Stable isotopic records of bleaching and endolithic algae blooms in the skeleton of the boulder forming coral Montastraea faveolata

Abstract

Within boulder forming corals, fixation of dissolved inorganic carbon is performed by symbiotic dinoflagellates within the coral tissue and, to a lesser extent, endolithic algae within the coral skeleton. Endolithic algae produce distinctive green bands in the coral skeleton, and their origin may be related to periods of coral bleaching due to complete loss of dinoflagellate symbionts or ''paling'' in which symbiont populations are patchily reduced in coral tissue. Stable carbon isotopes were analyzed in coral skeletons across a known bleaching event and 12 blooms of endolithic algae to determine whether either of these types of changes in photosynthesis had a clear isotopic signature. Stable carbon isotopes tended to be enriched in the coral skeleton during the initiation of endolith blooms, consistent with enhanced photosynthesis by endoliths. In contrast, there were no consistent d 13 C patterns directly associated with bleaching, suggesting that there is no unique isotopic signature of bleaching. On the other hand, isotopic values after bleaching were lighter 92% of the time when compared to the bleaching interval. This marked drop in skeletal d 13 C may reflect increased kinetic fractionation and slow symbiont recolonization for several years after bleaching.

Chromium‐isotope signatures in scleractinian corals from the Rocas Atoll, Tropical South Atlantic

“…Hartmann et al . () suggested that some endolithic algae can substitute coral symbionts (zooxanthellae) and promote enhanced biological activity (via photosynthesis), causing, among other changes, an alteration of the δ 13 C signal of the coral skeleton in direction to more negative values. This suggestion would be compatible with the observed enhanced variation of δ 13 C across the algae‐infected portion of the coral profile (Fig.…”

Evidence for the Thermal Bleaching of Porites Corals From 4.0 ka B.P. in the Northern South China Sea

“…During photosynthesis, zooxanthellae preferentially utilize forms of DIC that contain the light carbon isotope 12 C over the heavier carbon isotope 13 C. This carbon absorption model of zooxanthellae is called metabolic fractionation (Mcconnaughey, ; Swart, ). Therefore, changes in the photosynthetic intensity of symbiotic zooxanthellae could affect the isotopic composition of skeletal carbon (Hartmann et al, ). Photosynthetic intensity of symbiotic zooxanthellae is primarily controlled by irradiance and SST (Fairbanks & Dodge, ).…”

Kinetic and metabolic isotope effects in coral skeletal carbon isotopes: A re-evaluation using experimental coral bleaching as a case study

“…1). However, bleached corals do not always show this expected trend (i.e., a decrease in d 13 C s ) (Leder et al, 1991;Rodrigues and Grottoli, 2006;Hartmann et al, 2010;Levas, 2012), which is potentially due to strong kinetic effects masking changes in metabolism. The application of a data correction to remove kinetic isotope effects (Heikoop et al, 2000) might therefore reveal the masked metabolic isotope effects, and thus improve accuracy and interpretation of skeletal isotopes in bleached corals.…”