Assessment of grazing impact on deep canopy-forming species in the western Ionian Sea, Central Mediterranean

Marine forests are experiencing a severe decline in many Mediterranean areas. One of the major causes of the loss of the canopy-forming species is the overgrazing by herbivorous fishes. In the present study, the status of Treptacantha ballesterosii and Carpodesmia zosteroides populations was checked in two areas located along the central-eastern sector of Sicily. In addition, impact of herbivorous fishes, native or alien, on canopy-forming species was realized during monitoring of fish communities. It was observed that T. ballesterosii and C. zosteroides populations are in regression, particularly T. ballesterosii. Probably, the growth of this latter species may be limited by a strong herbivores’ pressure. During the monitoring period, the highest number of fish species has been observed at the depths where there are T. ballesterosii thalli. Moreover, an expansion of Sparisoma cretense populations has been observed that seems to be more competitive than the other herbivorous fish Sarpa salpa. Furthermore, the parrotfish has been observed several times in the bathymetric range where there is T. ballesterosii. Therefore, it may be hypothesized that in these areas the herbivorous fish which mostly hinder the development and growth of T. ballesterosii is S. cretense.