EFFECTS OF STRONTIUM ON THE EMBRYONIC DEVELOPMENT OFAPLYSIA CALIFORNICA

Abstract

Strontium is required in defined media for the development of normal shells and statoliths in the opisthobranch gastropod, Aplysia californica Cooper, 1863. Embryos grown in artificial seawater without strontium chloride become larvae with normally appearing soft tissue but with deformed shells and statocysts that lack the statolith granule. Shell and statolith formation is sensitive to concentration differences as small as one part per million strontium in the artificial seawater. Pulse experiments indicate a critical period of exposure for the requirement beginning at Day 4, (72 h after oviposition) and lasting no longer than 24 h. Animals exposed to artificial seawater containing 8 parts per million strontium only during this critical period develop normally. Conversely, animals immersed in artificial seawater lacking strontium during this same period, but exposed to the element during the rest of the 10-day embryonic phase, exhibit anomalous shells and statocysts. The effects are only marginally reversible if strontium is presented after Day 5. Strontium is also essential for the normal development of locomotory behavior. Animals that have been deprived of strontium swim erratically, spinning in tight circles. The pathogenesis of this behavioral disorder is explained by the lack of strontium during embryonic development which causes the major structural anomalies at the larval stage. The absence of the statolith results in a defective organ of balance which in turn causes the severe behavioral symptoms. A similar strontium effect in other molluscs, including Hermissenda crassicornis (Eschscholtz, 1831), is also documented.