Harmful Algal Species in the Tebrau Strait: An SEM Observation of the Dinofl agellate Assemblage

Harmful algal bloom (HAB) is a natural phenomenon due to the increase of algal cell density in the water column that subsequently causes deleterious effects to natural environments as well as mankind. HABs in the country mainly occurred when a particular group of dinofl agellate cells proliferate in the eutrophied semi-enclosed coastal water body. In this study, dinofl agellate species composition in the Tebrau Strait was determined by scanning electron microscope (SEM). Plankton samples were collected by a 20-micron plankton net haul at several locations of the strait. Samples were undergone fi xation, serial dehydration and followed by critical point drying. Samples were then observed under a JEOL analytical SEM. Total of 11 dinofl agellate species were identifi ed, with 7 species known to be associated with HABs events. The occurrence of a fi sh-killing unarmoured dinofl agellate, Karlodinium venefi cum was reported for the fi rst time from Malaysian waters. The presence of this and other potentially harmful dinofl agellate species in the strait should be taken seriously by the respective authorities in future expansion of aquaculture industry in the strait

Margalefidinium polykrikoides blooms and their impacts on fish mortalities in Malaysia Coastal

Harmful algal blooms (HABs) caused by the fish killer, Margalefidinium polykrikoides had expanded across Asia, North America and Europe and affected aquaculture, fishery and tourism industries. In Malaysia, the first occurrence of this species in coastal waters of Sabah was in 2005 and had caused loss up to RM 1 million to aquaculture industry. Since then, the bloom of this species has spread to many coastal areas in Malaysia causing devastating impacts. To decrease the impact, the Department of Fisheries Sabah (DOF) has performed monthly monitoring and come out with a strategy to safeguard community and aquaculture industry. Based on the monitoring from 2009-2022, several coastal areas in Sabah have higher frequency of M. polykrikoides occurrences. In this paper, the occurrences of M. polykrikoides at different coastal areas, the impacts and mitigation strategies will be discussed. This is important to ensure marine food industry is sustained to support rising human population and save the marine environment for future generation

Harmful microalgae assemblage in the aquaculture area of Aman Island, Northen Strait of Malacca

A field survey was carried out in Aman Island, the northern Strait of Malacca, to investigate the occurrence of harmful microalgae. The area is known for marine finfish cage-culture and blood cockle farming. Plankton samples were collected fortnightly between July 2011 and September 2013. A total of 58 phytoplankton genera were recorded; 37 belong to the diatoms, and 21 genera were dinoflagellates. Harmful microalgae species were identified microscopically, of which nine are bloom-forming species that responsible for fish kills. These included Akashiwo sanguinea, Chaetoceros affinis, Cha. curvisetus, Cha. laevis, Ceratium furca, C. fusus, Cochlodinium sp., Karlodinium australe and Noctiluca scintillans. Three Alexandrium species were identified from the samples, i.e. A. leei, A. affine and Alexandrium sp. Pulau Aman; some species in the genus have been known to associate with Paralytic Shellfish Poisoning (PSP). Diarrhetic Shellfish Poisoning (DSP)-toxin producers were also encountered in the water samples, viz. Dinophysis acuminata, D. caudata, Dinophysis sp. and Prorocentrum micans. The harmful diatom, Pseudo-nitzschia spp. that associated with Amnesic Shellfish Poisoning (ASP), was commonly found in the water samples. Cell abundance of each harmful microalga was enumerated. The results showed that cell densities of harmful microalgae were relatively low throughout the sampling period. The microalgae community was dominated by Ceratium furca in May 2012, with cell densities exceeding 70,000 cells L-1; no fish kill event was reported during the time. Even though no fish kill or shellfish poisoning was reported in the area, he presence of harmful microalgae albeit at low cell densities, may pose a potential threat to human health and seafood biosecurity. Therefore, regular phytoplankton monitoring is necessary to safeguard human health and seafood industries in the country

A bloom of Karlodinium australe (Gymnodiniales, Dinophyceae) associated with mass mortality of cage-cultured fishes in West Johor Strait, Malaysia

A recent (February 2014) mass mortality of fishes was observed in the cage-farming region of the West Johor Strait of Malaysia, involving over four different species of cultured fishes, numbering ∼50,000 fish. A field investigation at six stations along the West Johor Strait collected water samples and examined for the presence of harmful species. Dead fishes were collected for necropsy. The phytoplankton composition was dominated by a species of Karlodinium, at a considerably high cell concentration (0.31–2.34 × 106 cells l−1), and constituting 68.8–98.6% of the phytoplankton relative abundance at all stations. Detailed morphological assessment by light and scanning electron microscopy revealed that the species was Karlodinium australe de Salas, Bolch and Hallegraeff. This was supported by molecular evidence of the nuclear encoded large subunit ribosomal gene (LSU rDNA) and the second internal transcribed spacer (ITS2) via single-cell PCR. The sequences of LSU rDNA yielded 3.6–4.0% divergence when compared to the sister taxon, K. armiger; and >6.5% when compared to other Karlodinium species. Fish necropsy showed symptoms similar to those affected by karlotoxin ichthyotoxins. This is the first report of a mass mortality of cage-cultured and wild fishes attributed to the unarmored dinoflagellate K. australe

Tropical marine: diatoms and dinoflagellates

Phytoplankton is a primary producer, producing oxygen for us to breathe and the foundation of the aquatic food web. However, phytoplankton can also be the harbingers of death or disease. Certain species produce harmful toxins that can kil marine life and people who eat contaminated seafood. Phytoplankton can grow ni high cel numbers and are called 'harmful algal bloom' or red tides. This book provides a common marine phytoplankton (diatoms and dinoflagellates) from the coastal waters of Malaysia which include the morphology, physiology, habitat and current applications. Each phytoplankton species is presented with taxonomic description and picture(s) to enhance the understanding ni identifying the species. Most of the taxonomic books published elsewhere documented temperate species. This is the first of its kind to provide a comprehensive tropical marine phytoplankton species that can guide those who are interested ni phytoplankton and become a standard reference for marine tropical phytoplankton

Photocatalytic remediation of harmful Alexandrium minutum bloom using hybrid chitosan-modified TiO2 films in seawater: a lab-based study

The uncontrolled growth of harmful algal blooms (HABs) can negatively impact the environment and pose threats to human health and aquatic ecosystems. Titanium dioxide (TiO2) is known to be effective in killing harmful algae through flocculation and sedimentation. However, TiO2 in a dispersed form can harm other non-target marine organisms, which has raised concerns by environmentalists and scientists. This research seeks to explore the utility of immobilized titanium oxide as a photocatalyst for mitigation of HABs, where the Alexandrium minutum bloom was used as a model system herein. Chitosan was modified with 0.2 wt.% TiO2 (Chi/TiO2 (x mL; x = 1, 3 and 5 mL) and the corresponding films were prepared via solvent casting method. Scanning electron microscope (SEM) images of the films reveal a highly uneven surface. X-ray diffraction (XRD) analysis indicates the reduction in chitosan crystallinity, where the presence of TiO2 was negligible, in accordance with its dispersion within the chitosan matrix. The photocatalytic mitigation of A.minutum was carried out via a physical approach in a laboratory-scale setting. The negative surface charge of the films was observed to repel the negatively charged A.minutum causing fluctuation in the removal efficiency (RE). The highest RE (76.1 ± 13.8%) was obtained when Chi/TiO2 (1 mL) was used at 72 h, where the hydroxyl radicals generated were inferred to contribute to the deactivation of the algae cells by causing oxidative stress. An outcome of this study indicates that such hybrid films have the potential to replace the non-immobilized (dispersed) TiO2 for HAB mitigation. However, further investigation is required to deploy these films for field applications at a larger scale

Diversity of Heterocapsa (Dinophyceae) and the algal bloom event in the mariculture areas of Johor Strait, Malaysia

In November 2020, a high biomass multi-species algal bloom caused heavy water discoloration in the fish and mussel farm areas of the Johor Strait, Malaysia. A total of 19 microalgal taxa were identified from the plankton samples collected during the bloom event. Eleven genera were diatoms, and eight genera were dinophytes. The microalgal composition was dominated by the diatom Guinardia sp., with an average cell density of 1.7×106 cells L−1 , making up 65–80% of the phytoplankton composition. Concomitantly, high densities of the dinophytes Heterocapsa minima (3.8–5.3×105 cells L−1 ) and Karlodinium spp. (3.5–6.6×103 cells L−1 ) were found. This is the first record of the occurrence of H. minima in Malaysian waters. Detailed morphological observations of H. minima based on scanning electron microscopy are presented in this study. To have a better insight into the Heterocapsa species assemblages in the Johor Strait, the diversity of Heterocapsa species assemblages along the strait was investigated based on a metabarcoding approach. Environmental DNA collected between 2018 and 2019 was used for high throughput amplicon sequencing targeting the small subunit (SSU) ribosomal RNA gene marker. The metabarcoding analysis detected three rare Heterocapsa species in the waters, H. niei, H. rotundata, and H. steinii. The results showed that Heterocapsa species assemblages varied temporally across the strait, with higher species diversity and amplicon sequence variant (ASV) read abundances detected in the Eastern Johor Strait. Although no fish/shellfish kills were sighted during the 2020 bloom event, the presence of harmful microalgal species, such as Heterocapsa minima and Karlodinium spp., urged the need for a comprehensive HAB monitoring program in the Strait to safeguard the aquaculture industry in the areas