No abstract

Stable carbon (d 13 C) and nitrogen (d 15 N) isotope ratios were measured to investigate the migration of John's snapper Lutjanus johnii and its dependence on the food resources provided within the large Matang Mangrove Forest Reserve (40,151 ha), Malaysia. John's snapper, and its main prey food such as penaeids, Acetes shrimps and mysids, showed generally depleted d 13 C values in the inner mangrove area but more enriched values in the river mouth and coastal area. Some juveniles migrated into the inner mangrove areas, although they were also distributed near the river mouth areas. Isotopic signatures of snapper fish and prey reveal the ontogenetic migration of the youngest juvenile fish (\5 cm in total length) from the coastal area into the mangrove area, shifting their dependence from the coastal food web to the inner mangrove food web with their growth. The study shows the importance of the complex interconnected mangrove waterways and associated prey animals present in the large mangrove system to juvenile John's snapper.

No abstract

A mass mortality event of blood cockles, Anadara granosa, occurred in aquaculture ground in Selangor in mid-February 2012. To identify factors contributing to this event, we estimated the changes in survival rate and population density of the blood cockles using data from field surveys carried out in late-January and mid-March, 2012. In addition, blood cockle samples were used for histological observation of various tissues with a light microscope. Furthermore, we examined the environmental factors that seemed to be involved in this mass mortality event using environmental data obtained in two surveys and weather data for the Selangor region from late-January to mid-March 2012. As a result of the field surveys and the histological observation, the mortality was estimated to be 30 % over, and the blood cockles were shown to be in the spawning season at this time of year. In addition, numerous individuals collected in mid-March had no food in the digestive duct, which suggested low food availability. Precipitation data for the Selangor region showed rainfall of 30 mm/day over four days in mid-February, which suggested an impact of freshwater flooding from rivers on the aquaculture ground. Normally, the blood cockles are tolerant to low-salinity environments. However, the fact that the flooding and associated environmental changes occurred, when the population was debilitated by reproductive activity, may have led to the mass mortality event in association with low food availability.

The dissolved oxygen concentrations (DO) were measured during four expeditions between 2007 and 2008 in the Sangga Besar River Estuary in the Matang Mangrove Forest Reserve (MMFR), Peninsular Malaysia. Hypoxic conditions (DO < 3 mg/L) were observed during periods of well mixed spring tides almost throughout the estuary, while in the partially stratified neap tides, hypoxia in the estuary was restricted to the upper river and subsurface layers in the branch and creek area, where high Acid Volatile Sulfide and low oxidation-reduction potential values were observed in the surface sediments due to the accumulation and decomposition of mangrove derived organic matter. Based on the δ 13 C, the contribution of mangrove derived organic matter in the surface sediments of the creek area was estimated to be 77-87%. While in the coastal area, the contribution of phytoplankton was 58-68%. These results indicate that the formation of hypoxic waters in the estuary is mainly due to the tidal mixing of hypoxic waters from the creeks and branches with the estuarine waters during spring tides and probably oxygen consumption by resuspended sediments.