Mohd Hanafi Idris

Status of some fishery resources in a tropical mangrove estuary of Sarawak, Malaysia

Abstract This study was carried out to assess the fishery resources of the Sibuti River estuary, Sarawak, Malaysia. Data were collected from the study area for a period of one year in different seasons. The estuary is relatively species-rich and a total of 4675 individuals of 32 families from 60 species of fish (55), crab (four) and shrimp (one) were collected. Coilia dussumieri was the dominant species (22.63%) followed by Nemapteryx caelata (11.85%), Otolithes ruber (7.85%) and Ilisha elongata (5.80%). Marked seasonal variations were found among most of the hydrobiological factors; however, seasonal variations were not significant for the diversity indices such as Shannon–Wiener, Margalef and Evenness. The number of fish taxa caught in different mesh size gill nets was 1 inch (42 species) > 2 inch (36 species) > 4 inch (25 species), suggesting that smaller mesh nets are more suitable for assessing the diversity of fishery resources. SIMPER analysis showed that Coilia dussumieri was the most abundant species in the dry (10.3%) and intermediate (8.1%) seasons, whereas N. caelata was most abundant in the wet season (7.1%). Significant differences (ANOSIM and nMDS) were observed in the species community structure between dry–intermediate and dry–wet seasons; however, species compositions were not significantly different between intermediate and wet seasons. Canonical correspondence analysis (CCA) showed that most of the species assemblages were positively correlated with turbidity and chlorophyll a, followed by phosphate, nitrate and zooplankton density. The findings suggest that the Sibuti mangrove estuary is productive in terms of diversified fishery resources, which are influenced by the hydrobiological factors.

Seasonal Variation in the Occurrence and Abundance of Mangrove Macroalgae in a Malaysian Estuary

Abstract Mangrove macroalgae produce substantial proportion of biomass, which contributes to the coastal ecosystems. Relatively less is known for the seasonal variation in the occurrence and biomass of mangrove associated macroalgae. Consequently, mangrove macroalgae epiphytic on the pneumatophores of Avicennia marina (Forsk.) Vierh., were sampled from the Miri estuary of Sarawak during the four seasons of Malaysia namely southwest monsoon, northeast monsoon, and two inter-monsoons to elucidate seasonal variation in the occurrence and biomass production of macroalgae. Over the sample period, 11 species of mangrove macroalgae were identified from 6 genera. Six of these species such as Caloglossa leprieurii (Montagne) J.Agardh, C. adhaerens R.J.King & Puttock, C. stipitata E.Post, C. ogasawaraensis Okamura, Bostrychia kelanensis Grunow and Dictyota sp. were found to be common in each sample time. Considering four seasonal samples, maximum frequency of occurrence was observed for C. ogasawaraensis (66 ± 10%) and maximum biomass was observed for B. kelanensis (248 ± 95 g m-2). Marked seasonal variations were observed in the frequencies of occurrence and the biomass for the most of the dominant macroalgal species. To the best of our knowledge this is the first time to report the seasonal pattern data for occurrence and abundance of macroalgae from the mangrove systems of Malaysia.

Biomass and habitat characteristics of epiphytic macroalgae in the Sibuti mangroves, Sarawak, Malaysia

Mangroves support diverse macroalgal assemblages as epibionts on their roots and tree trunks. These algae provide nutrients to the primary consumers in the aquatic food web and have been reported to be substantial contributors to marine ecosystems. The species diversity, biomass, and habitat characteristics of mangrove macroalgae were investigated at three stations in the Sibuti mangrove estuary, Sarawak, Malaysia, from November 2012 to October 2013. Three groups of macroalgae were recorded and were found to be growing on mangrove prop roots, namely Rhodophyta (Caloglossa ogasawaraensis, Caloglossa adhaerens, Caloglossa stipitata, Bostrychia anomala, and Hypnea sp.), Chlorophyta (Chaetomorpha minima and Chaetomorpha sp.), and Phaeophyta (Dictyota sp.). The biomass of macroalgae was not influenced (p>0.05) by the season in this mangrove forest habitat. The macroalgal species Hypnea sp. contributed the highest biomass at both Station 1 (210.56 mg/cm2) and Station 2 (141.72 mg/cm2), while the highest biomass was contributed by B. anomala (185.89 mg/cm2) at Station 3. This study shows that the species distribution and assemblages of mangrove macroalgae were influenced by environmental parameters such as water nutrients, dissolved solids, and salinity in the estuarine mangrove habitats of Sibuti, Sarawak.

Phytoplankton in tropical mangrove estuaries: role and interdependency

Mangrove estuaries are claimed to be productive and important breeding grounds for fishery resources. The role of particulate organic matter (POM), especially derived from decomposed litter detritus, is well documented in mangrove estuaries. However, being a primary producer, phytoplankton may play a significant role, which has not been well discussed, in governing the productivity of mangrove estuaries. Based on relevant published literature, this paper focuses on the role of phytoplankton in mangrove estuaries in the tropical coastal region and their interdependency. Analysis reveals that there are two-way interactions between phytoplankton and mangrove estuaries. The POM enriched water in mangrove estuaries acts as an ideal medium for phytoplankton succession. Simultaneously, diversified phytoplankton assemblages play a significant role in the food web of the estuarine mangrove ecosystem. Biomass and diversity of phytoplankton are influenced by nutrient and environmental parameters in mangrove estuaries and, concurrently, phytoplankton play a significant role in fish diversity and primary production in the same system. This review reveals that the inconsistent relationships between mangroves and coastal production could probably be due to the influence of seasonal changes. This paper unveils the latent potential and role of phytoplankton in tropical mangrove estuaries, which could be a source of thought for future research in this arena.