Gamete Release at Low Tide in Fucoid Algae: Maladaptive or Advantageous?

This review discusses three questions pertaining to gamete releaseby fucoid algae at low tide: 1) Are gametes viable and doesfertilization occur at low tide?, 2) How many gametes are releasedat low tide versus at high tide? and 3) Is gamete release atlow tide maladaptive or is it selectively advantageous? Gameterelease at low tide (LT) in fucoid algae is observed commonlyin monoecious species from the lower and mid-intertidal zones(e.g., Fucus distichus, F. evanescens, F. gardneri, Pelvetiacompressa); in dioecious species, intact antheridia (containingsperm) are commonly released at low tide (e.g., in Ascophyllumnodosum, F. vesiculosus). Fertilization at low tide can be determinedwith a calcofluor white assay and occurs in at least three species(F. distichus, F. gardneri, P. compressa). In general, fucoidalgae have high levels of fertilization success, but substantialmortality occurs during early embryogenesis in some intertidalzones due to physical stresses. The agarose bead assay is usefulto assess desiccation on an egg-sized scale. Constitutive dehydrin-likeproteins are present in sperm, eggs, and embryos. The releaseof gametes at low tide appears to be a consequence of a mechanismselected to permit gamete release under calm conditions in seawater;this mechanism is described. The timing of adhesion by zygotesat low and high tide is unknown. Such information and additionaldata on the relative proportions of zygotes produced by moneciousspecies at low tide versus high tide are required in order toassess effects of gamete release at low tide upon dispersaland population structure.