Global sea temperatures are expected to rise by at least 1.4 degrees by 2100, and could rise by much more. This could have severe consequences on the marine ecosystem, and valuable ecosystem services eg fisheries. Harmful algal blooms (HABs) are of particular interest when studying the effects of climate change on these processes as they occur more frequently in higher temperatures. Climate change has also been shown to affect precipitation, which in the case of rivers such as the Rhine can cause an increase of the levels of fresh water entering coastal regions, which could in turn affect salinity. This could also increase the occurrence of HABs.
For the purposes of this investigation, a high-end rise in temperature was assumed (4oC). Several species of phytoplankton were assessed under changing salinity, temperature and daily irradiance. Emphasis was placed on harmful phytoplankton, as these have the most economic and environmental importance. The species tested were Prorocentrum micans, Prorocentrum minimum, Pseudonitzschia multiseries, Fibrocapsa japonica, Chattonella antique and P. globosa as these are the species found in recurrent HABs in the Dutch coastal zone. Also tested were the non harmful species: Skeletonema costatum and Rhodomonas sp.
This experiment involved two scenarios: one to represent the present day summer sea water temperatures in the area (18-22oC) and one to represent the predicted rise by the year 2100. In each experiment three groups of all the phytoplankton species were tested - one from the top of the water column (0-4m), one from the bottom (5-19m) and one mixed group (taken from the entire column). These were cultured and left to grow. The effect of salinity on phytoplankton growth was also separately tested in this investigation. The specimens were cultured under today’s salinity conditions and under the decreased salinity conditions expected for the year 2100.
The results showed that under present (today’s) mixed conditions, all phytoplankton species grew well. In the present surface conditions, phytoplankton growth increased and in present bottom conditions, the growth decreased to practically zero. In the year 2100 mixed group, most species were not affected, however, 2 species showed signs of thermal stress. P.globosa experienced a decreased growth rate of 32%, and P.multiseries completely died off at temperatures of above 22oC. Under surface conditions, the same species died off again, Rodomonas sp. and S. costatum showed a rate of growth similar to that of the present day, while the harmful species experienced a vastly increased growth rate. Any changes to the lower water column group are not mentioned, leading to the assumption that there was no difference between the two groups. There was also no difference in phytoplankton growth at all in conditions of changing salinity.
This investigation shows that there is a possibility of more HABs in the Dutch coastal region as sea surface temperatures rise in the future. The authors have identified several uncertainties with this experimental design however, as all variables are based on predictions that are far from certain. Phytoplankton could also react differently in situ, as the conditions within their natural ecosystem could be different to those in the laboratory.
With further research, the findings in this paper could be applied to many other areas experiencing harmful algal blooms.
A review of Peperzak, P. (2003) Climate change and harmful algal blooms in the North Sea, Acta Oecologica, 139-144
3 comments:
This is a very interesting topic leading me thinking to some considerations.
In some species there are toxic and non toxic strains: this can occur because toxicity is caused by the presence of symbionts.
Also Cyanobacteria can produce toxic compounds, eg freshwater Aphanizomenon flos-aquae.
Further,an increases in the distribution of algal species producing PSP has been detected during the last decades in tropical(warm!)water.
The stratification tipical of warm water is a barrier to nutrient contribution from the deep aphotic to the shallow euphotic zone,having several consequences on algal blooms. Under stress due nutrients limitation (P limitation, for instance) bacteria compete with algae for nutrients uptake. This stress condition promotes the Photosynthetic extracellular release (PER) by algae:it means that phytoplancton release the products of photosynthesis,increasing colloids and particulated organic matter content in the water. In some regions of Mediterranean sea,PER is a critical factor for the formation of huge aggregates called "mucillagine",which are not toxic by themselves but they are harmful for benthic organism,aquaculture,tourism and fishing.
Wendy A. Higman, David M. Stone, and Jane M. Lewis (2001) Sequence comparisons of toxic and non-toxic Alexandrium tamarense (Dinophyceae) isolates from UK waters. Phycologia: May 2001, Vol. 40, No. 3, pp. 256-262.
Valentina makes some interesting comments that complement the paper on marine micilage by Danovaro et al., reviewed by Nikie on 25 Oct. It is pretty certain that we are going to encounter more problems like this. Rapid changes are occurring in the North Sea and especially the Baltic.
I had missed Nikie's review of Danovaro et al. paper when she posted it. I read it and found interesting.
Anyway,i found another interesting paper of as much well-prepared italian researchers: they detected an important relation between meteorological and oceanographic conditions and massive mucilage formation in North Adriatic Sea. I hope it becomes available,so i can delve into this paper and let people know more on mucilage phenomenon and its ecological consequences.
De Lazzari, A., Berto, D., Cassin, D., Boldrin, A. and Giani, M. (2008), Influence of winds and oceanographic conditions on the mucilage aggregation in the Northern Adriatic Sea in 2003–2006. Marine Ecology, 29: 469–482. doi: 10.1111/j.1439-0485.2008.00268.x
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