Extreme spatial heterogeneity in carbonate accretion potential on a Caribbean fringing reef linked to local human disturbance gradients

The capacity of coral reefs to maintain their structurally complex frameworks and
to retain the potential for vertical accretion is vitally important to the persistence
of their ecological functioning and the ecosystem services they sustain. However,
datasets to support detailed along‐coast assessments of framework production rates
and accretion potential do not presently exist. Here, we estimate, based on gross bioaccretion
and bioerosion measures, the carbonate budgets and resultant estimated
accretion rates (EAR) of the shallow reef zone of leeward Bonaire – between 5 and
12 m depth – at unique fine spatial resolution along this coast (115 sites). Whilst the
fringing reef of Bonaire is often reported to be in a better ecological condition than
most sites throughout the wider Caribbean region, our data show that the carbonate
budgets of the reefs and derived EAR varied considerably across this ~58 km long
fringing reef complex. Some areas, in particular the marine reserves, were indeed
still dominated by structurally complex coral communities with high net carbonate
production (>10 kg CaCO3 m−2 year−1), high live coral cover and complex structural
topography. The majority of the studied sites, however, were defined by relatively
low budget states (<2 kg CaCO3 m−2 year−1) or were in a state of net erosion. These
data highlight the marked spatial heterogeneity that can occur in budget states, and
thus in reef accretion potential, even between quite closely spaced areas of individual
reef complexes. This heterogeneity is linked strongly to the degree of localized landbased
impacts along the coast, and resultant differences in the abundance of reef
framework building coral species. The major impact of this variability is that those
sections of reef defined by low‐accretion rates will have limited capacity to maintain
their structural integrity and to keep pace with current projections of climate change
induced sea‐level rise (SLR), thus posing a threat to reef functioning and biodiversity,
potentially leading to trophic cascades. Since many Caribbean reefs are more severely
degraded than those found around Bonaire, it is to be expected that the findings presented
here are rather the rule than the exception, but the study also highlights the
need for similar high spatial resolution (along‐coast) assessments of budget states and
accretion rates to meaningfully explore increasing coastal risk at the country level. The findings also more generally underline the significance of reducing local anthropogenic
disturbance and restoring framework building coral assemblages. Appropriately
focussed local preservation efforts may aid in averting future large‐scale above reef
water depth increases on Caribbean coral reefs and will limit the social and economic
implications associated with the loss of reef goods and services.

Acropora cervicornis, bioerosion, Bonaire, calcification, carbonate budget, Caribbean, climate
change, sea‐level rise


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