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Andersson, AJ, Venn AA, Pendleton L, Brathwaite A, Camp EF, Cooley S, Gledhill D, Koch M, Maliki S, Manfrino C.  2019.  Ecological and socioeconomic strategies to sustain Caribbean coral reefs in a high-CO2 world. Regional Studies in Marine Science. 29   10.1016/j.rsma.2019.100677   AbstractWebsite

The Caribbean and Western Atlantic region hosts one of the world's most diverse geopolitical regions and a unique marine biota distinct from tropical seas in the Pacific and Indian Oceans. While this region varies in human population density, GDP and wealth, coral reefs, and their associated ecosystem services, are central to people's livelihoods. Unfortunately, the region's reefs have experienced extensive degradation over the last several decades. This degradation has been attributed to a combination of disease, overfishing, and multiple pressures from other human activities. Furthermore, the Caribbean region has experienced rapid ocean warming and acidification as a result of climate change that will continue and accelerate throughout the 21st century. It is evident that these changes will pose increasing threats to Caribbean reefs unless imminent actions are taken at the local, regional and global scale. Active management is required to sustain Caribbean reefs and increase their resilience to recover from acute stress events. Here, we propose local and regional solutions to halt and reverse Caribbean coral reef degradation under ongoing ocean warming and acidification. Because the Caribbean has already experienced high coral reef degradation, we suggest that this region may be suitable for more aggressive interventions that might not be suitable for other regions. Solutions with direct ecological benefits highlighted here build on existing knowledge of factors that can contribute to reef restoration and increased resilience in the Caribbean: (1) management of water quality, (2) reduction of unsustainable fishing practices, (3) application of ecological engineering, and (4) implementing marine spatial planning. Complementary socioeconomic and governance solutions include: (1) increasing communication and leveraging resources through the establishment of a regional reef secretariat, (2) incorporating reef health and sustainability goals into the blue economy plans for the region, and (3) initiating a reef labeling program to incentivize corporate partnerships for reef restoration and protection to sustain overall reef health in the region. (C) 2019 The Authors. Published by Elsevier B.V.

Guest, JR, Edmunds PJ, Gates RD, Kuffner IB, Andersson AJ, Barnes BB, Chollett I, Courtney TA, Elahi R, Gross K, Lenz EA, Mitarai S, Mumby PJ, Nelson HR, Parker BA, Putnam HM, Rogers CS, Toth LT.  2018.  A framework for identifying and characterising coral reef "oases" against a backdrop of degradation. Journal of Applied Ecology. 55:2865-2875.   10.1111/1365-2664.13179   AbstractWebsite

1. Human activities have led to widespread ecological decline; however, the severity of degradation is spatially heterogeneous due to some locations resisting, escaping, or rebounding from disturbances. 2. We developed a framework for identifying oases within coral reef regions using long-term monitoring data. We calculated standardised estimates of coral cover (z-scores) to distinguish sites that deviated positively from regional means. We also used the coefficient of variation (CV) of coral cover to quantify how oases varied temporally, and to distinguish among types of oases. We estimated "coral calcification capacity" (CCC), a measure of the coral community's ability to produce calcium carbonate structures and tested for an association between this metric and z-scores of coral cover. 3. We illustrated our z-score approach within a modelling framework by extracting z-scores and CVs from simulated data based on four generalized trajectories of coral cover. We then applied the approach to time-series data from long-term reef monitoring programmes in four focal regions in the Pacific (the main Hawaiian Islands and Mo'orea, French Polynesia) and western Atlantic (the Florida Keys and St. John, US Virgin Islands). Among the 123 sites analysed, 38 had positive z-scores for median coral cover and were categorised as oases. 4. Synthesis and applications. Our framework provides ecosystem managers with a valuable tool for conservation by identifying "oases" within degraded areas. By evaluating trajectories of change in state (e.g., coral cover) among oases, our approach may help in identifying the mechanisms responsible for spatial variability in ecosystem condition. Increased mechanistic understanding can guide whether management of a particular location should emphasise protection, mitigation or restoration. Analysis of the empirical data suggest that the majority of our coral reef oases originated by either escaping or resisting disturbances, although some sites showed a high capacity for recovery, while others were candidates for restoration. Finally, our measure of reef condition (i.e., median z-scores of coral cover) correlated positively with coral calcification capacity suggesting that our approach identified oases that are also exceptional for one critical component of ecological function.

Yeakel, KL, Andersson AJ, Bates NR, Noyes TJ, Collins A, Garley R.  2015.  Shifts in coral reef biogeochemistry and resulting acidification linked to offshore productivity. Proceedings of the National Academy of Sciences of the United States of America. 112:14512-14517.   10.1073/pnas.1507021112   AbstractWebsite

Oceanic uptake of anthropogenic carbon dioxide (CO2) has acidified open-ocean surface waters by 0.1 pH units since preindustrial times. Despite unequivocal evidence of ocean acidification (OA) via open-ocean measurements for the past several decades, it has yet to be documented in near-shore and coral reef environments. A lack of long-term measurements from these environments restricts our understanding of the natural variability and controls of seawater CO2-carbonate chemistry and biogeochemistry, which is essential to make accurate predictions on the effects of future OA on coral reefs. Here, in a 5-y study of the Bermuda coral reef, we show evidence that variations in reef biogeochemical processes drive interannual changes in seawater pH and Omega(aragonite) that are partly controlled by offshore processes. Rapid acidification events driven by shifts toward increasing net calcification and net heterotrophy were observed during the summers of 2010 and 2011, with the frequency and extent of such events corresponding to increased offshore productivity. These events also coincided with a negative winter North Atlantic Oscillation (NAO) index, which historically has been associated with extensive offshore mixing and greater primary productivity at the Bermuda Atlantic Time-series Study (BATS) site. Our results reveal that coral reefs undergo natural interannual events of rapid acidification due to shifts in reef biogeochemical processes that may be linked to offshore productivity and ultimately controlled by larger-scale climatic and oceanographic processes.

Andersson, AJ, Bates NR, Mackenzie FT.  2007.  Dissolution of carbonate sediments under rising pCO(2) and ocean acidification: Observations from Devil's Hole, Bermuda. Aquatic Geochemistry. 13:237-264.   10.1007/s10498-007-9018-8   AbstractWebsite

Rising atmospheric pCO(2) and ocean acidification originating from human activities could result in increased dissolution of metastable carbonate minerals in shallow-water marine sediments. In the present study, in situ dissolution of carbonate sedimentary particles in Devil's Hole, Bermuda, was observed during summer when thermally driven density stratification restricted mixing between the bottom water and the surface mixed layer and microbial decomposition of organic matter in the subthermocline layer produced pCO(2) levels similar to or higher than those levels anticipated by the end of the 21st century. Trends in both seawater chemistry and the composition of sediments in Devil's Hole indicate that Mg-calcite minerals are subject to selective dissolution under conditions of elevated pCO(2). The derived rates of dissolution based on observed changes in excess alkalinity and estimates of vertical eddy diffusion ranged from 0.2 mmol to 0.8 mmol CaCO3 m(-2) h(-1). On a yearly basis, this range corresponds to 175-701 g CaCO3 m(-2) year(-1); the latter rate is close to 50% of the estimate of the current average global coral reef calcification rate of about 1,500 g CaCO3 m(-2) year(-1). Considering a reduction in marine calcification of 40% by the year 2100, or 90% by 2300, as a result of surface ocean acidification, the combination of high rates of carbonate dissolution and reduced rates of calcification implies that coral reefs and other carbonate sediment environments within the 21st and following centuries could be subject to a net loss in carbonate material as a result of increasing pCO(2) arising from burning of fossil fuels.