A Modelling Study of Emiliania huxleyi in the NE Atlantic

Journal of Marine Systems, special issue on Emiliania huxleyi (1995) 9(1/2):195-203.

Toby Tyrrell
Southampton Oceanography Centre
University of Southampton
Southampton SO14 3ZH, UK.
Email: T.Tyrrell@noc.soton.ac.uk

What was this work about? The problem that we addressed (myself in collaboration with Arnold Taylor of Plymouth Marine Laboratory, as a part of a wider European Community project called EHUX) was to try and investigate the ecological niche of Emiliania huxleyi. We applied a modelling approach to investigate this problem, and the model was specifically applied to trying to understand the distribution of blooms of E. huxleyi in the northeastern Atlantic, in particular a large bloom in the area in 1991 that was extensively studied.

This is a picture of the bloom [click on it to see it full size].

Click here to see the abstract of this paper.

This figure shows the structure of the model we used. Both a shallow, sunlit, photosynthetic zone and a deeper, inert layer were modelled. Several different species of phytoplankton and zooplankton were modelled, and the interactions between these biological components took place in a dynamically-varying chemical and physical environment. Nitrate, ammonium, silicate and phosphate nutrients were modelled, as was the transmission of irradiance in the water and the effect of water temperature. Mixing of nutrients, etc occurred between the two layers, and particles such as phytoplankton were able to sink out of the surface mixed layer. The phytoplankton compartment representing Ehux also had variables for the numbers of attached coccoliths and the numbers of free coccoliths.

We tested several different hypotheses with our model and found that it was not possible to reproduce the pattern of bloom occurrence when assuming reliance of Ehux on any single water parameter. On the other hand, we found that we were able to reproduce the distribution of blooms quite accurately (model results) when it was assumed that E. huxleyi does well at a combination of (i) phosphate in short supply in the water and (ii) light intensities on average high throughout the surface mixed layer. E. huxleyi also does better when the water is depleted of silicate which gives it an advantage in the competition against diatoms.

These are the conclusions to our paper.


Ehux home page

Toby Tyrrell : T.Tyrrell@noc.soton.ac.uk