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Fish distribution in the reefs of the Red Sea, El Quseir

Alba Hendier, Géraldine Ischer & Margot Calderoni

Coral reefs and fishes have evolved together since their association 450 million years ago (Bellwood & Wainwright, 2002). Their complex relationship in therms of ecology allowed a high richness in coral and fish species (Messmer et al., 2011).

The red sea is older than 5000 years and the entire coastal reef complex extends along 2000 km of shoreline. Furthermore, the red sea has been identified as a region with both high biodiversity and strong endemism (Berumen et al., 2013). For instance, generea Acropora and Porites are part of the 10% of endemic species of the coral reef. 

The main goal of our project was therefore to observe the distribution of fish families on three reef habitats (reef surface, crest and slope) and to do an association between the families, their functional feeding group (filtrer, grazer and predator) and their physical distribution. 

Introduction

Picture of a Clown fish, Amphiprion bicinctus, in the crest area. Photo by Margot Calderoni 

Hypothesis: the distribution of reef fishes depends on their functional feeding group.

Methods

Data collection

We used a GoPro camera in order to film and compare several 10 meters-transects in the three specific habitats, namely reef surface, crest and slope.

The reef surface is the zone found the closest to the shore and it extends until the reef crest, which separates the reef surface from the seaward slope. The crest is the zone with the highest wave action while the slope presents the largest corals on the reef due to limited waves presence.

During three days, we repeated the measurements for each habitat (three times in the morning and three times in the afternoon).

Data analysis

In order to see the fish functional feeding groups distribution in the reefs, we used a linear mixed model (LMER) to enable the proper use of random terms as the day and the period of the day (am and pm) in which the measurment were done. The response variable was the proportion of fishes observed for each diet in each region.

For the fish family distribution in the reef, we used a linear regression. The response variable is the proportion of species per area and the explanatory variable are the areas and the families.

Results

We were able to observe 10 different fish families. Among the predators there were the Tetraodontidae, Scorpaenidae, Pomacanthidae, Holocentridae, Fistulariidae, Cirrhitidae, Labridae and Chaetodontidae. These last two famlies also included grazer species, as also the Acanthuridae. On the other hand, Pomacentridae were the only filterer familiy (figure 1).

Filterers were found above all on the surface and few in the slope. Grazers were mostly present in the slope, even if there was a good proportion in the crest and in the surface too. Predators were evenly distributed in the three regions. The date and the period of the day (am, pm) had no effect. Only the area had a significant effect (***p<0.001) (Figure 2).

Only the crest area showed a significant effect on the repartition of the different fish families (*p= 0.0144) even if we can observe a trend in the other areas (Figure 3). For example Acanthuridae are prevalently found in the crest, Holocentridae in the slope and Pomacentridae in the surface. 

Discussion & Conclusion

The functional feeding group helps to understand the distribution of fishes in the reef.

 

Indeed, the complexity of the corals and the different conditions (e.g light, turbidity of the water) on the surface and down the sea bring many habitats and different food. Most of the filterers were found on the surface as for instance the Pomacentridae. Grazers were observed at most in the crest (i.e. Acanthirudae) while predators were evenly distributed. So, the habitat preference among a family can vary a lot depending on the functional feeding group. For instance, Chaetodontidae as well as Pomacanthidae are both found in the three different areas. In fact, depending on the phylogeny of a family, some reef associations can have nonreef origins (Sale et al., 2002) and this could explain why several genera and species of these two families are also found in deep water. This confirms that it is more relevant to look for the repartition of the functional feeding group instead of the family’s repartition as already described (Messmer et al., 2011). In fact, the diet in a same family varies at the level of the gender; so further studies should look at the gender level for the repartition.

Each area of the coral reef (slope, surface, crest) therefore provides the ideal conditions for a given functional feeding group. For instance, filterers might mostly be found in the surface because of the higher prevalence of plankton. On the other hand, grazers are mostly found in the crest, as most of the algal turfs are present in the crest compared to slope and surface (Russ, 2003).

 

As already seen the distribution of organisms in the red sea is greatly influenced by the variety of environmental factors, including irradiance, salinity, temperature, pressure, nutrients and wastes (Khalaf et al., 2014). Also, the specific ability of an organism to tolerate physical changes in these factors is important for determining its marine distribution.  

References

  • Berumen, Michael L., et al. "The status of coral reef ecology research in the Red Sea." Coral Reefs 32.3 (2013): 737-748.
     

  • Bellwood & Wainwright, "Chapter 1- The History and Biogeography of Fishes on Coral Reefs", Pages 5-32,  Coral Reef fishes (2002) : 978-0-12-615185-5
     

  • Khalaf, Maroof A., and Mohamed Abdallah. "Spatial distribution of fifty ornamental fish species on coral reefs in the Red Sea and Gulf of Aden." ZooKeys 367 (2014): 33.
     

  • Messmer, Vanessa, et al. "Habitat biodiversity as a determinant of fish community structure on coral reefs." Ecology 92.12 (2011): 2285-2298.
     

  • Russ, G. R. "Grazer biomass correlates more strongly with production than with biomass of algal turfs on a coral reef." Coral reefs 22.1 (2003): 63-67.
     

  • Sale, Peter F., ed. Coral reef fishes: dynamics and diversity in a complex ecosystem. Academic Press, 2002. 

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