172
U. Seeliger
completely covered by diatoms (i.e., Synedra, Amphora, Nitzschia, Pleurosira laevis, Melosira, Navicula, Rhopalodia, Mastogloia) and macroalgae
(i.e., Achrochaetium, Cladophora, Enteromorpha; Ferreira and Seeliger
1985). Ruppia beds also promote the entanglement of drifting macroalgae,
which may temporarily form an associated habitat of potential importance. Since drift-algae increase the drag force of waves and currents, plants
become more susceptible to dislodging, which causes the thinning of beds
during fall. The leaves, stems, rhizomes, and roots of Ruppia beds form a
structurally complex habitat of calm water and stable substrate which
tends to support high in- and epifaunal biomass (Garcia and Vieira 1997).
Ruppia beds provide protection and offer food for early life-cycle stages of
Farfantepenaeus paulensis, Callinectes sapidus, Cyrtograpsus angulatus, as
well as for some species of the Sciaenidae, Mugilidae, and Atherinidae;
however, the adults of these are also common in unvegetated shoals. The
conditions for faunal recruitment are often suboptimal because the initiation of growth, density of plants, and the permanence and total area of
Ruppia beds tends to vary significantly within and between years. As a consequence, the function of the beds as a nursery habitat for the development
of important estuarine fisheries stock may be severely limited during some
years (Seeliger 1997b).
12.3.4 Marginal Marshes
The extensive marshes of the estuary are irregularly flooded by waters of
varying salinity, with oligohaline waters prevailing during the winter and
spring and mesohaline conditions being more common in the summer
(Costa 1997, 1998). The interstitial waters of rarely flooded upper marsh
areas tend to be less saline than those of frequently inundated lower
marshes, owing to rapid leaching by rain. The spatially and temporally
heterogeneous marsh physiography has a pronounced influence on the
diversity, abundance, and distribution of species as well as on the fate of
organic matter production. About 50% of the annual production of marsh
plant litter undergoes autolysis/leaching and microbial decay in the sediments, while the larger part of the production and up to 20% of the annual
detritus pool is exported into the estuary during periods of prolonged
flooding. The high plant biomass and detrital matter concentrations in the
marshes attract in- and epifaunal macroinvertebrates. Detritivorous nematodes, annelids (i.e., Heteromastus similis, Laeonereis acuta, Nephtys fluviatilis), and gastropods (i.e., Heleobia australis) are common inhabitants
in superficial sediments and terrestrial isopods (Balloniscus spp.), amphipods ( Orchestia platens is), spiders, and insects are abundant throughout
U. Seeliger
completely covered by diatoms (i.e., Synedra, Amphora, Nitzschia, Pleurosira laevis, Melosira, Navicula, Rhopalodia, Mastogloia) and macroalgae
(i.e., Achrochaetium, Cladophora, Enteromorpha; Ferreira and Seeliger
1985). Ruppia beds also promote the entanglement of drifting macroalgae,
which may temporarily form an associated habitat of potential importance. Since drift-algae increase the drag force of waves and currents, plants
become more susceptible to dislodging, which causes the thinning of beds
during fall. The leaves, stems, rhizomes, and roots of Ruppia beds form a
structurally complex habitat of calm water and stable substrate which
tends to support high in- and epifaunal biomass (Garcia and Vieira 1997).
Ruppia beds provide protection and offer food for early life-cycle stages of
Farfantepenaeus paulensis, Callinectes sapidus, Cyrtograpsus angulatus, as
well as for some species of the Sciaenidae, Mugilidae, and Atherinidae;
however, the adults of these are also common in unvegetated shoals. The
conditions for faunal recruitment are often suboptimal because the initiation of growth, density of plants, and the permanence and total area of
Ruppia beds tends to vary significantly within and between years. As a consequence, the function of the beds as a nursery habitat for the development
of important estuarine fisheries stock may be severely limited during some
years (Seeliger 1997b).
12.3.4 Marginal Marshes
The extensive marshes of the estuary are irregularly flooded by waters of
varying salinity, with oligohaline waters prevailing during the winter and
spring and mesohaline conditions being more common in the summer
(Costa 1997, 1998). The interstitial waters of rarely flooded upper marsh
areas tend to be less saline than those of frequently inundated lower
marshes, owing to rapid leaching by rain. The spatially and temporally
heterogeneous marsh physiography has a pronounced influence on the
diversity, abundance, and distribution of species as well as on the fate of
organic matter production. About 50% of the annual production of marsh
plant litter undergoes autolysis/leaching and microbial decay in the sediments, while the larger part of the production and up to 20% of the annual
detritus pool is exported into the estuary during periods of prolonged
flooding. The high plant biomass and detrital matter concentrations in the
marshes attract in- and epifaunal macroinvertebrates. Detritivorous nematodes, annelids (i.e., Heteromastus similis, Laeonereis acuta, Nephtys fluviatilis), and gastropods (i.e., Heleobia australis) are common inhabitants
in superficial sediments and terrestrial isopods (Balloniscus spp.), amphipods ( Orchestia platens is), spiders, and insects are abundant throughout