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Plymouth Field Course 2019

Group 7

Estuary Phytoplankton

In order to sample phytoplankton populations, an amount of the sample water was preserved using Lugol’s iodine then stored in a cool, dark area until lab analysis. The samples were then reduced down to the settled particles at the bottom, and 100 squares of a Sedgewick-Rafter counting chamber were observed under a microscope to identify and count the contents.

One issue is that Lugol’s dissolves hard structures including coccolithophores and diatom frustules, potentially leading to some loss of phytoplankton and miscounts. Also, as different people were counting the phytoplankton some may have been disregarded as they may have not recognised the species.

Overall, the majority of the phytoplankton in station A0 (Figure 1) at Calstock were Chaetoceros spp.. In comparison, the following station that we sampled phytoplankton at, A4 (Figure 2), had no Chaetoceros identified in it, and was predominantly Ceratium lineatum. Chaetoceros was then again dominant at Station I, further out in Plymouth Sound. Chaetoceros is a diatom genus which is one of the most widespread and abundant genera that has been identified (Rines and Theriot, 2003), so as a whole can survive in a range of conditions. At station A4 7 Ceratium lineatum were identified; this comprises almost all the phytoplankton from this sample, as only 1 Rhizosolenia was identified as well as this. Ceratium lineatum also appeared in the samples from Station C1 and I, though not as the dominant species. At C1 (Figure 3), Rhizosolenia dominated over Ceratium, showing the opposite dynamics as seen at A4.

This data shows that there is a wide range of phytoplankton present in the estuary and that they are not constrained to one area by the differing salinities.   

Figure 1 - Proportion of phytoplankton for station A0

Phytoplankton counts: Chaetoceros: 75, Coscinodiscus:2, Ciliate:1. Total identified = 78

Figure 2 - Proportion of phytoplankton for Station A4

Phytoplankton counts: Rhizosolenia:1, Ceratium lineatum: 7. Total identified = 8

Figure 3 - Phytoplankton proportions for Station C1

Phytoplankton counts: Rhizosolenia:22, Ceratium lineatum: 1, Chaetoceros lauderi: 9. Total identified = 32

Figure 4 - Phytoplankton proportions for station I

Phytoplankton counts: Pleurosigma: 1, Ceratium lineatum: 1, Chaetoceros lauderi: 5. Total identified = 7

Estuary Zooplankton

Methods

A 200µm zooplankton net with a 50cm diameter opening and a flow meter to record volume of water was deployed and held in the upper 1m of the water column. The net was equipped with a flow meter to enable calculation of water volume processed. Spare water was used to wash plankton into the 1L sample bottle, before 100% formalin was added and the bottle stored in a cool box to preserve the sample.

Lab processing

Samples collected during the offshore boat work were then analysed within the lab on 09/07/2019. 10ml from each bottle was divided into 2x5ml counting chambers under a light microscope. Numbers of zooplankton were counted and subsequently scaled up to give the abundance per m3.

Results

Copepoda, Copepoda nauplii and dinoflagellates were generally the most abundant zooplankton throughout. Dinoflagellates have been included here although many are photosynthetic as they also have animal-like characteristics including heterotrophy in many species (Steidinger & Jangen, 1997). Station A0 (figure 10), located up the Tamar at Calstock at a low salinity of 9.02, has a high proportion of Copepoda and dinoflagellates, with polychaete larvae, hydromedusae, decapoda larvae, gastropod larvae and copepod larvae also being identified, showing a high species diversity. In comparison, Station J was located out by the breakwater at a high salinity of 34.92. This station (figure 7) has a visibly lower species diversity, with 257 dinoflagellates being identified and very few copepods and Appedicularia. Station H (figure 5) has the highest diversity, with 7 species being identified. This station was located at a salinity of 34.93, comparable to the salinity at station J, however station J had very little diversity suggesting that salinity is not the factor affecting it.

Figure 5 - Zooplankton proportions for station H

Zooplankton counts: Copepoda: 244, Copepoda Nauplii: 288, Cladocera: 10, Cirripedia larvae: 9, Gastropod larvae: 23, Siphonophorae: 17,  Echinoderm larvae: 2, Appendicularia: 32, Dinoflagellates: 231

Figure 6 - Zooplankton proportions for station I

Zooplankton counts: Copepoda: 236, Copepoda Nauplii: 37, Cladocera: 3, Cirripedia larvae: 8, Polychaeta larvae: 2, Siphonophorae: 5, Appendicularia: 1.

Figure 7 - Zooplankton proportions from Station J

Zooplankton counts: Copepoda: 18, Appendicularia:2, Dinoflagellates: 257

Figure 8 - Zooplankton proportions for station B0

Zooplankton counts: Copepoda: 8, Copepoda Nauplii: 5, Polychaeta larvae: 2, Hydromedusae: 2, Dinoflagellates: 84

Figure 9 - Zooplankton proportions for station A7

Zooplankton counts: Copepoda: 3, Dinoflagellates: 15

Figure 10 - Zooplankton proportions for station A0

Zooplankton counts: Copepoda: 15, Decapoda larvae: 2, Polychaeta larvae: 4, Gastropod larvae: 1, Hydromedusae: 3, Dinoflagellates: 13