MEPS 212:1-12 (2001)  -  doi:10.3354/meps212001

Spatial variability and human disturbance in shallow subtidal hard substrate assemblages: a regional approach

Simonetta Fraschetti1,*, C. Nike Bianchi2, Antonio Terlizzi1, Giovanni Fanelli3, Carla Morri4, Ferdinando Boero1

1Dipartimento di Biologia, Stazione di Biologia Marina di Porto Cesareo, CoNISMa, Università di Lecce, 73100 Lecce, Italy
2Marine Environmental Research Centre, ENEA Santa Teresa, PO Box 316, 19100 La Spezia, Italy
3Istituto Sperimentale Talassografico del CNR ŒA. Cerruti¹, Via Roma 4, 74100 Taranto, Italy
4DipTeRis, Dipartimento per lo studio del Territorio e delle sue Risorse, Università di Genova, Corso Europa 26, 16132 Genoa, Italy

ABSTRACT: Quantitative information about spatial patterns in subtidal hard substrate assemblages is scant. Such information is necessary to understand the responses to anthropogenic disturbances in these habitats. Along the coast of Apulia (Southern Italy), the collection of the European date mussel Lithophaga lithophaga is a strong source of disturbance: harvesting is carried out by demolition of the rocky substrate and causes epibiota disappearance. A hierarchical sampling design was used to quantify the spatial variability of subtidal epibenthic assemblages and the extent of rock damage due to L. lithophaga harvesting along 360 km of rocky coasts in Apulia. The surveyed coast was divided into 8 adjacent sectors, and replicate samples were taken by visual inspection at each of the 3 sites nested in each sector. Multivariate analyses indicated that assemblages differed consistently with spatial scale, variability being higher at the largest scale. However, variability among sites within each sector was also detected. Patchiness (i.e., average similarity among quadrats) was consistent among sectors. Some species were identified as Œimportant¹ in characterising and/or differentiating sectors. The pattern of distribution of these species as well as total cover and number of species were analysed 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 relationship between patchiness and disturbances by L. lithophaga fisheries was obtained. In particular, patchiness at a small scale was highest at Œintermediate¹ levels of damage, because disturbance produces patches of different size and/or age, leading to Œmosaic¹ landscapes of epibenthic assemblages.

KEY WORDS: Subtidal assemblage · Spatial scale · Human disturbance · Rocky substrate · Lithophaga lithophaga · Mediterranean Sea

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