Effects of salinity and temperature on the survival and byssal attachment of the lion's paw scallop Nodipecten nodosus at its southern distribution limit

The lion's paw scallop, Nodipecten nodosus, is subject to wide temperature variations on seasonal and short-term scales, and may be exposed to low-salinity events, caused by oceanographic and meteorological processes at its southern distribution limit (Santa Catarina State, Brazil). Such variations may have important implications on the distribution and on aquaculture site selection. The upper and lower temperature tolerances and the percentage of byssal attachment at different temperatures (11 to 35 degreesC) were studied for spat, juvenile and adult scallops. The lethal and sublethal effects of reduced salinity (13parts per thousand to 33parts per thousand) on spat, juvenile and adult scallops were studied at ambient temperature (23.5 degreesC) and on spat also at low (16 degreesC) and high (29 degreesC) temperatures during 96-h bioassays. In addition, the influences of short exposure (1 h) to low salinity (13parts per thousand and 17parts per thousand) at different temperatures (16 and 28 degreesC), and the effects of exposure (2 and 4 h) to high temperature (33 degreesC) at ambient salinity (33parts per thousand) were studied. N. nodosus is a moderately eurythermal but stenohaline tropical species, adults having lower tolerance to high temperature and low salinity than spat. Lethal temperatures for a 48-h exposure (LT50) were 29.8 degreesC for adult and juveniles, and 31.8 degreesC for spat. Maximum rate of byssal attachment occurred in a narrower temperature range for juveniles and adults (23 to 27 degreesC) than for spat (19 to 27 degreesC), which are suggested as the optimum ranges of temperatures for growth. Lethal salinities (LC50) for a 48-h exposure at ambient temperature were 23.2parts per thousand, 23.6parts per thousand and 20.1parts per thousand for adults, juveniles and spat, respectively, but the percent byssal attachment was significantly reduced below salinities of 29parts per thousand indicating that scallops were physiologically stressed. A 1-h exposure to 17parts per thousand was lethal to spat at 28 degreesC, but at 16 degreesC there was a 28.5% survival, 96 It after the exposure. Temperatures and salinity in coastal areas of southern Brazil can reach levels leading to sublethal effects, and in some sites, it may surpass the limits of tolerance for the survival of the species. (C) 2004 Elsevier B.V. All rights reserved.