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Results
Phytoplankton
The abundance of Rhizosolenia is possibly higher in the samples from Conway stations due to their preference of high nutrient, mild coastal waters[9]. Diatoms and cryptophytes are the most common dominant groups across the seasons in shallow and mixed estuarine systems as this is their preferred environment, and may explain their high proportions in the samples collected from the lower Fal estuary by the Conway[10].
Coscinodiscus is known to prefer areas of high shear, as it is reliant on TKE (turbulent kinetic energy) from shear to remain in the surface layers of the water column for optimum light levels. Thus, there is an increase in the populations as an ebbing/a flooding tide begins. However, it may be well mixed in the water column at high water (low shear). This may explain the high proportion of Coscinodiscus collected in the samples as samples were taken throughout a
Zooplankton
Copepods are mainly distributed near the seabed during the day and near to the surface at night[12]. Most copepod species are found above salinities of 27 psu; so, mostly near the outer estuary, e.g. at the Conway sample stations. This may explain the higher proportion of Copepod collected in the Conway samples[13].
The Nauplius stages of the copepod life cycle are more heavily influenced by currents and the tides. This results in a homogenous distribution both vertically and horizontally in space. However, they have been observed concentrating in surface waters[14]. The higher proportion of copepod nauplii collected from samples off Winnie the Pooh were not expected as most nauplii survive better at higher salinities – but this is species dependent and so may be different for the particular species collected in these locations[15].
Chlorophyll
Of the samples collected from the Conway, Station 14 was furthest out to sea and Station 17 furthest inland. The highest concentrations of chlorophyll were observed furthest out to sea and the lowest concentrations furthest inland. This may suggest a phytoplankton bloom at station 17 due to a considerably higher value than the remaining stations. A few possible reasons for this distribution may include: lower turbidity further out to sea resulting in a preferable environment with higher light levels (however, this is said to play a lesser role in affecting the horizontal distribution of plankton), less variable salinity further out to sea creating a more stable environment, or even a local input of nutrients driving them all to outer estuary. Temporal fluctuations in chlorophyll are also present due to diurnal and spring/neap tidal cycles – this could additionally be influencing the distribution[16].
The views expressed here are not representative of the University of Southampton.