Stable isotope ratio as a tracer of mangrove carbon in Malaysian ecosystems

Summary The ratio of stable carbon isotopes (¹³C) in plants and animals from Malaysian mangrove swamps, coastal inlets, and offshore waters was determined. Vascular plants of the swamps were isotopically distinct ( x±s.d.=-27.1±1.2) from plankton (-21.0±0.3) and other algae (-18.7±2.2). Animals from the swamps (-20.9±4.1) and inlets (-19.8±2.5) had a wide range of isotope ratios (-28.6 to-15.4), indicating consumption of both mangrove and algal carbon. Several commercially important species of bivalves, shrimp, crabs, and fish obtained carbon from mangrove trees. Mangrove carbon was carried offshore as detritus and was isotopically distinguishable in suspended particulate matter and sediments. Animals collected from 2 to 18 km offshore, however, showed no isotopic evidence of mangrove carbon assimilation, with ratios (-16.5±1.1, range-19.1 to-13.1) virtually identical to those reported for similar animals from other plankton-based ecosystems. Within groups of animals, isotope ratios reflected intergencric and interspecific differences in feeding and trophic position. In particular, there was a trend to less negative ratios with increasing trophic level.     

Mangroves as a habitat for fish and prawns

Mangrove inlets and creeks in Selangor, Malaysia are the habitat for 119 species of fish and 9 species of prawns. The majority of fish and all prawns sampled in the inlets were juveniles. The common fish species in the inlets in terms of weight wereArius sagor, Ambassis gymnocephalus, Liza subviridis, Toxotes jaculator, Sphyraena barracuda andLates calcarifer. Prawns were represented by juvenilePenaeus penicillatus, P. merguiensis, P. indicus, Metapenaeus brevicornis andM. affinis. Samples from enclosure traps set on mudflats during ebbing water captured 37 species of fish and 11 species of prawns. The role of mangroves as nursery and feeding grounds for fish and prawns is reviewed in the light of recent work in Selangor. It is apparent that mangroves support fisheries by providing habitat and food.     

Distribution and abundance of marine wood borers on the west coast of Peninsular Malaysia

Twenty one species of marine wood borers were recorded in this study. There are seventeen species of bivalves of which sixteen are from the family Teredinidae and one from the family Pholadidae. The crustaceans comprised the family Sphaeromatidae with three species and the family Limnoriidae with one species. Seven of the fourteen known genera of the teredinids were recorded. The bivalve wood borers were widely distributed in the local mangroves. Martesia striata was the most abundant wood borer at the Degaussing Range jetty, Lumut. Lyrodus pedicellatus was the most abundant shipworm in wooden panels. Shipworms were abundant on the subtidal panels where the genus Bankia, was most common while M. striata was abundant on the intertidal panels. M. striata numbers were higher on the top surfaces as compared to the under surfaces of wooden panels.     

The community structure of macroalgae in a low shore mangrove forest in Selangor,Malaysia

The macroalgal communities associated with pneumatophores, basal area of tree trunks and sediment surface in the mangrove forest at Sementa, Selangor consisted of nine main species. Biomass, frequency of occurrence and relative cover of the species along a belt transect, showed two major trends, a decrease in these parameters in the landward direction for Colpomenia sp. Gracilaria blodgettii and Gracilaria crassa and an increase in the landward direction for Dictyota dichotoma, Catenella nipae, Rhizoclonium sp. and Bostrichia radicans. Algal dominance varied with substratum. Pneumatophores were dominated by Caloglossa lepreurii and sediment surface by D. dichotoma. The 40 cm zone at the base of tree trunks was dominated by two algal species. The 0–20 cm region above the sediment surface was colonized by C. nipae, while the 20–40 cm region was dominated by Rhizoclonium sp. The study identified the importance of substrate in macroalgal colonization.     

Nitrogen concentrations in a mangrove creek with a large tidal range,Peninsular Malaysia

We report on various species of nitrogen in subsurface water samples taken at the mouth of Sungai Sementa Besar, a creek about 4.5 km long off the Straits of Malacca and draining a mangrove forest on the west coast of Peninsular Malaysia. This tide-dominated watercourse shows a range greater than 4.5 metres from low to high water during springs, only 1.0 m during neaps, and salinities at the mouth of 30 or greater. After heavy rains or when the tides inundate the forest floor, inorganic nitrogen values increase as much as tenfold at the mouth. Particulate and total organic nitrogen also increase at the mouth under these conditions. There were also comparative highs of organic inputs at other times.     

Studies on Gracilaria changii (Gracilariales,Rhodophyta) from Malaysian mangroves

Gracilaria changii, recorded from Malaysia and Thailand, is one of the more abundant agarophytic seaweeds found in Malaysia. A wild population of Gracilaria changii growing in mangroves was monitored for seasonal variation in agar content and gel strength as well as spore production. Agar yield and gel strength ranged from 12 to 25% dry weight and 294 to 563 g cm^–2, respectively, over a 15-month period. Gel strength but not yield was positively correlated with amount of rainfall. Cystocarps were observed throughout the study, but use of sporetraps showed that spore release peaked around July–August and January–February after the two monsoon periods.Mariculture of Gracilaria changii in shallow ponds in the mangroves, in an irrrigation canal and in a shrimp farm pond was conducted. Average growth rate of cuttings tied to monofilament lines was 3.3 ± 1.7% d^–1, 8.4 ± 1.8% d^–1 and 3.6 ± 1.6% d^–1 respectively. Cuttings were lost to siltation, wave action, predation and heavy epiphytisation.These studies show that Gracilaria changii has potential commercial application in the agar industry.     

Neap-spring tidal effects on dissolved oxygen in two Malaysian estuaries

The longitudinal distributions of dissolved oxygen change dramatically during neap-spring tidal cycles in the lower Selangor and Klang Rivers. An oxygen deficit develops in both estuaries when the tidal range is high. The Selangor River inflow is nearly saturated with D.O., but during spring tides D.O. falls to as little as 15% of saturation in the middle reaches of the estuary. The Klang River has low D.O. freshwater input, an oxygen minimum develops during neap tides, and anoxic conditions are produced by spring tides. These oxygen minima are attributed to the high oxygen demand of sediment that rests on the bottom during neap tides and is resuspended during spring tides. The ecological effects of tidal cycling patterns of dissolved oxygen in these Malaysian estuaries need further study, within the context of land use patterns and other human activities.     

The habitat function of mangroves for terrestrial and marine fauna: A review

Mangroves are defined by the presence of trees that mainly occur in the intertidal zone, between land and sea, in the (sub) tropics. The intertidal zone is characterised by highly variable environmental factors, such as temperature, sedimentation and tidal currents. The aerial roots of mangroves partly stabilise this environment and provide a substratum on which many species of plants and animals live. Above the water, the mangrove trees and canopy provide important habitat for a wide range of species. These include birds, insects, mammals and reptiles. Below the water, the mangrove roots are overgrown by epibionts such as tunicates, sponges, algae, and bivalves. The soft substratum in the mangroves forms habitat for various infaunal and epifaunal species, while the space between roots provides shelter and food for motile fauna such as prawns, crabs and fishes. Mangrove litter is transformed into detritus, which partly supports the mangrove food web. Plankton, epiphytic algae and microphytobenthos also form an important basis for the mangrove food web. Due to the high abundance of food and shelter, and low predation pressure, mangroves form an ideal habitat for a variety of animal species, during part or all of their life cycles. As such, mangroves may function as nursery habitats for (commercially important) crab, prawn and fish species, and support offshore fish populations and fisheries. Evidence for linkages between mangroves and offshore habitats by animal migrations is still scarce, but highly needed for management and conservation purposes. Here, we firstly reviewed the habitat function of mangroves by common taxa of terrestrial and marine animals. Secondly, we reviewed the literature with regard to the degree of interlinkage between mangroves and adjacent habitats, a research area which has received increasing attention in the last decade. Finally, we reviewed current insights into the degree to which mangrove litter fuels the mangrove food web, since this has been the subject of long-standing debate.     

Rediscovery of Ellobium scheepmakeri (Petit De La Saussaye, 1850) (Mollusca: Gastropoda: Ellobiidae), a rare ellobiid in Bukit Belimbing mangrove forest,Peninsular Malaysia

The ellobiid Ellobium scheepmakeri (Petit de la Saussaye, 1850) is reported from the banks of the Selangor River estuary, 57 years after it was first collected in Peninsular Malaysia. It was found in abundance under logs in the dryland mangrove forest of a dominantly Nypa swamp at the upper reaches of the Kuala Selangor estuary where sediment pore water salinity was recorded at 6–7 ppt.     

Litter production in three mangrove forest zones in the malay peninsula

Total litter fall, over a period of more than 22 months, was 4.22, 3.84 and 4.32 g dry wt. m⁻² day⁻¹ in the Avicennia, Sonneratia and Rhizophora forests, respectively. Leaves comprised 40–67% of the total. The Avicennia alba Bl. forest, however, showed a distinct peak from August to October when fruits comprised 50–65% of the total litter. Correlations of total and leaf component litters with the four meterological parameters of wind run, mean temperature, evaporation and rainfall accounted for less than 50% of the variation in litter fall. Wind run had the greatest influence in the seaward Avicennia forest while mean temperature had the greatest influence on the landward Rhizophora forest.