The effects of ocean acidification on demersal Zooplankton using natural carbon dioxide seeps as windows into the future

Abstract

The incessant progression of ocean acidification does not bode well for many marine ecosystems and their associated organisms. Coral reefs are especially in jeopardy due to direct and indirect effects of ocean acidification. Carbon dioxide seeps were used as natural laboratories to study the effects of ocean acidification on demersal zooplankton communities residing in coral reefs. The results from this thesis reveal yet another mechanism that may contribute to the degradation of coral reefs, since the very basis of their food webs, demersal zooplankton, was reduced in abundance under high carbon dioxide conditions. Different drivers influence different zooplankton taxa and collectively contribute to an overall decline in the demersal zooplankton community. Habitat loss was the primary cause for zooplankton abundance loss, but it was not the only cause, as seen with the pontellid copepods that were no longer associated with any type of substrata under high carbon dioxide conditions. The loss in zooplankton abundance will have implications for their predators, including corals. A case study on heterotrophy for the stony coral Galaxea fascicularis revealed, unexpectedly, that they consumed less zooplankton under ocean acidification. Fewer zooplankton particles available in the water column combined with depressed feeding rates suggests that corals may become nutrient limited, with likely consequences for their overall health. Decreased zooplankton quantities will have repercussions on the ecosystem that may be felt socially and economically.