Presenter: Ana Molina
Session: 3G - Budgetary breakdown: Can reef geo-ecological functions persist in the Anthropocene?
Location: Focke-Wulf Saal
Format: Talk
How have carbonate budgets transitioned in recent years in reefs that currently present low and even negative rates? Unfortunately, the disproportionate decline in the cover of primary reef-building species across the Western Atlantic has reduced their capacity to accumulate carbonate structure, jeopardizing the persistence and functionality of many coral reefs. Currently, many reefs present low and negative carbonate budgets or balances (i.e., erosion higher than production); however, our understanding of the temporal trajectories of these carbonate budgets is limited, in part because of a lack of historical data on the bioerosion side of the equation.
Here we use a temporal data set from 34 reef sites to explore how carbonate production and bioerosion rates, as well as the organisms underlying these processes, have changed over the past two decades in the absence of further severe acute disturbances. We find that despite fundamental benthic ecological changes, these ecologically shifted coral assemblages have exhibited a modest but significant increase in their net carbonate budgets. However, contrary to expectations, this trend was driven by a decrease in erosion pressure, mainly resulting from changes in the size-frequency distribution of the parrotfishes and in the abundance of excavating species, particularly of the stoplight parrotfish (S. viride), and not by an increase in rates of gross coral carbonate production. Although, in the short term, the carbonate budgets seem to have benefitted marginally from reduced parrotfish erosion, the absence of these parrotfishes may lock the system into low-budget states as they are also key herbivores that favor reef resilience. Our findings highlight the importance of the ecological-historical context in the interpretation of current carbonate values, especially when oriented to management and conservation efforts and environmental policy.
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