Western Indian Ocean Journal of Marine Science

Assessment of heavy metals and aflatoxins in cottonii and spinosum seaweeds from Tanzania

Lilian D Kaale — 2025-03-14

There has been little research on heavy metals and aflatoxins in Tanzanian seaweeds. Concentra- tions of lead (Pb), cadmium (Cd), total mercury (THg), and methyl mercury (MeHg) were meas- ured in cottonii (Kappaphycus alvarezii) and spinosum (Eucheuma denticilatum) seaweeds from Tanzania. Seaweeds were collected in February 2024 from Tanga, Pwani, and North Unguja. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to assess Cd and Pb, a direct mercury analyzer (DMA-80) was used to analyze THg and MeHg, and high-perfor- mance liquid chromatography was used to determine anti-aflatoxigenic activity. Heavy metal concentrations were highest for Cd, followed by Hg, Pb and MeHg, and varied significantly (p<0.05) between species and sampling locations. The concentrations of Cd, Pb, and MeHg were below safety thresholds set by the European Union and Codex Standard, while THg concentra- tions exceeded Codex limits but were within European Union limits, and can therefore safely be consumed. Aflatoxins were not detected in the seaweed samples. Further research on heavy metal concentrations and moisture stability in Tanzanian seaweeds is recommended, over a period of at least a year.

Assessing the potential for red seaweed Asparagopsis taxiformis aquaculture in Seychelles

Bas de Vos — 2025-03-26

Asparagopsis taxiformis macroalgae can potentially reduce methane emissions when fed to ruminants, thus reducing the emission of greenhouse gasses into the atmosphere. Literature indicates water temperatures above 24 °C limit A. taxiformes growth rates during culture, however, it grows wild in Seychelles where water temperatures range from 25 to 31.5 °C. The feasibility of cultivating the local strain of A. taxiformis in Seychelles was investigated, focusing on growth rates at higher temperatures and bromoform content, the compound responsible for methane reduction. Two tetrasporophyte growth trials were conducted in photobioreactors at 24 °C, 26 °C, 29 °C and 32 °C. In the first trial, unacclimated specimens showed poor growth, with no significant differences between temperatures. In the second trial, daily growth rates of acclimated specimens were 3.98 % across all temperatures, including 32 °C, where temperature did not significantly affect growth. Bromoform concentrations were lower than expected, likely due to storage conditions prior to sample processing. The local strain of A. taxiformis in Seychelles may therefore be adapted to higher temperatures, with potential for aquaculture. Further research to optimize cultivation techniques and ensure adequate bromoform content is required.

Reproductive characteristics of the big blue octopus, Octopus cyanea (Gray 1849) in Zanzibar coastal waters, Tanzania

Amini Ismail Hamad — 2025-04-18

The big blue octopus, Octopus cyanea (Gray 1849) is heavily fished in Zanzibar coastal waters, yet several aspects of its biology remain unstudied in the area. The reproductive biology of O. cyanea (Gray 1849) was investigated, including sex ratios, length-weight relationships, size at maturity, and seasonal variation in maturity and spawning activity. Sampling of specimens caught by local fishers was conducted monthly at four sites. Octopus size and weight were measured and the sex determined, whereafter their gonads were extracted and staged. Female octopuses dominated the sex ratio across most size classes and seasons. Males reached sexual maturity at a smaller size than females and mature individuals of both sexes were present throughout the year, suggesting continuous spawning activity. Based on the gonadosomatic index (GSI), peak spawning periods were in June and October. The new insights into the reproductive dynamics of O. cyanea are important for fisheries management efforts and effective conservation of the species.

Comparative bioactivity analysis of hard corals: antioxidant and antimicrobial responses three years after the MV Wakashio oil spill in Mauritius

Nadeem Nazurally — 2025-04-18

In 2020, the MV Wakashio spilled 1000 tons of low-sulphur fuel oil along the south-east coast of Mauritius. This study aimed to compare the bioactivity of healthy hard corals with those affected by the oil spill, three years after the incident. Acropora selago, Pocillopora damicornis, Millepora alcicornis, and Porites rus were collected from affected and unaffected regions. Extracts were prepared through solvent extraction and fractioning with ethyl acetate and hexane, followed by antioxidant activity analysis using the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay and antimicrobial testing via disc diffusion. All species exhibited significant antioxidant activity (p < 0.05), with P. rus showing the highest radical scavenging activity (RSA), 9.04 % and crude extracts demonstrating the strongest overall bioactivity. Bacillus subtilis, Staphylococcus aureus and Escherichia coli were resistant to all extracts. Only crude extracts of A. selago, M. alcicornis, and P. rus (among other fractions) could inhibit Pseudomonas aeruginosa, with A. selago exhibiting the largest inhibition zone (10.56 mm). No significant bioactivity differences were found between corals of oil-affected and unaffected regions, possibly due to the floating and rapid dispersion of low-sulphur fuel on the water surface. These findings highlight the pharmaceutical potential of hard corals and suggest further research on species-specific and environmental factors.

Long time no see - 117 years after its first and only record Praebebalia extensiva Rathbun 1911 (Decapoda, Leucosiidae) was collected from Saya de Malha

Bella Galil — 2025-04-18

The leucosiid crab Praebebalia extensiva Rathbun 1911 was formerly known from six specimens collected off Saya de Malha, Providence Island and Seychelles by the Sealark Expedition in 1905. More than a century later the Monaco Expedition in the Indian Ocean recovered 17 additional specimens. The species is redescribed and a colour photo provided.