Anthropogenic mortality on coral reefs in Caribbean Panama predates coral disease and bleaching

Abstract

Caribbean reef corals have declined precipitously since the 1980s due to regional episodes of bleaching, disease and algal overgrowth, but the extent of earlier degradation due to localised historical disturbances such as land clearing and overfishing remains unresolved. We analysed coral and molluscan fossil assemblages from reefs near Bocas del Toro, Panama to construct a timeline of ecological change from the 19th century-present. We report large changes before 1960 in coastal lagoons coincident with extensive deforestation, and after 1960 on offshore reefs. Striking changes include the demise of previously dominant staghorn coral Acropora cervicornis and oyster Dendrostrea frons that lives attached to gorgonians and staghorn corals. Reductions in bivalve size and simplification of gastropod trophic structure further implicate increasing environmental stress on reefs. Our paleoecological data strongly support the hypothesis, from extensive qualitative data, that Caribbean reef degradation predates coral bleaching and disease outbreaks linked to anthropogenic climate change.

Molluscan subfossil assemblages reveal the long-term deterioration of coral reef environments in Caribbean Panama

“…A recent reef coring program conducted at fringing reefs in Bocas' Almirante Bay found a general transition in coral dominance from Porites furcata to Agarica tenuifolia that occurred sometime after 1960 and was unprecedented over a millennial scale (Aronson et al, 2004(Aronson et al, , 2005. The analysis of subfossil coral assemblages excavated from large pits below modern reefs in Bocas confirmed that recent reef deterioration has deeper historical roots: the loss of the regionally co-dominant staghorn coral Acropora cervicornis occurred before 1960 and in some cases likely as far back as the early 1900s in lagoonal reefs, contemporaneous with the onset of land clearing for industrial agriculture (Cramer et al, 2012;Cramer, 2013). This change predated urchin and coral disease and coral bleaching events by at least two decades at lagoonal reefs, confirming the important role of local anthropogenic stressors.…”

“…The dominance of epifaunal suspension feeding bivalves in both environments is indicative of high-productivity coral reef environments dominated by hard substrates and influenced by terrigenous nutrients from river runoff (Birkeland, 1987;Todd et al, 2002). The prevalence of D. frons is a clear indication of the presence of branching colonies of the plexaurid and gorgoniid corals and staghorn coral A. cervicornis that are the primary hosts on which this oyster lives (Forbes, 1971;Cramer et al, 2012). The prevalence of dominant Chama congregata and subdominant C. macerophylla, typically found cemented to (dead) coral or other limestone debris (Jackson, 1972;Harries and Sorauf, 2010), indicates high availability of (live or dead) coral substrate.…”

“…These data were collected to provide ecological context for historical changes in coral communities observed on these same reefs (Cramer et al, 2012). First, we used the variability of the reef molluscan community across a known natural environmental gradient (lagoonal versus offshore reefs) to test the reliability of faunal differences as environmental proxies.…”

Tropical dead zones and mass mortalities on coral reefs

“…Changes in coral community structure were still evident nearly 4 y after the hypoxic event, with no apparent recovery in the cover of live coral (P > 0.10). Moreover, these changes occurred in an ecosystem where the coral community had already shifted toward more stress-tolerant species in recent centuries in association with human impacts, including fisheries exploitation and land-use change (30)(31)(32). The long-term effects of hypoxia are potentially different from, and more substantial than, those of other disturbances on coral reefs because hypoxia affects a broad range of taxa including consumers, habitat formers, and pathogens.…”

Evidence of size-selective evolution in the fighting conch from prehistoric subsistence harvesting

“…Almirante Bay (figure 1) was flooded sometime before 7.2 ka when modern fringing reefs began to develop [24]. Following the historical and more recent declines of the branching coral Acropora cervicornis [24,25], the fringing reefs of Bocas del Toro became dominated by a mixture of Porites and Agaricia [26].…”