Showing papers in "Wetlands Ecology and Management in 2002"
TL;DR: A review of the literature on satellite remotesensing of wetlands, including what classification techniques were most successful in identifying wetlands and separating them from other land cover types, is presented in this paper.
Abstract: To conserve and manage wetland resources, it is important to inventoryand monitor wetlands and their adjacent uplands. Satellite remote sensing hasseveral advantages for monitoring wetland resources, especially for largegeographic areas. This review summarizes the literature on satellite remotesensing of wetlands, including what classification techniques were mostsuccessful in identifying wetlands and separating them from other land covertypes. All types of wetlands have been studied with satellite remote sensing.Landsat MSS, Landsat TM, and SPOT are the major satellite systems that have beenused to study wetlands; other systems are NOAA AVHRR, IRS-1B LISS-II and radarsystems, including JERS-1, ERS-1 and RADARSAT. Early work with satellite imageryused visual interpretation for classification. The most commonly used computerclassification method to map wetlands is unsupervised classification orclustering. Maximum likelihood is the most common supervised classificationmethod. Wetland classification is difficult because of spectral confusion withother landcover classes and among different types of wetlands. However,multi-temporal data usually improves the classification of wetlands, as doesancillary data such as soil data, elevation or topography data. Classifiedsatellite imagery and maps derived from aerial photography have been comparedwith the conclusion that they offer different but complimentary information.Change detection studies have taken advantage of the repeat coverage andarchival data available with satellite remote sensing. Detailed wetland maps canbe updated using satellite imagery. Given the spatial resolution of satelliteremote sensing systems, fuzzy classification, subpixel classification, spectralmixture analysis, and mixtures estimation may provide more detailed informationon wetlands. A layered, hybrid or rule-based approach may give better resultsthan more traditional methods. The combination of radar and optical data providethe most promise for improving wetland classification.
1,030 citations
TL;DR: The traditional and medicinal uses, and recent investigations on the biological activities of extracts, and chemicals identified from mangroves and mangal associates are examined.
Abstract: This review article presents the traditional and medicinal uses, and examines recent investigations on the biological activities of extracts, and chemicals identified from mangroves and mangal associates. Metabolites identified from mangrove plants are classified according to ‘chemical classes’, and some of their structures are illustrated. The article also presents some of the functions of the chemicals present and attempt to emphasize and create an awareness of the great of potential mangroves and mangal associates possess as a source of novel agrochemicals, compounds of medicinal value, and a new source of many already known biologically active compounds.
530 citations
TL;DR: In this article, the authors compared soil matrix chroma, organic matter content, rock fragment content, bulk density, particle size distribution, vegetation species richness, total plant cover, and average wetland indicator status in created and natural wetlands in Pennsylvania.
Abstract: Recent research suggests that created wetlands do not look, or function, like the natural systems they are intended to replace. Proper planning, construction, and the introduction of appropriate biotic material should initiate natural processes which continue indefinitely in a successful wetland creation project, with minimal human input. To determine if differences existed between created and natural wetlands, we compared soil matrix chroma, organic matter content, rock fragment content, bulk density, particle size distribution, vegetation species richness, total plant cover, and average wetland indicator status in created (n = 12) and natural (n = 14) wetlands in Pennsylvania (USA). Created wetlands ranged in age from two to 18 years. Soils in created wetlands had less organic matter content, greater bulk densities, higher matrix chroma, and more rock fragments than reference wetlands. Soils in reference wetlands had clay loam textures with high silt content, while sandy clay loam textures predominated in the created sites. Vegetation species richness and total cover were both greater in natural reference wetlands. Vegetation in created wetlands included a greater proportion of upland species than found in the reference wetlands. There were significant differences in soils and vegetation characteristics between younger and older created wetlands, though we could not say older created sites were trending towards the reference wetland condition. Updated site selection practices, more careful consideration of monitoring period lengths, and, especially, a stronger effort to recreate wetland types native to the region should result in increased similarity between created and natural wetlands.
222 citations
TL;DR: Based on field observations and numerical experiments, it is inferred that this large scale erosion is caused by the transition of mangrove vegetation resulting from the long-term impact of humans since the late 19th century as mentioned in this paper.
Abstract: A coast in southern Vietnam, which is located in a wide and flat alluvial fan and neighbors tidal rivers fringed by wide mangrove swamps, has been eroded continuously by approximately 50 m/year since the early 20th century. Based on field observations and numerical experiments, it is inferred that this large scale erosion is caused by the transition of mangrove vegetation resulting from the long-term impact of humans since the late 19th century. This eroded coast is not in direct contact with mangrove swamps, but is strongly affected by the existence of mangrove forests through the intermediation of neighboring tidal rivers. Thus, with a view to coastal protection, it is argued that the mangrove vegetation in adjacent areas should be managed more sensitively.
105 citations
TL;DR: There appears to be one major underlying factor in the zonation of both crabs and trees, with most likely a complex multiple causality.
Abstract: Despite earlier efforts to understand the role played by grapsid crabs in mangroves, their importance in the structuring and functioning of such systems is fully appreciated, particularly with regard to small-scale studies. The present study provides some new data on the interaction between mangroves and crabs, namely the link between the distribution of particular mangrove tree species and the distribution of certain crab species at the assemblage level. Floristic and faunistic releves were made in Gazi Bay (2 sites) and Mida Creek (3 sites), 140 km apart on the Kenyan coast, along five transects in a series of quadrats covering the width of the mangrove belts. Zonation of both mangrove vegetation and brachyuran fauna was described and height above datum and distance to the mainland (limit of non-flooded area) measured. The relationship between the presence and the absence of crabs and trees was analysed using detrended correspondence analysis. Summarized, the mangrove tree zonation pattern contains four assemblages with a particular dominant species: first a landward Avicennia marina zone, followed by a mixed zone with Ceriops tagal, Rhizophora mucronata and Bruguiera gymnorrhiza, and finally a R. mucronata zone and a Sonneratia alba zone, both of which can mix with seaward A. marina. Ordination results show that the distribution of Neosarmatium meinerti and Sesarma ortmanni is linked to the landward A. marina zone, that of Neosarmatium smithii, Sesarma guttatum and Sesarma leptosoma corresponds to the R. mucronata zone and that of Metopograpsus thukuhar and Sesarma elongatum to the seaward A. marina and S. alba zone. There appears to be one major underlying factor in the zonation of both crabs and trees, with most likely a complex multiple causality. In certain cases the association between crabs and trees are causal, whereas in other cases it can be the result of an independent restriction to the same zones by a common cause.
81 citations
TL;DR: In this article, aerial remote sensing data were assessed for mapping of the main geomorphologicaland vegetation units of the Bragancapeninsula (North Brazil), which belongs to a vast though sparsely mapped mangrovecoast.
Abstract: Orbital remote sensing data were assessedfor mapping of the main geomorphologicaland vegetation units of the Bragancapeninsula (North Brazil), which belongs toa vast though sparsely mapped mangrovecoast. Wide wetland environmentscharacterize the region with extremevariations in extension, temporalevolution, and spatial complexity. Thiswork was based on different digitalprocessing techniques separately applied toLandsat TM and RADARSAT-1 images. Inaddition, both data were merged on apixel-to-pixel basis using algorithms,which rendered an enhancement of thecoastal landforms and a betterdiscrimination of wetlands and landformtypes. The interpretation of the integratedproduct, aided by field validation, made itpossible to significantly extend existingmapping. Nineteen geobotanical units wereidentified: estuarine channels, submergedsand banks, sandflats, old estuarinesandbanks, mudflats, ebb-tidal deltas,barrier-beach ridges, coastal dunes,chenier sand ridges, young intertidalmangroves, intertidal and supratidalmangroves, outer and inner marshes, fluvialflood plains, coastal plateau, degraded andregenerated mangroves, and an artificiallagoon. The digital integration of Fine RADARSAT-1 and Landsat TM data sensitivelyhighlighted geobotanical coastal features,providing a useful tool for a synopticanalysis of their natural and man-drivenchanges.
77 citations
TL;DR: In this paper, the authors investigated the use of aerial photographs, acquired in 1950 and1991, for assessing the temporal dynamics of mangroves along the WestAlligator River in Australia's Northern Territory.
Abstract: The study investigated the use of aerial photographs, acquired in 1950 and1991, for assessing the temporal dynamics of mangroves along the WestAlligator River in Australia's Northern Territory. For both years,mangrove extent was mapped using an unsupervised classification of thedigital orthomosaic and Digital Elevation Models (DEMs), or height maps,of the mangrove canopy were derived from stereo pairs. Helicopter andfield observations in 1998 and 1999 respectively provided ground truthfor interpreting the derived datasets. The comparison of mangrove extentrevealed a substantial movement over the 41-year period, perhaps inresponse to hydrological changes that have resulted in a landward extensionof saline conditions. Changes in the height of mangroves were observedbut were difficult to quantify due to the reduced quality of the 1950 DEM. The study demonstrated the viability of using time-series of aerialphotography for monitoring and understanding the long-term response ofmangroves to environmental change, including hydrological variations andsea level rise.
72 citations
TL;DR: In this paper, the community structure of a mangrove forest in Coringa Wildlife Sanctuary in the Godavari estuarine system on the East Coast of India revealed altogether 15 species of mangroves represented by 8 families and 10 genera besides, 6 associate plant species and 6 of marshgrass.
Abstract: Studies (1996–'99) on the community structure of a mangrove forest in Coringa Wildlife Sanctuary in the Godavari estuarine system on the East Coast of India revealed altogether 15 species of mangroves represented by 8 families and 10 genera besides, 6 associate plant species and 6 of marshgrass. Description of forest structure (PCQM method) included measures of species composition, tree density, basal area and spatial distribution patterns of component vegetation at 75 GPS fixed locations. Avicennia marina, A. officinalis, Excoecaria agallocha, Aegiceras corniculatum, Sonneratia apetala, Ceriops decandra, Rhizophora apiculata and R. mucronata were the important mangrove species. Tree density varied between 47 and 1731 stems/0.1 ha and basal area 0.1 and 10.9 m2/0.01 ha. With the help of multivariate analysis (PRIMER) and based on species composition and tree density, it was possible to subdivide the sites into five groups that showed characteristic zonation patterns. For example, E. agallocha was typical of landward locations. A. marina (along with A. officinalis and A. alba) represented sites at the bed level and neap high tide level. There was a large group of sites inhabited by diverse species (14) indicative of spring high tide level conditions. Tidal elevation and ambient salinity appeared important in determining the observed zonation.
71 citations
TL;DR: In this paper, the authors determined the abundance of crabs in mangrove communities along a latitudinal gradient along the eastern coast of Africa from 4°S to 32°S.
Abstract: The aim of this work was to determine the abundance of crabs inmangrove communities along a latitudinal gradient along the eastern coastof Africa from 4°S to 32°S. Surveys were made atMombasa (Kenya), Zanzibar (Tanzania), Maputo (Mozambique) and in theTranskei (South Africa). Crabs were estimated at three designated levelsin the mangroves by visual census using a common protocol, and numberswere converted to biomass.Even after standardising the selection of sites and methods of censusthere was still extensive variability in the data, emphasising the complexheterogeneity of mangrove ecosystems. Lunar phase (full versus new moonsprings) did not have a consistent effect on results, but shore height hadseveral effects. Total crab biomass was similar in the two lower shore strataexamined, but about twice as high at the top-Avicennia level. Theratio of grapsid biomass:ocypodid biomass also changed with height: fromnear unity in the lower mangrove, to 0.14 in the middle strata, but to 15at the top.There was no consistent latitudinal trend in total crab numbers, but totalcrab biomass increased from north to south. In addition there was aconsistent and marked change in the grapsid biomass:ocypodid biomassratio: this swung from 0.65 at Mombasa to 6.8 in the Transkei. This hasimplications for the transfer of primary production through the food chain. Grapsids are important macrophagous feeders on the leaves and other partsof mangroves, whereas ocypodids are microphagous deposit feeders.
54 citations
TL;DR: Comparisons show that the occurrence of macrofauna and especially of ecosystem engineers varies between sites, which can in turn explain the great variability in species abundance patterns recorded in benthic surveys of tidal flats within and between regions.
Abstract: Tidal flats extend seaward from mangrove forests along many tropicalcoastlines. This contribution compiles the current knowledge on tropicaltidal flats with regard to species richness, abundance, spatial distributionpatterns and ecological roles taken by major organisms. Tidal flatsencompass a variety of soft-sediment habitats which are inhabited by aspecies-rich fauna. Species numbers are generally higher than in temperatetidal flats, but vary widely between tropical sites where they have not yetbeen fully assessed due to lack of research and taxonomic problems. Theassessment of biodiversity is further complicated by a low species frequency,the small size of macroinfaunal organisms and variations in the occurrence ofspecies between sites. Mean abundance ranges from 1000–2000individuals m-2, although figures ten times higher have beenrecorded in a mudflat in Costa Rica, and there are great variations in general.Individual densities of small-sized macrofauna are about ten times higher than for larger macrobenthos. A generalized zonation scheme for intertidaldistribution patterns of tropical tidal flat fauna is presented. The comparisonshows that the occurrence of macrofauna and especially of ecosystemengineers varies between sites, which can in turn explain the great variabilityin species abundance patterns recorded in benthic surveys of tidal flatswithin and between regions. This review revealed similarities as well asdifferences between various tropical tidal flats, which underlines the need for further comparative studies to be done, using the same methodology, before generalizations can be made.
45 citations
TL;DR: In this paper, a long-term and spatially dense time series of total head measured along three forest-marsh piezometer transects across a finger marsh basin, together with bimonthly groundwater salinity measurements, reveal dynamic features that present challenges to the interpretation and modeling of this shallow water table aquifer.
Abstract: Long-term and spatially dense time series of total head measured alongthree forest-marsh piezometer transects across a finger marsh basin,together with bimonthly groundwater salinity measurements, reveal dynamicfeatures that present challenges to the interpretation and modeling of thisshallow water table aquifer These include:1 Rapid response of forest water table to rain events2 Daytime lowering (drawdown) of the water table in the forest and highmarsh due to evapotranspiration and its recovery due to rain, seepage ortidal inundation3 Upward gradients in head along the western margin of the marsh butdownward gradients in the eastern, more seaward, high marsh and forest4 Rapid head responses to the tide in parts of the high marsh andforest that are not actually inundated5 Asymmetrical distribution of salinity with higher values in theeastern marsh and forest than in the west6 Sharp salinity gradients across the tidal creek that bisects the basin We discuss modeling issues related to these features because acomprehensive understanding of them may have a bearing on patterns ofbotanical zonation and primary production, the transport of nutrients andcontaminants, and the response of this system to sea level rise
TL;DR: In this paper, a 24.3 ha impoundment was studied for 12 months to determine habitat use by fishes aftertidal reconnection and the implementation of Rotational Impoundment Management (RIM).
Abstract: Most of the wetlands located along the Indian River Lagoon (IRL) ineast-central Florida (USA) have been impounded since the 1950's and1960's to reduce mosquito reproduction. Impounded marsh (i.e.,impoundment) dikes physically separate the wetlands from the estuary toallow artificial flooding of the impoundments during the mosquito breedingperiod (May to October). Presently, Rotational ImpoundmentManagement (RIM) is the preferred impoundment management techniquein the IRL. Impoundments maintained under RIM have culverts installedthrough the dikes which are kept closed during the mosquito breedingseason (to control mosquitos) and are allowed to remain open for theremainder of the year (to allow tidal flow). A 24.3 ha impoundment8 km north of Sebastian Inlet that had been isolated from the IRL for over39 years was studied for 12 months to determine habitat use by fishes aftertidal reconnection and the implementation of RIM. Fish sampling wasconducted with a seine in the perimeter ditch and with clover and minnowtraps in the upper marsh and tidal creek areas of the impoundment. Waterlevel, impoundment bottom topography, and the seasonal nursery functionof the impoundment were factors that contributed to observed patterns offish habitat use during the study. Within the first 15 weeks of perimeterditch sampling, an increase from 9 to 40 species was observed. Transientspecies used the perimeter ditch almost exclusively and entered theimpoundment primarily during the spring open period. Juvenile Pogonias cromis (Linnaeus), Elops saurus Linnaeus, Centropomusundecimalis (Bloch), and Megalops atlanticus Valenciennes were themost abundant recreationally important species, respectively. Habitat useby the most abundant resident species (Gambusia holbrooki Girard,Poecilia latipinna (Lesueur), Cyprinodon variegatus Lacepede, andFundulus confluentus Goode & Bean) was influenced primarily bywater level fluctuations. Resident species used the upper marsh and tidalcreek habitats during summer flooded periods and the cyprinodontids leftthe interior surface of the impoundment last as water levels decreased. Thisstudy is the first to document the recovery of fish populations in areconnected impoundment north of Sebastian Inlet using both active andpassive sampling techniques.
TL;DR: The data do not support the general assumption that Phragmites leaf detritus is of poorer nutritional quality than Spartinaalterniflora leafdetritus to estuarine consumers, and also support the idea that fiddler crabs do not differ in metal concentrations after the feedingexperiment.
Abstract: Marsh vegetation plays an important role in trophic ecology of estuaries Once broken down to detritus, it is an important food source for manyorganisms In Atlantic Coast marshes, the reed Phragmites australis hasbeen invading many areas once dominated by smooth cordgrass, Spartina alterniflora In this study we evaluated the growth of and trophictransfer of metals to estuarine invertebrates when fed diets of detritus fromthese different plant species Decaying leaves from populations of Phragmites, natural Spartina, and restored Spartina from boththe Hackensack Meadowlands, New Jersey, and the more pristineAccabonac Harbor of East Hampton, New York, were collected from themarsh surface in the spring Decaying leaves were pureed and fed to thefiddler crabs Uca pugnax and U pugilator, and to the grassshrimp Palaemonetes pugio In fiddler crabs we monitored limbregeneration, molting and weight U pugilator regenerated limbs andmolted equally well on all six diets Most of the U pugnax arrestedgrowth midway through regeneration on all 6 diets A repeat experimentwith smaller crabs, which did complete the process, found no consistentdifferences among the six diets and control food, although control food andPhragmites detritus had higher N concentrations than the Spartinadetritus Grass shrimp fed all six diets did not survive beyond 3 weeks Inanother experiment using HM sediments from each vegetation type(containing detritus, meiofauna, and microflora), survival was equally highamong treatments and the shrimp fed sediments from the restored Spartina site or control food grew better than those fed sediments fromthe Phragmites or natural Spartina sites Although metalconcentrations in detritus varied between sites and plant species, the crabsof each group did not differ in metal concentrations after the feedingexperiment Our data do not support the general assumption that Phragmites leaf detritus is of poorer nutritional quality than Spartinaalterniflora leaf detritus to estuarine consumers
TL;DR: In this article, the authors found that water column phosphatedeclined as phosphate likely co-precipitated with iron on the sediment surfacewithin open-water or sparsely vegetated zones.
Abstract: Long-term effects of within-basin tillage can constrain condition andfunction of prairie wetlands even after uplands are restored. Runoff wassignificantly greater to replicate wetlands within tilled basins with orwithoutvegetated buffer strips as compared to Conservation Reserve Program restorationcontrols with revegetated uplands (REST). However, mean water levels for nativeprairie reference sites were higher than for REST controls, becauseinfiltrationrates were lower for native prairie basins, which had no prior history oftillage. Nutrient dynamics changed more in response to changes in water leveland vegetation structure than to increased nutrient inputs in watershed runoff.Dissolved oxygen increased between dry and wet years except in basins or zoneswith dense vegetation. As sediment redox dropped, water-column phosphatedeclined as phosphate likely co-precipitated with iron on the sediment surfacewithin open-water or sparsely vegetated zones. In response, N:P ratios shiftedfrom a region indicating N limitation to P limitation. REST sites, with densevegetation and low DO, also maintained high DOC, which maintains phosphate insolution through chelation of iron and catalysis of photoreduction. Referencesites in native prairie and restored uplands diverged over the course of thewet-dry cycle, emphasizing the importance of considering climatic variation inplanning restoration efforts.
TL;DR: Association with different mangroves species did not result in significant differences in the sex ratio, growth andproductive periodicity, and size-specific reproductive output of the crabs, which further reiterates the bi-directional nature of mangrove-crab interactions.
Abstract: The population biology of two sesarmine crabs, Perisesarma bidens andParasesarma affinis, was studied over a two-year period in twomangrove forests, one dominated by Kandelia candel and the other by Avicennia marina. Despite the fact that the mangrove forests werecontiguous, shared the same water supply and were less than 20 cmdifferent in tidal position, significant differences in population biology ofboth crab species were recorded. Individuals of both species associated withthe topographically higher Kandelia candel forest were more abundant,had a higher tissue organic content, higher gonosomatic and hepatosomaticindices than their counterparts in the Avicennia marina forest. Femaleindividuals of both species were also larger in size in the Kandeliaforest. These differences result in higher secondary production of the crabsat the Kandelia forest. By contrast, association with different mangrovespecies did not result in significant differences in the sex ratio, growth andreproductive periodicity, and size-specific reproductive output of the crabs.The results suggest significant influence by the associated mangrove specieson the population biology of the crabs, through processes such asmodification of the physical habitat fabric and/or provision of trophicresources of different quality and quantity by the mangroves. This influencefurther reiterates the bi-directional nature of mangrove-crab interactions andthe need to consider these intricate interactions in future studies on tropicalmangrove structure and function.
TL;DR: Dimensionless ammonium adsorption coefficients (K) were determined for tropical mangrove forest sediments and temperate Wadden Sea sediments, and the relationship between the two was described by a linear model.
Abstract: Dimensionless ammonium adsorption coefficients (K) were determined for tropical mangrove forest sediments and temperate Wadden Sea sediments. The K values were obtained from ammonium adsorption isotherms of KCl (2 M) extractable ammonium versus dissolved ammonium in the porewater; relationships that can be described by a linear model. Linearity was evident even at low porewater concentrations for mangrove sediment, according to isotherms based on KCl extractions on untreated sediment profiles. K-values were low in mangrove forest sediments (0.04–0.10), and higher in Wadden Sea sediments (0.17–1.12). The vertical range in K-values was larger at the vegetated sites, with highest values in subsurface sediments, which suggests differences in quantity and quality of the fine organic and inorganic fractions. The low ammonium adsorption in the mangrove sediments can be explained by a higher concentration of competitive cations, especially iron, in this iron-rich environment. The low adsorption of ammonium in mangrove sediments and vegetated surface sediment of the Wadden Sea was negatively related to the organic content of the sediments, which is in contrast to findings for other marine sediments. We suggest that organic material may have a diluting effect on the exchange capacity in fine-grained sediments, and that organic coatings may block ion exchange sites on clay surfaces. Thus, there may be a organic-rich ‘wetland’ versus organic-poor ‘sediment’ effect.
TL;DR: Temporal variations in the benthic assemblage of thetwotidal flats in Hinchinbrook Channel were higher than variations between sites, with a separation of assemblages before and after 1989.
Abstract: A survey of the benthic infauna (macro- and mesofauna) in tidalflats of Hinchinbrook Channel, north-east Australia, was carried out toassess the species diversity and individual abundances as well as theirtemporalvariations. Two sites were surveyed at five occassions from November 1988 toOctober 1991. In addition, spatial distributions over the intertidal gradientwere investigated once in May 1990. During the entire survey, over 200 specieswere recorded, with 53 species found on average at each sampling occassion.Species densities ranged from 4.0 to 8.2 species 177cm−2 for macrofauna and from 4.1 to 11.8 species10 cm−2 for mesofauna, but varied little betweensites. The average infaunal diversity (H') was 2.53. Individual abundancesreached median values of 14.0 individuals 177cm−2for macrofauna and 14.5 individuals 10 cm−2 formesofauna. Changes in total abundances were not related to season andinconsistent at the two study sites, with significantly higher abundancesoccurring either at site A or B on single sampling dates. Transects sampled inMay 1990 showed varying species compositions and abundances in the upper, midand lower intertidal, but no defined benthic communities were revealed bymultivariate analyses. Temporal variations in the benthic assemblages of thetwotidal flats in Hinchinbrook Channel were higher than variations between sites,with a separation of assemblages before and after 1989. Problems to assess andinterpret temporal changes in species rich tropical benthic communities arediscussed.
TL;DR: The gastropod Terebralia palustris (Linnaeus) is one of the largest prosobranchs found in tropical intertidal habitats and its effects on infaunal animals and macrofauna assemblage are tested, supporting the primary hypothesis and multidimensional scaling ordination suggested that there was increased variability of meiofauna within cages with high density.
Abstract: The gastropod Terebralia palustris (Linnaeus) isone of the largest prosobranchs found in tropical intertidal habitats. Theadults form feeding aggregations and frequently dominate the surface of muddysubstrates, where they clearly destabilize the sediment surface. We tested thefollowing hypotheses: 1. The gastropod has negative effects on the density ofinfaunal animals because of potential food competition and/or surface sedimentdisturbance. 2. The disturbance exerted by T. palustrisresults in more variable infaunal assemblages, especially where intensity ofdisturbance is high. To address these hypotheses gastropods were eitherenclosedor excluded from experimental cages, which were randomly assigned to blocks asfar as 300 m apart on an intertidal mudflat in East Africa. Afternine weeks of enclosure the gastropod at high densities clearly affected themeiofauna assemblages. Several meiofauna groups were found in significantlyreduced densities in the presence of the gastropod compared with control cageswithout the gastropods, supporting our primary hypothesis. In cages withoutT. palustris a cyanobacterial carpet developed while thiswas not evident in enclosure cages. T. palustris had nosignificant impact on the macrofauna assemblage. In support of our secondhypothesis, multidimensional scaling ordination (MDS) suggested that there wasan increased variability of meiofauna within cages with high density ofT. palustris.
TL;DR: The larval flux of several brachyuran crabs resident within a subtropical estuary on the east coast of South Africa was investigated in this article, where the data were discussed in relation to freshwater inflow problems facing South African estuaries and the active management of the tidal inlets of affected systems.
Abstract: Soon after hatching the larvae of many estuarine crabs migrate from estuaries to adjacent coastal waters soon, where larval development is completed before the post larval stages recruit to estuaries to settle This study investigated the larval flux of several brachyuran crabs resident within a subtropical estuary on the east coast of South Africa Plankton sampleswere collected over two intensive sampling periods during the spring of1997 (19 days) and the summer of 1998 (26 days) Larvae were releasedmaximally when high tide within the estuary was crepuscular, whilerecruitment occurred during nocturnal flood tides, with peak abundanceson the maximum amplitude nocturnal flood tides The data are discussedin relation to freshwater inflow problems facing South African estuaries andthe active management of the tidal inlets of affected systems
TL;DR: A field study of the hydrodynamics, water quality and adult and larval fish abundance in papyrus wetlands and surrounding coastal waters at Rubondo Island, Lake Victoria was conducted by.
Abstract: A field study was undertaken of the hydrodynamics, water quality and adult and larval fish abundance in papyrus wetlands and surrounding coastal waters at Rubondo Island, Lake Victoria. Because they were exposed to the prevailing wind, the two bays facing east had small (0.01 km2) wetlands and were well flushed, with minimal accumulation of organic detritus and little oxygen depletion. Because it faced west, the third bay, Mlaga Bay, was sheltered and poorly flushed; organic matter accumulated in a large (1.41 km2) papyrus wetland. The rises and falls of the lake level at decadal time scales, may, by drowning or drying out wetlands, contribute significantly to storing organic matter as detritus. Vegetation decay in the wetlands, as well as primary production, resulted in large diurnal fluctuations of pH and dissolved oxygen concentration. Shading in daytime and cooling at night, cooled the wetlands water sufficiently to generate a baroclinic circulation whereby cold, wetland water sank and moved offshore in the lake while warm, lake water intruded in the wetlands near the surface. This flushing prevented the occurrence of anoxic conditions in the wetlands which were used by adult and larval fish, mainly tilapia, and freshwater shrimps (Caridina nilotica). No fish larvae were found at more than 150 m from the shore in the three bays. Both larval fish and Caridina nilotica appeared to move in and out of the wetlands at night, possibly as a result of low dissolved oxygen as well as sheltering from predation. Their abundance varied with the lunar phase, with maximum near new moon and first quarter. Being the only protected wetlands in Lake Victoria, Rubondo Island may increasingly become an important source of replenishment for fisheries in the lake which elsewhere appears overfished.
TL;DR: The threesites, under different degrees of anthropogenic impacts, showed related values of species richness, diversity and abundance, as well as densities of mollusc taxa in oceanic communities associated with mangrove roots.
Abstract: This paper advances a qualitative and quantitative preliminarycharacterization of the mollusc fauna associated with the submerged rootsof Rhizophora mangle L. in three mangrove areas with differentdegrees of anthropogenic impact in the San Andres (Hooker and HondaBays) and Providence (Old Providence McBean Lagoon National Park)archipelago in the Western Caribbean. The study was carried out during thedry and rainy seasons (July and November, respectively) back in 1998.Samples were taken from 34 submerged roots which were not fixed to thesubstrate. Several physico-chemical parameters were also measured insitu. All molluscs were identified and counted and indexes of speciesrichness, diversity, uniformity, similarity, dominance of species and densityof individuals were calculated. All in all 5,771 individuals belonging to 21species of 17 families were counted. Most of the species were epibenthic,herbivorous and with undifferentiated planctonic larvae, but most of theindividuals were epifaunal and attached as well as filter-feeders withplanctonic larvae. Most individuals were found in juvenile stages. The threesites, under different degrees of anthropogenic impacts, showed relatedvalues of species richness, diversity and abundance, as well as densities ofmollusc taxa in oceanic communities associated with mangrove roots.Further research should be done to find similar responses in accompanyingsignificant groups, such as Crustacea and Polychaeta.
TL;DR: In this article, a red-colored, sandy marker horizon was placed on the emerging Skallingen salt marsh Sedimentation on top of the marker horizon since then shows two opposing tendencies Coincident with salt marsh development the sediments display up to 1964 a fining upward sequence with an increasing content of organic matter.
Abstract: In 1931 a red-colored, sandy marker horizon was placed on the emerging Skallingen salt marsh Sedimentation on top of the marker horizon since then shows two opposing tendencies Coincident with salt marsh development the sediments display up to 1964 a fining upward sequence with an increasing content of organic matter Since 1964 a nearby creek has meandered towards the sampling plot Consequently, the sediments become coarser with a decreasing organic matter content The morphological induced changes in sedimentary conditions strongly influence metal content in the sediments and thereby hide anthropogenic induced concentration variations Thus, an apparently diminishing Zn content (per kg dry weight) since 1964 could indicate lesser load to the area However, corrected for grain size effects there is an increasing content of Zn Other metal concentrations (eg Cu) show a diminishing trend when corrected for grain size effects and therefore indicate a reduced anthropogenic induced load of these metals to the salt marsh
TL;DR: To strengthen the regeneration and management of Cameroon's coastal ecosystems, the biological characteristics of seedlings of Avicennia germinans (L.) Stearn and associated species were analysed from January 1999 to December 1999 in the mangroves under different environmental conditions.
Abstract: To strengthen the regeneration and management of Cameroon's coastal ecosystems, the biological characteristics of seedlings of Avicennia germinans (L) Stearn and associated species were analysed from January 1999 to December 1999 in the mangroves under different environmental conditions Site factors such as temperature, conductivity, salinity and pH were studied in relation to species distribution, and showed significant variation within species These factors were strongly correlated in the case of A germinans The phenology of Avicennia extends throughout the year Structural parameters of the trees, seedlings and of associated species have been determined The survey of plant populations shows that A germinans species represent more than 95% of the total seedlings of the study area, in spite of their variable density A correlation was found between seedling diameter and height The intra-specific competition is high and the percentage of seedlings that reach maturity is extremely low (less than1%) Seedlings are over-scattered and weakly aggregated (Green index: GI = 0023) Floristic diversity is greater and A germinans zones appear to be the diversification centre of taxa in the mangroves
TL;DR: In this paper, the physical and geological factors necessary to design shoreline stabilization structures capable of confidently supporting suitable and stable habitat enhancement/restoration substrate are emphasized since this area of study generally may be unfamiliar to wetland resource managers.
Abstract: Shore protection and habitat enhancement along a residential island werethe main goals of this shoreline study. The physical and geological factorsnecessary to design shoreline stabilization structures capable of confidentlysupporting suitable and stable habitat enhancement/restoration substrate areemphasized since this area of study generally may be unfamiliar to wetlandresource managers. Erosion along the targeted shoreline is influenced by aunidirectional wave field from the south-southwest. Results of our analysesshowthat a headland control system comprised of headland breakwaters could be usedsuccessfully to stabilize the existing shoreline and provide resource managersflexibility in habitat restoration decisions. Headland breakwaters are designedto diffract wave energy so that shore planform equilibrium is attained and canbe sized and positioned to maximize the length of stabilized shoreline.Maximization of the new shoreline length provides increased subaerial,intertidal, and subaqueous environments for flexible habitat restorationalternatives. The final restoration design developed through this study willcreate approximately 69,000 m2 of new habitat includingstable beach, dune, tidal marsh, scrub shrub, and submersed aquatic vegetation.An additional 2,000 m2 of rock substrate habitat isprovided directly by the headland control structures.
TL;DR: The relatively high numbers of females with stage two ovaries indicated that spawning took place throughout the year with a possible peak in the second half of the year.
Abstract: The mud crab Scylla serrata was collected from Ramisi river estuaryfor a period of 14 months (January 1990–February 1991) using madema traps. For each crab, the carapace width (mm), sex and weightwere noted, and the number of ovigerous female crabs was recorded. Both ovigerous and non-ovigerous females were dissected in order to observeof the maturity stages of ovaries. The ovarian maturity stages weredescribed as stage zero – virgin/resting, stage one – developing, stage two– well developed and stage thre e– ripe. The most abundant was stage twothroughout the study period. The smallest ovigerous crab had a carapacewidth of 139 mm. A test of homogeneity of the binomial distributionof the sex ratio showed homoscedasticity (χ2 = 14.615; d.f. = 13; p> 0.05) and the overall sex ratio did not differ from 1:1 (χ2 = 0.776; d.f. = 1; p> 0.05). The variance test ofhomogeneity of the binomial distribution of sex in relation to size showeda very significant heterogeneity (χ2 = 32.83; d.f. = 9; p< 0.05). There was no significant difference when the overall mean sizesfor males and females were compared using t-test (t = 4.26; d.f. = 18;p< 0.001). The relatively high numbers of females with stage two ovariesindicated that spawning took place throughout the year with a possible peakin the second half of the year.
TL;DR: The change in area of mangrove forests since 1958 in Maputo Bay,Mozambique was studied in this paper, where a 44% reduction of the area was linked to differences in accessibility, the areas closest to Maputo suffering most.
Abstract: The change in area of mangrove forests since 1958 in Maputo Bay,Mozambique was studied. Around Maputo, a 44% reduction of the area was linkedtodifferences in accessibility, the areas closest to Maputo suffering most. Butsurprisingly, large expansions of mangrove forest were also observed. Thisincrease in area (+ 13%) was accompanied by an increase in tree cover from55 to 70%. The overall effect of mangrove forest reduction and growth resultedin a mean decrease of only 8%. The causes of the increase in mangrove area onInhaca island are discussed, and two possible factors are suggested: a changeinsedimentation and an increase in temperature. Sandbanks have increased atInhacaIsland, but no data are available for the other areas. An increase in sea andair temperature has also been noted by other authors and could explain thegrowth of the forests, which are situated at the southernmost limit of theirnormal distribution.
TL;DR: In this article, the impact of sediment coring on measured rates of sulfate reduction (SRR) by the whole core 35S-injection technique was assessed inmarshsediment vegetated by Spartina anglica.
Abstract: The impact of sediment coring on measured rates of sulfate reduction(SRR) by the whole core 35S-injection technique was assessed inmarshsediment vegetated by Spartina anglica. Simultaneously,therole of extraction method (centrifugation vs. sippers) for determination ofporewater DOC in vegetated sediment was evaluated. SRR was measuredinsitu with radiotracer injected directly into the sediment and in atime series from 1 to 24 h after coring. SRR incubations carriedout within 6 h (June) or 12 h (August) of coringyielded up to an order of magnitude higher rates than measured insitu. The enhancement of SRR was instantaneous but temporary andcorrelated with measured porewater DOC concentrations. Cores sampled fromrootedsediments should therefore not be used for sulfate reduction incubations withinthe first 12 h due to the effect of DOC leaching from roots cutduring the coring procedure. The labile fraction of leached DOC appears to beexhausted after a pre-incubation period of at least 12 h.Measurement of porewater DOC is also problematic in vegetated sediment.Porewater extraction by centrifugation of sediment may result in up to oneorderof magnitude higher DOC concentrations than in porewater obtained by anondestructive sipper technique. DOC is probably forced out of roots duringcentrifugation resulting in erroneously high porewater DOC concentrations.
TL;DR: The role and importance of foliar herbivory in severely affected forests and how such instances best not be ignored or treated as curiosities in future assessments of Herbivory and forest turnover in mangrove ecosystems are demonstrated.
Abstract: The moth larva, Doratifera stenosa (Lepidoptera: Limacodidae), was observed feeding voraciously in great numbers on mature leaves of Rhizophora stylosa in mangroves at Port Curtis in Central Queensland, NE Australia. This behaviour was considered unusual since mangroves, and the Rhizophora species in particular, reportedly harbour few herbivores and have relatively low levels of herbivory, less than 10%. During a two year period (1996–1998), larvae were observed consuming around 30–40% of leaves in the canopy each year, and the mangroves appeared able to sustain these high levels of herbivory. The impact on trees was assessed in conjunction with a study of the herbivore, its behaviour and life history, in an attempt to explain the occurrence. Larvae were 1–2 cm in length, bright green and gregarious, with numerous small, stinging hairs along their upper bodies. Feeding was in small cohort groups of 5–70 individuals that broke up immediately prior to each moult after which they regrouped in much larger numbers of mixed cohorts to form single-file processions across branches, stems and prop roots. In this way, they moved to neighbouring trees with less affected foliage. One of the outstanding characteristics of this herbivore was its ability to desist from killing host trees although it appeared quite capable of doing so had it remained on individual trees. By moving from tree to tree, the herbivore was able to heavily crop Rhizophora foliage in an apparently sustainable manner. These findings demonstrate the role and importance of foliar herbivory in severely affected forests and how such instances best not be ignored or treated as curiosities in future assessments of herbivory and forest turnover in mangrove ecosystems.
TL;DR: The populations of polychaetes, as a total group, seemed to be related to the root area available on both islands, independent of the season, however, during the rainy season, the populations were independent of root area availability, while during the dry season,The populations were dependent on it.
Abstract: This study records the polychaetes found on the submerged roots of Rhizophora mangl on San Andres and Providence Islands, ColombianCaribbean. Sampling was done in 1998 during the rainy (July) and dry(November) seasons; each season, 17 roots were collected in threedifferent stations with different kinds of human impact, two in San Andresand one in Providence. At the same time temperature, salinity anddissolved oxygen were measured in situ. Aromatic hydrocarbons weremeasured in the laboratory. The polychaetes were removed from the rootsand identified. The available root area for the organisms was alsomeasured.Five genera and 11 species were newly recorded for the ColombianCaribbean. The most abundant families were Terebellidae in Old ProvidenceMc Bean Lagoon, Syllidae in Honda Bay and Nereididae in Hooker Bayon the San Andres Island. Thelepus `setosus' (Terebellidae) and Amblyosyllis sp. (Syllidae) were highly abundant in less polluted samplingstations such as Old Providence Mc Bean Lagoon and Honda Bay. On theother hand, Neanthes `succinea' (Nereididae) were abundant inHooker Bay which was the most polluted station. Salinity seemed to be the mostimportant parameter for the polychaete populations. The populations ofpolychaetes, as a total group, seemed to be related to the root areaavailable on both islands, independent of the season. However, during therainy season, the populations were independent of root area availability,while during the dry season, the populations were dependent on it.
TL;DR: Taxonomic expertise should join forces with ecologists to establish the role of these worms in the mangrove ecosystems.
Abstract: Oligochaete worms often constitute an important component of the infaunaof sediments associated with marine and brackish-water mangroves. Thispaper reviews the present taxonomic and distributional information of thiscomponent, as well as its possible ecological functions. To date, 56 speciesof marine Oligochaeta have been recorded from mangroves, but probablythis is merely a fraction of the actual number occurring in these habitatsworldwide. Most of the taxa belong to the family Tubificidae, but severalspecies of Enchytraeidae are known from near the back of mangroves.Taxonomic expertise should join forces with ecologists to establish the roleof these worms in the mangrove ecosystems.