Recruitment, growth and survival of Lessonia nigrescens (Phaeophyta) at various tidal levels in exposed habitats of central Chile

Abstract

Mortality effects of ecological factors were not generally tested in field population studies of benthic algae. Recruitment, growth and survival of the low-intertidal/shallow-subtidal L. nigrescens were measured at 4 tidal levels in exposed rocky habitats in central Chile. Through experimental manipulation the effects of the abiotic environment, small-size grazers and mid-littoral algae on the survival of the juveniles of L. nigrescens recruited in the upper part of its vertical range were evaluated. Disturbance effects of adult plants and grazing effects of large-sized subtidal herbivores on juvenile recruitment, and effects of interspecific interference on the survival of newly settled juveniles were also evaluated. Interference by adult plants and grazing by large-sized subtidal herbivores completely inhibit recruitment. In their absence, the abiotic environment limits recruitment and growth of L. nigrescens at the uppermost tidal level while inter-specific interference owing to over-shading by the fastest growing individuals limits the lower-most extent of the belt. Interference by adult plants and grazing are patchy and often mutually exclusive in the field. Recruitment within the band of L. nigrescens is maximal in patchy vegetational openings which are large enough to experience reduced disturbance by adult plants and small enough for reduced grazing pressure. In mature, consolidated belts of L. nigrescens on vertical walls these openings correspond to roughly triangular areas with the hypotenuse formed by interholdfast distances of 1-2 m. Such patchy vegetation openings can be produced normally by dislodgement of old, eroded plants.