The importance of sponges and mangroves in supporting fish communities on degraded coral reefs in Caribbean Panama.

Janina Seemann,Alexandra Yingst,Andrew H Altieri,Rick D Stuart-Smith,Graham J Edgar

doi:10.7717/peerj.4455

Abstract

Fish communities associated with coral reefs worldwide are threatened by habitat degradation and overexploitation. We assessed coral reefs, mangrove fringes, and seagrass meadows on the Caribbean coast of Panama to explore the influences of their proximity to one another, habitat cover, and environmental characteristics in sustaining biomass, species richness and trophic structure of fish communities in a degraded tropical ecosystem. We found 94% of all fish across all habitat types were of small body size (≤10 cm), with communities dominated by fishes that usually live in habitats of low complexity, such as Pomacentridae (damselfishes) and Gobiidae (gobies). Total fish biomass was very low, with the trend of small fishes from low trophic levels over-represented, and top predators under-represented, relative to coral reefs elsewhere in the Caribbean. For example, herbivorous fishes comprised 27% of total fish biomass in Panama relative to 10% in the wider Caribbean, and the small parrotfish Scarus iseri comprised 72% of the parrotfish biomass. We found evidence that non-coral biogenic habitats support reef-associated fish communities. In particular, the abundance of sponges on a given reef and proximity of mangroves were found to be important positive correlates of reef fish species richness, biomass, abundance and trophic structure. Our study indicates that a diverse fish community can persist on degraded coral reefs, and that the availability and arrangement within the seascape of other habitat-forming organisms, including sponges and mangroves, is critical to the maintenance of functional processes in such ecosystems.

Highlights

Recent research has revealed ongoing degradation of coral reef fish communities from habitat destruction and other human impacts (Hughes et al 2003; Knowlton and Jackson 2008; Wilkinson et al 2008; Jackson et al 2014)
The disproportionate targeting and depletion of larger size classes and high trophic levels can contribute to trophic imbalance in the reef fish community (Pauly et al 1998)
Specific questions we address include: Does this southwestern Caribbean fish community show signals of reef degradation and over-fishing? Is the reef fish community affected by proximity to other biogenic coastal habitats? Do reef organisms other than hard corals support the biomass and structure of the fish community? Which factors support fish species richness, biomass and trophic structure?

Summary

Introduction

Recent research has revealed ongoing degradation of coral reef fish communities from habitat destruction and other human impacts (Hughes et al 2003; Knowlton and Jackson 2008; Wilkinson et al 2008; Jackson et al 2014). Human disturbances to coastal ecosystems, including pollution, sedimentation, degradation of water quality and climate change, are causing the decline of hard coral cover (Hughes 1994; Jackson et al 2001; Aronson et al 2003). The disproportionate targeting and depletion of larger size classes and high trophic levels can contribute to trophic imbalance in the reef fish community (Pauly et al 1998). These negative impacts on fish populations threaten livelihoods and food security, given that reef fishes provide a major food source for coastal communities across the tropics (Cesar et al 2003)

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Conclusion