Community structure of macrobenthos in two tropical sandy ... - UFF

Fernandes & Soares-Gomes
Community structure of macrobenthos in two tropical sandy beaches
(1990), who suggested that the only valid zonation
scheme might be a division of the air-breather, high-shore
assemblages from the water-breather, lower shore assemblages.
Giménez & Yannicelli (1997) suggested that on beaches
with a steeper slope, E. brasiliensis and D. hanleyanus
could define the zones more properly, while the high
zone was characterized by E. braziliensis.
Species that depend upon swash have their distribution
limited to reflective beaches because on those beaches the
slope is steeper and the swash is shorter. Correlation analysis
between swash and slope suggested that slope controls
zonation patterns on sandy beaches. At Costa Azul,
the steep slope might act as a barrier hindering the migration
of species that occupy the lower zone. As a result of
the fast water drainage at the intermediate zone, only
organisms adapted to dry sand such as E. braziliensis can
persist.
At Pontal Beach, P. brasiliensis and E. brasiliensis cooccur
in the supralittoral zone. The occurrence of these
cirolanid isopods at higher levels on the coast is opposite
to the pattern proposed by Dahl (1952). The same occurrence
was also reported by Jaramillo (1978), Gianuca
(1983), Defeo et al. (1992) and Brazeiro & Defeo (1996)
for temperate sites in South America.
Defeo et al. (1997) studied the distribution of E. armata
and E. braziliensis, and observed that when these species
co-occur, E. braziliensis is found in lower densities and
occupies the high mediolittoral zone, above the zone where
E. armata occurs. The same was observed in the present
study at Costa Azul.
Few studies of beaches include samples taken in the
sublittoral zone. Some studies showed that the sublittoral
assemblages are more structurally variable than intertidal
ones (Borzone et al. 1996). Hill & Hunter (1976); Leber
(1982) and Knott et al. (1983). In our study the results
were contradictory. At Pontal, the density of S. squamata
was higher in the sublittoral zone while the richness of
species was lower, while at Costa Azul, the species richness
was higher in the sublittoral zone.
Hill & Hunter (1976), Leber (1982) and Knott et al.
(1983) concluded that species composition between the
intertidal and sublittoral zones differs. Contrary to those
results, no exclusive species were found in the sublittoral
zones at Costa Azul and Pontal.
Fleischack & Freitas (1989) studied the sublittoral portion
of several beaches and suggested an inverse relationship
between species diversity and turbulence in the
sublittoral zone. Barros et al. (2001) studied six beaches
of the Paraná state coast (South Brazil), and found that
higher values of species diversity occurred in a reflective
beach. The same was found in our study, where the
diversity was higher in the reflective beach of Costa Azul.
The reflective beaches, being more stable, possibly also
have more stable macrofaunal assemblages, but this test
would need careful temporal sampling, considering the
great variability in time and space of these environments
(Barros et al. 2001).
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