ecological effects of marine protected areas empafish project ...

EMPAFISH Booklet no. 1 Ecological effects of Atlanto-Mediterranean MPAs in the EU
the protected area. Comprehensive scientific studies on the impact of divers
are lacking, but observations point to a noticeable erosion of the benthic
communities around the preferred diving spots (Zabala 1993). Some
landscape-forming invertebrates, such as the gorgonian Paramuricea clavata,
the red coral Corallium rubrum, or fragile bryozoans, and the spiny lobster
Palinurus elephas that have been intensively studied show the negative effect
of excessive frequentation by divers on benthic assemblages (Zabala 1993).
Surveys of diving activity conducted from 1992 to 1995 on a study site where
no diving was permitted before showed that diving increased 60-fold at the
impact location. A significant decrease in the density of colonies of the
bryozoan Pentapora fascialis was observed at the impact location one year
after the start of the diving disturbance (Garrabou et al. 1998).
An undesired side-effect of excessive frequentation by divers is the possible
change in behaviour of a paradigmatic species such as Epinephelus
marginatus, which has become accustomed to hand-feeding by divers and is
not shy to humans (Zabala et al. 1997a, b).
� Indirect effects (trophic cascades, changes in assemblage –
trophic structure, etc.)
Studies on the changes in fish assemblages and sea urchins derived from the
establishment of the MIMR have shown the decrease of sea urchins parallel
with an increase in herbivorous fishes in the MIMR, especially Diplodus
sargus, D. vulgaris and Coris julis (Sala & Zabala 1996). Considering that the
sea urchin Paracentrotus lividus is the major benthic herbivore in the NW
Mediterranean, this study showed that the removal of fishing pressure on
predatory fish would have a positive effect on herbivorous fishes, algal cover
and sessile assemblages, through a cascade effect (Sala & Boudouresque
1997; Pinnegar et al. 2000).
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