Algal blooms or Harmful Algal Blooms (HABs) are becoming more and more prevalent over the past two decades in both frequency and size, which as we are aware can be to the detriment of the ecosystems in which they occur. They consist of phytoplanktonic organisms with the most harmful being dinoflagellates and diatoms which can be toxin producing and can effect a multitude of marine organisms. In 1991 the first major event (for Monterey Bay, California) occurred where more than 200 brown pelicans and cormorants were found dead on the beaches. The cause of all these deaths was found to be a neurotoxin called domoic acid (DA) which was transferred from the diatom Pseudo-nitzschia and there have been similar incidents involving birds and sea lions since.
In 2000 the authors of this paper set out to understand if Euphausiids (krill) were a potential vector for DA in marine food webs. Krill are important members of the zooplankton grazer community and are also the primary diet of squid, baleen whales and many seabirds, if they are potential vectors DA could also affect many other marine organisms.
The sample location was Monterey Bay, California between March and August 2000 with six collection sites within the area. A 0.7m Bongo net with a 333µm mesh was used to collect the krill and the samples were frozen immediately after collection and stored at -20°C. Scanning electron microscopes (SEM) were used to determine the gut contents of the krill and to see if Pseudo-nitzschia were present. To determine if DA was present receptor binding assays were used. The authors also took samples of the water column to see if the diatoms and or DA were present and at what concentrations using cell counts and receptor binding assays. As krill were a new matrix for measuring DA measurement the authors had to also test the efficiency of the toxin extraction process before running any field samples.
The authors found that DA in Euphausia pacifica ranged from 0.1-44µg DA equiv. g-1 tissue. The DA content of krill varied with the concentration of Pseudo-nitzschia species found in the water column. The highest concentration reaching 106 cells L-1 of Pseudo-nitzschia australis.
Given the strong correlation between DA concentration found in krill and the concentration of the diatoms in the water column, the authors have provided compelling evidence for the role of krill as a potential transfer agent of the phycotoxin DA to higher trophic levels. It is difficult to record all deaths because not all of the victims will wash ashore and the authors do point out that there is still much to learn about the transmission of DA to higher level consumers and the affects DA may have to krill behaviour, development and or mortality.
A Review of: Sibel Bargu, Christine L. Powell, Susan L. Coale, Mark Busman, Gregory J. Doucette, Mary W. Silver. (2002). Krill: a potential vector for domoic acid in marine food webs. Marine Ecology Progress Series. 237, 209-216.
1 comment:
There have been a few papers since this showing just how prevalent DA is in the food chain. I have often wondered whether it might accumulate in sufficient qunatities to affect commercial fishery products (e.g anchovies).
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