The Response ofTigriopus californicusto Chlorophytic Macroalgae, IncludingCladophora trichotomaKützing

The harpacticoid copepodTigriopus californicusis not observed to maintain populations in supralittoral pools containing the algaCladophora trichotoma. Laboratory microcosms and field treatments in Barkley Sound, British Columbia, Canada were inoculated withT. californicusand monitored seasonally (winter, spring, summer). After 5 days,C. trichotomamicrocosms held fewer survivors (18•6±7•3%) compared to treatments without vegetation (95•6±0•1%) or those containing the algaEnteromorpha compressa(93•8±5•4%), mean±SE. Though more difficult to determinein situ, results from inoculated field sites were similar. Copepodite and adultT. californicuswere the most adversely affected, while the survival of nauplii was generally maintained over 5-day intervals of observation. Other invertebrates, including littorines, barnacles and mussels were more abundant inC. trichotomapools at lower tidal elevations. Although several factors (exposure, nutrient supply, predation) are likely to contribute to the observed ‘ exclusion ’ ofT. californicusfrom pools containingC. trichotoma, the present results additionally suggest the deleterious influence of an unidentified chemical exudate fromC. trichotoma. The particular susceptibility of matureT. californicusto this exudate precludes the establishment of viable copepod populations in these pools. 1997 Academic Press Limited