Seasonal occurrence of the potentially toxic benthic armoured dinoflagellates in Nha Trang Bay, South Central Coast of Viet Nam

Seasonal variations of the potentially toxic benthic dinoflagellates (bHABs) were studied during one year in the Bai Lan, Nha Trang Bay, South Central Viet Nam. Physical conditions (temperature, salinity, photosynthetically active radiation) and nutrient (NO3-N, PO4-P, DIN) concentrations were measured. The quantitative density of bHABs on the window screen sampling devices was determined in a range of seafloor types (dead coral, sand, and seaweeds) and retrieved within 24 h after placement. Results showed that twenty-one species of bHABs were recorded with Coolia malayensis, Ostreopsis lenticularis, O cf. ovata, O. siamensis, Prorocentrum emarginatum, and P. lima occurring throughout the year. The cell density of bHABs showed unclear seasonality, with Bystmatrum spp., Gambierdiscus spp., Ostreopsis lenticularis, and Coolia spp. absent in November 2020, concurrent with a peak in rainfall. The non-metric multidimensional scaling (NMDS) analysis showed that there was a high similarity between Gambierdiscus abundance and phosphate content. The densities of O. lenticularis, O. siamensis, and P. emarginatum were, in contrast, more closely associated with photosynthetically active radiation (PAR). Ostreopsis cf. ovata was less influenced by environmental conditions. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Seasonal variations of potentially toxic benthic dinoflagellates (bHABs) were studied in Bai Lan, Nha Trang Bay, South Central Vietnam for one year. Physical conditions and nutrient concentrations were measured. The study identified 21 species of bHABs, with some species occurring throughout the year. The cell density of bHABs did not show clear seasonality, but some species were absent during high rainfall. Different species of bHABs were associated with different environmental conditions.