Molluscs are a group of commercially valuable species found notably in coastal and nearshore areas which include the clam and snail families. Because of the decline in harvest of many of these valuable species, basic research which attempts to explore which environmental variables are most important in regulating the success and distribution of these species is of significant interest. This research by Dr. McDowell of the Woods Hole Oceanographic Institute will explore the role of strontium and salinity in regulating the growth and development of molluscs. Salinity has traditionally been thought to play a major role in structuring both benthic and planktonic estuarine communities. Whereas this may be true for many invertebrate organisms, recent evidence suggests that the development and survival of molluscan embryos may be limited more by the concentration of strontium in seawater than by the capacity to maintain homeostasis under salinity stress. Two pieces of information have led to this deduction: 1) as a conservative element in seawater, strontium concentration should convary with salinity, and 2) strontium is required for a brief period near its oceanic concentration during embryonic mineralization of shell of all molluscs tested to date. It follows that molluscs must have evolved mechanisms for maximizing the potential for exposure of their embroyos to high strontium levels. These investigators will conduct laboratory experiments designed to disentangle the effects of salinity stress and the requirement for strontium during molluscan development. The objectives of this study are the following: 1) to determine the strontium dose-response curves for embryonic shell formation as a function of salinity in four molluscan species representing a range of habitats and requirements for formation of mineralized tissues, 2) to compare the strontium dose-response curves to the capacity of embryos and larvae to volume regulate over ontogeny, and 3) to compare strontium levels with embryonic development in field-collected seawater. The study represents the first attempt in delineating how the stringent requirements for strontium during embryogenesis may have influenced evolution of present-day distributional patterns of molluscan populations.
