Changing global climate due to anthropogenic emissions of CO 2 are driving rapid changes in the physical and chemical environment of the oceans via warming, deoxygenation, and acidification. These changes may threaten the persistence of species and populations across a range of latitudes and depths, including species that support diverse biological communities that in turn provide ecological stability and support commercial interests. Worldwide, but particularly in the North Atlantic and deep Gulf of Mexico, Lophelia pertusa forms expansive reefs that support biological communities whose diversity rivals that of tropical coral reefs. In this study, L. pertusa colonies were collected from the Viosca Knoll region in the Gulf of Mexico (390 to 450 m depth), genotyped using microsatellite markers, and exposed to a series of treatments testing survivorship responses to acidification, warming, and deoxygenation. All coral nubbins survived the acidification scenarios tested, between pH of 7.67 and 7.90 and aragonite saturation states of 0.92 and 1.47. However, net calcification generally declined with respect to pH, though a disparate response was evident where select individuals net calcified and others exhibited net dissolution near a saturation state of 1. Warming and deoxygenation both had negative effects on survivorship, with up to 100% mortality observed at temperatures above 14 • C and oxygen concentrations of approximately 1.5 ml·l −1 . These results suggest that, over the short-term, climate change and OA may negatively impact L. pertusa in the Gulf of Mexico, though the potential for acclimation and the effects of genetic background should be considered in future research.

Here, the development and construction of recirculating aquaria for the long-term maintenance and study of deep-water corals in the laboratory is described. This system may be applied to the maintenance and experimentation on marine organisms in the absence of a natural seawater supply. Since 2009, numerous colonies of Lophelia pertusa as well as several species of associated invertebrates from the Gulf of Mexico have been maintained in the described systems. The behavior of some of these species, including L. pertusa, the corallivorous snail Coralliophila sp., the polychaete Eunice sp., and the galetheoid crab Eumunida picta in the laboratory is described. Additionally, these systems were used for the manipulation of pH and dissolved oxygen for shortterm experiments using L. pertusa. The detailed manipulation of carbonate chemistry in artificial seawater is described for use in ocean acidification experiments.

Ocean acidification (OA) projections predict ocean pH to decline between 0.2 and 0.4 by 2100 with potential negative consequences for marine calcifiers without acclimation or adaption strategies to accomodate greater [H + ] in seawater. Biotic control of calcified reef macroalgae thalli surface diffusive boundary layer (DBL) chemistry may overcome low pH in seawater as one strategy to accommodate OA conditions. To investigate this strategy, we examined surface DBL O 2 and pH dynamics in five calcifying macroalgae (Halimeda, Udotea, Jania, Neogoniolithon, crustose coralline algae [CCA]) from the Florida Reef Tract under ambient (8.1) and low (7.65) pH using microsensors (100 μm) at the thalli surface in a flow-through flume. The role of photosynthesis and photosystem II (PSII)-independent proton pumps in controlling DBL pH were examined. Four of the five macroalgae exhibited a strong positive linear relationship between O 2 production and increasing pH in the first 15-30 s of irradiance. Once a quasi-steady-state O 2 concentration was reached (300 s), all species had DBL pH that were higher (0.02-0.32) than bulk seawater. The DBL pH increase was greatest at low pH and dependent on PSII. Some evidence was found for a light-dependent, but PSII-independent, proton pump. High DBL Δ pH upon illumination was likely in response to carbon concentrating mechanisms (CCMs) for photosynthesis. CCMs may be a HCO 3 −-H + symport, OHantiport or other DIC transport system, accompanied by proton efflux. HCO 3 dehydration by external carbonic anhydrase (CA ext) also produces OHthat can neutralize H + in the DBL. CO 2 or HCO 3 uptake for photosynthesis may also engage H + /OHfluxes as part of intracellular acid-base regulation changing DBL pH. A higher Δ pH within the DBL at low pH could be accounted for by greater CO 2 diffusion and/ or lower efficiencies in exporting cellular H + across a lower concentration gradient, and/or a more efficient removal of H + by CA ext-driven dehydration of HCO 3 −. In the dark, Δ pH was less than in the light as these dynamics were primarily due to photosynthesis. We present a conceptual model of inorganic carbon uptake and ion transport pathways, as well as other processes associated with photosynthesis that drive DBL Δ pH and sustain tropical macroalgal calcification in the light under OA. In the dark, unless PSII-independent proton pumps are present, which do not appear to be ubiquitous amongst species, acidification processes likely dominate, resulting in CaCO 3 net dissolution, particularly under OA conditions. nate (CO 3 2−) by~50-60% (Fabry et al., 2008; Koch et al., 2013). The decline in CO 3 2lowers the saturation state (Ω) of carbonate minerals of calcite and aragonite (~60%). The high concentration of Ca 2+ in

Barnacles are dominant members of marine intertidal communities. Their success depends on firm attachment provided by their proteinaceous adhesive and protection imparted by their calcified shell plates. Little is known about how variations in the environment affect adhesion and shell formation processes in barnacles. Increased levels of atmospheric CO 2 have led to a reduction in the pH of ocean waters (i.e., ocean acidification), a trend that is expected to continue into the future. Here, we assessed if a reduction in seawater pH, at levels predicted within the next 200 years, would alter physiology, adhesion, and shell formation in the cosmopolitan barnacle Amphibalanus (=Balanus) amphitrite. Juvenile barnacles, settled on silicone substrates, were exposed to one of three static levels of pH T , 8.01, 7.78, or 7.50, for 13 weeks. We found that barnacles were robust to reduced pH, with no effect of pH on physiological metrics (mortality, tissue mass, and presence of eggs). Likewise, adhesive properties (adhesion strength and adhesive plaque gross morphology) were not affected by reduced pH. Shell formation, however, was affected by seawater pH. Shell mass and base plate area were higher in barnacles exposed to reduced pH; barnacles grown at pH T 8.01 exhibited approximately 30% lower shell mass and 20% smaller base plate area as compared to those at pH T 7.50 or 7.78. Enhanced growth at reduced pH appears to be driven by the increased size of the calcite crystals that comprise the shell. Despite enhanced growth, mechanical properties of the base plate (but not the parietal plates) were compromised at the lowest pH level. Barnacle base plates at pH T 7.50 broke more easily and crack propagation, measured through microhardness testing, was significantly affected by seawater pH. Other shell metrics (plate thickness, relative crystallinity, and atomic disorder) were not affected by seawater pH. Hence, a reduction in pH resulted in larger barnacles but with base plates

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Tropical macroalgae serve importance ecological roles on coral reefs but can supplant corals in phase shifts as shown worldwide. Thus, it is important to understand their fundamental photophysiology and calcification mechanisms. We examined organic d13C, organic+inorganic d15N, inorganic CaCO3 d13C and d18O, and organic %C, %N, C:N of abundant macroalgae on Little Cayman Island (LCI) reefs across irradiance gradients (5-2,000 mmol m-2 s-1). We hypothesized macroalgae utilize greater CO2 in low light as carbon concentration mechanisms (CCMs) for HCO3- uptake have higher energetic costs. We proposed that calcification mechanisms are influenced by light and Ci-use strategy in addition to taxonomy. LCI macroalgae had organic d13C values (-12‰ to -25‰) indicative of CCMs and exhibited only 1-3‰ 13C depletion in irradiances <5 mmol photons m-2 s-1. Ochrophyte d13C values were enriched in 13C at low nitrogen indicative of efficient CCMs. Macroalgae exhibited four clusters of thalli CaCO3 d13C that were distinctly taxon-specific. Rhodophytes exhibited the most negative inorganic d13C and d18O values (-4.1‰ ± 0.7‰; -3.7‰ ± 0.4‰) an indication of high calcifying space pH and rapid calcification, potentially reliant on active ion transport. Relatively higher organic C fractionation when utilizing greater CO2 for photosynthesis was reflected in depleted thalli carbonates in species/genus with positive d13C values. Increasing ocean CO2 is not likely to enhance dominant LCI macroalgal photosynthesis as these reef macroalgae utilize CCMs across a broad range of irradiances; however, effects on calcification may be taxon specific based on the degree of biotic control elucidated in thalli carbonate isotopes.