Hertotrophic nanoflagellates employ a wide range of feeding strategies. There are 3 main strategies adopted by Hertotrophic nanoflagellates for feeding, 1. the ingestion of whole cells, 2. use of a feeding tube called a peduncle and 3. use of a cytoplasmic veil e.g. pallium. Many Hertotrophic nanoflagellates compete with copeopods for ciliates and other microorganisms. Photosynthetic nanoflagellates only use light from the sun to produce energy. We found a great deal of mixotrophic ciliates in our sample. We focused our attention on Flavella spp. These mixotrophic ciliate photosynthesise, but also feed on live prey. Organisms like Flavella spp are extremely important, as they are hetrotrophic, which means they regenerate nutrients, thus they take Dissolved Inorganic Nitrogen and re introduce it to the cycle by a means that is possible to uptake by other organisms.
There were vast numbers of Dinoflagellate caught in our sample. Dinoflagellates tend to be more successful in stratified water columns, and adopt a diel vertical migration pattern to prolong their life span, where they feed near the surface at night and return to greater depths in the day to avoid visual predators. This means they have the ability to move around in the water column. There have been some recordings of some dinoflagellates being toxic. Half of dinoflagellates are hetrotrophic (Williams et al, 2005). Another type of primary producer we encountered was the diatom. Diatoms are the most common type of phytoplankton. These organisms are non-motile which is why they usually thrive in well-mixed areas. They have a high growth rate which is evident as spring blooms often occur.
Copepods were the highest member of our food web. Copepods are crustaceans and many species are planktonic. The play a key role in food webs, not only as predators on phytoplankton by prey for larger fish and whales. Many planktonic copepods adopt a diel vertical migration.
I concentrated on the dinoflagellate Dinophysis c.f. acuta as part of my primary producer in the food web. The Dinophysis c.f. acuta is a bigger more distinct species of dinoflagellate. One of its main prey is a ciliate. However some ciliates feed on Dinophysis spp (Williams et al, 2005). Skeletonema costatum was another phytoplankton that I placed as a primary producer in my food web. It is one of the most common diatom in our waters, particularly during spring bloom. It favours waters of high salinities (Williams et al, 2005). Chaetoceros c.f. decipens was the last primary producer I inserted in my food web. Chaetoceros c.f. decipens is one of the most wide spread Chaetoceros spp found around our waters. It is present all year round, and thrives during spring bloom. It can survive in coastal and estuarine environments (Rines & Hargraves, 1988).
Flavella spp is a small phytoplankton species, which is also mixotrophic. They are important predators of nanophytoplankton (Heinbokel & Beers, 1979) It requires dinoflagellate as food. Flavella can recognise between dinoflagellates of different size and shape from non-dinoflagellates (Stoecker et al, 1981). It can tolerate a wdie range of salinities (Williams et al, 2005). Leptocylindrus danicus is usually found in the North sea and in the Bristol channel (Newell & Newell, 1963). However we had many recordings of this species. It is usually co dominant with Skeletonema costatum in spring and fall blooms (Williams et al, 2005). Helicostomella subulata is a ciliate. It is a vital link between connecting bacteria and pico/nanoplankton to larger zooplankton. Up to 50% of bacterial and phytoplankton production may be taken up by ciliates. Copepods, decapod larvae and other larger organisms pray upon ciliates. Ciliates are capable of rapid growth with cell divisions every hour (Williams et al, 2005)
Temora longicornis is a copepod and is very common in coastal waters around the British Isles (Newell & Newell, 1963). They mainly feed during the night as they have adopted a diel vertical migration strategy (Head et al, 1984). It mainly feeds on phytoplankton such as diatoms, dinoflagellates, ciliates, and tintinnids. Acartia c.f. clausi is thought to be restricted to the North Atlantic, but studies have shown that they are to be found in the Mediterranean and the Black sea (Bradford, 1976).
The food web shows the interactions between key species of plankton and Inorganic and Organic Matter. Bacteria is key in this food web as it takes up dissolved organic mater and inorganic matter, this in turns allows Hetrotrophic nanoflagellates to ingest organic matter, which is extremely important for growth. The Hetrotrophic nanoflagellates is either taken up by Helicostomella subulata, or dies and converts into Organic and Inorganic matter by bacterial work. Dissolved inorganic matter is also taken up by Chaetoceros c.f. decipens, which is also fed on by Helicostomella subulata. Skeletonema costatum takes up dissolved inorganic matter, which is then prayed upon by Flavella spp. This Flavella spp is taken up by Dinophysis c.f. acuta, Temora longicornis and Acartia c.f. clausi. It also secrets dissolved organic matter. Helicostomella subulata takes up Hetrotrophic nanoflagellates, Skeletonema costatum and Dinophysis c.f. acuta. The top 2 predators excrete Dissolved and particulate organic matter. Thus completing the food web.
The mesh sizes we used did were not capable of catching smaller bacteria, nano/picoplankton. To do this we would have had to use smaller mesh sizes. To make the food web more quantitative we could have looked at rate of ingestion between species, include more species in the food web and see how concentration of specific species would alter the rate or life span of certain species.
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References
Bradford, J., 1976 Partial Revision of the Acartia Subgenus Acartiura (Copepoda: Calanoida: Acartiidae). New Zealand Journal of Marine and Freshwater Research 10 (1): 159-202.
Head, E. J. H., Wang, R., Conover R. J. 1984 Comparison of diurnal feeding rhythms in Temora longicornis and Centropages hamatus with digestive enzyme activity. Oxford University Press
Heinbokel. J. F. Beers, J. R. 2004 Studies on the functional role of tintinnids in the Southern California Bight. III. Grazing impact of natural assemblages. Springer Berlin / Heidelberg
Newell, G. E., Newell R. C. 1963 Marine Plankton a practical gudie. Hutchinson educational LTD
Rines, J. E. B.;Hargraves, P. E.: 1988 The Chaetoceros Ehrenberg (Bacillariophyceae) Flora of Narragansett Bay, Rhode Island, U.S.A science publisher Stuttgart
Stoecker, D., Guillard R. R. L., Kavee, R. M., 1981 Selective predation by Favella ehrenbergii (Tintinnia) on and among dinoflagullates. Woods Hole Oceanographic Institution, Wood Hole.
William S. J., Dennis M. A., Marni F., 2005 Zooplankton of the Atlantic and Gulf coasts: a guide to their identification . JHU Press, 2005
