The Subtropical Estuarine Complex of Paranagua Bay, Brazil
141
copepods (Acartia lilljeborgi, Temora turbinata, Paracalanus quasimodo,
Corycaeus spp.) on the phytoplankton standing-stock ( <0.0 1-0.22 mg
Chl-a m- 3 day- 1 ) is low ( <5% on a daily basis) and does not appear to be
seasonal. However, grazing might be a major source of phytoplankton
mortality in the euhaline sector, at least during part of the winter and summer (Lopes 1997).
Spartina marshes in high-energy euhaline areas of Paranagua Bay have
low biomass and productivity, probably as a result of high salinity and high
sediment accretion rates, conditions that usually favor salt marsh replacement by mangroves. In general, below-ground biomass of Spartina is
strongly seasonal, being 1.72 and 5.69 tons ha- 1 at the end of summer and
spring, respectively, and below-ground production (up to 3.58 tons ha- 1
year- 1 ) exceeds above-ground production (1.01-1.79 tons ha- 1 year- 1 ; Lana
et al. 1991). The production of mangrove litter at euhaline sites is approximately 650 g m- 2 year- 1 (mainly Rhizophora) and litter is almost entirely
(80%) composed ofleaves. Litter fall rates are four to six times higher (up
to 18.82 g m- 2 day- 1 ) in rainy summers than in winter (Sessegolo 1997). Leaf
litter decomposition rates are high, probably owing to grazing macrofauna;
however, rates vary between 10.5 and 249 days for permanently immersed
Avicennia schaueriana and emersed Rhizophora mangle leaves, respectively (Sessegolo and Lana 1991). The detritus production cycles in mangrove
swamps and Spartina marshes seem to be seasonal; while Spartina produces detritus mainly in winter, mangrove litter fall is highest in summer.
Since detritivorous species depend on the availability of mangrove and salt
marsh detritus as a potential food source, seasonal differences in the behavior of benthic invertebrate populations are to be expected. In general,
richness and abundance of benthic species is significantly lower in mangroves than in marshes and adjacent non-vegetated tidal flats. Population
density of infaunal species, especially of those (i.e. the polychaetes Isolda
pulchella and Nereis oligohalina) which use Spartina roots as substrate or
refuge, correlates with below-ground plant biomass and increases with
higher rhizome biomass at the end of winter and the beginning of spring
(Lana and Guiss 1992).
10.5 Human Impacts and Management Needs
The estuarine complex of Paranagua Bay is one of the least impacted
coastal systems in southeastern Brazil, the present state of conservation
being the result of the regional process of colonization. Contrary to most
coastal regions in Brazil, the urban, agricultural and industrial develop-
141
copepods (Acartia lilljeborgi, Temora turbinata, Paracalanus quasimodo,
Corycaeus spp.) on the phytoplankton standing-stock ( <0.0 1-0.22 mg
Chl-a m- 3 day- 1 ) is low ( <5% on a daily basis) and does not appear to be
seasonal. However, grazing might be a major source of phytoplankton
mortality in the euhaline sector, at least during part of the winter and summer (Lopes 1997).
Spartina marshes in high-energy euhaline areas of Paranagua Bay have
low biomass and productivity, probably as a result of high salinity and high
sediment accretion rates, conditions that usually favor salt marsh replacement by mangroves. In general, below-ground biomass of Spartina is
strongly seasonal, being 1.72 and 5.69 tons ha- 1 at the end of summer and
spring, respectively, and below-ground production (up to 3.58 tons ha- 1
year- 1 ) exceeds above-ground production (1.01-1.79 tons ha- 1 year- 1 ; Lana
et al. 1991). The production of mangrove litter at euhaline sites is approximately 650 g m- 2 year- 1 (mainly Rhizophora) and litter is almost entirely
(80%) composed ofleaves. Litter fall rates are four to six times higher (up
to 18.82 g m- 2 day- 1 ) in rainy summers than in winter (Sessegolo 1997). Leaf
litter decomposition rates are high, probably owing to grazing macrofauna;
however, rates vary between 10.5 and 249 days for permanently immersed
Avicennia schaueriana and emersed Rhizophora mangle leaves, respectively (Sessegolo and Lana 1991). The detritus production cycles in mangrove
swamps and Spartina marshes seem to be seasonal; while Spartina produces detritus mainly in winter, mangrove litter fall is highest in summer.
Since detritivorous species depend on the availability of mangrove and salt
marsh detritus as a potential food source, seasonal differences in the behavior of benthic invertebrate populations are to be expected. In general,
richness and abundance of benthic species is significantly lower in mangroves than in marshes and adjacent non-vegetated tidal flats. Population
density of infaunal species, especially of those (i.e. the polychaetes Isolda
pulchella and Nereis oligohalina) which use Spartina roots as substrate or
refuge, correlates with below-ground plant biomass and increases with
higher rhizome biomass at the end of winter and the beginning of spring
(Lana and Guiss 1992).
10.5 Human Impacts and Management Needs
The estuarine complex of Paranagua Bay is one of the least impacted
coastal systems in southeastern Brazil, the present state of conservation
being the result of the regional process of colonization. Contrary to most
coastal regions in Brazil, the urban, agricultural and industrial develop-