TEMPORAL FLUCTUATIONS AND SPATIAL GRADIENTS OF ENVIRONMENTAL P-O2, TEMPERATURE, H2O2 AND H2S IN ITS INTERTIDAL HABITAT TRIGGER ENZYMATIC ANTIOXIDANT PROTECTION IN THE CAPITELLID WORM HETEROMASTUS-FILIFORMIS

Activity levels of 2 antioxidant enzymes, catalase (CAT) and superoxid e dismutase (SOD), and the rate of oxygen consumption were investigate d in body wall tissue of the capitellid polychaete Heteromastus filifo rmis in response to the variability of abiotic factors in the worm's i ntertidal habitat. A head-down deposit feeder, H. filiformis displayed oxyconformity between 1.3 and 13 kPa (10 to 100 torr) P-O2 under labo ratory conditions. An extremely low standard metabolic rate (SMR) equi valent to an oxygen consumption of 0.1 mu mol O-2 g(-1) fw h(-1) (fw = fresh weight) is consistent with the capacity of the worms to coloniz e anoxic and potentially sulphidic sedimentary environments. Maximal ( M) overdot(O2) was 0.3 +/- 0.09 pmol g(-1) fw h(-1) for small (<300 mg body fw) and 0.25 +/- 0.09 mu mol g(-1) fw h(-1) for large (>500 mg b ody fw) worms. CAT and SOD activities were higher in summer than in wi nter worms. Under laboratory conditions, SOD activity in winter worms was not inducible upon acclimation to elevated temperatures, while CAT activity was significantly higher at 20 than at 5 degrees C. Summer w orms were unaffected by temperature reduction with respect to CAT acti vities, while SOD activity was significantly reduced upon cooling. Und er laboratory conditions, hypoxia as well as elevated P-O2 led to a si gnificant increase in CAT activity, while changes in SOD activity were marginal. Experimental hydrogen peroxide (H2O2) exposure resulted in an increase in CAT activity, whereas hydrogen sulphide (H2S) led to a decrease in CAT activity only if applied under anoxia. SOD activities of H. filiformis were insensitive to H2S in vivo. In situ exposure to elevated H2O2 concentrations confirmed that just 1 tidal emersion peri od was sufficient to cause the inducing effect of reactive oxygen spec ies on CAT activities in the worms' natural habitat. It is concluded t hat short-term changes in CAT activity are triggered by specific envir onmental stress factors, Like fluctuating P-O2 and hydrogen peroxide c oncentrations in the upper sediment layer. In contrast, SOD did not re spond spontaneously under experimental conditions, but under in situ c onditions at the sediment surface of an intertidal sandflat a shift of SOD activity occurred towards the end of an ebb tide emersion period, which led to an increase of SOD activity in the tail compared to the head end of the worms. It is hypothesized that short-term variations i n P-O2 and temperature at the sediment surface, in combination with th e vertical gradients of P-O2, H2S, temperature, and pH, elicit the obs erved changes in SOD activity.