Relationships between environmental variables and the abundance of peracarid fauna in Algeciras Bay (southern Iberian Peninsula)

The distribution and abundance of peracaridean fauna associated with the br yozoan Bugula neritina have been analysed according to their possible relat ionships with environmental stress on the coastline of Algeciras Bay. The s patial environmental variability along this bay has been established based on the analysis of five abiotic variables (hydrodynamism, siltation, suspen ded solids, and organic matter content) at six stations over a 12-month per iod. The temporal variability of these abiotic variables was not taken into account due to the method used in collecting the samples. The abundance an d beta diversity of the peracarid fauna were also calculated monthly. Hydro dynamism was the only abiotic variable significantly correlated with beta d iversity, with a linear regression model between the two variables (r = 0.8 1). The distributional pattern of the peracarids (based on the abundance ma trix) was correlated with the environmental variables by matching samples' similarities using the Spearman rank correlation. This analysis showed that the combination of variables that best explains the patterns of distributi on is hydrodynamism and siltation (p(s) = 0.665). Of the species considered the amphipods Ischyrocerus inexpectatus, Jassa marmorata and Podocerus var iegatus were negatively correlated with hydrodynamisin and positively with temperature. The caprellidea Phtisica marina was also negatively correlated with hydrodynamism. On,the other hand, the amphipods Cressa mediterranea a nd Stenothoe dollfusi preferred environments with high hydrological forces and low sedimentation rate. Due to the particular environmental conditions where they live and their requirements, Gammaropsis maculata, Corophium acu tum, J. marmorata, 1, inexpectatus, and P. variegatus were categorised as g ood indicator species in port environments. Others such as Aora spinicornis , Microjassa cumbrensis, and C. mediterranea were categorised as species we ll adapted to high hydrological forces.