Mapping and Modeling Harmful Algal Blooms

(8/17/2019 12:00:00 AM)

Algal blooms are caused by a combination of several factors including water flow intensity, water temperature, water mixing, amount of sunlight, and salinity levels.  See the figure below for an explanation of the factors.

Example 1: Occurrences of harmful algal blooms (HABs) associated with ocean environments in the South China Sea

Abstract

Harmful algal blooms (HABs) occur frequently in the South China Sea (SCS), causing enormous economic losses in aquaculture. We analyzed historical HAB records during the period from 1980 to 2003 in SCS. We found that HABs affected areas have expanded and the frequency of

HABs varied during this period. The seasonal and annual variations, as well as causative algal species of HABs are different among the four regions. Areas with frequent HABs include the Pearl River Estuary (China), the Manila Bay (the Philippines), the Masinloc Bay (the Philippines), and the western coast of Sabah (Malaysia). HABs occurred frequently during March–May in the northern region of SCS, May–July in the eastern region, July in the western region, and year-round in the southern region. Among the species that cause HABs, Noctiluca scintillans dominated in the northern region, and Pyrodinium bahamense in the southern and eastern regions. Causative species also varied in different years for the entire SCS. Both P. bahamense and N. scintillans were the dominant species during 1980–2003. Some species not previously

recorded formed blooms during 1991–2003, including Phaeocystis globosa, Scrippsiella trochoidea, Heterosigma akashiwo, and Mesodinium rubrum. Variations in HABs are related to various regional conditions, such as a reversed monsoon wind in the entire SCS, river discharges in the northern area, upwelling in Vietnam coastal waters during southwest winds and near Malaysia coastal waters during northeast winds, and eutrophication from coastal aquaculture in the Pearl River estuary, Manila Bay, and Masinloc Bay.

Example 2: Remote sensing oceanography of a harmful algal bloom off the coast of southeastern Vietnam

Abstract

Harmful algal blooms (HABs) in the southeastern Vietnamese coastal waters have caused large economic losses in aquaculture and wild fisheries in recent years; however, there have been few oceanographic studies on these HAB events. The present study reports an extensive HAB off southeastern Vietnamese waters during late June to July 2002 with in situ observations and analyzes the oceanographic conditions using satellite remote sensing data. The HAB had high chlorophyll a (Chl a) concentrations (up to 4.5 mg m_3) occurring ~200 km off the coast and ~200 km northeast of the Mekong River mouth for a period of ~6 weeks. The bloom was dominated by the harmful algae haptophyte Phaeocystis cf. globosa and caused a very significant mortality of aquaculture fish and other marine life. In the same period, sea surface temperature (SST) imagery showed a cold-water plume extending from the coast to the open sea, and QuikScat data showed strong southwesterly winds blowing parallel to the coastline. This study indicated that the HAB was induced and supported by offshore upwelling that brings nutrients from the deep ocean to the surface and from coastal water to offshore water and that the upwelling was driven by strong wind through Ekman transport when winds were parallel to the coastline. This study demonstrated the possibility of utilizing a combination of satellite data of Chl a, SST, and wind velocity together with coastal bathymetric information and in situ observations to give a better understanding of the biological oceanography of HABs.

Example 3: Ideas of application remote sensing techniques for algal bloom detection in marine regions of Vietnam

Abstract

Algal bloom is a rapid increase of the community of algae. It can cause several negative impacts on environment and toxicity effects. Therefore, detection of algal bloom considers of preventing environment impacts. This paper reviewed the remote sensing techniques for algal bloom detection from ocean color images, including peak shift, red tide index and bio-optic methods. The paper also discussed the advantaged and disadvantaged potential application in the case of Vietnamese waters. By the results of testing algal bloom detection in the southern marine regions of Vietnam, the paper suggested that the bio-optic method could be used, but it is necessary to determinate the experiment constants of absorption and back-scattering of specific algal species.

VIFEP  (USAID workshop)