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- Species-specific consequences of ocean acidification for the calcareous tropical green algae Halimeda
- Ocean acidification (OA), resulting from increasing dissolved carbon dioxide (CO2) in surface waters, is likely to affect many marine organisms, particularly those that calcify. Recent OA studies have demonstrated negative and/or differential effects of reduced pH on growth, development, calcification and physiology, but most of these have focused on taxa other than calcareous benthic macroalgae. Here we investigate the potential effects of OA on one of the most common coral reef macroalgal genera, Halimeda. Species of Halimeda produce a large proportion of the sand in the tropics and are a major contributor to framework development on reefs because of their rapid calcium carbonate production and high turnover rates. On Palmyra Atoll in the central Pacific, we conducted a manipulative bubbling experiment to investigate the potential effects of OA on growth, calcification and photophysiology of 2 species of Halimeda. Our results suggest that Halimeda is highly susceptible to reduced pH and aragonite saturation state but the magnitude of these effects is species specific. H. opuntia suffered net dissolution and 15% reduction in photosynthetic capacity, while H. taenicola did not calcify but did not alter photophysiology in experimental treatments. The disparate responses of these species to elevated CO2 partial pressure (pCO2) may be due to anatomical and physiological differences and could represent a shift in their relative dominance in the face of OA. The ability for a species to exert biological control over calcification and the species specific role of the carbonate skeleton may have important implications for the potential effects of OA on ecological function in the future. © 2011 Inter-Research., Cited By (since 1996):12, Seaweeds, CODEN: MESED
- Price, Hamilton, Tootell, Smith
- Quantifying patterns of fish herbivory on Palmyra Atoll (USA), an uninhabited predator-dominated central Pacific coral reef
- On many coral reefs, herbivorous fish play an essential role in regulating algal growth and influencing the outcome of coral-algal competition. Working on a remote predator-dominated coral reef on Palmyra Atoll, USA, we used behavioral foraging observations to quantify the roles of common parrotfish and surgeonfish in the roving herbivore guild. We recorded species-specific bite rates on different benthic organisms, quantified the relative abundance of those benthic organisms, and estimated benthos-specific grazing intensities as a function of bite rates, fish abundance, and percent cover. These grazing metrics were compared between the exposed fore reef (∼10 m depth) and protected reef terrace (∼5 m depth) habitats. We observed large differences in feeding rates and substrate selectivity among fish species. Most species fed predominately on algal turfs; however, some species foraged broadly among fleshy macroalgal taxa, while others specialized on calcified green algae of the genus Halimeda. The highest bite rates were recorded from species targeting algal turfs, while the highest rates of defecation were recorded from species targeting Halimeda. Per capita bite rates of all species were higher in the fore reef habitat (mean 45% more bites min-1); however, overall grazing intensities on turf algae (bites cm-2 d-1) were 5 times higher on the reef terrace than on the fore reef. Despite habitat-specific differences in the herbivore assemblages, the estimated distribution of total bites showed consistency among habitats, with strong guild-level positive foraging selectivity for algal turf. Comparisons of bite and defecation rate data for these herbivores across the Indo-Pacific highlight phylogenetic constraints on grazing activities. Overall, this study illustrates the importance of herbivore functional redundancy, variability in species-specific grazing, and provides a framework for assessing guildwide grazing impacts on coral reefs. © Inter-Research 2014.
- Hamilton, Smith, Price, Sandin