Phytoplankton

Collection

In order to study the phytoplankton present in the water column, samples were collected from each station, at a range of depths along the Fal estuary. These phytoplankton samples, of 100ml each, were placed in dark glass bottles containing 1ml of Lugols, in order to preserve them.

Preparation

On returning to the laboratories the water samples were placed in a settling column and left overnight, the top 90ml being subsequently removed by a pump. This resulted in a concentration of phytoplankton tenfold greater than would be expected to be observed in the water column. The remaining 10ml had lugols iodine added in order to stain the phytoplankton, before being placed in a sample vial.

Analysis

Each of the four sample vials were divided among group members, with repeats done of each vial. One ml of a sample was pipetted into a Sedgewick Rafter, which was placed under a light microscope. At least 60 squares were then counted, with a tally of phytoplankton species counted and each individual identified, to species level where possible. Calculations were then run to work out the total number of individuals per millilitre of estuarine water.

Results and Discussion (Winnie the  Pooh):

Station N is the furthest up the river Fal and the freshest, with Station Q being the furthest down the estuary (towards the sea) and therefore the most saline. Interestingly there seems to be no trend in proportions of diatoms to cryptophytes, the two dominating groups, with increasing salinity. Ciliates, however, show a trend of increasing with increasing salinity, perhaps due to their successful out-competition of diatoms. Figure1 shows a definite increase of cells per millilitre with increasing salinity, with cell counts more than five times higher at station Q than station N, reflecting the marine species’ lower tolerances to fresh water. Dinoflagellates were only recorded at Station O. Of all the diatoms, Cylindrotheca closterium was the most commonly observed species, with some Mesodinium rubrum being identified among the ciliates (a species which can cause red tides and has been previously linked to polluted waters [Selifonova, 2000; Parker, 1983].)

Estuary Biology

Results and Discussion (Bill Conway) :

Only two different stations were sampled from the Conway, due to the bad weather conditions making further stations too dangerous to reach. The first station, 48, had two phytoplankton samples taken at the same depth in order to analyse consistency between samples (two different niskin bottles, fired at the same depth of 0.71m, were sampled for phytoplankton). The second station, 51, was further up the Fal estuary, in fresher water. Both samples were taken from the surface waters, though the station 51 sample was half a metre shallower than station 48. Immediately it is obvious that the two stations had very different compositions of phytoplankton, with a dominance of cryptophytes at station 51, as well as a significant numbers of dinoflagellates: with neither cryptophytes nor dinoflagellates present, at all, at station 48.

Parker, J. (1983); Ciliated Protozoa in Marine Pollution Studies: A Conspectus; Ecotoxicology and Environmental Safety 7: 172-178

Selifonova, Z. (2000); Heterotrophic Nano- and Microplankton under Conditions of Anthropogenic Eutrophication of the Bay of Novorossiisk; Russian Journal of Ecology; 32 (4): 291-296

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Zooplankton

Collection

Two zooplankton samples were collected on 05/07/2017 at two stations located at the North of the Fal estuary: station Q (50°14.9655 N, 005° 02.3148 W) and station N (50°14.6110 N, 005°01.4535 W). A further two zooplankton samples were taken on 11/07/2017: at site 13B (50°12.370 N, 005°02.256 W) and site 13C (50°13.480 N, 005°01.139 W). Zooplankton nets were run for 5 minutes at each station, each using a 210 micron net mesh, with a 50cm diameter opening. Formalin was added to preserve the zooplankton in the samples for later laboratory analysis.

Analysis

Zooplankton samples collected in the field were prepared by inverting the sample bottles, in order to ensure that the collected zooplankton were re-suspended and evenly mixed. A 10ml water sample was extracted from each of the samples collected at each station using a pipette and placed in a measuring cylinder. A third of this sample was then poured into a Bogorov chamber and placed under a light microscope so that the zooplankton could be identified and counted. This process was repeated until the entire 10ml water sample was analysed for each station. Count data per 10ml were then used to produce a population density value for each zooplankton group per m3 at each station, taking into account the towing distance of the zooplankton net.

At both the upstream station Q and the downstream station N sampled on 05/07/2017, Copepoda were the most dominant group, comprising 96% of the sample population at station Q, and 63% of the sample population at station N. Station N also showed a notable population density of Cladocera, comprising 25% of the sample.

At station C on 11/07/17, Copepoda were the most dominant group to be sampled, comprising 62% of the sample population at the upstream location, site 13C. Cirripedia larvae were the next dominant group at this location, comprising 32% of the sample population. At site 13B, the furthest location sampled downstream, both Copepoda and Cirripedia larvae were equally dominant, comprising 43% of the sampled population each.

The zooplankton samples were taken on two different days in differing weather conditions. As a result, it is difficult to compare the zooplankton population densities in the samples taken at stations Q and N, at the Northern end of the River Fal, on 05/07/2017 with the samples taken at sites B and C further downstream on 11/07/2017.

Results and Discussion: