The persistence of Caribbean-reef-fish communities

Background/Question/Methods

The dynamics, productivity, persistence, resilience of biological communities, and the services they provide are greatly affected by the way in which species interact. It is therefore necessary to understand how human activities affect those networks of interactions. Both, interactions and impacts, occur in a spatial dimension. However, the vast majority of ecological networks are compiled at specific locations in a non-standard fashion. This have so far precluded the study of how network structural and dynamical properties are distributed across space. We manage to overcome this limitation, and in this paper we study how trophic network structure is distributed in 701 locations across the Caribbean Sea. Moreover, we provide insight on how network persistence correlates with human-driven impacts.

Results/Conclusions

In agreement with previous knowledge, we find that human density and fishing effort have a significant negative effect in species richness and fish biomass. However, the invisible web of connections between species is also impacted. We found that community persistence is significantly lower than expected, the larger is fishing effort or human population density. This shows how the community is impacted beyond its size or composition, leading to a weaker structure that would be more prone to systemic collapse. The impacts studied erode community stability by altering network structure. Modularity decreases significantly with fishing effort and with population density. This implies that, when facing a perturbation, there will be more co-extinctions in already impacted communities than in healthier, highly-modular networks. Moreover, we can test the effectivity of marine protected areas. They have been proven to increase fish biomass, however most MPAs in the Caribbean are not effective in the protection of trophic structure. Only by ensuring the recover of trophic structure, the community will be resilient enough to prevail in the long term.