PHYSIOLOGICAL-RESPONSES TO FLUCTUATION IN TEMPERATURE OR SALINITY IN INVERTEBRATES - ADAPTATIONS OF ALPHEUS-VIRIDARI (DECAPODA, CRUSTACEA),TEREBELLIDES-PARVA (POLYCHAETA) AND GOLFINIGIA-CYLINDRATA (SIPUNCULIDA) TO THE MANGROVE HABITAT

The snapping shrimp Alpheus viridari (Armstrong, 1949), the polychaete Terebellides parva Solis-Weiss, Fauchald and Blankensteyn 1990, and t he sipunculan Golfingia cylindrata (Keferstein, 1865) are commonly fou nd in the same mangrove habitat, where they experience frequent, acute fluctuations in temperature and salinity. Ecological studies indicate a temporal variation, including occasional absence, in the distributi on of both G. cylindrata and T. parva; this led us to examine the phys iological adaptations of the three species (collected at Western Bay, Twin Cays, Belize in 1985, 1986 and 1988). Each was subjected to acute , repeated exposure to either control (35 parts per thousand S) and de creased (25 parts per thousand S) salinity or to control and increased (45 parts per thousand S) salinity. Ability to regulate water and ion content (g H2O or mu mol g(-1) solute free dry wt) was examined. A. v iridari behaved as a hyperosmotic conformer at decreased salinity but as an osmoconformer at increased salinity. Regardless of direction of salinity change, A. viridari regulated water content through change in Na+, K+, and Cl- contents. In contrast, G. cylindrata behaved as an o smoconformer and did not demonstrate ability to regulate water content . T. parva behaved as an osmoconformer, showed incomplete regulation o f water content via change in Na+, K+, and Cl- contents but had limite d survival following exposure to 45 parts per thousand S. Each species was also exposed to change in temperature. Species were subjected to acute, repeated exposure either to control (28 degrees C) and decrease d (21 degrees C) temperature or to control and increased (35 degrees C ) temperature. A. viridari regulated water and ion content under both experimental conditions. In contrast, T. parva did not regulate water and ion content under either experimental temperature. G. cylindrata d id not regulate water and ion content during exposure to decreased tem perature and did not survive exposure to increased temperature. For A. viridari, weight specific oxygen uptake rates (mg O-2 g(-1) ash-free dry wt) were determined. Exposure to decreased salinity or to increase d temperature resulted in a small sustained elevation in O-2 uptake. I t is concluded that, unlike A. viridari, T. parva and G. cylindrata ar e only marginally adapted to withstand the salinity and temperature st resses, respectively, of the mangrove habitat. The inability of T. par va and G. cylindrata to fully adapt to extremes in the mangrove habita t could well explain the temporal variation seen in the distribution o f these two species.