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

Abstract

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 land‐based 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.

Commentary: Managing Recovery Resilience in Coral Reefs Against Climate-Induced Bleaching and Hurricanes: A 15 Year Case Study From Bonaire, Dutch Caribbean

“…Sommer et al (2011) also present data collected at the same time (in 2008 and 2009) from 12 sites on the leeward side of Bonaire at 10 m depth and finding 20% coral cover. Our own data from 115 sites in Bonaire result in a coral cover estimate of 19% (De Bakker et al, 2019) which is very much in line with the estimate of Sommer et al (2011). Data from more researchers are shown in Table 1.…”

Impact of terrestrial erosion on coral reef health at Bonaire: a plea for nature-inclusive "watershed-to-reef" based coastal management

“…Future research aimed at identifying soil types across Bonaire, would therefore greatly benefit the accuracy of model estimations of watershed-specific run-off of sediments and nutrients. While hard coral cover is regarded as a reliable indicator of coral reef health, recent research efforts have recognized the added value of regarding species-specific life-history traits such as accretion rates and colony morphology when assessing the functional and ecological status of coral reefs (González- Barrios & Álvarez-Filip 2018, de Bakker et al 2019. Most opportunistic coral species are relatively stress tolerant, yet they lack the capacity to maintain the structural framework necessary to support ecological functioning and biodiversity (de Bakker et al 2019).…”

“…While hard coral cover is regarded as a reliable indicator of coral reef health, recent research efforts have recognized the added value of regarding species-specific life-history traits such as accretion rates and colony morphology when assessing the functional and ecological status of coral reefs (González- Barrios & Álvarez-Filip 2018, de Bakker et al 2019. Most opportunistic coral species are relatively stress tolerant, yet they lack the capacity to maintain the structural framework necessary to support ecological functioning and biodiversity (de Bakker et al 2019). Therefore, we encourage future studies to explore the relationship between watershed-specific properties and other metrics for coral reef health.…”

“…The leeward fringing reefs of Bonaire (Southern Caribbean) are known to display a wide range of ecological degradation from almost pristine configurations to reefs that are approaching full functional collapse (de Bakker et al 2017, de Bakker et al 2019. This spatial heterogeneity in coral reef degradation has been attributed to spatial variation in a variety of local disturbances, both at sea and on land (Roberts et al 2017, de Bakker et al 2019, which suggests that management of these local stressors, once identified, can benefit coral reef health. The island has a long history of terrestrial degradation, with invasive herbivores introduced in the 16 th Century, and widespread tree clearance in the early 1900s (Freitas et al 2005).…”

Adding insult to injury: Effects of chronic oxybenzone exposure and elevated temperature on two reef-building corals

“…Significant growth inhibition cannot be excluded at higher oxybenzone levels, longer exposure intervals or more sensitive coral species. The ecological and economic consequences of coral growth inhibition could be severe, as currently some reefs already cannot outgrow sea-level rise, posing a critical threat to the adjacent coastal region (De Bakker et al, 2019). Additional studies should focus on impaired PSII and related growth inhibition by UV filter exposure in more detail in order to evaluate its ecological significance.…”