Production and carbonate dynamics of Halimeda incrassata (Ellis)Lamouroux altered by Thalassia testudinum Banks and Soland ex König

• Published in: Journal of Experimental Marine Biology and Ecology
• Main Authors: Barry, S.C., Frazer, T.K., Jacoby, C.A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Biology; Chemistry; Ecology; Environment; Calcareous algae; Calcification; Ocean acidification; Photosynthesis; Respiration; Seagrass
• Online Access: http://hdl.handle.net/1834/35724; https://doi.org/10.1016/j.jembe.2013.03.012

Ocean acidification poses a serious threat to a broad suite of calcifying organisms. Scleractinian corals and cal-careous algae that occupy shallow, tropical waters are vulnerable to global changes in ocean chemistry be-cause they already are subject to stressful and variable carbon dynamics at the local scale. For example, netheterotrophy increases carbon dioxide concentrations, and pH varies with diurnal fluctuations in photosyn-thesis and respiration. Few researchers, however, have investigated the possibility that carbon dioxide con-sumption during photosynthesis by non-calcifying photoautotrophs, such as seagrasses, can amelioratedeleterious effects of ocean acidification on sympatric calcareous algae. Naturally occurring variations inthe density of seagrasses and associated calcareous algae provide an ecologically relevant test of the hypoth-esis that dielfluctuations in water chemistry driven by cycles of photosynthesis and respiration withinseagrass beds create microenvironments that enhance macroalgal calcification. In Grape Tree Bay off LittleCayman Island BWI, we quantified net production and characterized calcification for thalli of the calcareousgreen algaHalimeda incrassatagrowing within beds ofThalassia testudinumwith varying shoot densities. Re-sults indicated that individualH.incrassatathalli were ~6% more calcified in dense seagrass beds. On an arealbasis, however, far more calcium carbonate was produced byH.incrassatain areas where seagrasses wereless dense due to higher rates of production. In addition, diel pH regimes in vegetated and unvegetatedareas within the lagoon were not significantly different, suggesting a high degree of water exchange andmixing throughout the lagoon. These results suggest that, especially in well-mixed lagoons, carbonate pro-duction by calcareous algae may be more related to biotic interactions between seagrasses and calcareousalgae than to seagrass-mediated changes in local water chemistry.