Blooming Marvellous
Increased
knowledge of the microbial world and the factors which influence it are essential
to assess the effect of present and future climate change on the marine system.
Marine microbes form much of the primary production biomass within the oceans
and are an essential lower trophic level prey, any alteration of their numbers
or health can have a negative impact upon other trophic levels. Climate change can
alter the ocean temperature which changes the environmental conditions of the
marine ecosystem. This can create a more suitable environment for previously less
dominant species and cause shifts in the marine ecosystems. These shifts can
have detrimental or beneficial effects on existing marine organisms and marine
productivity.
The Olson et
al paper addresses the existing theory that parasite and virus infections influence
phytoplankton population dynamics. The presence of parasites among
phytoplankton communities (specifically in this study; diatoms) are key to increased
host mortality and bloom decline. Over a period of seven years from 2007 to
2013, the study monitored the presence and interactions of a nanoflagellate
parasite within the host G. delicatula located at 41° 19.5’ N, 70° 34.0’ W, off shore from Marthas’ Vineyard, Massachusetts,
USA. This provides further
insight into the mechanisms which drive diatom bloom fluctuations.
Through the morphological
examination of the parasite within two of its life stages, identification
within the G. delicatula was possible. The author therefore deemed the presence
of one or more parasites within the G.delicatula as an infected cell. This
permitted an evaluation of infection to be visual and straight forward with
microscopic examination. The identification of the parasite taxonomically was
not possible; the author consequently compared the morphological and life cycle
characteristics with the known parasite Cryothecomonas aestavalis. Parasite infection
of G.delicatula at greater than 10% was identified in every year of the study,
leading the author to surmise that the presence of the parasite within blooms
of G.delicatula “further suggests that infection is ecologically
important”.
Mortality of
the diatom due to parasite infection was at a greater level than that
experienced through zooplankton predation, this reinforced the theory of
parasitic infection being a microbial control of diatom population
fluctuations. The data tell us that the largest blooms of G.delicatula were present when parasites were absent or very low in
number, primarily in winter when temperatures are lower than 4°c. Occasional
incidences of parasite presence during temperatures of 4°c were experienced,
however, this only happened when temperatures were fluctuating around 4°c and
above, or high numbers had been present before a temperature drop. In further
support of the parasite effect on G.delicatula
populations, when the
temperature was below 4°c and parasite numbers dropped the G.delicatula population
began to increase. The author believes that cold temperatures push the lethal
boundaries of the parasite within its environment, permitting the G.delicatula to
form blooms for longer periods of time. Light, temperature, nutrient and
zooplankton are also deemed as contributing factors to population dynamics,
however, winter blooms appear to be prominently controlled by the parasite
presence.
With global temperatures rising via climate change,
warmer seas are a given. The environmental change could permit the G.delicatula parasite to survive within
the winter season restricting
G.delicatula
populations from growing. The result could be a vast ecosystem shift due to a
loss of major primary biomass from the base of the food web, leading to the
possible loss of predators and even trophic levels within the marine system.
Further study, preferably based upon the effect of climate change on marine
microbial parasites would be beneficial. Additionally, the impact of
temperature variation upon parasites specific to different phytoplankton
species could provide further insight to the effect of climate change on the
microbial world.
Reference
Olson, R., Peacock,
E., Sosik, H. (2014) Parasitic infection of the diatom Guinardia delicatula, a
recurrent and ecologically important phenomenon on the New England Shelf. Marine Ecology Progress Series. 503,
1-10.
Hi Emma
ReplyDeleteThanks for posting an interesting article on an area of microbiology that I'm not very familiar with. I was wondering if, with future climate change and the predicted rise in sea surface temperatures around coastlines, that the upper latitudinal boundary of G. delicatula would move northwards into colder waters where the parasite would be unable to survive? This may become a species that is more common in Arctic waters in the future.
Anita
Hi Emma,
ReplyDeleteThank you for the interesting review, linking our understanding of microbiology with climate change is extremely important.
I have to say one downside of the study was that Olson et al., could not identify the parasite, because if they knew the parasitic species they could then see which other hosts it occupies and if it has the same effects, as in the paper they seem very unsure whether the parasite is actually species specific Quote: ''of a parasite that seems specific to this host''. It will be useful for a study to confirm whether Guinardia delicatula blooms increase with a warmer climate too. A study by Sommer and Leqandowska, 2011 have shown that warmer waters actually decrease diatom biomass as zooplankton grazing increases as well, so does this lead to accusations that diatoms will decline in abundance with warmer waters regardless if parasites can survive more seasons? Or, as this parasites ecology has not been specified, will this parasite then go on to inhibit the zoo plankton grazers, which could lead to much larger impacts?
I thoroughly agree with your comment, that more research like this needs to be done using other members of the phytoplankton, for example, dinoflagellates. As harmful dinoflagellate blooms are predicted to rise with climate change (Dolah, 2000), the increase in mortality by parasites could actually be beneficial? Even the potential of artificially manipulating these blooms by introducing parasites could be considered- maybe this is a bit too far! What do you think?
I feel this paper has opened up further insight into how many more implications global warming could have on the ocean ecosystem! There also needs to be studies carried out on how lower pH and the change in global circulation could change microbiological ecosystems, which very closely links with Tom's recent blog post 'Distribution by Depth, Deep Trouble?'.
Thankyou, Elyssa
Sommer, U., & Lewandowska, A. (2011). Climate change and the phytoplankton spring bloom: warming and overwintering zooplankton have similar effects on phytoplankton. Global Change Biology, 17(1), 154-162.
Van Dolah, F. M. (2000). Marine algal toxins: origins, health effects, and their increased occurrence. Environmental health perspectives, 108(Suppl 1), 133.
This is a good point Anita, the shift of species latitudinal range is a possibility for G.delicatula due to increased ocean temperatures. I believe this would be difficult to assess with the G.delicatula parasite, as its identification has not been affirmed, restricting comparison with other closely related parasites. Further experimentation of temperature effect upon the parasite would provide more information. Although it is worth bearing in mind, if the temperature rises allowing the northward movement of G.delicatula, it will probably also be enough of an increase for the parasite to continue to survive. I will keep you up dated with any further information relevant to your question that I find. I will be adding a reply to Elyssa which you may also find interesting
ReplyDeleteThanks, Emma
I am so sorry Elyssa, after our chat this morning I checked and this reply never got posted somehow. My fullest apologies
ReplyDeleteI am glad you liked the subject Elyssa, you have had lots of thoughts from the look of it. Through personal experience and other papers, I can confirm that the identification of a parasite can be time consuming and expensive. Additionally due to the difficulty of identifying parasites through microscopy (the small size of some parasites reduce the ability to identify key morphological features) many different methods need to be employed. The identification of parasites can be attempted using flow cytometry, DNA analysis or cellular stains, (Olson et al, 2014) although this work alone can take months.
Warmer ocean surface temperatures and increased grazing by zooplankton as a top down control, could well reduce the G.delicatula bloom numbers, however, laboratory experimental results can differ greatly to experiments conducted in the field. By conducting experiments in the field, the addition of uncontrolled physical and biological stressors permit a realistic view of the ecosystem effect upon the experiment. In the laboratory, conditions are sterile with very little uncontrolled physical or biological stressors. Taking this into consideration the increase in warm temperature may increase zooplankton grazing, yet may also increase the predation of the zooplankton by other marine organisms, reducing the zooplankton numbers. The effects of the zooplankton as a grazer on G.delicatula could possibly be explored, although this is not addressed in this paper.
It is unlikely that the G.delicatula parasite will move on to parasitize grazing zooplankton, as host shifts of any large extent are deemed to be a rare occurrence for parasites, (Bass et al, 2014). I believe that a shift from phytoplankton to zoo plankton would require many adaptation of the parasite, what do you think?
Bass, D., Bulman, S., Kirchmair, M and Neuhauser, S. (2014) Cross-kingdom host shifts of phytomyxid parasites. BMC Evolutionary Biology. 14, Article 33.
Olson, R., Peacock, E., Sosik, H. (2014) Parasitic infection of the diatom Guinardia delicatula, a recurrent and ecologically important phenomenon on the New England Shelf. Marine Ecology Progress Series. 503, 1-10.