Podolsky, R.D.: Intertidal embryos: temperature tradeoffs during early development

Species from several phyla brood or deposit benthic embryo masses in intertidal habitats. These habitats can expose embryos to extreme environmental change on short time-scales, which can have diverse effects on development. In the mollusc Melanochlamys diomedia environmental (= developmental) temperature can change from 11 to 34-degrees C and back over a tidal exchange. In the laboratory, time to hatching was influenced by temperature regimes associated with large vs. small exchanges, and with variable vs. constant temperatures. Although embryos developed fastest under a regime characteristic of a large exchange, they are also the most vulnerable to heat stress during such periods in the field. Embryos are especially vulnerable during their first one or two low tides when the induction of heat shock protein expression is minimal or absent. In addition, embryo masses face a threat of premature dislodgment from the substrate, which may be greater during periods of greater exchange, or may be reduced overall by more rapid development. These results indicate a complex set of tradeoffs that influence the success of development under variable tidal conditions.