Discussion

We expected coral complexity to play an important role in promoting fish family diversity and abundance. This prediction is based on previous studies where positive correlations between habitat diversity and associated animal communities have been reported (Hortal et al., 2009; Messmer et al., 2011). However, our study showed that coral reef complexity had no significant effect on both fish family richness and total fish abundance, supporting the null hypothesis in both scenarios. Similar results have been reported for terrestrial habitats, where the relationship between tree and vertebrate richness appeared to be poor (Currie, 1991). 

The fact that habitat diversity, in this case, coral complexity, does not necessarily predict fish family richness and fish abundance can be explained by multiple factors. First, biodiversity is an intrinsic and complex concept to study, and we just considered one out of many possible links. Other variables, such as climate, energy, and historical factors can shape the correlation among biodiversity patterns, or other aspects of habitat diversity. Additionally, it is possible that family diversity is linked to particular corals, i.e., only specific coral forms promote biodiversity: it is not the different number of forms, but the presence or absence of certain forms. Certain coral forms can support more abundant and diverse fish assemblages than others, although there are fewer coral forms. This could be the case with the forms that promote specialists and generalists as well. Further studies should address these hypotheses. Secondly, in this study, we focused on reef complexity, without considering other aspects of the habitat. For instance, rocks can provide 3D shelters and host a wide range of animals communities. However, from the definition of how we calculated the coral complexity, we gave a score of 0 to rocks, losing precious data on habitat diversity and complexity. Thirdly, the significant correlation between reef complexity and fish abundance and family diversity could exist, but we did not have enough data (low sampling size) to detect it. Furthermore, our study is based on a relatively poor dataset, because we only selected specific fish families. By not considering all fish families we have lost important data regarding biodiversity. Additionally, we missed potential data by not considering species richness. For this reason, our data are not strongly conclusive.

Despite this, we still detected that higher reef complexity predicted higher numbers of fish individuals for Surgeonfish. This significant trend is not present with the other fish families. This fact is surprising because we would have expected this trend for more resident fish families, as the non-territorial fish tend to move a lot and might not be the most representative for a study on reef complexity. However, this result is important in the context of conservation for this specific family. It would be interesting to further investigate the relationship between coral complexity and Surgeonfish species richness.

As for the depth analysis, not only we had a small and unbalanced sample size to consider depth as an explanatory variable, but also 15 meters depth is potentially not enough to detect significant differences.

Other problems with our dataset include the individual bias during the fish survey because different surveyors had different sensibility in detecting fish. As well as the individual estimation of coral structure percentage represents an important bias. Additionally, there was the risk of fish misidentification, especially for Damselfish, Butterflyfish, and Surgeonfish. Finally, we only sampled in Mangrove Bay, which is a major bias because the possible conclusive results are only valid in this area. A better methodology would have been to sample at different sites on the coast around the Red Sea, because there may be special phenomena going on in Mangrove Bay.