Harmful Algal Blooms (HAB’s) are a risk
to the health of humans and marine organisms, costing the economy millions of
pounds. During 1998, 400 Californian sea lions (Zalophus californianus), were found dead along the Central California
coast, whilst numerous others exhibited signs of neurological dysfunction. At
this same time observations of a toxic diatom Pseudo-nitzshia australis, known for the production of domoic acid (DA)
were made in the area. DA had been detected in planktivorous fish and within
the body fluids of sea lions in the surrounding area, leading to the theory of
domoic acid moving through the trophic web.
Within the study by Scholin et al., (2000) a diatom bloom of P.nitzschia was examined to determine its
effect on the marine organisms of the Central Californian Coast. During early spring
of 1998 diatom communities observed in Monteray Bay were mainly comprised of
Chaetoceros spp. with a clear absence of P.nitzschia
sp., additionally tests at this time provided no trace of DA activity. In the beginning of May there began a transfer of dominant
diatom species to P.australis, which
coincided with the presence of DA. This was followed in June with transfer of
dominant diatom species from the P.australis
to Pseudo pseudodelicatissima, the
level of DA decreased in correlation with the end of the P.australis bloom. Through the use of several assays, performed
using surface seawater samples of the time, a fluctuation of nutrients could be
observed. Immediately before the P.australis
bloom occurred, an increase of NO3-, HPO4-2
and H2SiO3 was detected, possibly stimulating the growth
of the toxic diatoms.
During the bloom of P.australis the
stomachs of small fish within the area were examined, species investigated included
anchovies and sardines. The results of the examinations show the level of DA in
the fish rose and fell with the appearance and disappearance of P.australis. In addition to the DA level,
species of diatom which had been ingested were also assessed. Where high levels
of DA were observed the ingestion of P.australis
was also noted, in comparison, when low levels of DA were observed the ingestion
of other P.nitzschia strains were
noted, whilst P.australis was absent.
During the P.australis bloom, an
increase in marine mammal and bird carcases were observed along the Central
California Coast. Although this supports the effect of DA causing marine
organism death, no official surveys had been conducted on the number of marine
animal deaths, and their specific causes.
Of the 400 Z. californianus deaths,
70 were cared for by the Marine Mammal Centre (TMMC), of which 48 died. Tissues
from the 48 Z. californianus which
died were examined, and displayed unique brain and heart lesions, which have
previously been identified in studies of animals exposed to DA. Reports of sick
sea lions along the coast reduced in June at the same time the P.australis bloom declined, stopping
completely by the end of June. To assess the P.australis bloom for toxicity and its effects, DA receptor binding
assays and DNA probes were used. Liquid Chromatography –tandem mass
spectroscopy (LC-MS/MS) confirmed the presence of DA in plankton, anchovies and
sea lions; which had died during the bloom. The urine, serum and faeces of the
48 examined sea lions was analysed, DA was identified in the faeces along with P.australis, therefore ingestion of the
toxin appears to occur at the same time as the P.australis ingestion. As anchovies feed on P.australis and are a main food source of sea lions, there appears
to be a trophic transfer of the DA through the marine food web. This would
explain the deaths of higher trophic feeders opposed to those lower down the
food web. As the period of P.australis
bloom only lasted for around a month, it is clear to see the amount of damage
caused can be vast, within a short period of time.
The study provides a great deal of evidence from investigations; which
support the presence of P.australis when
DA levels are high. Repeated DA and diatom species presence studies within the
same location would offer either supporting evidence to this study, or even add
to the species of diatoms which produce DA to marine systems. Due to the nature
of HAB’s this area of study is of great importance, due to its effect on the
health of humans and marine animals, along with the negative impact it can have
on fisheries and tourist economies.
Scholin, C.A., Gulland, F., Doucette,
G.J., Benson, S., Busman, M., Chavez, F.P., Cordarok, J., Delong, R., De Vogelaere,
A., Harvey, J., Haulena, M., Lefebvrel, K., Lipscomb, T., Loscutoff, S.,
Lowenstine, L.J., Marin III, R., Miller, E. M., McLellan, W.A., Moeller,
P.D.R., Powell C.L., Rowleeskk, T., Silvagni, P., Silverl, M., Spraker, T.,
Trainer, V and Van Dolah, F.M. (2000) Mortality of sea lions along the central
California coast linked to a toxic diatom bloom. Nature 403 pp. 80-83.
Hi Emma,
ReplyDeleteGreat post! Has there been any incidents of that extend more recently? There has been a few posts of how to control HABs. Do you think any of them could be a good solution for problems like here? I wonder if NO3-, HPO4-2 and H2SiO3 may have a direct effect on the health of marine mammals, like weakening their immune system. Is DA only associated with HAB? I definately agree with you that there has to be more research done on the exact causes of death in marine mammals.
Oh my... I have just finished a post I am about to submit that is very similar to this, but on Scottish harbour seals (great minds etc...). However, my review highlights the potential increased susceptibility due to low level chronic exposure and how perhaps, the severity of HABs (depending of its exposure level), may affect the distribution and mortality of Scottish harbour seals.I'll post it now for you to read :)
ReplyDeleteHi Dean,
ReplyDeleteI enjoyed reading your post. It is clear to see that toxic blooms and their impacts on higher marine organisms are still occurring, and are a global issue rather than a country issue. I am glad that we created similar posts, it provides some great comparable information on HAB's.
Hi Tabea/Dean,
ReplyDeleteI think Dean’s post concerning the toxic bloom in Scotland has answered some of your questions Tabea. The risk to the health of marine mammals from DA also stretches to other higher marine organisms and humans, as Dean noted in his post. Dean and I both noted the requirement for further research into toxic species of P.nitzschia, especially with the limited phytoplankton monitoring. It would be interesting to look at the history of p.nitzschia blooms and see if there has been an increase in number through the years. By applying this information to multiple ecosystem models it may be possible to see any patterns or correlation with temperature, pollution or precipitation occurrences. The use of historical records such as those gathered by the SAPHOS CPR could provide some interesting information.
I am not sure about the methods of HAB control which have been examined to date; they may be a possibility if further research is conducted on their effects on the greater environment. As you stated in your post the Wolf in a Wolf Skin, the effects of VLP’s with cytotoxic compounds may be useful against specific blooms. However, whilst the identity of some microalgae is still unknown, it is not possible to tell whether the VLP’s will have a negative effect on them. Again, it is possible that the prevention or reduction of toxic blooms could be more suitable than a solution once the bloom has occurred. It would be useful to know if HAB’s provide any essential role to the marine system which would be compromised by their removal. Have you any thoughts or have you found any other interesting information on the presence of harmful blooms?