Br.) Hook. f., Nanozostera capensis Setchell., Syringodium isoetifolium (Ascherson) Dandy, Thalassia hemprichii (Ehrenberg) Asherson and Thalassodendron ciliatum (formerly Cymodocea ciliata) (Forskål) den Hartog. Thalassodendron ciliatum is often mixed with Cymodocea serrulata at Inhaca Island (Bandeira, 2002). This can be compared with one of the most diverse areas in the world, Shark Bay in Australia, which inhabits twelve species in an area 84 times bigger than the seagrass area of Inhaca (Walker et al., 1988). Moreover, there are only around 60 different species of seagrass worldwide (Short et al., 2007).

Three seagrass meadows around Inhaca were selected based on observation during a pilot study the first three weeks. Two of them were subject of anthropogenic activity in terms of invertebrate fishery (exploited 1 and exploited 2) and the third one was a marine reserve without any major impact from invertebrate fishing (unexploited), (Figure 2). The dominant species in all localities were Halodule univeris and Halodule wrightii (hereafter mentioned as Halodule sp.) but Thalassia hemprichii, Cymodocea serrulata, Cymodocea rotundata, Halophilia ovalis and Nanozostera capensis could also be found in the Halodule-dominated seagrass meadows.

Site descriptions

Exploited 1 This site is located in the southwest region of the island, in direct contact with the shore and close to a local village (Figure 1b). It is an area easily available to humans and also sheltered by being situated in the bay. In this area, many women and children are daily collecting invertebrates. The bottom substrate is very fine and muddy.

Exploited 2 This site is also located in the southwest region of the island but on a sandbank at the other side of main channel (Figure 1b), and is available during the lowest spring tide. It is, like Exploited 1, also sheltered because of its location in the bay. To reach the area the

5 collectors have to cross the channel but still it was a very popular area. Also here the bottom substrate is very fine and muddy.

Unexploited site This site is the control site, located in the northwest region of the island (Figure 1b). This area is a land reserve, Ilha de Portugese, and is watched round the clock by two guards. Therefore, fishing and/or invertebrate collection are not performed within seagrass meadows of this site. The bottom substrate is sandier and has larger grain size then the two exploited sites. It is also more exposed from winds and waves.

Halodule sp.

The seagrass Halodule sp. plays an important role as pioneer colonizer, especially in areas with high disturbance. Halodule species, like many other seagrass species, do have an important rhizome system, binding sediment and stabilizing the sea bottom (Waycott et al., 2004). They are relatively small with a leaf width of 0.2-4 mm and a maximum length of 25 cm (Fig 2). The species are widely distributed and H. wrightii can be found in the temperate North Atlantic, the tropical Atlantic, the Mediterranean Sea, the temperate North Pacific and the tropical Indo-Pacific Ocean, whereas H. univeris is found in the tropical Indo-Pacific Ocean solely (Short et al., 2007).

Figure 2. A seagrass meadow dominated by Halodule sp.

Methods

Field work

The field work was carried out during low spring tide at a depth of 0-40 cm during a period of 8 weeks. On each sampling locality a transect of 4.5 m was placed randomly four times in the seagrass meadow. The transect had five squares each with a size of 0.5 x 0.5m (Figure 3). Seagrass was collected from 1/4, 1/6, or 1/9 of the area in the top left corner of the square, respectively. The size of the area was chosen so that at least 200 shoots were collected. From the whole square animals were collected using a sieve of 1 mm in mesh size. Thus, from each locality 20 squares was sampled.

4,5m

Figure 3. Transect of 4.5 meters with 5 squares of 0.25m2

Laboratory work

In the laboratory, different seagrass parameters were examined, including identification of different seagrass species, counting of shoots for density estimates of each seagrass species, and separation of shoots and roots for biomass estimations. Identification was performed with the same methodology as used by Waycott et al. (2004). For biomass estimates, shoots and roots were first wet-weighted and subsequently dry-weighted after being dried for at least 24 hours in 70°C.

Invertebrates were identified to species or the lowest taxonomic level possible, counted and weighted wet. Then they dried for at least 24 hours in 70°C and weighed again. The nomenclature used for identification of invertebrates were Kensley (1973), Fauchald (1977), Kilbum and Rippey (1982), Branch et al. (1994), Bosch et al. (1995), Richmond (1997), and Ruppert et al. (2004).

Invertebrate collection by woman

To be able to get a picture of what kind of animals that are collected by the local women, Elena, one of the women,was hired for sampling invertebrates. At every site a sampling area of 450 m2 was set up. Within each area Elena collected edible animals for 3 hours, with a starting point 1.5 hours before the lowest tidal point.

Analysis

One-way ANOVAs and post-hoc Tukey’s test were used to test for differences among the three different localities for total seagrass biomass, above-ground seagrass biomass, below-ground seagrass biomass, shoot density, animal biomass, number of animals and species richness, respectively. Prior to the analyses, the data have been tested for equal variances and for normality with Anderson Darling and log-transformed when necessary to meet basic assumptions. Regarding the parameter number of shoots one value was very

7 deviant but when removed the data followed normality. The significance value was set at 0.05 and all univariate analyses were performed using MINITAB Release 15.

An ordination with principal components analysis, PCA, implemented with the program CANOCO 4, was carried out to summarize and to examine spatial variation of invertebrate community structure that was based on the biomass data, both within and among seagrass meadows of different exploitation. Other factors such as seagrass biomass and number of different species were also included in the analysis. Axis 1 does always show the greatest variation. The axes are plotted and the objects that are similar will appear close to each other and the dissimilar will appear far apart (ter Braak and Šmilauer, 1998).

Results

In total, 1628 animals belonging to 74 different species were collected (Appendix 1). In general, the most common taxa were Bivalvia, Crustacea and Gastropoda, which built up almost 80 % of the invertebrate community (Fig 4).

The different taxa found in all localities (%).

Other taxa 14,9%

Echinodermata Bivalvia 6,8% 39,2%

Gastropoda 17,6%

Crustacea 21,6%

Figure 4. Diagram showing the proportion of different taxa (%) in the three localities studied (n=1628).

The five most common animals (written in order of commonness) in the sites were:

Exploited 1 Exploited 2 Unexploited area

Modilous sp. Holothuria sp. Sabellariidae Sipunculus sp. Cypraea annulus Polychaetae Gafrarium divaricatum Polychaetae sp. Scleractinia Pinna muricata Nuculoma lyardii Amphiolus sp. Pinnotheres dolfini Modilous sp. Modiolus sp

There were significant differences in seagrass biomass as well as below-ground biomass between the unexploited and the exploited 2 sites and also between the exploited 2 and the exploited 1 (Table 1, Fig 6,8). However, no differences were found for above-ground seagrass biomass or for the number of shoots (Table 1, Fig 7,9). In terms of animal biomass and number of animals, there were significant differences between the exploited 1 site and the other two sites, while there were no significant differences between the unexploited and the exploited sites for any of the two variables (Table 1, Fig 10-11). Species richness was significantly lower in the unexploited area compared to the exploited 2 and the exploited 1 site, respectively (Table 1, Fig 12). However, there was no significant difference between the exploited 2 and exploited 1 site (Table 1).

Table 1. Results of testing different responses; seagrass biomass, above-ground seagrass biomass, below-ground seagrass biomass, number of shoots, animal biomass, number of animals, number of different animal species between localities; unexploited (UE), exploited 1(E1) and exploited (E2) with general linear model and post-hoc Tukey’s test. Bar charts can be found in figure 6-12). Significant values are showed in italic bold.

Response variable Figure p p UE – E2 p UE – E1 p E2 – E1 Seagrass biomass 6 0.001 0.0014 1.000 0.0014 Above ground seagrass biomass 7 0.332 0.5705 0.3162 0.8955 Below ground seagrass biomass 8 0.001 0.0004 0.9219 0.0001 Number of shoots 9 0.409 0.9994 0.4879 0.4683 Animal biomass 10 0.001 0.0516 0.0001 0.0001 Number of animals 11 0.001 0.6017 0.001 0.0001 Species richness 12 0.001 0.0006 0.0001 0.0848

Total dry weight seagrass (g) per square meter + SE 180 160 b 140 120 a a 100 80 60 40 20 0 Dry weight seagrass (g) seagrass weight Dry Exploited 1 Exploited 2 Unexploited

Locality

Figure 6.Differences between localities for seagrass biomass in total dry weight seagrass (g) per square meter + SE. The same letters indicate non-significant differences and different letters significant differences.

Total dry weight shoots (g) per square meter + SE 30

Dry weight shoots (g) shoots weight Dry 0 Exploited 1 Exploited 2 Unexploited

Locality

Figure 7.Differences between localities for above ground biomass in total dry weight shoots (g) per square meter + SE. Sites did not differ significantly.

Total dry weight roots (g) per square meter + SE 160 140 b 120 100 a a 80 60 40 20

Dry weight roots (g) roots weight Dry 0 Exploited 1 Exploited 2 Unexploited

Locality

Figure 8.Differences between localities for below ground biomass in total dry weight roots (g) per square meter + SE. The same letters indicate non-significant differences and different letters significant differences.

Number of shoots per square meter + SE 3500

3000

2500

2000

1500

1000

500 Number of shootsof Number 0 Exploited 1 Exploited 2 Unexploited

Locality

Figure 9.Differences between localities for number of shoots + SE. Sites did not differ significantly.

Total dry weight (g) animals per square meter + SE 160 140 a 120 100 80 60 40 b 20 b

Dry weight animals (g) animals weight Dry 0 Exploited 1 Exploited 2 Unexploited Locality

Figure 10.Differences between localities for animal biomass in total dry weight animals per square meter + SE. The same letters indicate non-significant differences and different letters significant differences.

Number of animals per square meter + SE 40 a 35 30 25

20 b 15 b 10 5

Number of animals of Number 0 Exploited 1 Exploited 2 Unexploited Locality

Figure 11.Differences between localities for number of animals.+SE. The same letters indicate non-significant differences and different letters significant differences.

Animal species richness per square meter + SE 14 a

12 a 10 b 8

0 Animal species richness species Animal Exploited 1 Exploited 2 Unexploited

Locality

Figure 12.Differences between localities for animal species richness per square meter + SE. The same letters indicate non-significant differences and different letters significant differences.

Multivariate analysis

The data set contained 74 animal species and 60 samples. The eigenvalues for the first four PCA ordination axes were 0.38, 0.12, 0.11 and 0.07. Axis 1 explains most of the variation in animal abundance as can be concluded from its high eigenvalues compared to that of axis 2 (Figure 13).

Like the ANOVA tests the multivariate analysis show that animal biomass was the lowest in the unexploited site whereas exploited 1 and exploited 2 were more similar. The seagrass shoot/root ratio increased from unexploited to exploited 1 and exploited 2. Root dry weight and total dry weight of seagrass did not differ among the localities. The shoot dry weight and the number of shoots tended to increase towards the exploited 2 and exploited 1 sites (Figure 13).

Animal biomass

2,7 Axis 2

1,7

Exploited 1 0,7 Exploited 2 Ratio shoot/root dw Axis 1 Unexploited

-1 -0,5 -0,3 0 0,5 1 1,5 2 2,5

Shoots DW -1,3 Roots DW Total DW Seagrass # of Shoots

-2,3

Figure 13. PCA ordination showing sample scores marked according to locality. Animals collected in the area.

A summary of the species the hired collecting woman Elena found in the three different localities can be found in Table 2. The most common species collected in all the three localities were, by far, Modiolus sp. representing 55% of the total number of animals in exploited 1, 94% of the total number of animals in exploited 2 and 57% of the total number of animals in the unexploited site. Regarding the weight, Modiolus sp. represents 49% of the dry weight in exploited 1, 83% of the dry weight in exploited 2 and 39% of the dry weight in the unexploited site. The total catches in dry weight (kg) in the different localities with a total collecting time of 6 hours at two different occasions and two different sites within each locality were 2.5 kg in exploited 1, 2.5kg in exploited 2 and 1.3 kg in the unexploited.

Total number Total number Total number Taxon Species of animals of animals of animals collected in E1 collected in E2 collected in UE Bivalvia Anadara natalensis 14 8 7 Gafrarium divaricatum 16 0 1 Modiolus sp. 284 302 107 Pinctada sp. 95 0 14 Tapes sulcarius 4 0 0 Crustacea Calappa hepatica 3 0 2 Lupa pelagica 0 0 5 Thalamita poissoni 0 0 1 Echinodermata Astropecten polycanthus 0 0 1 Gastropoda Chicoreus ramosus 0 0 2 Conus tessulatus 37 0 6 Cypraea annulus 34 0 0 Nassarius coronatus 1 0 3 Polinices mamilla 0 0 7 Polinicinae simiae 2 0 0 Strombus gibberulus 5 0 29 Trachycardium pectiniforme 12 10 1 Volema paradisiaca 8 0 1 Table 2. Animals collected by the local invertebrate collecting woman Elena and the total number of each species in the three different localities exploited 1 (E1), exploited 2 (E2) and unexploited (UE). The most common specie collected was Modiolus sp. Representing 49% of the dry weight in exploited 1, 83% of the dry weight in exploited 2 and 39% of the dry weight in the unexploited site.

Discussion

The present study shows that there are differences in seagrass characteristics and fauna between the two exploited sites and the unexploited site around the island of Inhaca, though the invertebrate collecting is most likely not the main reason for the observed pattern.

The study showed that the total seagrasss biomass was significantly higher in the exploited site 2 compared to the other sites. This can be explained by the significantly higher root biomass in the same site, as there were no differences regarding the above ground seagrass biomass or the number of shoots. The animal biomass and animal abundance was significantly higher in the exploited site 1 compared with the two other sites and the species richness was significantly highest in the exploited site 1 followed by exploited site 2 compared with the unexploited site. These differences could depend on several factors, as the seagrass communities are exposed to a number of external factors such as wind, water movement, temperature, salinity and tides, which all interact and vary over time. These factors in a combination with the natural variations in the meadows themselves like patch size, fragmentation and grain size, are all most likely to affect and contribute to the complexity and differences of various seagrass meadows (Boström et al., 2006) maybe even a larger impact than the pressure from the collection.

In my case, looking closer into the unexploited site it differed in many aspects from the two exploited sites. The unexploited site was chosen because it functioned as a marine and land reserve and it was the only area more or less untouched by local collectors. The unexploited site was located in the northern part of the island where the tidal streams were strong and the beach was steeper resulting in a shorter time when the meadow was dry comparing with the two exploited. This may cause a different competition regime as the stress from the dry period is less and this opens up for an interspecific competition where the species that are the most competitive are the dominating ones, hence a lower species richness. The strong currents may also cause a lower recruitment and settlement as the larvae may flow by instead of settle (Todd, 1998).

Overall the two exploited sites were much more similar, in grain size and also in exposure to winds, waves and currents. But differences between the two exploited sites also appeared. The exploited site 2 had a significant higher below-ground seagrass biomass compared to site 1. The faunal composition for the two sites differed in both number of animals and dry weight, the exploited site 2 showed both a lower number of animals as well as a lower total dry weight compared to the exploited site 1. There was no significant difference in species richness between the sites. The big difference in animal dry weight is due to the larger number of animals in the exploited 1 site.

A possible explanation to the observed pattern might be that the exploited site 1 functions as a source, containing source populations of the fauna. A source population is a population where reproduction exceeds mortality and an excess of individuals dispersing to sink populations where mortality exceeds local reproduction. A sink population is dependent on individuals from a source population to sustain the population (Pulliam, 1988, Watkinson and Sutherland, 1995). Many of the organisms living in the sea grass meadows have a life-history including high dispersal, with high fecundity and externally fertilized pluteus larvae (Miller and Harley, 1999). These can travel with the ocean currents and spread to other places. The exploited site 1 may have very large populations that can contribute with the surplus of individuals (source population) to other sites (sink population).

Future studies, which investigate the source - sink relationships around Inhaca Island would be interesting as knowledge about source and sink populations are very important for management and a sustainable utilization of the area.

Another explanation for the differences in species richness and number of animals could be that a certain amount of disturbance can have a positive effect and stimulate the biodiversity and animal growth. According to the intermediate disturbance hypothesis a low frequency of disturbance results in that the strongest competitor wins and a high frequency of disturbance results in that only the most resistant species survive. But a mediate frequency of disturbance will generate the highest biodiversity (Krebs, 2001).

Regarding the results from the collection by the local woman Elena, an interesting and a bit surprising result was that the most common species by far, for all sites, was Modiolus sp., a result that do not agree with the results from my field samples. This could be an

effect of Elena’s non-random sampling method; she collected the species that could be utilized for food or for sale, compared to my sampling method, sampling/collecting all animals present.

In addition the dry weight of the animals, collected by Elena in the different sites does not agree with the results from my field work. Her results shows that the two exploited sites rendered twice the weight of the unexploited, which might indicate that the collection is very thorough and will “clear the area” of all valuable species, at least in the long run.

The complexity of seagrass meadows does not make an investigation easy but as the meadows are decreasing around the world (Short and Wyllie-Echeverria, 1996, Short et al., 2006), partly due to the human pressure it is vital to act fast. A loss of this important habitat can lead to large habitat loss and fragmentation (Eckrich and Holmquist, 2000), which will lead to sandy bottoms and decline in macroinvertebrate abundance and diversity (Boström and Bonsdorff, 1997).

In this study the results do not indicate that invertebrate collectors affect the invertebrate fauna in the seagrass meadows examined. But looking at how much one single person collected in only six hours the possibility of an impact should not be discarded as the full effects are not entirely recognized by this study. For a greater understanding of how the seagrass meadows and its fauna are affected it is of great importance to learn more about how much the seagrass communities means for a sustainable marine coastal environments and apply this knowledge in marine conservation and management.

Acknowledgment

This study had not been possible without my dear and true friend Lina Nordlund with whom it also was carried out, thank you. Thank you to my supervisors Prof. Anders Berglund, Uppsala University, Dr. Martin Gullström, Göteborg University and Dr. Salomão Bandeira, Eduardo Mondlane University in Mozambique. The study was mainly financed by the Swedish International Development Cooperation Agency (Sida) through SLU External Relations, thank you SLU External Relations. Two people I will never forget is Johan Öckerman and Anneli Alström that embraced me like family and was a big support all the way through my stay in Mozambique. Let’s talk about Meredith Ferdie, you came to the island like a whirlwind and made our days a lot sunnier, thank you Meredith. Other people I want to thank at Inhaca Island Biological station is Señor Pedro Saofrão, Rosario, Alberto, Castigo, Elena, Graza, Sergio, Valdimir and August.

Thanks to Pauli Snoeijs, Dept. of Plant Ecology, Uppsala University for the statistical help and to Bengt Lundén, department of Physical Geography and Quaternary Geology at Stockholm University for the satellite image.

I also would like to thank Josefine Larsson and Tove Porseryd for helping me finalize this theses.

Finally I would like to thank my mother, Ulla Britt Andersson and my father Jan Andersson for their support all the way and also my brother Gustav Järperud for your visit and support.

Reference list

Attrill, M.J., Strong, J.A., Rowden, A.A. 2000. Are macroinvertebrate communities influenced by seagrass structural complexity? Ecography 23: 114-121

Bandeira S. O. 2002. Diversity and distribution of seagrasses around Inhaca island, soutern Mozambique. South African journal of botany 68: 191-198

Bandeira S. O. 2000. Diversity and ecology of seagrass in Mozambique: Emphasis on Thalassodendron ciliatum structure, dynamics, nutrients and genetic variability. Dept of Marine Botany, Göteborg university

Bosch D.T., Dance S. P., Moolenbeek R. G., Oliver P. G. 1995. Seashells of Eastern Arabia. Motivate Publishing; London House, 19 Old Court Place, Kensington High Street, London W8 4PL

Boström C, Jackson E. L., Simenstad C. A. 2006. Seagrass landscapes and their effects on associated fauna: A review. Estuarine, Coastal and Shelf Science 68: 383-403

Boström C, Bonsdorff E. 1997. Community structure and spatial variation of benthic invertebrates associated with Zostera marina (L.) beds in SW Finland. Journal of Sea Research 37: 153-166 ter Braak, C.J.F., Smilauer, P. 1998. CANOCO reference manual and user's guide to Canoco for windows: software for canonical community ordination (version 4). Microcomputer Power, Ithaca, NY, USA

Branch G. M., Griffiths M. L., Beckky I. E. Branch M. L. 1994. Two Oceans: a guide to the marine life of Southern Africa. National Book printers, Zelda Street, Goodwood, Cape, South Africa

Conservation International. 2008. Economic Values of Coral Reefs, Mangroves, and Seagrasses: A Global Compilation. Center for Applied Biodiversity Science, Conservation International, Arlington, VA, USA. de la Torre-Castro M., Rönnbäck P. 2004. Links between humans and seagrasses- an example from tropical East Africa. Ocean and Coastal Management 47: 361-387

Costanza R., d’Arge R., de Groots R., Farber S., Grasso M., Hannon B., Limburg K., Naeem S., O¨Neill R.V., Paruelo J., Raskin R.G., Sutton P., van den Belt M. 1997. The value of the world's ecosystem services and natural capital. Nature 387:253-260

Cowen R.K., Sponaugle S. 2009. Larval dispersal and marine population connectivity. The Annual Review of Marine Science, 1, 443-66

Duarte C. M., 2002. The future of seagrass meadows. Environmental Conservation 29 (2): 192–206

Eckrich C. E., Homlquist J. G., 2000. Trampling in a seagrass assemblage: direct effects, response of associated fauna, and the role of substrate characteristics. Marine ecology progress series 201: 199-209

Fauchald K., 1977, The Polychaete worms; Definitions and Keys to the Orders, Families and Genera. Science Series 28

Fonseca M.S., Fisher J.S. 1986. A comparison of canopy friction and sediment movement between four species of seagrass with reference to their ecology and restoration. Marine Ecology Progress Series 29: 15-22

Green E.P., Short F.T., 2003. World atlas of seagrasses. Berkeley: University of Californa press

Gullström M., de la Torre-Castro M., Bandeira S. O., Björk M., Dahlberg M., Kautsky N., Rönnbäck P., Öhman M. C. 2002. Seagrass Ecosystems in the Western Indian Ocean, Ambio Vol 31 No. 7-8

Kalk M. 1995 3rd ed. A natural history of Inhaca Island, Mozambique. Witwatersrand University Press, 1 Jan Smuts Avenue, Joburg 2001 South Africa

Kensley B., 1973. Sea Shells of Southern Africa- Gastropods. Published by Maskew Miller Ltd, 7-11 Bury Street, Cape Town, in collaboration with the South African Museum. Printers Ltd, Cape Town

Kilbum R., Rippey E., 1982. Sea Shells of Southern Africa (1982) Published by Macmillan South Africa (Publishers) (Pty) Ltd Braamfontein Centre, Jorissen Street Johannesburg

Krebs C. J., 2001. Ecology 5th ed. Pp 452-453. Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Macnae W., Kalk M. 1962. The fauna and flora of sand flats at Inhaca Island, Moçambique. The journal of animal ecology Vol. 31 1: 93-128

Miller, S.A., Harley, J.P. 1999. Zoology. 4th ed. pp 408-409. WCB McGraw-Hill, USA

Mukai H. 1993. Biogeography and freshwater research. Australian journal of marine freshwater research Vol. 4 1: 1-17

Orth R.J., Carruthers T. J. B., Dennison W. C., Duarte C. M., Fourqurean J. W., Heck K. L. Jr., Hughes A. R. Kendrick G. A., Judson Kenworthy W., Olyarnik S., Short F. T., Waycott M., Williams S. L. 2006. A global crisis for seagrass ecosystems. BioScience Vol. 56 12: 987-996

Orth R.J., Heck K. L. Jr., van Montfrans J. 1984. Faunal communities in seagrass beds: A review of the influence of plant structure and prey characteristics on predator-prey relationships. Estuaries Vol 7 No. 4A: 339-350

Pulliam R.H. 1988. Sources, sinks and population regulation. The American Naturalist, 132, 652-661

Richmond M.D., 1997. A Field Guide to the Shores of Eastern Africa and the Western Indian Ocean Islands 2nd ed. Published by Sida/Department for Research Cooperation, SAREC, and University of Dar es Salaam

Ruppert E.E., Fox R.S., Bames R. D. 2004. Invertebrate Zoology 7th ed. Books/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a Trademark used herein under license

Short F.T., Carruthers T., Dennison W., Waycott M. 2007. Global seagrass distribution and diversity: A bioregional model. Journal of Experimental Marine Biology and Ecology 350: 3–20

Short F.T., Koch E., Creed J.C., Magalhaes K.M., Fernandez E.,Gaeckle J.L., 2006. SeagrassNet monitoring across the Americas: case studies of seagrass decline. Marine Ecology 27: 277–289

Short F.T., Coles R.G. 2001. Global Seagrass Research Methods, Elsevier Science

Short F.T., Wyllie-Echeverria S. 1996. Natural human-induced disturbance of seagrasses. Environmental conservation 23: 17-27

Terrados J., Duarte C.M. 2000. Experimental evidence of reduced particle resuspension within a seagrass (Posidonia oceanica L.) meadow. Journal of Experimental Marine Biology and Ecology 243: 45-53

Todd C.D., 1998. Larval supply and recruitment of benthic invertebrates: do larvae always disperse as much as we believe? Hydrobiologia 375/376: 1–21

Walker D.I., Kendrick G.A., McComb A.J. 2006. Decline and recovery of seagrass ecosystems – the dynamics of change In: Larkum A.W.D., Orth R.J. and Duarte C.M. (Eds.) Seagrasses: biology, ecology and conservation, Dordrecht, Springer, pp. 551-565

Walker D.I., Kendrick G.A., McComb A.J. 1988. The distribution of seagrass species in Shark Bay, Western Australia, with notes on their ecology. Aquatic Botany 30: 305-317

Watkinson A.R., Sutherland W.J. 1995. Sources, sinks, and pseudo-sinks. Journal of Animal Ecology, 64, 126-130

Waycott, M., McMahon, K., Mellors, J., Calladine, A., Kleine, D. 2004. A guide to tropical seagrasses of the Indo-West Pacific. James Cook University, Townsville

Reference list for species identification

Bosch, D.T., Dance, S.P.(editor), Moolenbeek, R.G. and Oliver, P.G. 1995. Seashells of Eastern Arabia. Published by Motivate Publishing; London House, 19 Old Court Place, Kensington High Street, London W8 4PL. Printed by Emirates Printing Press, Dubai UAE

Branch, G.M., Griffiths, C.L., Branch M.L. and Beckky I.E. (text); Branch, M.L. (line drawings; photographers as credited). 1994. Two Oceans: a guide to the marine life of Southern Africa. Printed by National Book printers, Zelda Street, Goodwood, Cape, South Africa

Fauchald K. 1977. The Polychaete worms; Definitions and Keys to the Orders, Families and Genera Science Series 28 February 3

Kensley B. 1973. Sea Shells of Southern Africa- Gastropods. Maskew Miller Ltd, 7-11 Bury Street, Cape Town, in collaboration with the South African Museum

Kilburn, R. and Rippey, E. 1982. Sea Shells of Southern Africa. Published by Macmillan South Africa (Publishers) (Pty) Ltd Braamfontein Centre, Jorissen Street Johannesburg. Printed in Hong Kong by South China Printing Co

Richmond, M.D. 1997. A Field Guide to the Shores of Eastern Africa and the WIO Islands. 2nd ed. Published by Sida/Department for Research Cooperation, SAREC, and University of Dar es Salaam. Printed in Italy by Eurolitho, Milano, 2002, through Italgraf, Västerås, Sweden

Ruppert, E.E., Fox, R.S. and Barnes, R.D. 2004. Invertebrate Zoology: a Functional Evolutionary Approach. 7th ed. Thompson, Books/Cole, Belmont

Waycott, M., McMahon, K., Mellors, J., Calladine, A., Kleine, D. 2004. A guide to tropical seagrasses of the Indo-West Pacific. James Cook University, Townsville

Reference list for maps http://www.pactworld.org/programs/country/images/mozambique_map.gif http://z.about.com/d/geography/1/0/C/J/mozambique.jpg http://www.birdingecotours.co.za/africa/images/tr_inhaca_map.jpg

Appendix 1. Animal species and other taxa in study localities.

Taxon Species Taxon Species Anguilliformes Gymnothorax undulatus Crustacea Macrophthalmus boscii Annelida Class Oligochaeta Menaethius monoceros Anthozoa Order Scleractinia Myra fugax Bivalvia Anadara antiquata Order Decapoda Anadara natalensis Philyra platychira Anodontia edentula Pilumnus verspetillo Anomia achaeus Pinnotheres sp. Atrina squamifera Thalamita cf. picta Codakia tigerina Thalamita poissoni Crassostrea cucullata Thalamita prymna Diplodontia sp. Thalamita sp Dosinia sp. Echinodermata Amphioplus sp. Eastonia solanderi Echinocardium cordatum Gafrarium divaricatum Holothuria sp. Gastrana matadoa Ophiocoma valenciae Gregariella sp. Tripneustes gratilla Loripes clausus Gastropoda Conus tessulatus Mactra ovalina Costellaria sp. Meropesta nicobarica Cypraea annulus Modiolus sp. Family Muricidae Modiolus ligneus Murex brevispina Nuculoma layardii Nassarius albescens gemmuliferus Pinctada sp. Nassarius coronatus Pinna muricata Polinices mamilla Pitar abbreviatus Polinicinae simiae Semele striata Strombus gibberulus Solen sloanii Strombus mutabilis Tapes literatus Tonna sp. Tapes sulcarius Ziba pretiosa Tellina sp. Hemichordata Class Enteropneusta Trachycardium pectiniforme Mollusca Dentalium bisexangulatum Venus tiara Polycheta Class Polychaeta Crustacea Alpheus sp. Eurithoe complanata Diogenes sp. Family Sabellariidae Family Ocipodidae Porifera Aaptos cf. chromis Family Xanthidae Sipuncula Siphonosoma cumanense cumanense Gonodactylus glabrous Sipunculus sp