316
M.-L. De Casabianca
The first two biotopes have a number of species in common as a result
of the hard substrate, and both include species associated with the presence of shelter-providing pebbles (Sphaeroma ghigii) andlor marly cliffs
(Cerianthus, Pholas). Compared to the abrupt cliffs, the shallower slope
of the pebble beaches results in the presence of fine particles. As a
consequence, a belt of specific attached algae and their associated fauna
has developed. The third clear sand biotope includes a zone devoid of
large algae and with infaunal (Amphioxus, Tapes) and surface dwelling
animals (Asterina, Holthuria, Murex, Diogenes).
The Urbino lagoon, which has a lower annual salinity variation than
the Diana lagoon, has a more diversified population structure. It is noteworthy that the communities have a narrower depth distribution compared to the marine coastal environment.
The communities of the brackish water type are independent of substrate type. They occur on slopes from 3 to 30%. They are composed of a
small core of euryhaline species (phanerogams and macroalgae) and a
euryhaline fauna that is mainly benthic and detritus-feeding, associated
with the living plant or with decomposing organic plant material (Fig. 13.4).
From the centre of the basin towards the shore, the following zones
can be distinguished:
1. Ruppia maritima beds with associated herbivorous fauna and seagrass dependent species (Hydrobia acuta, Idotea viridis, Hyppolite
squilla, Brachydontes marioni).
2. An intermediate zone, invaded by macro algae such as the widespread
Cladophora vagabunda and Ulva lactuca which are most abundant at
the beginning of spring at salinities from 2 to 17 PSU. Chaetomorpha
Unum occurs at salinities between 1.8 to 38 PSU, while Enteromorpha
intestinalis seems to prefer a brackish environment with a tendency to
become hypersaline. The associated fauna is comprised of microparticulated detritus feeders (Corophium insidiosum and ostracods) and
primary predator fishes (Pomatoschistus marmoratus, P. microps).
3. A third zone close to the edge, where the algae are predominantly
decomposed, is dominated by a high density of macroparticulate detritus feeders (Sphaeroma hookeri and Gammarus aequicauda).
From the study of the various biotopes with different salinity regimes
from almost stable marine conditions towards extreme salinity variations
(1.8-45 PSU), the following conclusions can be drawn:
1. There is a shift from a high diversity of communities and species to a
single community with a low species diversity.
2. A change from stenohaline communities and species, which are finely
tuned indicators of salinity and of certain types of substrate, to a
M.-L. De Casabianca
The first two biotopes have a number of species in common as a result
of the hard substrate, and both include species associated with the presence of shelter-providing pebbles (Sphaeroma ghigii) andlor marly cliffs
(Cerianthus, Pholas). Compared to the abrupt cliffs, the shallower slope
of the pebble beaches results in the presence of fine particles. As a
consequence, a belt of specific attached algae and their associated fauna
has developed. The third clear sand biotope includes a zone devoid of
large algae and with infaunal (Amphioxus, Tapes) and surface dwelling
animals (Asterina, Holthuria, Murex, Diogenes).
The Urbino lagoon, which has a lower annual salinity variation than
the Diana lagoon, has a more diversified population structure. It is noteworthy that the communities have a narrower depth distribution compared to the marine coastal environment.
The communities of the brackish water type are independent of substrate type. They occur on slopes from 3 to 30%. They are composed of a
small core of euryhaline species (phanerogams and macroalgae) and a
euryhaline fauna that is mainly benthic and detritus-feeding, associated
with the living plant or with decomposing organic plant material (Fig. 13.4).
From the centre of the basin towards the shore, the following zones
can be distinguished:
1. Ruppia maritima beds with associated herbivorous fauna and seagrass dependent species (Hydrobia acuta, Idotea viridis, Hyppolite
squilla, Brachydontes marioni).
2. An intermediate zone, invaded by macro algae such as the widespread
Cladophora vagabunda and Ulva lactuca which are most abundant at
the beginning of spring at salinities from 2 to 17 PSU. Chaetomorpha
Unum occurs at salinities between 1.8 to 38 PSU, while Enteromorpha
intestinalis seems to prefer a brackish environment with a tendency to
become hypersaline. The associated fauna is comprised of microparticulated detritus feeders (Corophium insidiosum and ostracods) and
primary predator fishes (Pomatoschistus marmoratus, P. microps).
3. A third zone close to the edge, where the algae are predominantly
decomposed, is dominated by a high density of macroparticulate detritus feeders (Sphaeroma hookeri and Gammarus aequicauda).
From the study of the various biotopes with different salinity regimes
from almost stable marine conditions towards extreme salinity variations
(1.8-45 PSU), the following conclusions can be drawn:
1. There is a shift from a high diversity of communities and species to a
single community with a low species diversity.
2. A change from stenohaline communities and species, which are finely
tuned indicators of salinity and of certain types of substrate, to a