268
120
1
N
40
E
0
1.1'\
N
.... 30
Q)
0.
~
~
::I 20
"U
.>
'6
£
10
0
2
I
3
4
5
R. Sarda . M. Fluvia
_
Protected area (HF)
c::::::::J Protected area (MF)
Non protected area (IF)
6
7
8
9
10
11
Fish species
Fig. 14.8. Densities expressed as mean number of individuals per 250 m' (±s.e.) of different common
fish species in protected areas of the Medes Islands with high fish densities (HF) and medium fish
densities (MF), and compared with non protected (LF) areas of the vicinity. Fish included are:
1 Scorpaena porcus, 2 Serranus cabril/a, 3 Diplodus sargus, 4 Diplodus vulgaris,s Diplodus cervinus,
6 Diplodus annularis, 7 Diplodus puntazzo, 8 Sparus aurata, 9 Sciaena umbra, 10 Symphodus tinea, and
11 Symphodus mediterraneus (Adapted from Garcia-Rubies and Zabala 1990)
pared against control zones on the Coast, demonstrated the positive effect of the creation of marine reserves. In the absence of human predation, the number of littoral
fishes and their size increased greatly (Fig. 14.8). Furthermore, the presence of more
or less fish on tqe coast can control other species such as the sea-urchins. Increased
fishing pressure may directly reduce the populations of herbivorous fishes and indirectly mediate an increase in sea-urchin populations, by eliminating sea-urchin predators, which then remove fleshy alga communities. The scenery then changes to a community dominated'by encrusting calcareous algae (Sala 1996), which has altered the
natural habitat.
Recreational use of coastal areas may have other adverse ecological consequences
derived from the frequentation of habitats. In some Marine Protected Areas (MAPs)
the acceptability of damage by divers has been calculated (Dixon 1993; Ramos-Esphi
and Bayle-Sempere 1989). Diver impacts appear to become significant above a certain
critical visitation level. The effects of divers on Mediterranean sublittoral and
circalittoral habitats have been studied in the protected area of the Medes Islands where
diver licenses have been established on 450 visits per day in 1997. The density and size
of the colonies of the bryzoan Pentapora fascialis were significantly lower at frequented
sites than at unfrequented sites (Sala et al. 1996). Mortality rates of the gorgon ian
Paramuricea clavata were also higher at frequented sites (Coma and Zabala 1994). The
mean size of the red coral Corallium rubrum also appeared to be larger at unfrequented
sites (Sala and Garrabou 1994, unpublished.). Diver visitation is a causal factor that plays
a major role in determining the structure of coralligenous communities at higher fre-
120
1
N
40
E
0
1.1'\
N
.... 30
Q)
0.
~
~
::I 20
"U
.>
'6
£
10
0
2
I
3
4
5
R. Sarda . M. Fluvia
_
Protected area (HF)
c::::::::J Protected area (MF)
Non protected area (IF)
6
7
8
9
10
11
Fish species
Fig. 14.8. Densities expressed as mean number of individuals per 250 m' (±s.e.) of different common
fish species in protected areas of the Medes Islands with high fish densities (HF) and medium fish
densities (MF), and compared with non protected (LF) areas of the vicinity. Fish included are:
1 Scorpaena porcus, 2 Serranus cabril/a, 3 Diplodus sargus, 4 Diplodus vulgaris,s Diplodus cervinus,
6 Diplodus annularis, 7 Diplodus puntazzo, 8 Sparus aurata, 9 Sciaena umbra, 10 Symphodus tinea, and
11 Symphodus mediterraneus (Adapted from Garcia-Rubies and Zabala 1990)
pared against control zones on the Coast, demonstrated the positive effect of the creation of marine reserves. In the absence of human predation, the number of littoral
fishes and their size increased greatly (Fig. 14.8). Furthermore, the presence of more
or less fish on tqe coast can control other species such as the sea-urchins. Increased
fishing pressure may directly reduce the populations of herbivorous fishes and indirectly mediate an increase in sea-urchin populations, by eliminating sea-urchin predators, which then remove fleshy alga communities. The scenery then changes to a community dominated'by encrusting calcareous algae (Sala 1996), which has altered the
natural habitat.
Recreational use of coastal areas may have other adverse ecological consequences
derived from the frequentation of habitats. In some Marine Protected Areas (MAPs)
the acceptability of damage by divers has been calculated (Dixon 1993; Ramos-Esphi
and Bayle-Sempere 1989). Diver impacts appear to become significant above a certain
critical visitation level. The effects of divers on Mediterranean sublittoral and
circalittoral habitats have been studied in the protected area of the Medes Islands where
diver licenses have been established on 450 visits per day in 1997. The density and size
of the colonies of the bryzoan Pentapora fascialis were significantly lower at frequented
sites than at unfrequented sites (Sala et al. 1996). Mortality rates of the gorgon ian
Paramuricea clavata were also higher at frequented sites (Coma and Zabala 1994). The
mean size of the red coral Corallium rubrum also appeared to be larger at unfrequented
sites (Sala and Garrabou 1994, unpublished.). Diver visitation is a causal factor that plays
a major role in determining the structure of coralligenous communities at higher fre-