This study looked at the general hypothesis that domoic acid (DA) contaminates benthic organisms during local blooms of Pseudo-nitzchia australis, which is a widespread toxin producer along the west coast of the United States. Trophic transfer and uptake of DA into the benthic food web was also tested.
DA is a water soluble phycotoxin which has a rigid analog of the amino acid glutamate that binds to glutamate receptors causing neuro-excitation or cell degeneration in vertebrate brains. In high concentrations, DA can also cause disorientation, memory loss, seizures, comas and death.
The study took place in Monterey Bay, California. Eight representative species from four trophic groups (filter feeders, predators, scavengers and deposit feeders) from the benthic food web were sampled. It was found that both P. australis and P. multiseries were occasionally quite abundant on beach sites. During the study period, two major DA-producing bloom events occurred, with DA being detected in all 8 of the benthic species collected. The levels of DA in each body varied within species and temporally in relation to DA-producing bloom events. The highest average DA concentrations during bloom periods were found in the filter feeders, the others trophic groups all had moderate to low average concentrations of DA. During DA-producing bloom periods, the lowest concentrations of DA were detected in the deposit feeders.
Overall, the results demonstrate the potential for accumulation of substantial Da reservoirs in diverse trophic groups. All species sampled were contaminated in some way. The reason for the highest levels of DA being detected in the filter feeders could be because they feed on particles. Algal blooms transported onshore can supply toxic food to filter feeders.
This study shows that, under certain bloom conditions, a range of benthic invertebrates and bottom-feeding fish can represent potent toxin source for higher level marine predators. The duration and frequency of DA-producing Pseudo-nitzchia blooms is still unknown. Contamination from DA of benthic communities is often overlooked. However, keystone predators have shown signs of DA poisoning, meaning that large populations are at risk. Better ecosystem monitoring, including relevant benthic species is required, in order to forecast harmful algae.
Kvitek R.G., Goldberg J.D., Smith G.J., Doucette G.J., Silver M.W. 2008. ‘Domoic acid contamination within eight representative species from the benthic food web of Monterey Bay, California, USA’. Marine Ecology Progress Series, 367, 35-47.
http://seafloor.csumb.edu/publications/m367_KvitekEtAl08.pdf
Hi Sophie,
ReplyDeleteDid the authors mention which species they used? Ie. were they economically important species? If a species that is commonly consumed by people eg. mussels were used then this would make the study much more relevant! Also, did the predators feed on any of the other species that were sampled? And did they mention if they therefore had higher levels of DA?
Thanks,
Robyn
The species used were Emerita analoga, Urechis caupo, Citharichthys sordidus, Nassarius fossatus, Pagurus samuelis, Neotrypaea californiensis, Dendraster excentricus and Olivella biplicata. These species are not eaten by humans but serve as important connections to higher trophic levels. Some benthic species contain fish that are marketed commercially but they are not used in this study. Shore birds, surf fish and sea otters have all been known to feed on some of the species used in the study. They didn’t actually test these predators, however it is mentioned that they are at risk of contamination from DA.
ReplyDeleteHi Sophie,
ReplyDeleteI actually reviewed this paper in January! One of the points observed was that the transfer of DA noted here for benthic organisms was different than for pelagic: in the pelagic food web, the concentration of DA increases with each trophic level. For instance, transfer of DA from diatoms to anchovies to sea lions (Ramsdell and Zabka, 2008).
In this study the feeding style seemed to impact the concentration of DA in the organism with filter feeders containing the highest concentrations. I presume this is due to the natural sinking of phytoplankton creating higher densities of the toxin producing Pseudo-nitschia species. Benthic filter feeders here will take up a large proportion of these, thereby explaining the high concentrations despite them belonging to a low trophic level. Pelagic filter feedings will naturally intake less DA from their environment, therefore the increase in concentration of DA up the trophic levels is observed, unaffected by this anomaly that occurs in the benthic food web.
Another point I just thought of was if the build-up of the toxin could be advantageous to the organisms in some way, considering it is not causing fatalities at its current level. For example, poisonous frogs display particular colours in order to ‘warn’ predators that they are dangerous due to toxins. It would be interesting to see if the toxins build up acting as a predatorily deterrent for some species that suffer fatality after consumption.
One final point, which is admittedly a bit ‘out there’. Apparently harmful algal blooms like this are increasing worldwide (Goldstein et al, 2008). CO2 levels in the atmosphere have also been increasing, and more atmospheric CO2 is being dissolved into marine environments due to temperature increases. Photosynthetic organisms, such as these, flourish under these conditions. I wonder if the deaths of marine organisms caused by the toxins of these organisms are linked with CO2 increases. Yet another reason to stop burning fossil fuels!
The papers I referred to can be found here:
Goldstein et al (2008) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2593718/
Ramsdell and Zabka (2008) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2525490/
Megan
That's all really interesting!
ReplyDeleteI wonder if there are seasonal variations depending on the water conditions (stormy, calm, etc.) and whether they affect the amount of DA that is able to sink, as well as when the blooms occur. It would also be really interesting to know how much it bioaccumulates and whether this eventually leads to the death of higher trophic level organisms (those that exhibit some level of tolerance to the toxin, anyway).
Robyn
Ah right, that is interesting! Thanks for the extra information on this Meg!
ReplyDeleteSophie
Hi Robyn,
ReplyDeleteI actually read a paper yesterday stating that the seasons are partially responsible for the blooms, hence why they occur roughly annually in some regions, such as those investigated in this paper. It is interesting that temperature declines impact the division of cells however they do not degrade DA (sadly I cannot find this source again!). This could explain why in some cases the toxin remains after the bloom, or indeed when a bloom cannot be detected.
Megan