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The link between shrimp farm runoff and blooms of toxic Heterosigma akashiwo in Red Sea coastal waters

Mohamed Z.A., Al-Shehri A.M.

Oceanologia

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2012

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No. 54 (2)

287-309

EN

In May 2010 a copious bloom of the raphidophyte Heterosigma akashiwo was observed for the first time in Red Sea waters off the coasts of Saudi Arabia. This bloom was confined to an area where water and phytoplankton flow freely between the sea and a shrimp farm. The phytoplankton density and physico-chemical characteristics of the sea water were therefore investigated weekly at bloom and non-bloom sites in order to gain insight into the environmental factors prevailing at the bloom site and their link with the shrimp farm runoff. The bloom site showed higher nutrient concentrations than the non-bloom site, indicating the possible role of the shrimp farm in flushing nutrients into this site. The bloom appeared on 27 May, coinciding with a decrease in salinity (< 30 per mille) and an increase in temperature (> 19°C). The results of toxicological assays showed that both bloom samples and batch cultures of H. akashiwo were toxic to Artemia salina and exhibited haemolytic activity with respect to rabbit erythrocytes. Bloom samples showed a higher toxicity (LC50 = 8.9 × 104 cells ml-1) and haemolytic activity (EC50 = 3.64 × 104 cells ml-1) than the batch cultures (LC50 = 11.6 × 104 cells ml-1, EC50 = 5.1 × 104 cells ml-1). In the light of the results of this study, the link between H. akashiwo blooms and shrimp farm runoff should be considered during the monitoring of Red Sea coastal waters for the presence of harmful algal blooms.

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Occurrence and germination of dinoflagellate cysts in surface sediments from the Red Sea off the coasts of Saudi Arabia

Mohamed Z.A., Al-Shehri A.M.

Oceanologia

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2011

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No. 53 (1)

121-136

EN

The distribution and abundance of dinoflagellate cyst assemblages were investigated in surface sediments from south-western Red sea coasts of Saudi Arabia at six sites during March 2010. A total of 19 taxa of dinoflagellate cysts were identified from all sites. The sampling sites showed a similar cyst assemblage, but they differed in total cyst abundance (3 to 4083 cysts g-1 dry weight). Cyst abundance was strongly correlated with sediment characteristics, the highest numbers being recorded in sediments with large contents of organic carbon, silt and clay. Cyst assemblages were dominated by cysts of potentially toxic species, including Cochlodinium polykrikos, Prorocentrum minimum, Dinophysis acuminata, Alexandrium catenella and Scrippsiella trochoidea. Most cysts germinated successfully at different rates at 15 and 25°C. This study suggests that surface sediments from all Saudi Red Sea coasts should be monitored for the presence of dinoflagellate cysts to give ample warning of the presence and abundance of toxic species in a given area

3

Toxin-producing blooms of the cyanobacterium Microcystis aeruginosa in rainwater ponds in Saudi Arabia

Al-Shehri A.M.

Oceanological and Hydrobiological Studies

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2010

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Vol. 39, No.4

171-187

EN

The present study describes for the first time the toxin production by Microcystis aeruginosa blooms in three rainwater ponds in Saudi Arabia. The cell density of M. aeruginosa correlated with chlorophyll-a, temperature and nutrient concentrations. Microcystis blooms produced the hepatotoxin microcystin (MCYST) with concentrations of 0.988-3.04 mg g-1 dry weight, and a toxin profile consisting mainly of MCYST-RR, -YR and -LR. MCYSTs were also detected in pond waters at levels exceeding the WHO guideline value (11.2-34.6 μg l^-1). The study suggests the monitoring of toxic cyanobacteria in such potable water sources to protect the public from potent toxins.