Harmful dinoflagellate blooms caused by Cochlodinium sp.: Global expansion and ecological strategies facilitating bloom formation:

 

 

As algal blooms are currently being studied in our lectures I figured this study/review was relevant. As dinoflagellates are one of the ever present causes of blooms and the Cochlodinium sp. is no exception, over the past two decades it has been witnessed that there has been a massive and global expansion of harmful algal blooms by this genus. These blooms are characterised by large red blooms that are easy to distinguish and recognise.

 

There are over 40 different species within this group; however this review is looking at only two of them as these are the ones that are the main harmful algal bloom producers, C.polykrikoides and C.fulvescens.  In the 1990’s these blooms were observed and recorded only in South East Asia and North America, nowadays the blooms have spread globally occupying areas such as the whole of Asia and Europe so a mass expansion has occurred within the past two decades.

 

The blooms caused by these two species are strongly ichthytoxic which essentially means poisonous to fish, however they do still cause mortality within other marine organisms. The compounds responsible for these blooms are still unknown and due to the recent expansion and sheer lack of evidence there is a lot less known about this species compared to other harmful algal bloom causing species.

 

This review in essence compares lots of studies and aspects that have been done on this species to try and come to a conclusion as to why this expansion has occurred so suddenly, obviously the key observations made are that there is an increase in anthropogenic factors and/or climate change, and this may be the case but as mentioned previously due to the sheer lack of evidence no firm conclusions can be drawn as yet.  The general methods used to study these blooms fall into 3 categories; microscopy, molecular techniques and remote sensing.

 

The areas this review looked at to study were temperature, salinity and grazing. The comparisons found that both species showed clear overlaps in temperature and salinity tolerances, with the general habitat and conditions for optimum growth being moderate temperatures and high salinities, these conditions are often associated with offshore tropical and sub-tropical areas. It was found that by altering their chain length these species could survive in altered conditions down to a low temperature of ten degrees but no lower, and all that they showed was mild stress. To further back this up it was observed in North America that some species preferred and could survive in areas that had cool water intrusions and more brackish salinities. So the results present the fact that just due to alterations physically these species have been able to relocate to new niches and survive with only a minor metabolic cost.

 

Regarding the grazing concept, as in any environment this species are mildly grazed but it was seen that when there is a lack of top down control grazing, or even a minor amount of grazing this species thrived by upping their chain length and therefore size, so it doesn’t appear that grazing or predation affects the growth or location of these blooms, evidently if there were predators in a large scale this might affect the locations but there haven’t been any noted. Finally it has been noted that under different conditions these two species have a wide range of nutrient strategies and so have a lot of flexibility, this leads to the hypothesis that with the fact that nutrients then shouldn’t be a problem they can survive and move out of their general habitat.

 

This hasn’t been studied as to whether this was a recently inherited thing or whether it has always been present but it poses a possible explanation with the fact that there is a such a large window of variability with optimum conditions I believe (and so do the authors) that this is how and why the dinoflagellate blooms have been able to thrive elsewhere. Especially if climate change is a driver, then an increase in water temperature will lead to this species being able to thrive a lot more, it obviously depends on what the salinity levels do but all that can be hypothesised is that with an increase in temperature there will be a dramatic increase in the abundance of these species and therefore algal blooms.

 

Although it is only a review and to be frank there isn’t that much out there as this review is from 2012 it is still important and poses a lot of useful information and potential for future studies. It’s only an up and coming field of study, but if these blooms are spreading and getting a sort of resistance and tolerance to changing conditions then it needs to be heavily studied before the whole range of oceans and their inhabitants are in trouble.

 

Reference:

 

Kudela,R., Gobler,C. (2012)  Harmful dinoflagellate blooms caused by Cochlodinium sp.: Global expansion and ecological strategies facilitating bloom formation. Harmful Algae 14, 71-86.

 

 

The paper can be located at this website:

 

http://www.sciencedirect.com/science/article/pii/S1568988311001430