Mangrove Estuary Research Articles

Behavior of Aluminum and DOC in waters of the Gesashi mangrove estuary, Okinawa, Japan

Behavior of Aluminum and DOC in waters of the Gesashi mangrove estuary, Okinawa, Japan

Linking fish assemblages and attributes of mangrove estuaries in tropical Australia: criteria for regional marine reserves

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 305:41-57 (2005) - doi:10.3354/meps305041 Linking fish assemblages and attributes of mangrove estuaries in tropical Australia: criteria for regional marine reserves J. A. Ley Department of Fisheries and Marine Environment, Australian Maritime College, PO Box 21, Beauty Point, Tasmania 7270, Australia *Email: j.ley@amc.edu.au ABSTRACT: Quantifying natural features important in structuring fish assemblages is an essential pre-requisite to implementation of measures to conserve regionally representative whole ecosystems. Tropical estuaries are high in priority for protection, but fish-ecosystem relationships have rarely been analysed at multiple scales. Fishery-independent surveys (gill nets 19 to 152 mm mesh) were replicated seasonally (wet, dry) in 11 large estuaries along 1400 km of coast adjacent to the Great Barrier Reef. Fundamental differences in physical forces (river, wave, tidal) apparently generated variation in abiotic attributes, which distinguished Tide- from Wave-dominated systems. These trends correlated with patterns observed among estuarine fish assemblages, mediated by ecological and biological processes. Tide-dominated systems (n = 7), located in drier catchments, had greater mangrove area, wide deltaic mouths, and muddy substrate; in these systems, diversity was high with Ariidae, Belonidae and Haemulidae characterising the fish assemblages. Wave-dominated systems (n = 4), located in higher rainfall catchments, had constricted mouths, less mangrove area, and sandy substrate. For Wave-dominated systems, deltas (n = 2), had high diversity with Megalopidae characterising the fish assemblages, while true estuaries (n = 2) were relatively depauperate. Notably, none of the estuarine attributes explained the greater catch rates of Carangidae and Carcharhinidae observed in east Cape York. This trend may be attributed to negligible fishing pressure in the remote Cape York region. Overall, a substantial amount of the variation in fish assemblages (42.9%) was related to catchment hydrology, configuration of the estuary mouth, substrate and mangrove area. The results here support management programs incorporating a surrogate approach aimed at conserving the biodiversity of estuarine fish assemblages by combining regional and estuary scales in defining networks of reserve systems. KEY WORDS: Marine reserves · Mangroves · Fish assemblages · Multivariate analysis · Estuaries · Habitat · Great Barrier Reef · Ecosystems Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 305. Online publication date: December 23, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

A Circa-decadal Change in the Gastropod Fauna on a Tidal Flat in an Island Mangrove Estuary

An investigation on gastropod fauna was carried out on a tidal flat in the Nagura Estuary on Ishigaki Island, the Ryukyu Islands in 1989 and 1998 using similar methods. 470-480 quadrats covering ca. 1900 m2 were surveyed during low tides from February to April in each year. Of the total 19 species recorded, the ranges of eight species had varied significantly between the two surveys, with six species expanding their range and two species contracting their range. Percentage in abundance of muddy-bottom species and tropical (<29 degrees N) species increased significantly between the two years. Topography of the flat also changed: the mouth of the river was narrowed and the elevated sections of the tidal flat expanded. During the period from 1984 to 1998, the farmland development around the study site caused influxes of soil into the estuary and the sea-water temperature was rising. These results suggest that the topographical changes due to soil influx and the rising temperature affected the gastropod assemblage at the study site, by increasing the abundance of muddy-bottom species and tropical species. The methodology used in this study, i.e. surface observation at low tides, includes more than 95% of the gastropod fauna, demonstrating the usefulness of surface counts for the study of soft-bottom fauna.

Qualitative modelling for the Caeté Mangrove Estuary (North Brazil): a preliminary approach to an integrated eco-social analysis

The sustainability of different integrated management regimes for the mangrove ecosystem of the Caeté Estuary (North Brazil) were assessed using a holistic theoretical framework. As a way to demonstrate that the behaviour and trajectory of complex whole systems are not epiphenomenal to the properties of the small parts, a set of conceptual models from more reductionistic to more holistic were enunciated. These models integrate the scientific information published until present for this mangrove ecosystem. The sustainability of different management scenarios (forestry and fishery) was assessed. Since the exploitation of mangrove trees is not allowed according Brazilian laws, the forestry was only included for simulation purposes. The model simulations revealed that sustainability predictions of reductionistic models should not be extrapolated into holistic approaches. Forestry and fishery activities seem to be sustainable only if they are self-damped. The exploitation of the two mangrove species Rhizophora mangle and Avicenia germinans does not appear to be sustainable, thus a rotation harvest is recommended. A similar conclusion holds for the exploitation of invertebrate species. Our results suggest that more studies should be focused on the estimation of maximum sustainable yield based on a multispecies approach. Any reference to holistic sustainability based on reductionistic approaches may distort our understanding of the natural complex ecosystems.

Mangrove filtration of anthropogenic nutrients in the Rio Coco Solo, Panama

Measurements of the distribution pattern of several nutrients (ammonia, nitrite, nitrate, and phosphate) and indicators (dissolved oxygen and conductivity) were conducted along the river Coco Solo on the Caribbean coast of Panama. The project investigated the extent to which mangrove forests could act as a vegetative buffer zone between disturbed freshwater sources and coastal water. Upriver freshwater samples were collected in known areas of human disturbance to assess levels of the nutrients near points of origin and exhibited elevated concentrations of nutrients. Samples were taken along the mangrove estuary to study the concentrations of nutrients as they moved through the estuary into the ocean. Expected and observed values were compared to see whether concentration levels of the chemicals exhibited normal dilution patterns. Graphs show that the nutrient levels at the estuary points are significantly lower than expected through normal dilution, indicating the removal of nutrients through another mangrove mediated method. In this way, mangrove forests can act as effective coastal buffers of anthropogenic effects to the ocean environment. Further studies must be done to determine the actual removal mechanisms of nutrients in the mangrove estuarine system.

A comparison of brachyuran crab community structure at four mangrove locations under different management systems along the Melaka Straits-Andaman Sea Coast of Malaysia and Thailand

Brachyuran crab community structure was compared between mangrove sites under different management systems from four locations along the Melaka Straits-Andaman Sea Coast. Klong Ngao, a mangrove estuary in Ranong Province of southern Thailand, lies within a Biosphere Reserve designated in 1997. Sites were positioned in plantations at a former charcoal concession forest, a disused tin mine, and an abandoned shrimp pond along this estuary. The Merbok estuary in Kedah, Malaysia, is partially managed: the mangroves are cut for charcoal and poles on a small scale and the forests are left to regenerate naturally. The Matang Mangrove Forest Reserve in Perak, Malaysia, is heavily exploited but well managed, forRhizophora wood to produce charcoal, and has been for 100 years. Sites were positioned in plantations of different ages. Kuala Selangor Nature Park, Selangor, Malaysia, was established as a nature reserve in 1987 and contains mature mangrove forest regenerating naturally from previous selective felling. At Klong Ngao and Matang, mature reserve forest sites were also studied for comparison with plantation sites. The sites included both upstream and downstream locations and were of similar area, minimizing effects from possible species-area relationships. Sites were chosen with similar environmental conditions and with a dominance ofRhizophora spp. At each site per location, the brachyuran crabs were sampled quantitatively in 100 m2 quadrats by three independent 15-min timed crab catches. The crab community recorded was analyzed by univariate and multivariate statistical techniques. Management history plays an important role in moderating the crab community structure. The crab community also changes with the age of the mangrove forest stand. Sesarmid crabs consistently dominated in mature forests, whereas young plantations were colonized mainly by ocypodid crabs. The findings show that heavily effected sites—e.g., disused tin mining areas, former concession forests, and abandoned shrimp ponds—can be rehabilitated by planting mangroves and that the crab community is a useful ecological indicator of habitat status.

Distribution and feeding habits of juvenile and young John's snapper Lutjanus johnii in the Matang mangrove estuary, west coast of Peninsular Malaysia

ABSTRACT: The aim of the present paper was to provide some information on the distribution pattern and feeding habits of juvenile and young Lutjanus johnii in the Matang mangrove estuary on the west coast of Peninsular Malaysia. Sampling was carried out at five sites using otter trawl nets from October 1998 to January 2000. Ninety-three individuals of juvenile and young L. johnii were collected during the research period. The range in total length varied from 3.4 to 21.1 cm, and the gonads of all fish were at the immature stage. Fish were caught at the river mouth and neighboring sites in Matang at a water depth of 1.6–7.5 m, salinity of 12.4–28.3, and temperature of 27.3–31.6°C. Individuals fed mainly on Natantia and Mysidacea, although the type of food varied with size. Large-sized individuals fed mainly on Natantia, and small-sized individuals on Mysidacea.

Juvenile and small fishes in a mangrove estuary in Trang province, Thailand: seasonal and habitat differences

Juvenile and small resident fish assemblages at three sites (beach with mangroves, beach without mangroves and middle reach of mangrove creek), comprising the major habitat types of a mangrove estuary in Trang Province, Thailand, were studied for 3 years. A total of 6616 individuals, comprising 89 species (30 families), were collected using a small seine net. In terms of number of species per family, Gobiidae (18 species) was the most diverse, followed by Engraulidae (nine species) and Leiognathidae (seven species). In terms of individuals, Engraulidae, Leiognathidae, Gerreidae, Atherinidae and Gobiidae were the dominant families. Species richness was significantly greater in the mangrove creek than at the two beach sites, and greater in the wet season than the dry season. Fish abundance (individuals per tow) was also greater in the wet season, with no significant differences among sites. On the other hand, biomass (weight per tow) was greater in the mangrove creek than the mangrove beach, but with no significant difference between seasons. Cluster and ordination analysis based on the number of individuals of each species demonstrated that the fish assemblage structures were markedly different between the beach and creek sites, the assemblages at the two beach sites being similar in the wet season. Most species were specific to a particular habitat type (or types), some occurring exclusively in the creek or beach sites, and some in both the mangrove sites. Such distributional differences were found even between species within a single family. The results indicated that creek and beach habitats function as nursery sites for different fish species, the former being utilized by a grater diversity of species than the latter.

Organochlorine pesticide residues in sediments of a tropical mangrove estuary, India: implications for monitoring

The paper examines the concentrations of isomers of hexachlorocyclohexane (HCHs), dichlorodiphenyl trichloroethane and its metabolites (DDTs), α-endosulfan and endosulfan sulfate in surface sediment samples collected from the mouth of Hugli estuary in the vicinity of Sundarban mangrove environment, eastern part of India. An overall pattern of accumulation of these pesticides was in the order of: ΣHCH>endosulfan sulfate>ΣDDT>α-endosulfan. The concentration of these compounds was quite low. An elevated level of ΣHCH, ΣDDT and endosulfan sulfate were marked during premonsoon months, a period characterized by high salinity and pH values. Among the isomers and metabolites of HCH and DDT, β-HCH, pp′-DDT and pp′-DDE were found to be dominant. The sources of contamination are closely related to human activities, such as domestic and industrial discharges, agricultural chemical applications and soil erosion due to deforestation. The study is compared to other estuarine environment in India and abroad. The present data will serve as a baseline against which future anthropogenic effects may be assessed.

Black Rice: The African Origins of Rice Cultivation in the Americas

Black Rice: The African Origins of Rice Cultivation in the Americas

High resolution mapping of tropical mangrove ecosystems using hyperspectral and radar remote sensing

Mangrove ecosystems are in serious decline around the world and various initiatives are underway to assess their current coverage and loss in cover. These ecosystems occur as thin strips along coastlines or rivers and, due to the strong environmental gradients present, mangroves show high spatial variability along short transects. Remote sensing tools that offer high spatial resolution mapping and high information content are needed to provide good differentiation of the various mangrove zones and types. The added complexities of tropical atmospheric conditions provide further challenges in terms of the selection of sensors and image analysis methodologies. This paper explores the possibility of combining a high spatial/spectral resolution scanner, 'Compact Airborne Spectrographic Imager' (CASI), with the airborne National Aeronautics @ Space Administration's polarimetric radar, 'AIRSAR', for mapping and monitoring of mangrove estuaries. The Daintree River estuary in far North Queensland, Australia was chosen for this study due to its diversity of mangrove species. Imagery acquired by both the CASI airborne scanner (14 bands, 2.5 m pixel) and the AIRSAR (L- and P-band polarimetry, C-band interferometry, 10 m pixel) has been used to produce detailed maps of the mangrove zones in the estuary. The advantages and difficulties associated with multi-source data integration are investigated in this paper. While radar provides general structural information in relation to mangrove zonation, high-resolution hyperspectral scanners allow for finer-detailed analysis and green-biomass information. Classifications (maximum likelihood) of both the individual and integrated datasets are performed, with the latter producing more accurate results. Application of a hierarchical neural network classification is also explored, where the more general mangrove zones are separated first based on structural information, then species or specie-complexes are extracted in subsequent levels using spectral differences.

The influence of fish cage aquaculture on pelagic carbon flow and water chemistry in tidally dominated mangrove estuaries of peninsular Malaysia

The impact of floating net cages culturing the seabass, Lates calcarifer, on planktonic processes and water chemistry in two heavily used mangrove estuaries in Malaysia was examined. Concentrations of dissolved inorganic and particulate nutrients were usually greater in cage vs. adjacent (≈100 m) non-cage waters, although most variability in water-column chemistry related to water depth and tides. There were few consistent differences in plankton abundance, production or respiration between cage and non-cage sites. Rates of primary production were low compared with rates of pelagic mineralization reflecting high suspended loads coupled with large inputs of organic matter from mangrove forests, fishing villages, fish cages, pig farms and other industries within the catchment. Our preliminary sampling did not reveal any large-scale eutrophication due to the cages. A crude estimate of the contribution of fish cage inputs to the estuaries shows that fish cages contribute only ≈2% of C but greater percentages of N (32–36%) and P (83–99%) to these waters relative to phytoplankton and mangrove inputs. Isolating and detecting impacts of cage culture in such heavily used waterways—a situation typical of most mangrove estuaries in Southeast Asia—are constrained by a background of large, highly variable fluxes of organic material derived from extensive mangrove forests and other human activities.

Fish fauna of the Sikao Creek mangrove estuary, Trang, Thailand

: Between September 1996 and March 1999, a total of 135 fish species in 43 families were recorded from the mangrove estuary of Sikao Creek, Trang Province, Thailand, using two sizes of beach seine and a bag net. A checklist of the species is given, with preliminary descriptions of their assemblage structure. In terms of the number of species per family, Gobiidae was the most diverse (28 species), followed by Leiognathidae (11 species) and Engraulidae (10 species). In terms of individual numbers, Engraulidae, Leiognathidae and Ambassidae were the most dominant, whereby the 20 most abundant species comprised 88.5% of the total number of individuals collected. The fish assemblage structure was compared with published accounts of other tropical Indo-West Pacific mangrove estuaries, and found to be similar to those of tropical Australia. Although a grater number of species were recorded from Sikao Creek than in comparable studies in other geographic regions, all of the studies were similar in that they have relatively few species that are clearly dominant in abundance.

Diversity of benthic organic matter flows through polychaetes and crabs in a mangrove estuary: δ13C and δ34S signals

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 227:145-155 (2002) - doi:10.3354/meps227145 Diversity of benthic organic matter flows through polychaetes and crabs in a mangrove estuary: δ13C and δ34S signals Hwey-Lian Hsieh1,*, Chang-Po Chen1,2, Yue-Gau Chen3, Hsiao-Hui Yang1,2 1Institute of Zoology, Academia Sinica, Nankang Taipei, Taiwan 115, ROC 2Institute of Fisheries Science, National Taiwan University, Sec. 4, Rooseveld Road, Taipei, Taiwan 106, ROC 3Department of Geology, National Taiwan University, 245 Choushan Road, Taipei, Taiwan 106, ROC *E-mail: zohl@ccvax.sinica.edu.tw ABSTRACT: Estuaries are biologically diverse systems, especially in the spatial relationships between macrobenthos and their food sources. In a mangrove estuary in northern Taiwan, spatial patterns of organic matter flows from primary producers and detritus derived from vascular plants to macrofaunal polychaetes and crabs were examined using stable isotopes of carbon and sulfur. Sampling was conducted mainly from August 1996 to May 1997 on 2 mud flats, 1 on a tidal creek (Creek site) and the other on a tidal riverbank (River site). The δ13C and δ34S ranges at the River site were broader than those at the Creek site (δ13C: -28.3 to -13.6” vs -28.3 to -19.3”, δ34S: 8.1 to 15.9” vs 7.1 to 13.1”). This is due to the presence of a C4 plant, the cogon grass Imperata cylindrica at the River site. Although the mangrove Kandelia candel was the largest source of carbon at both study sites, our isotopic analyses showed that it was not as important a source of nutrition to consumers as particulate organic matter (POM), benthic microalgae, and cogon grass. When their δ13C and δ34S values were plotted against each other, the 4 crab and 2 polychaete species were differentiated into several distinguishable assemblages which correspond to sites where they reside. The conspecific nereids and fiddler crabs utilize different food sources when inhabiting different sites. Stable isotopic analyses revealed 3 kinds of feeding interactions at the Creek site. Along with detritivory (which uses POM) and herbivory (which uses microalgae), carnivory occurs between the grapsid crab Helice formosensis and its sabellid prey. Thus, trophic interactions are more complicated and diverse at the Creek than at the River site where detritivory (using POM plus detritus of cogon grass) is prevalent. A wider range of δ13C and δ34S values in a food web does not necessarily mean that the macrobenthos have a greater food variety, nor can one interpret how diverse an estuarine food web is. Instead, the diversity of an estuarine food web is characterized by a series of factors related to spatial differences in flow regimes, the availability and relative contribution of food sources, the opportunistic dietary choices of consumers, and consequently, spatially varying trophic interactions. KEY WORDS: Diversity · Organic matter flow · Polychaete · Crab · Mangrove estuary · δ13C · δ34S Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 227. Online publication date: February 13, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Ecosystem effects of fishing closures in mangrove estuaries of tropical Australia

Along the section of Australia's coast adjacent to the Great Barrier Reef, certain mangrove- dominated estuaries have been closed to commercial net fishing for over 5 yr. During a 2 yr bimonthly sampling program aimed at evaluating the effect of these closures, fish communities were compared among 3 pairs of neighbouring estuaries (1 closed and 1 open to commercial net fishing per pair). We employed a complete factorial design to test effects of fishing (open or closed), region of the study area along the coast of Queensland (north, middle or south), and position (upstream or downstream). Stan- dardised sets of gill nets (19 to 152 mm stretched mesh) were used, with the largest-mesh research nets (152 mm) comparable to smallest mesh (150 mm) nets permitted for commercial gill net fishing within open estuaries. In comparison with open systems, catch rates in the largest-mesh research nets in closed systems were 3 times greater for total abundance, 3.7 times greater for the main target species barramundi Lates calcarifer (Centropomidae), 4.4 times greater for juvenile sharks Carcharhinus leucas (Carcharhinidae), and 2.9 times greater for queenfish Scomberoides commersonianus (Carangidae). Furthermore, in comparison with open systems, catch rates in 102 mm mesh research nets in closed systems were 2.5 times greater for L. calcarifer. While lower catch rates of target and by- catch species in 152 mm mesh nets could be readily attributed to commercial operations in open sys- tems, reasons for lower catch rates in the 102 mm research nets were less apparent, since gill nets with <150 mm mesh were prohibited within the open estuaries. Reduction in numbers of large barramundi may have had an impact on recruitment of juveniles in the fished estuaries, leading to these lower catch rates in smaller size classes. Despite substantial depletion in numbers of piscivorous predators in fished systems, there was no evidence of impacts on lower trophic levels sampled with the 2 smallest- mesh research nets (51 mm and multipanel 19/25/35 mm mesh). In these estuaries, prey species assemblages were comprised of 92 species, mainly planktivores, scavengers and detritivores. As in coral reef systems, high diversity and productivity in tropical mangrove-dominated estuaries may strengthen the resilience of prey-base communities to disturbances such as fishing. However, since substantially greater abundances of target and bycatch species occurred among replicate mangrove estuaries protected from commercial fishing, our results significantly strengthen the case in favour of the effectiveness of reserves in conserving populations of exploited species.

Energy budget and ecological role of mangrove epibenthos in the Caeté estuary, North Brazil

Epibenthic community structure, somatic production and energy flow were studied in the Caete mangrove estuary in North Brazil on for 3 representative strata: high intertidal forest (F), small creeks in the forest (SC) and open mudbanks of large intertidal creeks (LC). Seven decapod crustaceans and 1 gastropod accounted for >95% of total epifaunal biomass, with highest values in the forest followed by large and small creeks (228.2, 103.6 and 69.7 kJ m -2 respectively). The leaf- consuming crab Ucides cordatus was clearly dominant in the forest, followed by the fiddler crabs Uca rapax and U. vocator. The large creek stratum was strongly dominated by the fiddler crab U. mara- coani, while in the small creek 4 species (Uca cumulanta, U. maracoani, Pachygrapsus gracilis and Eurytium limosum) contributed similar quantities to total biomass. Per area somatic production (P) and respiration (R) was highest in the large creek, followed by the forest and small creek stratum. Based on the contribution of each stratum, total biomass (332.8 kJ m -2 ), production (455.8 kJ m -2 yr -1 ) and assimilation (2959.6 kJ m -2 yr -1 ) were estimated for the whole area. While the herbivorous feed- ing guild with U. cordatus was the most prominent in terms of biomass (75% of the total), the detri- tivorous fiddler crabs and P. gracilis clearly dominated in terms of respiration and somatic production (60 and 90% respectively). Carnivores (Eurytium limosum and Thais coronata) contributed <2% to the epibenthic energy budget. A system picture emerges whereby energy flow is strongly dominated by herbivorous and detritivorous species. Both guilds probably promote mangrove primary produc- tion by (1) conserving nutrients in the system, (2) enhancing nutrient remineralization, and (3) oxy- genizing the soil through their burrowing and feeding activities. A resulting positive feedback loop between mangroves, crabs and bacteria could explain the very high mangrove productivity and the high efficiency with which mangrove primary production is assimilated by the crabs (almost 15%).

Chemical Properties of Mangrove Sediments in Relation to Sulfur Dynamics

One of the most important biogeochemical processes in estuary sediment is microbial sulfate reduction, producing iron sulfide (pyrite) - the significant form of sedimentary sulfur. The oxidation of iron sulfide causes acidification of the environment. To study these biogeochemical processes, estuary water salinity and sulfate concentrations were determined and sediments from the Klong Ngao mangrove estuary were sampled during the August 2000 wet season. In situ sediment pH and the sediment oxidation-reduction potential were measured. Organic matter concentrations and total sulfur concentrations of the air-dried sediments and the chemical properties of the sediment water were investigated. The estuary water salinity and sulfate concentrations at the head were remarkably lower than at the mouth of the estuary. The in situ pH of mangrove sediments was neutral and the sediment metabolism was anaerobic. The sedimentary organic matter concentrations were relatively high. The amount of sulfur deposited in the sediments at the head was higher than at the mouth of the estuary. Dissolved iron and soluble sulfate, as well as an acid solution, were clearly found in the sediment water at the head of the estuary, whereas the sediment water pH at the mouth remained neutral apparently in association with the presence of soluble bicarbonate ions, and accordingly, dissolved iron was not found in the solution.

River or mangrove? Tracing major organic matter sources in tropical Brazilian coastal waters

The influence of mangrove-fringed tropical estuaries on coastal carbon budgets has been widely recognised. However, a quantitative differentiation between riverine and mangrove-derived inputs to the dissolved (DOM) and microparticulate organic matter (POM) pool of these environments has been hitherto not possible. Based on lignin-derived phenols and stable carbon isotopes a chemical signature for mangrove, terrestrial and marine-derived organic matter was established for a mangrove estuary in North Brazil. A mixing model was applied to calculate the contribution of each of the three sources to the DOM and POM pool in the estuary throughout 18 tidal cycles in the course of one year. Best source assignment for POM was reached with the yield of lignin phenols and δ13C as paired indicators, while the origin of DOM was best identified by the yield of lignin phenols and the acid to aldehyde ratio of vanillyl phenols. Although only about 6% of the fluvial catchment area is covered by mangroves, their contribution to the estuarine DOM and POM pool generally exceeded several times the terrigenic input from the hinterland. This outwelling of mangrove-derived organic matter was enhanced during the rainy season. DOM and POM were exported from the mangrove to the estuary in similar proportions. Most mangrove-POM was rapidly removed from the water column, while mangrove-DOM behaved conservatively. In contrast, terrestrial DOM was almost entirely removed in the outer part of the estuary, which was accompanied by a concomitant increase in terrestrial POM. This seems to be the result of a geochemical barrier zone for this type of DOM in the estuary. Generally, a high proportion of mangrove-DOM was present in the outer part of the estuary, even at high tide. This indicates DOM outwelling from mangroves in adjacent bays or estuaries and points to similar driving forces controlling this process on a regional scale. Mangroves probably play a more important role than rivers for marine carbon budgets along the North Brazilian coast south of the Amazon estuary.

The Impact of Shrimp Pond Effluent on Water Quality and Phytoplankton Biomass in a Tropical Mangrove Estuary

Water quality and phytoplankton biomass were examined over a three-year period in a mangrove estuary receiving periodic inputs of effluent from adjacent shrimp ponds, and in two adjacent, non-impacted estuaries, in north Queensland, Australia. Chlorophyll a, dissolved oxygen (DO), biological oxygen demand (BOD), pH, and salinity at the discharge site in the receiving estuary were significantly higher than in the two control estuaries. There were no significant differences between the impacted and control estuaries in total suspended solids (TSS) and dissolved nutrient concentrations. Water quality and phytoplankton biomass were within ambient levels within 1 km downstream of the discharge site, based on a comparison with long-term, pre-impact data for the estuary. Within 1–2 months after pond discharge ceased, water quality and phytoplankton biomass at the discharge site returned to levels equivalent to those in the control estuaries. The limited spatial and temporal impact suggests that the effluent was dissipated by tides and assimilated and/or mineralized by the estuarine food web. Our results imply that tidal mangrove estuaries have some capacity, at least over short spatial and temporal scales, to process intermittent inputs of pond-derived nutrients.

A Trophic Flow Model of the Caeté Mangrove Estuary (North Brazil) with Considerations for the Sustainable Use of its Resources

The Caeté Estuary lies within the world's second largest mangrove region, 200km south-east of the Amazon delta. It has an extension of about 220km2and is subjected to a considerable human impact through intensive harvest of mangrove crabs (Ucides cordatus) and logging of mangroves. In order to integrate available information on biomass, catches, food spectrum and dynamics of the main species populations of the system, a trophic steady state model of 19 compartments was constructed using the ECOPATH II software (Christensen & Pauly, 1992). Ninety-nine percent of total system biomass is made up by mangroves (Rhizophora mangle, Avicennia germinans andLaguncularia racemosa ), which are assumed to cover about 45% of the total area and contribute about 60% to the system's primary production. The remaining biomass (132gm−2) is distributed between the pelagic and benthic domains in proportions of 10% and 90% respectively. Through litter fall, mangroves inject the main primary food source into the system, which is either consumed directly by herbivores (principally land crabs, Ucides cordatus) or, when already metabolized by bacteria, by detritivors (principally fiddler crabs, Uca spp.). These two groups are prominent in terms of biomass (80g and 14·5gm−2), and food intake (1120gm−2yr−1and 1378gm−2yr−1respectively). According to the model estimates, energy flow through the fish and shrimp compartments is of relatively low importance for the energy cycling within the system, a finding which is contrary to the situation in other mangrove estuaries reported in the literature. The dominance of mangrove epibenthos is attributed to the fact that a large part of the system's production remains within the mangrove forest as material export to the estuary is restricted to spring tides, when the forest is completely indundated. This is also the reason for the low abundance of suspension feeders, which are restricted to a small belt along the Caeté River and the small creeks which are watered daily. Phytoplankton, temporarily refloating benthic diatoms, neritic zooplankton and small pelagic fish dominate the (low) pelagic biomass. Total system throughput (10559gm−2yr−1) and mean transfer efficiency between trophic levels (9·8%) calculated by the model fit well into the range reported for other tropical coastal ecosystems. The very high gross efficiency of the fishery (catch/net primary production) of 8·6% and its low trophic level (2·1) is explained by a high harvesting rate of mangroves and the fact that the main animal resource in the system are the mangrove crabs (Ucides cordatus), which feed at the first trophic level. The model was balanced asuming a turnover rate for the land crabs of P/B=0·25 (P/B: production per unit of biomass) which is possibly too high. If this value was replaced by a (possibly more realistic) lower value, the model would not balance, suggesting a situation in which more biomass is being harvested than produced, which hints to an overexploitation of this resource A ranking of the various system components in terms of their contribution to the system function (ascendency sensu Ulanowicz, 1997) revealed that detritus and associated bacteria contribute 34%, mangroves 19%, fiddler crabs 13%, phytoplankton and microphytobenthos 10%, mangrove crabs 10%, and the remaining 14 groups 14% to the total ascendency. Summary statistics of the model are given and compared with those of other coastal ecosystems.