Physiological responses of the endolithic community in the massive coral Porites lutea under healthy and bleached conditions

Composition and role of endolithic algae associated to the coral <i>Porites lutea</i> were investigated. Healthy and induced partially bleach corals were incubated to assess primary production and nitrogen fixation using incubations with an addition of natural isotope as ¹³C and ¹⁵N in seawater (a type) and ¹³C was directly injected to coral skeleton (b type). Endolithic algae were microscopically identified, their pigments were studied using high-performance liquid chromatography (HPLC) and photosynthetic activity yield (<i>Fv/Fm</i>) were measured using a pulse-amplitude-modulated (PAM) fluorometer. <i>Ostreobium quekettii</i> largely dominated and combined with <i>Plectonema terebrans </i>in endoliths photosynthesis community. The photosynthesis pigments which are Chlorophyll <i>a</i>, Chlorophyll <i>b</i> and Carotenoids also showed the presence of endolithic algae and cyanobateria, and these results consisted with the endolithic community observed under light-microscopic. Changing Chl <i>a</i> : Chl <i>b</i> and Chl <i>a</i> : carotenoids ratio of endolithic community during incubation showed they can adapt to environmental change. <i>Fv/Fm </i>was similar under healthy and bleached at both type incubation, the values in endolithic algae are not significant difference during 12 and 24h incubations. The primary production (a type and b type) in the tissue of bleached corals was increased while endolithic algae was decreased at 24h incubation. These results consisted with the ¹³C atom (%) in bleached corals. The nitrogen fixation also similar trend with primary production. These results suggest that bleaching coral lost zooxanthellae and translocation of organic matters from zooxanthellae but the endolithic algae colonizing the skeleton of corals could help to translocate photo-assimilate and nitrogenous compound to corals under high-irradiances stress under the bleaching period.