Marine lakes, with populations in landlocked seawater and clearly delineated contours, have the potential to provide a unique model to study early stages of evolution in coastal marine taxa. Here we ask whether populations of the mussel Brachidontes from marine lakes in Berau, East Kalimantan (Indonesia) are isolated from each other and from the coastal mangrove systems. We analyzed sequence data of one mitochondrial marker (Cytochrome Oxidase I (COI)), and two nuclear markers (18S and 28S). In addition, we examined shell shape using a geometric morphometric approach. The Indonesian populations of Brachidontes spp. harbored four deeply diverged lineages (14–75% COI corrected net sequence divergence), two of which correspond to previously recorded lineages from marine lakes in Palau, 1,900 km away. These four lineages also showed significant differences in shell shape and constitute a species complex of at least four undescribed species. Each lake harbored a different lineage despite the fact that the lakes are separated from each other by only 2–6 km, while the two mangrove populations, at 20 km distance from each other, harbored the same lineage and shared haplotypes. Marine lakes thus represent isolated habitats. As each lake contained unique within lineage diversity (0.1–0.2%), we suggest that this may have resulted from in situdivergence due to isolation of founder populations after the formation of the lakes (6,000–12,000 years before present). Combined effects of stochastic processes, local adaptation and increased evolutionary rates could produce high levels of differentiation in small populations such as in marine lake environments. Such short-term isolation at small spatial scales may be an important contributing factor to the high marine biodiversity that is found in the Indo-Australian Archipelago.

In less than two decades, from 45000 to 70000 ha, or up to 70%, of the mangroves in the Mahakam Delta, East Kalimantan, were converted to shrimp ponds. This is expected to affect the productive and buffering function of intact mangroves, observable as shifts in composition and a possible reduction in productivity of the coastal fisheries. The trade-off between mariculture and fisheries is explored with data from fisheries statistics, surveys and reported information. Analysis of trends and developments in total catch, catch by species category, catch rate, fishing effort, pond production and productivity gave no direct quantitative evidence of reduced coastal production and productivity. Shrimp-pond productivity (125 kg/ha/year) is low, stable and highly variable (CV=69%) at the aggregated level of the delta. Since 1989, fishing efforts have increased and patterns diversified, but aggregated catch rates did not decrease. Catches of rays and sharks decreased and the pelagic/demersal catch ratio increased. A shift towards more resilient species categories with a high turnover rate took place from 1993 to 1999, 4 to 10 years after the boom in pond construction. However, these clear shifts are not self-evidently related to mangrove conversion. Reasons for this are discussed. The potential for detection of changes in resource outcome and assessment of the trade-off between mariculture and fisheries, at both the local level and through aggregated fisheries statistics, is limited because of the high variability in outcome. This implies a limited capacity for resolution of resource-use conflicts when evaluating competing claims informed by existing data and information on resource change.

A first survey  on a community marine species in  river of Mahakam East Kalimantan was performed in December 2015 and May 2016. Fish samplings were carried out from two locations the lower and the middle part of Mahakam. Whilst hydrometric observation of current velocity, water depth and tide was measured not only at the locations but also along the river from 2013 to 2017, tide was only observed in the lower part of Mahakam.  However, marine fish species were recognized to reach up the middle part of Mahakam, 230 km from coastline.  To describe a community fish structure and its dissimilarity of the two surveyed locations, diversity and bray Curtis index were applied.  Almost 15 marine fish species identified in river of Mahakam was demersal fish and index of the similarity of marine fish community between the locations only 0.106.

Suyatna I, Bratawinata AA, SidikAS, Ruchaemi A (2011) Demersal fishes and their distribution in estuarine waters of Mahakam Delta, East Kalimantan. Biodiversitas 12: 204-210. The study aimed (i) to identify of the demersal fishes, (ii) to analyze the diversity and (iii) to determine their distribution. Surveys were carried out between August 2009 and January 2010 in Mahakam Delta, East Kalimantan. Data were analyzed using several indices of Shannon Weaver, Simpson, Margalef species richness, and Bray Curtis distance. The canonical correspondence analysis (CCA) was also used to correlate between fish species and their environmental factors and to show the fish distribution. Sixty samplings were done using bottom-trawl at various water depths from one to forty two meters to collect the data. Taxonomically, during the study, 10 orders, 61 families, 87 genera and 131 species of fish with 43340 individuals were identified. Among the families, Leiognathidae was the most important group of fish, they distributed throughout the depths. Meanwhile CCA showed that Leiognathidae and Sciaenidae were observed to be rich in the shallow water. Generally, index of Shannon Weaver, Simpson and Margalef species richness ranged between; 0.52 and 2.48; 0.11 and 0.82; 2.24 and 18.61 respectively. Bray Curtis distanceindicated the significant difference of individual number of demersal fishes between shallow and deep waters.Key words: Mahakam delta, water depth, trawl, demersal fish, canonical correspondence analysis

The aim of the study was to describe the coral reef condition Background: in Bangka Belitung Islands, particularly from Gaspar Strait. This research location is well known for its underwater archaeological discovery and shipwreck sites. Recent increases in mining, fishing and tourism activities in the surrounding islands might have affected the condition of the coral reef.Nine islands inside the strait were visited (i.e. Langer, Kembung, Methods: Piling, Aur, Salma, Pongok, Celagen, Kelapan, and Lepar Island), and a line transect was used to observed coral reef conditions.Coral cover was found to be predominantly in fair conditions Results: (25-50%). Coral mortality index also tended to be high, which indicated that the coral reef ecosystem was in threatened conditions. Previous and recent reports also reported the same condition as found by this study.Degradation of the coral community in Bangka Belitung Conclusion: Islands is likely caused by human activities. This suggests that increasing human activities significantly affects the coral reef condition. Protection of coral reefs with sustainable management for mining activity, tourism and fishing practices are needed.