Newly dominant benthic invertebrates reshape competitive networks on contemporary Caribbean reefs
Competition is a fundamental process structuring ecological communities. On coral reefs, space is a highly contested resource and the outcomes of spatial competition can dictate community composition. In the Caribbean, reefs are increasingly dominated by non-scleractinian species like sponges, gorgonians, and zoanthids, yet there is a paucity of data on interactions between these increasingly common organisms and historically dominant corals. Here, we investigated interactions among these groups of sessile benthic invertebrates to better understand the role of spatial competition in shaping benthic communities on Caribbean reefs. We coupled surveys of competitive interactions on the reef with a common garden competition experiment to determine the frequency and outcome of interference competition among eight focal species. We found that competitive interactions were pervasive on Florida reefs, with 60% of sessile benthic invertebrates interacting with at least one other invertebrate. Increasingly common non-scleractinian species were some of the most abundant taxa and consistently outcompeted the contemporarily common scleractinian species Porites porites and Siderastrea siderea. The encrusting gorgonian, Erythropodium caribaeorum, was the most aggressive species, reducing the live area of its competitors on average 42% ± 7.04 (SE) over the course of 5 months. Surprisingly, the most aggressive species declined in size when competing, while some less aggressive species were able to increase or maintain area, suggesting a trade-off between aggressiveness and growth. Our findings suggest that competition among sessile invertebrates is likely to remain an important process in structuring coral reefs, but that the optimal strategies for maintaining space on the benthos may change. Importantly, many non-scleractinian species that now dominate reefs appear to be superior competitors, potentially increasing the stress on corals on contemporary reefs.
KeywordsCompetition Coral Sponge Zoanthid Gorgonian Coral reef Interference competition Acropora cervicornis Non-transitive network Competitive network
This work was conducted under permits FKNMS-2011-159, FKNMS-2014-060, FKNMS-2014-073, SAL-14-1579, and facilitated by a Grant from the National Science Foundation, Biological Oceanography program (OCE-1130786) to DEB. We thank the Florida Keys National Marine Sanctuary coral nursery in Key West and the Coral Restoration Foundation for providing corals for this experiment. We thank A. Durán, S. Csik, L. Shaver, C. Fuchs, M. Roycroft, and S. Ladd for assistance in the field.
MCL, AAS and DEB designed the study, MCL and AAS conducted fieldwork, MCL analyzed the data, all authors wrote the manuscript.
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
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