Direct versus indirect effects of wave exposure as a structuring force on temperate cryptobenthic fish assemblages |
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Authors: | Selvaggia Santin Trevor J Willis |
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Institution: | (1) Centro Interdipartimentale di Ricerca per le Scienze Ambientali in Ravenna, Università di Bologna, Via Sant’Alberto 163, 48100 Ravenna, Italy;(2) Dipartimento di Biologia Evoluzionistica e Sperimentale, Università di Bologna, Via Selmi 3, 40126 Bologna, Italy;(3) National Institute of Water and Atmospheric Research, P.O. Box 893, Nelson, New Zealand |
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Abstract: | The structure of cryptic reef fish assemblages was assessed on sheltered and exposed aspects of coastal breakwaters at two
locations in the northwestern Adriatic Sea. There were distinct differences between the two levels of exposure, which were
consistent between locations. Habitat characteristics, measured on scales of tens of centimetres, explained 50% of the variability
in assemblage structure between exposures, whereas ‘exposure’ alone (implying direct effects of wave energy on the fish) explained
<5% of the variation. The most important explanatory variables were the presence of macroalgae, sandy habitat and oyster shell,
the last of which increased the degree of small-scale complexity and provided nesting sites for blennies. We found little
evidence to suggest that wave action had large direct effects on the fish assemblages, although this may be in part due to
the relatively small degree of difference between ‘exposed’ and ‘sheltered’ samples under the calm conditions of a sea with
a relatively short fetch. These results suggest that wave action acts mainly indirectly as a structuring force on cryptic
reef fish communities, by altering the composition and/or the relative density of epibiota that influence the distribution
of fish. Thus, relative wave energy may provide a useful means of predicting fish assemblage structure only at large spatial
scales. Microhabitat, composed of a combination of physical complexity and biological elements, always explained the greater
part of variability at small (<1 m) spatial scales. |
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