Use of marine sponges as stress indicators in marine ecosystems at Algeciras Bay (southern Iberian Peninsula)

Infralittoral sponge fauna was studied as part of a multidisciplinary investigation of benthic communities in Algeciras Bay. On a monthly basis over 1 year, a series of environmental variables were measured (hydrodynamism, silting, suspended solids, dissolved organic matter, % organic matter in silt). The only abiotic variable that was significantly correlated with beta diversity was hydrodynamism, with a linear regression model between the 2 variables showing a correlation coefficient of 0.66. The distributional pattern of the sponges (based on the relative abundance matrix) was correlated with the environmental variables by matching sample similarities using the Spearman rank correlation, thus showing that the variable combination that best explains the patterns of distribution is hydrodynamism/organic matter in silt (rho(s) = 0.6). Of the species considered, Phorbas fictitius, Cliona celata, Cliona vinidis, Crella elegans, Oscarella lobularis, Dysidea fragilis were among those showing the greatest adaptive plasticity in their relationship to environmental variables, depth, and selection by substrate, and are categorized as eurytopic species present in areas subject to great environmental stress. Other species such as Phorbas tenacior, Reniera fulva, Reniera mucosa, Cliona rhodensis proved to be much more sensitive to these variables, and were categorized as stenotopic species, indicators of normal conditions. Due to the particular environmental conditions where it is located, Mycale micracanthoxea was categorized as a good indicator species in port environments. Others such as Dysidea avara, Halichondria bowerbanki or Crella elegans presented morphological differentiations which have permitted them to adapt to sedimentary environments.