Gamete Release At Low Tide In Fucoid Algae: Maladaptive Or Advantageous?

This review discusses three questions pertaining to gamete release by fucoid algae at low tide: 1) Are gametes viable and does fertilization occur at low tide?, 2) How many gametes are released at low tide versus at high tide? and 3) Is gamete release at low tide maladaptive or is it selectively advantageous? Gamete release at low tide (LT) in fucoid algae is observed commonly in monoecious species from the lower and mid-intertidal zones (e.g., Fucus distichus, F. evanescens, F. gardneri, Pelvetia compressa); in dioecious species, intact antheridia (containing sperm) are commonly released at low tide (e.g., in Ascophyllum nodosum, F. vesiculosus). Fertilization at low tide can be determined with a calcofluor white assay and occurs in at least three species (F. distichus, F. gardneri, P. compressa). In general, fucoid algae have high levels of fertilization success, but substantial mortality occurs during early embryogenesis in some intertidal zones due to physical stresses. The agarose bead assay is useful to assess desiccation on an egg-sized scale. Constitutive dehydrin-like proteins are present in sperm, eggs, and embryos. The release of gametes at low tide appears to be a consequence of a mechanism selected to permit gamete release under calm conditions in seawater; this mechanism is described. The timing of adhesion by zygotes at low and high tide is unknown. Such information and additional data on the relative proportions of zygotes produced by monecious species at low tide versus high tide are required in order to assess effects of gamete release at low tide upon dispersal and population structure.