Tropical Coastal Wetlands Research Articles

Nursery ground value of an endangered wetland to juvenile shrimps

Although urban development impacts wetlands around the world, until now there have been no studies of its effects on coastal wetlands in tropical regions of developed countries such as Australia. In fact the ecological value of such wetlands is poorly understood. This study provides an initial step in evaluating the ecological value of urbanised, tropical coastal wetlands by determining (a) the extent to which a remnant wetland, in a highly urbanised estuary in northern Australia, is used by juvenile commercial penaeid shrimps, and (b) the extent to which the shrimps rely on food chains based on wetland plants versus marine based food chains. Juvenile penaeids were abundant in the 11 wetland pools sampled. Catches included 5 commercial penaeids with two species, Fenneropenaeus merguiensis and Metapenaeus bennetae, comprising half the catch. Densities in the wetland pools were usually substantially higher than in adjacent estuarine habitats. Stable isotope analysis indicated that much of the nutrition of juvenile shrimps was supplied by marine primary producers (phytoplankton, epiphytic and epilithic algae, microphytobenthos, green filamentous algae) however the locally abundant saltmarsh grass Sporobolus virginicus was also a major contributor. In contrast, there was little indication of nutritional support from mangrove carbon. The lack of importance of mangrove carbon is surprising because the catches of F. merguiensis are often closely linked to the area or extent of mangroves, suggesting that aspects of mangrove systems other than the supply of mangrove carbon may determine the distribution of juvenile F. merguiensis.

The Trial Intensive Management Area for Crocodiles: A Crocodile Removal Zone in Queensland, Australia

The Estuarine Crocodile (Crocodylus porosus) is the world's largest living crocodile, and in Queensland it inhabits tropical coastal wetlands and waterways. From 1990 to 2001, there have been nine substantiated crocodile attacks on people in Queensland, resulting in one death and eight serious injuries. Several crocodile attacks occurred in the Cairns area during these years, and Cairns's popular swimming beaches have been closed on a number of occasions because of crocodiles. Human safety from crocodile attack is an issue of great public and political concern in Queensland. From May 1998 to June 2001, the Queensland Parks and Wildlife Service operated a trial crocodile removal program in the Cairns area, with a removal zone that extended 70 km along the coast. The program was named the Trial Intensive Management Area for Crocodiles (TIMAC), and its primary purpose was to protect the Cairns's popular swimming beaches from crocodiles. The program was expanded to provide a problem crocodile response service throughout north Queensland and to train additional rangers in crocodile management skills. During the three years of the TIMAC program, 80 crocodiles were captured in north Queensland: 46 crocodiles from within the removal zone, and 34 from outside the removal zone. There were no crocodile attacks in the removal zone during the three-year trial program. At the request of local governments, the program became permanent in July 2001. In effect, Cairns is the only tropical city whose popular swimming beaches are protected by a combination of a lifeguard service, a shark control program, netted enclosures (seasonal) for protection from dangerous Box Jellyfish (Chironex fleckeri), and a crocodile removal program.

Distribution and behavior of trace metals in the sediment and porewater of a tropical coastal wetland

Vertical profiles (0–30 cm below surface) of four trace metals—Cadmium (Cd), Chromium (Cr), Lead (Pb) and Zinc (Zn)—in the sediment and sediment porewater of an ecologically important intertidal mudflat in the Mai Po and Inner Deep Bay Ramsar Site were thoroughly studied over a period of 10 months (from March 1999 to January 2000). Two surveys, one in summer and another in winter, involving a total of eight sampling stations were conducted to study the seasonal variation of the remobilization characteristics of these trace metals in the mudflat sediment. The range of depth averaged concentration of these trace metals in the mudflat sediment was: 0.3–0.8 μg/g (Cd); 9.8–91.0 μg/g (Cr); 7.3–69.1 μg/g (Pb); and 39.5–192.0 μg/g (Zn), while that in the sediment porewater was: 0.3–121.1 μg/l (Cd); 3.0–2704.1 μg/l (Cr); 2.6–105.6 μg/l (Pb); and 32.6–4238.3 μg/l (Zn). In general, levels of dissolved trace metals in the sediment porewater were much higher in the summer than in the winter while their concentrations in the sediment were more or less the same throughout the year. Enrichment of Cd, Pb and Zn in the sediment porewater of the upper oxic layer and that of Cr in the oxic–sub-oxic boundary was generally observed. Regions in the vicinity of the Mai Po mangroves and the river mouths of Shenzhen River and Shan Pui River were found to be hotspots of trace metal pollution. Benthic diffusive fluxes of trace metals from the mudflat sediment were also estimated. Of the four trace metals, cadmium showed the greatest tendency toward remobilization from the sediment phase to the more bio-available porewater phase.

Water quality and presence of pesticides in a tropical coastal wetland in southern Mexico

The water quality of the Pozuelos–Murillo lagoon system in southern Mexico was evaluated during three periods between March and October 2002, with particular emphasis on the detection of organochlorine and organophosphorous pesticide residues in water and sediments. Physicochemical and microbiological parameters of water were also measured and integrated in a water quality index (WQI). Multivariate analysis was used to regionalise the lagoon system as a function of the behaviour of all measured parameters. Solid phase micro-extraction followed by gas chromatography (SPME-GC) was used for pesticide analysis. The concentration of phosphorous was found to be higher than that of nitrogenous compounds. This, besides a deficiency in dissolved oxygen and a high organic matter concentration (as COD), reflects eutrophication processes in some areas of the system. Measured levels of faecal coliforms and oils and greases were above the limits established by Mexican law and comparable to the concentrations reported for other highly polluted systems in Mexico. Residues of DDD (2.0 μg L −1) in water and DDE (247 ng g −1) and endosulfan I (814 ng g −1) sediments were detected by SPME-GC. The spatial distribution of these contaminants implies major potential risks because the most polluted sites were found to be those with the highest fishing activity. Although in general the WQI is on acceptable levels (65–80%), some contamination problems are evident.

Methane emissions from a coastal lagoon: Vembanad Lake, West Coast, India

An attempt has been made to estimate methane fluxes from a tropical coastal wetland the Vembanad Lake, a lagoon along the West Coast of India. It has been found that Vembanad Lake contributes significant amount of methane to the atmosphere. Average emissions varied spatially within the lake. Methane emissions were 193.2±24.5 mg m −2 h −1 at Kumaragam (fresh water) as compared to 9.3±9.6 mg m −2 h −1 at Pullot (brackish water) site. Seasonal variation was significant between pre- and post-monsoons. Soil temperature, time of the day, salinity sediment organic carbon, all control the rate of methane emissions from the Vembanad Lake.

Ecology of Mangrove Growth and Recovery in the Lesser Antilles: State of Knowledge and Basis for Restoration Projects

AbstractWhereas the increasing knowledge on tropical coastal wetlands highlights the ecological and economical importance of such ecosystems, anthropogenic activities within the coastal zone have caused substantial, irreversible losses of mangrove areas in the Lesser Antilles during the last decades. Such a paradox gives strength to compensatory policy efforts toward mangrove restoration. We review the available knowledge on the ecology of mangrove growth and recovery in the Lesser Antilles as a contribution to possible restoration projects in such islands. Distribution of species follows a general pattern of seaward/landward zonation according to their respective tolerance to flooding and to pore‐water salinity. An experimental study of seedling growth following simulated oil spill has documented the tolerance of Rhizophora mangle and Avicennia germinans seedlings to oil concentration in soils and the effects of natural biotic and abiotic factors on seedlings growth and survival. Monitoring mangrove recovery following hurricane Hugo has given information on growth patterns, from seedling to sapling stages, according to species and site conditions. Forest recovery was mostly due to pre‐established seedlings. For the large Rhizophora propagules, buoyancy appears to be a quite inefficient way of dispersal far inland from the sea shore or riversides. Causes of recovery failure are discussed. From these results we attempt to answer the questions when, where, how to plant mangroves, and what species to use.

Perceptions of environmental change in a tropical coastal wetland

To assess whether local knowledge can contribute to the identification and evaluation of natural and anthropogenic disturbances in a mangrove forest, interviews were conducted with local fisherman of the Teacapan-Agua Brava lagoon–estuarine system of Mexico. The results indicate that an increase in water salinity, following the opening of an artificial canal, has resulted in a major disturbance in the mangroves of this region. Observations of changes in the fauna of the mangroves also coincide with this modification. The responses of the fishermen further suggest that the degree of impact from the salinity on the mangroves varies by species (e.g. Laguncularia racemosa is less tolerant than Rhizophora mangle). Other factors identified as inciting disturbances, but not previously reported for this system, include a hurricane and an infestation by caterpillars. According to the fishermen, the continued modification of the water salinity and hurricanes are the two greatest threats to the remaining mangroves. Copyright © 2000 John Wiley & Sons, Ltd.

Paysans-pêcheurs du terroir et marins-pêcheurs du parcours. Les géographes et l'espace aquatique

Geographers and aquatic spaces: the farmer- fishermen's aquatic 'terroir' and the marine fishermen's 'fishing territory'. — The paper proposes a definition of «aquatic space», both as a physical support and as the historical product of social relationships, based on fieldwork and a review of the literature on tropical coastal wetland management. The many uses and constructions found in aquatic areas among coastal communities emphasize the difference between the farmer- fishermen's aquatic «terroir» and the marine fishermen's «fishing territory». The former is a closed, limited, managed area, while the latter is a flexible, more or less open, spatial structure, consisting of marine roads and specific controlled sites. The discussion of this opposition, based on case studies, should contribute to solving the «tragedy of the commons».

Bottom-up and top-down development of acid sulphate soils

This paper outlines a model of soil profile development in potential acid sulphate soils and their change into actual acid sulphate soils. Some such model is needed as a basis for soil survey and land evaluation, especially in tropical coastal wetlands where access is often difficult, local soil variations often confusing, and where vegetation and soil conditions change dramatically following any change in hydrology. Since this is a soil surveyor's model, emphasis is placed on identification of the situation in the field, even for these most chemical of soils.

Palaeogeography and palaeoenvironments of a tropical coastal wetland and offshore shelf during Holocene submergence, Jamaica

From a series of maps representing selected Holocene time periods, the palaeogeography and palaeoenvironments of the coastal wetland and adjacent offshore shelf at Negril, western Jamaica, are described and discussed. Wetland began to form at about 8250 yr B.P. and went through a major expansion of surface area between 7250 and 6500 yr B.P. Vegetation influenced by saline water formed during the earlier stages of wetland development, but a significant salinity decrease occurred in the Late Holocene, which is attributed to increased freshwater input possibly driven by climatic change. Discharge from rivers draining through the wetland retarded growth of a sill-reef that had become established on a break-of slope offshore by 8250 yr B.P. Beach development by c.6500 yr B.P. and subsequent inland migration controlled lateral expansion of the wetland, although its vertical build-up has continued in pace with sea-level rise.