Falmouth Field Course 2017

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Estuarine Biology

Introduction

Whilst surveying the surface waters of the Fal Estuary on the 04/07/2017 we took samples of the phytoplankton and zooplankton to see how the species composition varies from the upper to lower estuary.

Methodology

Phytoplankton: Using a 50ml measuring cylinder, 100ml of surface water was stored in a sample bottle containing Fugol’s Iodine to preserve the plankton in situ for analysing later in the lab. During the lab, water was placed on a slide with Fugol’s Iodine and analysed under a light microscope. The organisms were identified using books and pictures. The number of species found in 100 squares (ml) was written and the number of individual members of that species was tallied.

Zooplankton: 10ml of sample water collected from the zooplankton nets was placed in a clear dish and analysed under a microscope. Using pictures and books, we noted every species seen and tallied the individual organisms of that species.

Limitations: It was very difficult to identify phytoplankton down to species level as the light microscopes were not very powerful therefore many organisms such as Ciliates could only be identified to family or even genus level.

References:

D.G Raffaelli, C.F Mason, 1981, ‘Pollution monitoring with meiofauna, using the ratio of nematodes to copepods’, Marine Pollution Bulletin, 12, pp. 158-163.

K Rhew, R.M Baca, C.A Ochs, S.T Threlkeld, 1999, ‘Interaction effects of fish, nutrients, mixing and sediments on autotrophic picoplankton and algal composition’, Freshwater Biology, 42, pp. 99-109.

W Yih, H.S Kim, H.J Jeong, G Myung, Y.G Kim, 2004. ‘Ingestion of cryptophyte cells by the marine photosynthetic ciliate Mesodinium rubrum’, Aquatic Microbial Ecology, 36, pp. 165-170.

Results: Phytoplankton

Species which are dominant in the upper estuary are generally less dominant or absent in the lower estuary. 346 per m-3 As seen in Figure 1 e,f and g, Mesodinium were calculated in samples collected from the upper estuary (stations O,N, P and Q) but none were found in the lower estuary samples (stations 17, 14 and 13). Cilliates were seen in samples from both the upper and lower estuary but there was approximately 56% more Cilliates in the upper estuary samples. Similarly, many dominant phytoplankton species in the lower estuary are either absent or have reduced populations in the upper estuary. For example, it was calculated that 70 Chaetoceros per m-3 were in samples from the lower estuary but only 3 per m-3 were found in lower estuary samples. Cryptomonas has the greatest abundance in all our samples as 884 per m-3 was calculated. Samples were collected from stations N and O which were located at the furthest point up the Fal Estuary.

Discussion: Phytoplankton

Mesodinium is a mixotrophic, planktonic ciliate that forms incomplete symbionts by ingesting Cryptophytes and including their cells in its protoplasm (Yih et al, 2004). Although it is a marine ciliate, it may be found in the upper estuary due to the flood tide that was occurring during sample collection and because there was a high abundance of their prey, Cryptomonas. Station O, which is in the upper estuary, is dominated by Cryptomonas. Studies by Rhew et al (1999) found that Cryptomonas blooms occurred in unmixed, high nutrient water which are conditions found in station O. This suggests that the high abundance of Cryptomonas at stations O and N could be due to a bloom.

Discussion: Zooplankton

Copepods are abundant in all samples except the sample collected in station O. Station O was the furthermost area we could reach up the area but we observed that it was highly polluted due to small oil slicks on the surface. The absence of copepods in station O could be due to their high sensitivity to pollution as suggested in a study by Raffaelli and Mason (1981).

Results: Zooplankton

Fifteen different zooplankton species were identified in 3 water samples up the Fal estuary. Zooplankton samples collected on the Bill Conway had 20 -27% more species than both samples collected on the Winnie the Pooh. As seen in Figure 2a, copepods were the most abundant organisms found in our samples and we calculated that there was 390 copepods per m-3 in the lower estuary and 231.8 per m-3 in the upper estuary. However, decapoda larvae were the only organisms to be found in all 3 samples.

Figure 2a-b. A stacked vertical bar chart of the main zooplankton species numbers (per m-3) at each of the samples. Figure 2a. consists of all of the identified species that had a total of above 5 for all their sites, the remaining species are compiled as ‘other’ in Figure 2a. Figure 2b. contains the quantities of the ‘other’ species shown in figure 2a. Zoo-1 and Zoo-2 where taken from the Winnie the Pooh on the upper Fal estuary and was the mean from 2 replicates. Zoo-f was collected by R.V. Bill Conway and was the mean from 4 replicates. All samples were taken on 04/07/17.

Figure 1 a-g. A bar chart showing the quantity of each phytoplankton species (per ml) found at each of the locations (13 (figure1a), 14 (figure1b), 17 (figure1c), N (figure1d), O (figure1e), P (figure1f), Q (figure1g)). Station 13 contained a replicate that that the mean was then taken to give the final result. Station’s 14 and 17 were taken at 0.5 metres depth and station 13 was taken at 1 metres depth.  Stations N, O, P, Q were collected by the Winnie the Pooh on the upper Fal estuary. Stations 13, 14 and 17 were collected by R.V. Bill Conway on the lower Fal estuary.  All samples were taken on 04/07/17.