Mitigating human disturbance: can protection influence trajectories of recovery in benthic assemblages?

1. Understanding whether Marine Protected Areas (MPAs) can be considered as a suitable tool for restoring the structure and function of populations and assemblages is urgently needed to achieve an effective policy of mitigation of human impact in coastal management. However, to date, the role played by MPAs in enhancing ecosystems resilience has been more advocated than unambiguously documented. 2. This study was designed to test whether full protection in marine reserves facilitates recovery of benthos impacted by the date mussel Lithophaga lithophaga fishery, one of the most harmful human activities affecting subtidal rocky habitats in the Mediterranean Sea. 3. The effects of this destructive fishery were reproduced at one fully protected location (P) and at two unprotected control locations (Cs) in the SW Mediterranean Sea. At each location, three plots (4 m2) of rocky surface at 4-6 m depth were disturbed experimentally, while another three plots served as reference. In each plot, the species composition and relative cover of the sessile benthic assemblages were sampled photographically on each of five occasions during a period of 20 months. 4. Over and above variation in habitat features among locations, multivariate and univariate analyses revealed significant differences between P-vs.-Cs in patterns of assemblage recovery and showed that, at the fully protected location, recovery was faster than at the unprotected control locations. 5. Our results suggest that MPAs have the potential to change the trajectories of recovery of disturbed assemblages by accelerating the processes of recolonization and call for further investigation to identify the specific mechanisms underlying increased resilience.     

Impact of date mussel harvesting on the rocky bottom structural complexity along the Istrian coast (Northern Adriatic, Croatia)

A survey of 50 km of the coast, including islands, rocks and offshore shallows, in the region of Rovinj (North Adriatic, Croatia) showed that the harvesting of the European date mussel Lithophaga lithophaga (L., 1758) is restricted to inclined, approximately vertical, surfaces. Usually, a stratum of rock, varying from several to about ten cm is removed by hammering, resulting in the complete eradication of sessile organisms. The damage was heavily widespread up to 6 m depth (47% of the total inclined surfaces for the whole area). Between 6 and 14 m depth, the damage was much less (14% from 6 to 10 and 7% from 10 to 14 m depth); below this depth, no damage was observed. The damage patterns coupled with the date mussel distribution, which was constrained by the nature of the substratum (limestone or dolomitic limestone), the general architecture of the rocky bottom and the depth. The structural complexity of inclined surfaces was quantified by 5 indices previously used in biota-substratum interaction studies. Heights of 11 pins placed 3 cm apart in a profile gauge were measured to determine the standard deviation of heights, the coefficient of variation of heights, the sum of squared heights, chain and tape ratio and circular variance of angles. Comparisons of these indices, among damaged and intact surfaces in different habitats and sites within habitats, showed a substantial decrease in complexity of the rocky substratum due date mussel harvesting. Thus, this human disturbance can permanently affect rocky shallow water communities as physical features of the substratum may exert strong effects on species.     

Date mussel harvesting favours some blennioids

The consequences of date mussel Lithophaga lithophaga harvesting (DMH) on blennioid assemblages was evaluated at Capo Noli‐Bergeggi (Savona, north‐western Mediterranean Sea) in summer 2005, under the hypothesis that holes bored by L. lithophaga, and left empty by the collection of the bivalve, may represent refuges for these cryptobenthic fishes. Blenniidae and Tripterygiidae were identified to species, and their individuals counted together with the number of empty L. lithophaga holes. The results were compared between ‘impact’ sites affected by the destructive DMH and control sites using two‐way ANOVA, and showed that extensive removal of the boring mussels, dramatically increasing the availability of empty holes, favours total number of observed blennioid species and especially Parablennius zvonimiri abundance.