Species associations and seasonal population densities of marine phytal harpacticoid copepods from Cook Strait

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Abstract
A quantitative study was made on occurrence, density, seasonal periodicity, and associations of 27 species of harpacticoid copepods collected from. 6 species of marine algae at Island Bay, Wellington, New Zealand, from April 1973 to March 1974. The dominant species on each alga fluctuated in abundance seasonally, and the timing of population maxima differed noticeably between species. Fluctuations in abundance were usually related to reproductive activity, which was largely unrelated to environmental temperature. Total densities on algae were highest in the spring for Corallina (578 individuals per 10 cm2) and Ecklonia (6 per 10 cm2), in summer for Enteromorpha (366 per 10 cm2), Zonaria (86 per 10 cm2), and Pterocladia (66 per 10 cm2) and in autumn for Xiphophora (39 per 10 cm2). Population densities from Corallina are as high as those recorded elsewhere from level‐bottom sand. Overall, Paralaophonte meinerti was the most abundant species, constituting 14.5% of the total copepods collected. Six species (Porcellidium dilatation, Scutellidium armatum, S. macrosetum, S, plumosum, Porcellidium sp. C, and Alteutha littoralis) co‐occur in a large number of samples and are considered characteristic ‘indicators’ of the marine algal biotope at Island Bay. The effect of high levels of trapped sediments in Corallina is discussed in relation to the density and species composition of the resident copepods. As well as seasonal separation, the commonest species on Corallina are spatially segregated into those inhabiting the fronds and those inhabiting the sediments. Such partitioning is believed to result in decreased competition for available habitat resources. Two parallel assemblages were recognised: one amongst sublittoral algal fronds, and the other in Corallina sediments. Both have dominant genera in common with assemblages on similar substrates elsewhere. Small differences in the physical environment may give rise to a transitional fauna, in which the assemblage composition is altered or the dominant species replaced. Caution in classifying parallel assemblages as distinct faunal entities is necessary because of the degree of substrate variability which most species can tolerate.