Abstract
In recent years, harmful algal blooms (HABs), commonly known as red tide, have started to occur year-round in the warm tropical marine waters of Eastern Visayas, Philippines. These are a threat to public safety and cause enormous loss in industries relying on marine resources. The first step in solving this problem is to establish the distribution and succession of phytoplankton communities and harmful microalgae that exist in the region. For the first time, simultaneous monthly monitoring of the phytoplankton community was conducted in five HAB-affected bays of Leyte and Samar islands. We observed spatial differences on the environmental profiles between the five bays in the two islands and these differences may, in part, influence the distribution and abundance of the phytoplankton community residing within these areas. Diatom associated groups were prevalent in all sampling sites, however, HAB causative species were abundant in the bays in Samar during the sampling period. Five (5) genera and nine (9) species that may cause HAB were identified in all five bays. These are potential vectors for paralytic shellfish poisoning, amnesic shellfish poisoning, diarrhetic shellfish poisoning, and fish kill due to hypoxia. The correlation analysis confirmed that the majority of potential HAB vectors correlated with temperature, dissolved oxygen, rainfall, nitrate, and phosphate. The abundance of Pyrodinium bahamense observed in October to November in Samar coincided with several red tide alerts announced by the region’s fishery agency. This however, was never observed to dominate the phytoplankton community. Instead, the following diatoms dominated the five bays; Skeletonema, Pseudo-nitzschia, Bacteriastrum, Chaetoceros, Rhizosolenia and Thalassionema. This is a pioneering study that shows a simultaneous snapshot on the community structure and environmental profiles in these five bays in Eastern Visayas in 2020–2021. It discusses the effects of mariculture to its phytoplankton community and vice versa. Relationships between different phytoplankton species were further observed. This contributes to the knowledge of phytoplankton ecology in warm waters which is necessary to understand future phytoplankton ecosystems affected by sea temperature rise due to climate change.
Highlights
Phytoplankton are known as biological indicators of water and its ecological health status (Wu, 1993; Roelke et al, 2003)
The distinctness observed between these bays provides insights on the structure of the phytoplankton community present in these areas, especially on species that cause harmful algal blooms (HABs)
The diatoms that dominated in the bays were Skeletonema, Pseudo-nitzschia, Bacteriastrum
Summary
Phytoplankton are known as biological indicators of water and its ecological health status (Wu, 1993; Roelke et al, 2003). Phytoplankton respond quickly to different environmental parameters including physical (i.e., light, temperature, rainfall), chemical (inorganic carbon, nutrient, dissolved oxygen), and biological (competition and predation) factors (Maddux and Jones, 1964). These factors have implications in their growth, abundance, availability, and distribution. These understandings on phytoplankton ecology mostly come from studies in temperate areas Knowing which of these aspects exert a greater influence to the behavior of phytoplankton species in tropical marine waters becomes exceedingly important in understanding the condition of the environment they proliferate, especially in the context of harmful algal blooms. This will provide knowledge on what to anticipate when seawaters warm due to climate change
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