Abstract
Intertidal organisms, especially the sessile species, often experience long-term periodic air exposure during their lives. Learning the biochemical and physiological responses of intertidal organisms to long-term periodic air exposure and the relationship to duration of air exposure provides insight into adaptation to this variably stressful environment. We studied the Manila clam, Ruditapes philippinarum, an important species in world aquaculture, as a model to evaluate survival, growth, lipid composition, oxygen consumption, oxidative damage, and antioxidant enzyme activity in relation to the duration of air exposure in a long-term (60 days) laboratory study of varying durations of periodic emersion and re-immersion. Our results show: (1) clams undergoing a longer period of air exposure had lower survival and growth compared to those given a shorter exposure, (2) levels of oxidative damage and activities of antioxidant enzymes were higher in all air exposure treatments, but did not increase with duration of air exposure, and (3) the content of docosahexaenoic acid increased with duration of air exposure. Our results can largely be interpreted in the context of the energy expenditure by the clams caused by aerobic metabolism during the daily cycle of emersion and re-immersion and the roles of docosahexaenoic acid against oxidative stress.
Highlights
Field investigations have revealed that both survival and growth of bivalves from high intertidal zones are lower than those of congeners inhabiting lower intertidal zones[11,19]
Intertidal organisms are usually exposed to thermal stress, solar radiation, and hypoxia, which make the production of reactive oxygen species (ROS)[17,21,22]
The correlation between polyunsaturated fatty acids (PUFA) and oxidative stress defense is mainly examined in mammals, but it will be interesting to address this question in marine bivalves because of the prevalent oxidative stress in marine environments[2,3] and due to the potential capability of marine bivalves to synthesize n-3 long-chain PUFA (e.g., docosahexaenoic acid (DHA))[33]
Summary
Field investigations have revealed that both survival and growth of bivalves from high intertidal zones are lower than those of congeners inhabiting lower intertidal zones[11,19]. When juvenile clams settle in muddy and sandy sediments of the intertidal zone and live buried a few centimeter deep[34], they experience daily rhythms of air exposure throughout their lives, leading to physiological stresses caused by water loss, oxygen deficiency, thermal stress, and food limitation[1,13,14] Both field and laboratory observations reveal the gaping behavior of Manila clams when they are in immersion[15,34,35], which is associated with siphon extension behavior and is considered to be related with the feeding[34,35]. We tested the following hypotheses: 1) clams undergoing a longer period of air exposure have lower survival and growth compared to those in shorter exposure regimens, 2) level of oxidative damage and activity of antioxidant enzyme in clams increase with duration of emersion, and 3) the content of DHA in clams increases with the duration of air exposure
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
