Habitat-diversity relationships in rocky shore algal turf infaunal communities.

Harmful benthic microalgae blooms represent an emergent phenomenon in temperate zones, causing health, ecological and economic concern. The main goal of this work was to compile records of Ostreopsis at large temporal and spatial scales, in order to study the relationship between cell abundances, the periodicity and intensity of the blooms and the role of sea water temperature in 14 Spanish, French, Monegasque and Italian sites located along the northern limits of the Mediterranean Sea. General trends were observed in the two considered basins: the north-western Mediterranean Sea, in which higher cell abundances were mostly recorded in mid-summer (end of July), and the northern Adriatic Sea where they occur in early fall (end of September). The sea-water temperature does not seem to be a primary driver, and the maximal abundance periods were site and year specific. Such results represent an important step in the understanding f armful benthic microalgae blooms in temperate areas, and provide a good base for policy makers and managers in the attempt to monitor and forecast benthic armful microalgae blooms.

Relationships between habitat complexity and biodiversity are a cornerstone of ecology. On many rocky shores, the cryptic macrofauna that live in the biogenic habitat created by larger organisms adds considerably to biodiversity. Algal turfs are commonly considered to facilitate high species richness of resident organisms by moderating the physically stressful characteristics of the rocky shore. We conducted a multi-scale study to describe scales of patchiness within sites and define the strength of local habitat and broader environmental variables on infaunal turf communities. Species richness contributed by sampling turf dwelling infauna increased our estimates of rocky shore diversity by >100% compared to traditional visual quadrat sampling. Generalised linear models of the species density and abundance of infaunal turf organisms and canonical correspondence analysis of community structure did not indicate a strong role for algal turf habitat complexity. Multivariate partitioning was used to assess the importance of processes operating on site and regional scales in influencing the infaunal turf community. The analysis demonstrated the importance of cross-scale relationships and high levels of unexplained variation. Analysis of biological traits demonstrated widely dispersing species were strongly influenced by broad-scale environmental factors. Feeding traits indicated that the infaunal turf community was dominated by species capable of switching strategies between autotrophic and detrital based foodwebs, with the exception of suspension feeding species. Overall, and contrary to previous studies, our results indicate wide niches for infaunal turf species and weak relationships between the infaunal community and turf habitat characteristics. Spatial variation in turf habitat characteristics was not the main driver of spatial variation in turfdwelling organisms, implying that the habitat variability we observed was not strongly influencing physical stresses, such as temperature and wave disturbance. © Inter-Research 2011.