This study provides the first marine gastropod checklist from the Sarawak Exclusive Economic Zone (EEZ). Gastropod samples were collected from selected stations in the Sarawak EEZ using an otter trawl net with a stretched mesh size of 38 mm at the cod end. The trawling operations were conducted more than 12 nautical miles from the coast, and the area was divided into three depth strata: I) 20-50 m, II) 50-100 m and III) 100-200 m. A total of 23 gastropod species were identified during the two-month sampling period from 16 August until 6 October 2015, representing 8 superfamilies, 15 families and 20 genera. Superfamily Tonnoidea was represented by 7 species, followed by Muricoidea (5 species), Cypraeoidea (4 species), and Buccinoidea and Conoidea (both with 2 species). Other superfamilies were represented by a single species. Only 3 species were obtained in 2 depth strata, namely Melo melo, Murex aduncospinosus and Tonna galea. In addition, 9, 13 and 4 species of gastropods were found in strata I, II and III, respectively. The information on gastropod distributions at different depth strata in the Sarawak EEZ could be useful in updating the Malaysian species diversity database.
Sediment distributions in deep sea influence the benthic community structure and thus play an important role in shaping the marine ecosystem. Several studies on sediment characteristics had been conducted in South China Sea (SCS), but only limited to coastal areas of regions within SCS territories. Therefore, this study was carried out to analyze the benthic sediment profile in an area beyond 12 nautical miles off the coast of Sarawak, southern SCS. Sediment samples were collected from 31 stations, comprising three depth ranges: (I) 20-50 m, (II) 50-100 m, and (III) 100-200 m. The total organic matter (TOM) contents were determined and subjected to dry and wet sieving methods for particle size analysis. TOM contents in the deep area (>50 m) were significantly higher (p = 0.05) and positively correlated (r = 0.73) with silt-clay fraction. About 55% and 82% of stations in strata II and III, respectively, were dominated by silt-clay fractions (<63 μm mean diameter), coherent with TOM data. In addition, sediments in the deep area (>50 m) tend to be poorly sorted, very fine skewed, and platykurtic. Unlike data obtained 20 years ago which reported high content of silt-clay (58%), this study recorded a lower content (35%); therefore, changes in sediment load had been observed in southern SCS.
The demersal brown banded bamboo shark Chiloscyllium punctatum is a major component of sharks landed in Malaysia. However, little is known about their population structure and the effect of high fishing pressure on these weak swimming sharks. Both mitochondrial DNA control region (1072 bp) and NADH dehydrogenase subunit 2 (1044 bp) were used to elucidate the genetic structure and connectivity of C. punctatum among five major areas within the Sundaland region. Our findings revealed (i) strong genetic structure with little present day mixing between the major areas, (ii) high intra-population genetic diversity with unique haplotypes, (iii) significant correlation between genetic differentiation and geographical distance coupled with detectable presence of fine scale geographical barriers (i.e. the South China Sea), (iv) historical directional gene flow from the east coast of Peninsular Malaysia towards the west coast and Borneo, and (v) no detectable genetic differentiation along the coastline of east Peninsular Malaysia. Genetic patterns inferred from the mitochondrial DNA loci were consistent with the strong coastal shelf association in this species, the presence of contemporary barriers shaped by benthic features, and limited current-driven egg dispersal. Fine scale population structure of C. punctatum highlights the need to improve genetic understanding for fishery management and conservation of other small-sized sharks.
A background study is important for the conservation and stock management of a species. Terapon jarbua is a coastal Indo-Pacific species, sourced for human consumption. This study examined 134 samples from the central west and east coasts of Peninsular (West) Malaysia and East Malaysia. A 1446-bp concatenated dataset of mtDNA COI and Cyt b sequences was used in this study and 83 haplotypes were identified, of which 79 are unique haplotypes and four are shared haplotypes. Populations of T. jarbua in Malaysia are genetically heterogenous as shown by the high level of haplotype diversity ranging from 0.9167-0.9952, low nucleotide diversity ranging from 0.0288-0.3434, and high FST values (within population genetic variation). Population genetic structuring is not distinct as shown by the shared haplotypes between geographic populations and mixtures of haplotypes from different populations within the same genetic cluster. The gene flow patterns and population structuring observed among these regions are likely attributed to geographical distance, past historical events, allopatric speciation, dispersal ability and water currents. For instance, the mixture of haplotypes revealed an extraordinary migration ability of T. jarbua (>1200 km) via ancient river connectivity. The negative overall value of the neutrality test and a non-significant mismatch distribution are consistent with demographic expansion(s) in the past. The median-joining network concurred with the maximum likelihood haplotype tree with three major clades resolved. The scarcity of information on this species is an obstacle for future management and conservation purposes. Hence, this study aims to contribute information on the population structure, genetic diversity, and historical demography of T. jarbua in Malaysia.