ecological effects of marine protected areas empafish project ...

EMPAFISH Booklet no. 1 Ecological effects of Atlanto-Mediterranean MPAs in the EU
short-term, the removal of macroalgal fronds (i.e. canopy reduction) caused
evident changes in invertebrate and crypto-benthic fish densities although
these indirect effects were species-specific (Milazzo et al., 2004).
Fish feeding influenced the fish assemblages within the Ustica MPA, and
significant spatio-temporal changes occurred (Milazzo et al. 2005). In
particular, the saddled bream Oblada melanura noticeably increased its
density in the impacted location as a result of fish feeding, although its
average total length was unaffected. Moreover behavioural changes occurred,
with twelve fish species, in the presence of tourists, abandoning their natural
habitat and exhibiting a human positive behaviour (Milazzo et al. 2006). The
non-natural aggregations of fishes around snorkelers, which evolve as a result
of fish feeding by the public, have negative effects on local populations of
fishes that make up their prey (Milazzo et al. 2006).
� Indirect effects
Some circumstantial evidence for fish-mediated trophic cascade effects in the
Ustica Island MPA is given by different studies. There has been indirect
concern of changing rocky bottom community state since the early 1980s.
Dominance by canopy-forming brown algae as Cystoseira spp. and Dyctiota
spp. was consistent in shallow rocky areas through 1980s (Giaccone et al.
1985). In 1991 the effective institution of the MPA restricted the human
exploitation of marine organisms (including sea urchin harvesting) all around
the island. Some years later (i.e. from 1994-1997), canopy forming brown
algae in shallow waters were still dominant at large scales (10 2 -10 3 m) (La
Mesa & Vacchi 1999; Milazzo et al. 2000), but unstable in patches of coralline
barrens at smaller spatial scale (10 0 -10 1 m) mainly boulders. Almost during
that period, sea urchin populations of Paracentrotus lividus dramatically
increased, although evidence of this is only qualitative. In 2001, a
homogeneous coralline barren habitat took place all around the island coast
from about 1.5 to 7-8 m depth (Cianciolo et al. 2005). The occurrence of the
barren habitat seemed not to be related to fishing restrictions (La Mesa &
Vacchi 1999; Palmeri 2004).
In the island of Ustica, the barrens state appeared several years later the
institution of the MPA and it seems started in the integral zone, where human
access is forbidden. Several reasons may explain the presence of extensive
coralline barrens along the shallow waters of the Ustica MPA, among them the
scarce presence both inside than outside the MPA of high density of Diplodus
spp. (Palmeri 2004), considered the most important sea urchin predators.
Probably also the prohibition of sea urchin harvesting by humans has played
an important role.
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