The Patos Lagoon Estuary, Brazil
173
the marsh. In mid- and lower marshes the crabs Metasesarma rubripes and
Chasmagnathus granulata hide between Spartina alterniflora, Spartina
densiflora, and Scirpus maritimus plants or in burrows, respectively, and
compete for space and food. Both species act upon the fragmentation and
remobilization of the below-ground macrophyte biomass, thus decisively
influencing the recycling of organic matter in the marshes. The dense
marsh vegetation also offers potential breeding sites for birds, like the redgartered coot (Fulica armillata), the black-necked swan Cygnus melancorhyphus, the snowy egret (Egretta thula), the green heron (Butorides striatus), as well as for shorebirds like the brown-hooded gull Larus
maculipennis and Trudeau's tern Sterna trudeaui (Costa 1998).
12.3.5 Artificial Hard Substrates
The overwhelming dominance of unconsolidated sediments in the estuary
reinforces the importance even small areas of permanent substrate may
assume for colonization and development of encrusting organisms. Apart
from estuarine salinity gradients, substrate characteristics clearly divide
the local benthic algal flora into species with permanent substrate requirements growing on the rocky jetties at the inlet and those inside the estuary
which tolerate unstable substrates (Seeliger 1998). The lack of permanent
substrate, reduced tidal oscillation and turbid waters inside the estuary
account for an encrusting community of low diversity. Here the dominant
encrusting organism is the cirriped Balanus improvisus which settles on
wooden pilings and piers together with a few tolerant species of algae (i.e.,
Gomontia lignicola, Polysiphonia sp., Ulvaria oxysperma). The dense layer
of Balanus continuously hatches, liberating large quantities of larvae
(12,473 m- 3 ) into the water column which are food for plankton feeders
or re-settle on available substrates. The density of Balanus eventually
decreases, owing to crowding and to predation by Stylochus sp., and new
niches open for colonization by the polychaete Boccardia hamata, the
amphipod Amphithoe ramondi, the tanaiid Tanais stanfordi, and larvae of
Obelia. In contrast, the rocky jetties at the inlet provide suitable conditions
for a diverse encrusting community (Capitoli 1997). Furthermore, they
also assume a biogeographic significance because they represent the only
permanent substrate for northern tropical and southern cold temperate
organisms along 700 km of sandy beaches in the southwestern Atlantic
(30-34°S; Coutinho and Seeliger 1986).
173
the marsh. In mid- and lower marshes the crabs Metasesarma rubripes and
Chasmagnathus granulata hide between Spartina alterniflora, Spartina
densiflora, and Scirpus maritimus plants or in burrows, respectively, and
compete for space and food. Both species act upon the fragmentation and
remobilization of the below-ground macrophyte biomass, thus decisively
influencing the recycling of organic matter in the marshes. The dense
marsh vegetation also offers potential breeding sites for birds, like the redgartered coot (Fulica armillata), the black-necked swan Cygnus melancorhyphus, the snowy egret (Egretta thula), the green heron (Butorides striatus), as well as for shorebirds like the brown-hooded gull Larus
maculipennis and Trudeau's tern Sterna trudeaui (Costa 1998).
12.3.5 Artificial Hard Substrates
The overwhelming dominance of unconsolidated sediments in the estuary
reinforces the importance even small areas of permanent substrate may
assume for colonization and development of encrusting organisms. Apart
from estuarine salinity gradients, substrate characteristics clearly divide
the local benthic algal flora into species with permanent substrate requirements growing on the rocky jetties at the inlet and those inside the estuary
which tolerate unstable substrates (Seeliger 1998). The lack of permanent
substrate, reduced tidal oscillation and turbid waters inside the estuary
account for an encrusting community of low diversity. Here the dominant
encrusting organism is the cirriped Balanus improvisus which settles on
wooden pilings and piers together with a few tolerant species of algae (i.e.,
Gomontia lignicola, Polysiphonia sp., Ulvaria oxysperma). The dense layer
of Balanus continuously hatches, liberating large quantities of larvae
(12,473 m- 3 ) into the water column which are food for plankton feeders
or re-settle on available substrates. The density of Balanus eventually
decreases, owing to crowding and to predation by Stylochus sp., and new
niches open for colonization by the polychaete Boccardia hamata, the
amphipod Amphithoe ramondi, the tanaiid Tanais stanfordi, and larvae of
Obelia. In contrast, the rocky jetties at the inlet provide suitable conditions
for a diverse encrusting community (Capitoli 1997). Furthermore, they
also assume a biogeographic significance because they represent the only
permanent substrate for northern tropical and southern cold temperate
organisms along 700 km of sandy beaches in the southwestern Atlantic
(30-34°S; Coutinho and Seeliger 1986).