Mon, Aug 02, 2021:On Demand
Background/Question/Methods
As coral reefs face an unprecedented suite of stressors that threaten to reduce biodiversity and drastically alter ecosystem function, it is more important than ever to understand what factors affect and alter community structure. The south shore of O‘ahu, Hawai‘i, is largely characterized by spur-and-groove coral reefs dominated by pocilloporid corals, including antler coral, the large and highly branching morphology of which attracts many fish and macroinvertebrate species. The Arc-eye Hawkfish (Paracirrhites arcatus), a mesopredator of fish recruits and macroinvertebrates, and the Blue-eye Damselfish (Plectroglyphidodon johnstonianus), an interference competitor, are common residents. On six 100m2 square reef plots, each centered around a 35-65cm diameter antler coral colony, I conducted a press removal of both focal species, leaving six other plots as unmanipulated controls, to determine the combined effects of these strong interactors on resident communities. I removed all non-focal fishes from this central colony at the start of the experiment, and then monitored fish and macroinvertebrate colonization, as well as planktivorous fish recruitment to the entire plot for six months.
Results/Conclusions Preliminary results suggest that, in the absence of the mesopredator and the interference competitor on the central antler coral, there was a resulting increase in (1) total resident fish abundance, (2) fish species richness, (3) colonization by a common planktivorous damselfish (Dascyllus albisella), and (4) macroinvertebrate abundance. Furthermore, there was evidence of increased recruitment of trapezid guard crabs, which have been shown to aid the host coral in several critical ways, including defense against invertebrate corallivores. Lastly, there was also evidence suggesting that recruitment of the planktivorous damselfish to the surrounding area may also increase slightly in the absence of the two strong interactors. These changes to community structure could, in turn, affect the host colony, as previous studies have found that the fertilizing excreta of greater resident fish biomass, particularly of planktivores, can significantly increase coral growth. These planktivores have also been shown to provide key benefits to the host coral such as aeration of internal branch tissue and sediment removal. Understanding such combined effects of predation and competition on community structure and potential indirect effects on coral demographic rates may provide insight on future changes in coral reefs as the oceans continue to warm and acidify.
Results/Conclusions Preliminary results suggest that, in the absence of the mesopredator and the interference competitor on the central antler coral, there was a resulting increase in (1) total resident fish abundance, (2) fish species richness, (3) colonization by a common planktivorous damselfish (Dascyllus albisella), and (4) macroinvertebrate abundance. Furthermore, there was evidence of increased recruitment of trapezid guard crabs, which have been shown to aid the host coral in several critical ways, including defense against invertebrate corallivores. Lastly, there was also evidence suggesting that recruitment of the planktivorous damselfish to the surrounding area may also increase slightly in the absence of the two strong interactors. These changes to community structure could, in turn, affect the host colony, as previous studies have found that the fertilizing excreta of greater resident fish biomass, particularly of planktivores, can significantly increase coral growth. These planktivores have also been shown to provide key benefits to the host coral such as aeration of internal branch tissue and sediment removal. Understanding such combined effects of predation and competition on community structure and potential indirect effects on coral demographic rates may provide insight on future changes in coral reefs as the oceans continue to warm and acidify.