Baia de Guanabara, Rio de Janeiro, Brazil
113
measure of flushing in a coastal bay is the time it takes to renew 50% of the
water volume. Using a mean bay water volume of 1.87 x 10 9 m\ Kjerfve
et al. ( 1997) calculated 11.4 days for the renewal of 50% of the bay water
volume. This relatively rapid water renewal explains why Baia de Guanabara has reasonable water quality in the lower parts of the bay, in spite of
input of huge quantities of untreated sewage.
8.8 Coastal Ecosystems
Besides urban and industrial areas, the drainage basin consists of agricultural fields and cattle lands in addition to high relief mountains, the Serra
do Mar, with a maximum elevation of 2,263 m (Pedra do Sino) within the
watershed. The catchment used to be covered by Mata Atlantica, the Atlantic rain forest, but nowadays the basin is only partially vegetated. The Mata
Atlantica still extends to the shoreline in a few places to the southwest of
the Baia de Guanabara. Much of the indigenous vegetation has been cut,
but appears as small areas of intact rain forest on mountain slopes and as
preserved mangrove wetlands along the fringes of the bay.
In spite of being encroached on by urban development, the interior margins of Baia de Guanabara are still bordered by 90 km 2 of fringing mangroves (Pires 1992), of which 43 km 2 is the Guapimirim conservation area.
Other mangroves suffer from the impact of oil spills from ships and petrochemical facilities along the inner bay shores. These mangrove communities are composed of opportunistic species of the Aizoacea and Amaranthacea, which have replaced mangrove trees in many areas. However,
biodiversity is decreased and it is difficult for mangroves to recolonize
after a spill (Lacerda and Hay 1982). Existing fringe stands of mangroves
consist of Avicennia schaueriana, Rhizophora mangle, and Laguncularia
racemosa, which occur along the lower river courses of the northern coast
of the bay. At the inner reaches of the mangrove wetlands, more than 100
taxa of plants have been recorded, and the wildlife is abundant. There are
more than 68 species of birds, including local and migrating species and
threatened species, such as the roseate spoonbill (Ajaja ajaja) and the
purple gallinule (Porphyrula martinica). Crabs are represented by approximately 30 species, including Callinectes danae, Goniopsis cruentatata, and
Cardisoma guanhumi, which are of major economic importance to artisinal fishermen (Araujo and Maciel1979).
Notwithstanding the high degradation of Baia de Guanabara resources,
the bay is still an important fisheries resource and supports 6,000 artisanal
fishermen and their families. The annual catch measures 3,000 tons, in-
113
measure of flushing in a coastal bay is the time it takes to renew 50% of the
water volume. Using a mean bay water volume of 1.87 x 10 9 m\ Kjerfve
et al. ( 1997) calculated 11.4 days for the renewal of 50% of the bay water
volume. This relatively rapid water renewal explains why Baia de Guanabara has reasonable water quality in the lower parts of the bay, in spite of
input of huge quantities of untreated sewage.
8.8 Coastal Ecosystems
Besides urban and industrial areas, the drainage basin consists of agricultural fields and cattle lands in addition to high relief mountains, the Serra
do Mar, with a maximum elevation of 2,263 m (Pedra do Sino) within the
watershed. The catchment used to be covered by Mata Atlantica, the Atlantic rain forest, but nowadays the basin is only partially vegetated. The Mata
Atlantica still extends to the shoreline in a few places to the southwest of
the Baia de Guanabara. Much of the indigenous vegetation has been cut,
but appears as small areas of intact rain forest on mountain slopes and as
preserved mangrove wetlands along the fringes of the bay.
In spite of being encroached on by urban development, the interior margins of Baia de Guanabara are still bordered by 90 km 2 of fringing mangroves (Pires 1992), of which 43 km 2 is the Guapimirim conservation area.
Other mangroves suffer from the impact of oil spills from ships and petrochemical facilities along the inner bay shores. These mangrove communities are composed of opportunistic species of the Aizoacea and Amaranthacea, which have replaced mangrove trees in many areas. However,
biodiversity is decreased and it is difficult for mangroves to recolonize
after a spill (Lacerda and Hay 1982). Existing fringe stands of mangroves
consist of Avicennia schaueriana, Rhizophora mangle, and Laguncularia
racemosa, which occur along the lower river courses of the northern coast
of the bay. At the inner reaches of the mangrove wetlands, more than 100
taxa of plants have been recorded, and the wildlife is abundant. There are
more than 68 species of birds, including local and migrating species and
threatened species, such as the roseate spoonbill (Ajaja ajaja) and the
purple gallinule (Porphyrula martinica). Crabs are represented by approximately 30 species, including Callinectes danae, Goniopsis cruentatata, and
Cardisoma guanhumi, which are of major economic importance to artisinal fishermen (Araujo and Maciel1979).
Notwithstanding the high degradation of Baia de Guanabara resources,
the bay is still an important fisheries resource and supports 6,000 artisanal
fishermen and their families. The annual catch measures 3,000 tons, in-