Recruitment and mortality of early post-settlement stages of benthic algae

Four transitional life history stages are generally recognized for benthic marine algae. On the basis of differences in size, we propose two more: young germlings and young juveniles. Three of these (spores or zygotes, young germlings, and germlings) are considered early post-settlement (EPS) stages. Many of the available data on recruitment and mortality were not collected with EPS stages specifically in mind, and considerable extrapolation and inference are required to interpret effects on early phases. Data on EPS stages, and grazing in particular, are based on the disappearance of early stages (laboratory or field experiments, including outplantings), on indirect information on mortality from manipulations of grazers or juvenile stages, and combinations of observation and manipulation. We also provide original data on the effects of water motion and canopy sweeping on zygote mortality. The most notable finding is the variability in, and multiplicity of, factors preventing successful recruitment of early life stages. Six intrinsic and about 17 extrinsic factors and/or processes were reported to affect recruitment and mortality. Grazing, canopy, and turf effects appear to be most important, but less well studied factors such as desiccation and water motion may be as important for early stages. Our review indicates that recruitment is highly variable, even episodic, and that mortality at this period is high. Combined, these elements suggest that chance events during EPS stages may play a large role in survival, and perhaps the evolution of benthic algae.