1. Enochs, I.C., D.P. Manzello, A. Tribollet, L. Valentino, G. Kolodziej, E.M. Donham, M.D. Fitchett, R. Carlton, and N.N. Price. Elevated colonization of microborers at a volcanically acidified coral reef. PLoS ONE, 11(7):e0159818, doi:10.1371/journal.pone.0159818 2016

    Abstract:

    Experiments have demonstrated that ocean acidification (OA) conditions projected to occur by the end of the century will slow the calcification of numerous coral species and accelerate the biological erosion of reef habitats (bioerosion). Microborers, which bore holes less than 100 μm diameter, are one of the most pervasive agents of bioerosion and are present throughout all calcium carbonate substrates within the reef environment. The response of diverse reef functional groups to OA is known from real-world ecosystems but, to date, our understanding of the relationship between ocean pH and carbonate dissolution by microborers is limited to controlled laboratory experiments. Here we examine the settlement of microborers to pure mineral calcium carbonate substrates (calcite) along a natural pH gradient at a volcanically acidified reef at Maug, Commonwealth of the Northern Mariana Islands (CNMI). Colonization of pioneer microborers was higher in the lower pH waters near the vent field. Depth of microborer penetration was highly variable both among and within sites (4.2–195.5 μm) over the short duration of the study (3 mo.), and no clear relationship to increasing CO2 was observed. Calculated rates of biogenic dissolution, however, were highest at the two sites closer to the vent and were not significantly different from each other. These data represent the first evidence of OA-enhancement of microboring flora colonization in newly available substrates and provide further evidence that microborers, especially bioeroding chlorophytes, respond positively to low pH. The accelerated breakdown and dissolution of reef framework structures with OA will likely lead to declines in structural complexity and integrity, as well as possible loss of essential habitat.

  2. Enochs, I.C., D.P. Manzello, G. Kolodziej, S.H.C. Noonan, L. Valentino, and K.E. Fabricius. Enhanced macroboring and depressed calcification drive net dissolution at high CO2 coral reefs. Proceedings of the Royal Society B, 283(1842):20161742, doi:10.1098/rspb.2016.1742 2016

    Abstract:

    Ocean acidification (OA) impacts the physiology of diverse marine taxa; among them corals that create complex reef framework structures. Biological processes operating on coral reef frameworks remain largely unknown from naturally high-carbon-dioxide (CO2) ecosystems. For the first time, we independently quantified the response of multiple functional groups instrumental in the construction and erosion of these frameworks (accretion, macroboring, microboring, and grazing) along natural OA gradients. We deployed blocks of dead coral skeleton for roughly 2 years at two reefs in Papua New Guinea, each experiencing volcanically enriched CO2, and employed high-resolution micro-computed tomography (micro-CT) to create three-dimensional models of changing skeletal structure. OA conditions were correlated with decreased calcification and increased macroboring, primarily by annelids, representing a group of bioeroders not previously known to respond to OA. Incubation of these blocks, using the alkalinity anomaly methodology, revealed a switch from net calcification to net dissolution at a pH of roughly 7.8, within Intergovernmental Panel on Climate Change's (IPCC) predictions for global ocean waters by the end of the century. Together these data represent the first comprehensive experimental study of bioerosion and calcification from a naturally high-CO2 reef ecosystem, where the processes of accelerated erosion and depressed calcification have combined to alter the permanence of this essential framework habitat.

  3. Enochs, I.C., D.P. Manzello, E.M. Donham, G. Kolodziej, R. Okano, L. Johnston, C. Young, J. Iguel, C.B. Edwards, M.D. Fox, L. Valentino, S. Johnson, D. Benavente, S.J. Clark, R. Carlton, T. Burton, Y. Eynaud, and N.N. Price. Shift from coral to macroalgae dominance on a volcanically acidified reef. Nature Climate Change, 5(12):1083-1088, doi:10.1038/nclimate2758 2015

    Abstract:

    Rising anthropogenic CO2 in the atmosphere is accompanied by an increase in oceanic CO2 and a concomitant decline in seawater pH. This phenomenon, known as ocean acidification (OA), has been experimentally shown to impact the biology and ecology of numerous animals and plants, most notably those that precipitate calcium carbonate skeletons, such as reef-building corals. Volcanically acidified water at Maug, Commonwealth of the Northern Mariana Islands (CNMI) is equivalent to near-future predictions for what coral reef ecosystems will experience worldwide due to OA. We provide the first chemical and ecological assessment of this unique site and show that acidification-related stress significantly influences the abundance and diversity of coral reef taxa, leading to the often-predicted shift from a coral to an algae-dominated state. This study provides field evidence that acidification can lead to macroalgae dominance on reefs.