Size Distribution, Length-Weight Relationship, and Size at Morphometric Maturity of the Mud Spiny Lobster Panulirus polyphagus (Herbst, 1793) in the Johor Strait

Spiny lobsters of the genus Panulirus are economically important and support local fishing communities. However, mud spiny lobster Panulirus polyphagus is among the least known species within this genus in terms of their biological information. This study relates to the size distribution, length-weight relationship, and size at morphometric maturity of P. polyphagus in the Johor Strait. Within the year 2010, 300 specimens were collected off the coast of Johor Strait, Malaysia. There was no significant difference in body size (cephalothorax length, CL) and body weight (BW) between sexes. CL and BW were highly correlated and males of P. polyphagus displayed positive growth allometry, whereas the opposite was observed in females. Based on the merus (ML) and carpus length (CPL) of the third right walking leg, the piecewise linear regression analysis estimated that the size at maturity for male was 6.58 cm CL (based on ML) and 7.58 cm CL (based on CPL), whereas it was 8.18 cm CL (based on ML) and 6.75 cm (based on CPL) for females. Two discriminant functions of high classification and revalidation rates (> 98.6% in males and > 98.7% in females) that can discern maturation status in males and females of P. polyphagus were derived using the discriminant function analysis. Biological information derived from this study serves as an essential baseline for future fishery management and conservation of P. polyphagus.

Effect of dissolved oxygen deficiency on 210Pb content in mussel's tissues at the Johor strait, Malaysia

Aim: To investigate the effect of dissolved oxygen deficiency on the level of 210Pb in mussel's tissues, Perna viridis which has been reported to be highly tolerant to hypoxia. Methodology: Mussels (Perna viridis), seawater and sediment samples were collected from nine stations along the Johor Straits during North-east monsoon (November 2017), inter-monsoon (March 2018), and South-west monsoon (August 2018). The 210Pb contents were extracted and estimated by Gross Alpha-beta Counter. Results: The lowest dissolved oxygen was recorded at Station 4 which decreased from 2.14 mg l-1 to 2.10 mg l-1 and subsequently to 1.63 mg l-1 during first to third samplings. In sediment, 210Pb activities increased with the increase in organic matter. Meanwhile, in mussels, the 210Pb activities showed almost similar trend with sediment where 210Pb activities were much higher adjacent to the causeway structure, especially at the East part of Johor Strait. The level of 210Pb in mussel's tissue and sediment also increased with decreasing level of dissolved oxygen. Interpretation: A causeway structure disrupted the water quality of Johor Straits and caused almost hypoxic conditions nearby. The coverage of oxygen depletion expanded during inter-monsoon. An inverse relationship between 210Pb activities and dissolved oxygen prove that deficiency of dissolved oxygen potentially influenced the bioaccumulation of 210Pb in mussels to correspond to the build-up of concentration factor in their tissues which exceeded the recommended value.

Dusky Langurs Trachypithecus obscurus (Reid, 1837) (Primates: Cercopithecidae) in Singapore: potential origin and conflicts with native primate species

The introduction of exotic species can have detrimental effects on local populations via factors such as resource competition and new threats from disease. Singapore has three native species of non-human primates: Sunda Slow Loris Nycticebus coucang, Long-tailed Macaque Macaca fascicularis, and Raffles’ Banded Langur Presbytis femoralis. Over the past few months, several non-native Dusky Langurs Trachypithecus obscurus were observed in Singapore. We document our observations, compile reports from social media, and attempt to assess the potential impacts on local primates. Whenever Dusky Langurs were encountered, we recorded the date, time, GPS coordinates, group demographics, and behaviour, including interactions with native primates. We also monitored sighting reports of Dusky Langurs posted on local major Facebook groups from 30 December 2019 to 31 January 2020, and privately messaged the person(s) for more information. On 31 August 2019, three Dusky Langurs were seen near a residential area in the northern part of Singapore, and two to three individuals were reported on 14 subsequent occasions. During one encounter on 18 January 2020, an adult male Long-tailed Macaque chased a group of Dusky Langurs from a feeding tree. The next day the same group of Dusky Langurs chased a group of 11 Banded Langurs from another feeding tree. The Dusky Langurs appeared to be healthy and wild, indicating that they may have swum across the Johor Strait and/or traveled on the Johor-Singapore Causeway from Malaysia. Further monitoring of these Dusky Langurs will be required to assess their impact on local primates.

Temporal and spatial dynamics of Bacteria, Archaea and protists in equatorial coastal waters

Singapore, an equatorial island in South East Asia, is influenced by a bi-annual reversal of wind directions which defines two monsoon seasons. We characterized the dynamics of the microbial communities of Singapore coastal waters by collecting monthly samples between February 2017 and July 2018 at four sites located across two straits with different trophic status, and sequencing the V6-V8 region of the small sub-unit ribosomal RNA gene (rRNA gene) of Bacteria, Archaea, and Eukaryota. Johor Strait, which is subjected to wider environmental fluctuations from anthropogenic activities, presented a higher abundance of copiotrophic microbes, including Cellvibrionales and Rhodobacterales. The mesotrophic Singapore Strait, where the seasonal variability is caused by changes in the oceanographic conditions, harboured a higher proportion of typically marine microbe groups such as Synechococcales, Nitrosupumilales, SAR11, SAR86, Marine Group II Archaea and Radiolaria. In addition, we observed seasonal variability of the microbial communities in the Singapore Strait, which was possibly influenced by the alternating monsoon regime, while no seasonal pattern was detected in the Johor Strait.

Temporal dynamics of Bacteria, Archaea and protists in equatorial coastal waters

ABSTRACTSingapore, an equatorial island in South East Asia, is influenced by a bi-annual reversal of wind directions which defines two monsoon seasons. We characterized the dynamics of the microbial communities of Singapore coastal waters by collecting monthly samples between February 2017 and July 2018 at four sites located across two straits with different trophic status, and sequencing the V6-V8 region of the small sub-unit ribosomal RNA gene (rRNA gene) of Bacteria, Archaea, and Eukaryota. Johor Strait, which is subjected to wider environmental fluctuations from anthropogenic activities, presented a higher abundance of copiotrophic microbes, including Cellvibrionales and Rhodobacterales. The mesotrophic Singapore Strait, where the seasonal variability is caused by changes in the oceanographic conditions, harboured a higher proportion of typically marine microbe groups such as Synechococcales, Nitrosupumilales, SAR11, SAR86, Marine Group II Archaea and Radiolaria. In addition, we observed seasonal variability of the microbial communities in the Singapore Strait, which was possibly influenced by the alternating monsoon regime, while no seasonal pattern was detected in the Johor Strait.

Characterising planktonic dinoflagellate diversity in Singapore using DNA metabarcoding

Dinoflagellates are traditionally identified morphologically using microscopy, which is a time-consuming and labour-intensive process. Hence, we explored DNA metabarcoding using high-throughput sequencing as a more efficient way to study planktonic dinoflagellate diversity in Singapore’s waters. From 29 minimally pre-sorted water samples collected at four locations in western Singapore, DNA was extracted, amplified and sequenced for a 313-bp fragment of the V4–V5 region in the 18S ribosomal RNA gene. Two sequencing runs generated 2,847,170 assembled paired-end reads, corresponding to 573,176 unique sequences. Sequences were clustered at 97% similarity and analysed with stringent thresholds (≥150 bp, ≥20 reads, ≥95% match to dinoflagellates), recovering 28 dinoflagellate taxa. Dinoflagellate diversity captured includes parasitic and symbiotic groups which are difficult to identify morphologically. Richness is similar between the inner and outer West Johor Strait, but variations in community structure are apparent, likely driven by environmental differences. None of the taxa detected in a recent phytoplankton bloom along the West Johor Strait have been recovered in our samples, suggesting that background communities are distinct from bloom communities. The voluminous data obtained in this study contribute baseline information for Singapore’s phytoplankton communities and prompt future research and monitoring to adopt the approach established here.