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University of Southampton Falmouth Field Course 2013    26th June - 6th July 2013    Group 9

4th July 2013 – Estuary Sampling

Falmouth Tides (UTC): HW 02:09 4.20m

LW 09:31 1.50m

HW 15:39 4.30m

LW 22.03 1.5m

Biological Discussion

As can be seen from figure EB.2, the phytoplankton species change along the estuary at different stations. This could be due species having different salinity tolerances, nutrient inputs from tributaries and temperature effects. Figure EB.2 shows that there were limited numbers of phytoplankton at Station 1. This Station was in the upper part of the estuary and had a low salinity (figure EB.2). This could be a challenging environment for many phytoplankton species which have poor salinity tolerances. Species richness of phytoplankton peaks at Station 4. This could be due to riverine inputs from the River Fal and the River Truro bringing nutrients such as phosphate and nitrate.

It can be noted from figure EB.2 that there is a large bloom of Chaetoceros spp.at Station 6. This could be due to nutrient inputs from Pill Creek and other small tributaries inputting at Station 6. Furthermore, the temperature increases down the estuary, and as Station 6 is near the mouth, the increased temperature could lead to an increase in growth rate of Chaetoceros spp. (Hemalatha et al.,2012).However, the abundance of Chaetoceros spp. drops at Station 8. This coincides with a drop in dissolved silicon, which potentially limits growth rates.

Figure EB.1 shows that in contrast to phytoplankton, zooplankton shows very little change in species composition along the estuary. This could be due to more zooplankton species being euryhaline and tolerating a wider range of salinity. It can be seen that there is a large number of copepod larvae at Station 6. This is consistent with research from Jerling & Wooldridge (1991) who noted that abundance of copepod nauplii peaks higher up estuaries than adult copepods. Additionally, Sobczak et al. (2002) noted that clam invasion in San Francisco leads to competition between clams and zooplanktons for food, limiting zooplankton growth. This could explain why there is a low number of zooplankton at Station 6 compared to Station 8 (due to the nearby mussel farms at Station 6).

Furthermore, Intxausti  et al. (2012) observed that small zooplankton (i.e. nauplii) were more sensitive to climate-related factors and larger zooplankton (adult copepods) were sensitive to water quality. This would further explain why copepod nauplii are more abundant further up the estuary; with heavy metal contamination from mining affecting water quality (Warwick, 2001) having a smaller effect on nauplii than adult copepods. Conversely, as seen in figure EB.1, there are more ‘large’ zooplankton (Copepoda and Hydromedusae) at Station 8 than Station 6. This is because Station 8 is exposed to more climate-related factors than Station 6, and therefore larger zooplankton are more prevalent (Intxausti et al., 2012).

Station 1 shows there to be little zooplankton; however of those species that are present, ¾ are meroplankton. Some planktonic larval stages (meroplankton) are able to adjust their buoyancy so to adjust their position along the estuary (Kruczynski & Fletcher, 1998). This could explain why there is a large range of meroplankton species counted at the surface at low tide.

References

Hemalatha, A., Karthikeyan, P., Manimaran, K., Anantharaman, P. and Sampathkumar, P. 2012, Effect of Temperature on the Growth of Marine Diatom, Chaetoceros simplex (Ostenfeld, 1901) with Different Nitrate: Silicate Concentrations,  Asian Pacific Journal of Tropical Biomedicine, 2, 3, 1817-1821.

Jerling, H. and Wooldridge, T.1991, Population dynamics and estimates of production for the calanoid copepod Pseudodiaptomus hessei in a warm temperate estuary, Estuarine, Coastal and Shelf Science, 33, 2, 121-135.

Kimmerer, W., Burau, J. and Bennett, W. 1998, Tidally-oriented vertical migration and position maintenance of zooplankton in a temperate estuary. Limnology and Oceanography, 43, 1697-1709.

Sobczak, W., Cloern, J., Jassby, A. and Müller-Solger, A.. 2002, Bioavailability of organic matter in a highly disturbed estuary: The role of detrital and algal resources, Proceedings of the National Academy of Sciences, 99, 12, 8101-8105.

Warwick, R. 2001, Evidence for the Effects of Metal Contamination on the Intertidal Macrobenthic Assemblages of the Fal Estuary, Marine Pollution Bulletin, 42, 2, 145-148.

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