We examined the effects of host species identity and spatial variability on animals inhabiting subtidal coralline algal turfs, by comparing the assemblages of small (1-8 mm) mobile invertebrates associated with five coralline turf species across a number of subtidal rocky reefs in northeastern New Zealand. Coralline turf fauna were abundant (average of 16,000 to 80,000 ind.m −2 ) and diverse (129 taxa in total), with assemblages dominated by arthropods, gastropods and polychaetes. Despite substantial differences in the morphologies of the coralline turf species, host identity had little effect on total abundance and richness of the fauna, and a moderate effect on taxonomic composition. Spatial variation at the scale of 10 2 -10 3 m had a stronger influence than host identity on all three assemblage-level properties, with wave exposure and depth having the most explanatory power of the environmental factors measured. Host-specificity was low, probably due to the close taxonomic relatedness of the host algal species and their inedibility (with consequent lack of dietary specialisation by fauna). For our study system, the results justify the common practice of lumping coralline turf species in ecological studies with regard to the description of the total abundance and richness of the associated fauna, but not the taxonomic composition of the fauna.

Biological traits relating to the behaviour, morphology and life history of organisms can influence ecological functioning, and this principle is becoming increasingly used to examine the functional response of communities to environmental variation. We quantified the taxonomic and biological traits composition, and the overall abundance and richness, of small (1−8 mm) mobile invertebrate assemblages inhabiting subtidal coralline algal turf (Corallina officinalis) along an environmental gradient ranging from (1) relatively deep, wave-exposed sites with short turf containing a low proportion of fine sediment to (2) shallow wave-sheltered sites with taller turf containing a higher proportion of fine sediment. Turf fauna were diverse (118 taxa) and abundant (12 000−53 000 ind. m −2 ), with assemblages dominated by amphipods and gastropods. Total abundances of invertebrates were higher at the wave-exposed sites. When analysed in multivariate space using proportional abundance, replicates based on taxonomic composition grouped more strongly by site along the overall gradient than those based on traits. As proportions of biological traits remained relatively stable along the gradient, numbers of all traits possessed by individuals were higher at the wave-exposed end of the gradient. Although some environmental variables contributed significantly to explaining multivariate trait and taxa patterns, most individual correlations between environmental variables and traits and taxa were weak. This study shows that biological traits can be shared between taxonomically distinct assemblages of turf-dwelling invertebrates, and indicates a relatively small influence overall of environmental variables on the composition of traits and taxa.KEY WORDS: Temperate rocky reef · Diversity · Algal morphology Resale or republication not permitted without written consent of the publisher

Benthic primary producers such as seaweeds and seagrasses are often inhabited by high densities of small arthropods, but little is known about the impact of these animals on their hosts, which could be positive if they keep them free of fouling epiphytes. We assessed the impact of small arthropods on algal epiphytes growing on coralline algal turf on a shallow, wave-exposed, rocky reef in warm temperate northeastern New Zealand. Plaster blocks impregnated with the insecticide carbaryl were used to reduce arthropod densities (by 96% relative to unmanipulated controls in the case of amphipods). By the end of the ~3.5 mo experiment total epiphyte cover was 88% when arthropods were excluded compared to 38% in unmanipulated controls, a 2.3-fold increase. Brown (Colpomenia spp.), green (Ulva spp.) and 'filamentous and microscopic' algal epiphyte taxa were responsible for the increase, while the cover of red foliose algal epiphytes decreased slightly. Hyalid amphipods (Protohyale spp.) were likely responsible for suppressing the epiphytes, as they were the most abundant arthropod mesograzer taxon and ate both Colpomenia spp. and Ulva spp. in a laboratory no-choice feeding assay. During the field experiment 2 large storms removed most of the epiphytes that had grown in the mesograzer exclusion treatment. Overall, our results indicate that the amphipods prevented overgrowth of the turf by epiphytes during calm periods. These results provide the first in situ cageless example of arthropod mesograzer-exerted control on the abundance and composition of primary producers on a subtidal rocky reef.

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