Spatial variability and human disturbance in shallow subtidal hard bottom assemblages: a regional approach
Fraschetti, S.; Bianchi, C.N.; Terlizzi, A.; Fanelli, G.; Morri, C.; Boero, F. (2001). Spatial variability and human disturbance in shallow subtidal hard bottom assemblages: a regional approach. Mar. Ecol. Prog. Ser. 212: 1-12
Quantitative information about spatial patterns in subtidal hard substrate assemblagesis scant. Such information is necessary to understand the responses to anthropogenic disturbances inthese habitats. Along the coast of Apulia (Southern Italy), the collection of the European date musselLithophaga lithophaga is a strong source of disturbance: harvesting is carried out by demolition of therocky substrate and causes epibiota disappearance. A hierarchical sampling design was used toquantify the spatial variability of subtidal epibenthic assemblages and the extent of rock damage dueto L. lithophaga harvesting along 360 km of rocky coasts in Apulia. The surveyed coast was dividedinto 8 adjacent sectors, and replicate samples were taken by visual inspection at each of the 3 sitesnested in each sector. Multivariate analyses indicated that assemblages differed consistently withspatial scale, variability being higher at the largest scale. However, variability among sites withineach sector was also detected. Patchiness (i.e., average similarity among quadrats) was consistentamong sectors. Some species were identified as ‘important’ in characterising and/or differentiatingsectors. The pattern of distribution of these species as well as total cover and number of species wereanalysed by analysis of variance. Results recorded a considerable source of variation at site level.Damage by L. lithophaga fishing was shown to be extremely widespread. A humped relationshipbetween patchiness and disturbances by L. lithophaga fisheries was obtained. In particular, patchinessat a small scale was highest at ‘intermediate’ levels of damage, because disturbance producespatches of different size and/or age, leading to ‘mosaic’ landscapes of epibenthic assemblages.
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