Frozen at low tide

Abstract

This picture shows intertidal algae (Ascophyllum nodosum and Fucus vesiculosus) completely encased in ice during a winter low tide on the Gulf of St Lawrence coast of Nova Scotia, Canada. I have seen this phenomenon on various occasions, although how often it occurs during the winter remains to be determined. Ice encasement could influence these canopy-forming algae both positively and negatively. On the one hand, air temperature can be as low as –20°C on this coast in winter, but a stable ice cover prevents temperatures on rocky intertidal substrates from dipping that low. Thus, ice-encased seaweeds could be similarly insulated and might have a higher chance of survival as a result. On the other hand, waves could break some ice-encased algal fragments and remove biomass from these canopies. Whether removed algal fragments would simply die or aid in the dispersal of these algae is also unknown. Overall, the net influence of ice encasement on these seaweeds could depend on the prevailing environmental conditions, making these organisms interesting subjects of study for winter intertidal ecology.