ABSTRACT: This paper deals with sublethal salinity stress on reef building corals in the Inner Gulf of Thailand. Maximum photosynthetic and respiratory rates were measured in Porites lutea and Pocillopora damicornis as changes in dissolved oxygen levels per hour and the gross production to respiration ratio (Pg:R)calculated. Pg:R ratios were significantly lowered in both species when exposed to sudden salinity drops from ambient 30o/oo to 20 and 10o/oo, but P. lutea was less affected. Photosynthetic rates were lowered in proportion to the salinity reductions in both species, whereas respiration rates were either slightly decreased or unaltered. When calculating the Pg:R ratios on a 24 h basis both species displayed values below 1, even at ambient salinity (P. lutea 0.71 ± 0.04 and P. damicornis 0.89 ± 0.02), thus indicating that they do not solely depend on internal primary production for their maintenance. In an experiment on the capacity of heterotrophic feeding with Artemia salina, P. damicornis showed a clearance rate 4 times higher than P. lutea,indicating that P. damicornis may be more capable of compensating for a low Pg:R ratio by heterotrophic feeding.

KEY WORDS: Coral · Porites lutea · Pocillopora damicornis · Salinity · Photosynthesis · Respiration

Published in MEPS Vol. 157 (1997) on October 16
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1997