Tuesday, April 27, 2010

Pollution in Guanabara Bay, Rio de Janeiro, Brazil: reflections on the hydroid fauna of the intertidal zone at Governador and Paquetá Islands

The species richness, morphological plasticity, ecological specialization, and varying physiological tolerances of hydroids (phylum Cnidaria) have led many investigators to use them as environmental indicators (BOERO 1984, MERGNER 1987, GILI and HUGHES 1995). This became relevant in recent work carried out in Guanabara Bay, Rio de Janeiro, Brazil. According to water-quality parameters, the bay can be divided into three areas: northwest (the most environmentally stressed), northeast (next to a protected area), and the entrance area, with the two latter directly influenced by tidal currents. 

Five species were identified from rocks and dock pilings at three locations on Governador Island and three on Paquetá during a six-month study: Dipurena reesi Vannucci, 1956 (Corynidae), Ventromma halecioides (Alder, 1859) (Kirchenpaueriidae), and Obelia dichotoma Linnaeus, 1758, Clytia gracilis (M. Sars, 1850), and Clytia hemisphaerica (Linnaeus, 1767) (Campanulariidae). This small number contrasts with that recorded in the intertidal zone by investigators in other parts of Brazil and elsewhere worldwide.

The presence or absence of hydroids in marine environments is due to the influence of a complex of abiotic and biotic variables including salinity, substrate type, hydrodynamism, and pollution. According to CALDER (1976, 1983, 1991a, 1991b) and CALDER and MAŸAL (1997) reductions in salinity along estuarine haloclines are accompanied by decreases in numbers of species. Moreover, species richness is low in areas subjected to wide salinity oscillations. In Guanabara Bay, salinity usually varies from a maximum of 35.02 to a minimum of 8.7 psu (VALENTIN et al. 1999a). In terms of substrate, some species actively select the bottom type upon which they settle (NISHIHIRA 1969), while others are substrate generalists. In this study, the most common species, Obelia dichotoma, appeared to be a substrate generalist, whereas species of Clytia were collected predominantly on algae or polychaete tubes. Hydrodynamism varied at the different localities: in Paquetá, waters at station P1 become choppy in the afternoon, when southerly winds gain strength, whereas at P2 and P3 waters remain calm. On Governador Island, stations G1 and G2 are gently sloping, making these beaches relatively low energy (tranquil); by contrast, G3 is influenced by currents of the Boqueirão Channel that is more than 10m deep at some points. 

Finally, hydroid populations tends to be richer in clean waters but much less so in localities with a high degree of pollution. Guanabara Bay adjoins the second-largest industrial complex and the second-largest demographic center of the country. The presence of (1) the Rio- Niterói ferry docks, (2) the Rio de Janeiro port, (3) approximately 16 terminals for oil derivatives, (4) two oil refineries, (5) nearly 6,000 factories, (6) domestic trash discarded in huge dumps around its shores, (7) discharge of inadequately treated domestic effluents, and (8) the large amounts of organochlorate and organophosphate agrochemicals leaching into the rivers have, unhappily, made Guanabara Bay one of the most polluted ecosystems in the world (MAYR et al. 1989, LAVRADO et al. 1991, VALENTIN et al. 1999a, 1999b, RIBEIRO and KJERFVE 2002). Thus, the main factor limiting species richness of hydroids in the study area is believed to be the degree of disturbance to which the ecosystem has been exposed in recent years, principally in the northwest sector where this research was undertaken.


Text by Priscila A. Grohmann (IB-UFRJ)
This report was based upon the article entitled “Hydroids (Cnidaria, Hydrozoa) of the intertidal zone of Governador and Paquetá islands, Guanabara Bay, Rio de Janeiro, Brazil”. Iheringia, Sér.Zool., Porto Alegre, 99(3):291-294.
Dale R. Calder (ROM, Canada) reviewed and improved the English version.

Financial support by FAPERJ (Proc.E-26/171.674/2001).

No comments:

Post a Comment