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

26th June 2013 - Offshore Sampling
Falmouth Tides (UTC): HW 07:20 5.1m
LW 13:50 0.3m
Cloud cover: 100% - 0%
Sea State: Flat - Slight
Air Temperature: 14.9°C

Biological Results

Zooplankton

Zooplankton Station 1 (G9)

The highest total number of zooplankton (8,650,000 cells/L) was found at depths of 0-16m. The most common group at this depth was Hydromedusae (2,700,000 cells/L). Between 16-30m the total number of zooplankton present was 4,550,000 cells/L, dropping to 4,110,000 cells/L between 30-40m. At these depths the most common group of zooplankton were the Copepoda with numbers of 1,850,000 cells/L and 1,930,000 cells/L respectively.

Figure OB.1: Abundance of zooplankton groups at different depth intervals within the water column at Station 1 (G9).

Zooplankton Station 2 (G9)

Only one zooplankton net was deployed between 10-20m and the most common zooplankton group were the Copepoda of which 2,950,000 were counted per litre.

Figure OB.2: Abundance of zooplankton groups at different depth intervals within the water column at Station 2 (G9).

Zooplankton Station 1 (G11)

The zooplankton net was deployed between 0-12m and as at Station 2 the most abundant zooplankton group were the Copepoda, with approximately 1,330,000 counted per litre. Diversity at this station was considerably less compared to Station 2, with only four groups identified (Copepoda, Decapod larvae, Polychaete larvae and Ctenophora).

Figure OB.3: Abundance of zooplankton groups at different depth intervals within the water column at Station 1 (G11).

Phytoplankton

Phytoplankton Station 1 (G9)

As seen in figure B.4, the most abundant phytoplankton species was Chaetoceros spp. at a depth of 27m. The highest total number of phytoplankton was observed at a depth of 27m whilst the lowest total number was observed at 41m. However this value of 18,000cells/L was only 1000 cells/L less than that counted at 1.2m (19,000 cells/L).

Figure OB.4: Abundance of phytoplankton species at different depths within the water column at Station 1 (G9).

Phytoplankton Station 2 (G9)

At a single depth of 32.5m, Chaetoceros spp. showed the highest measured abundance of 26,000 cells/L. It can be noted that the only species present at all depths was Ceratium furca, with values of 2,000 cells/L, 1,000 cells/L and 1,000 cells/L at 5.8m, 16.4m and 32.5m respectively. The highest total number of phytoplankton was observed at a depth of 32.5m at a value of 34,500 cells/L.

Figure OB.5: Abundance of phytoplankton species at different depths within the water column at Station 2 (G9).

Phytoplankton Station 1 (G11)

As observed at station 2, Chaetoceros spp. was the most abundant species at a single depth (37,000 cells/L at 18m). Furthermore Chaetoceros spp. was the only species present at each depth measured with values of 1,600 cells/L, 3,000 cells/L and 37,000 cells/L at depths of 1.3m, 14.1m and 18m respectively. The highest total number of phytoplankton was observed at a depth of 18m at a value of 47,000 cells/L.

Figure OB.6: Abundance of phytoplankton species at different depths within the water column at Station 1 (G11).

Diatoms Vs. Silicon Station 1 (G9)

As can be seen below in figure B.7, silicon concentration shows an overall increase with depth. The concentration can be seen to drop slightly between 0 and 15m (0.78µmol/L and 0.62µmol/L respectively), before increasing to 3.0 µmol/L at 41m. Diatom abundance shows a similar trend to silicon concentration between 0m-27m, however diatom abundance drops from 38,500 cells/L at 27m to 17,000 cells/L at 41m, whereas silicon concentration increased from 1.33µmol/L to 3.03µmol/L between the same depths.

Figure OB.7: Abundance of diatoms with silicon concentration at different depths within the water column at Station 1 (G9).

Diatoms Vs. Silicon Station 2 (G9)

Figure B.8 shows that the number of diatoms decreases between 5.8m and 16.4m from 6,000 cells/L to 0 cells/L. The number then increases rapidly and at 32.5m the number of diatoms has reached a value of 33,000 cells/L. On the other hand, silicon concentration rises between 5.8m and 16.4m (increasing from 0.49µmol/L to 1.72µmol/L), before dropping to 0.91µmol/L at 32.5m. The two plots show opposite trends.

Figure OB.8: Abundance of diatom species with silicon concentration at different depths within the water column at Station 2 (G9).

Diatoms Vs. Silicon Station 1 (G11)

Diatom abundance can be seen to have a value of 2000 cells/L at a depth of 1.31m, before increasing to 9,000 cells/L at 14.13m. This increase is followed by a large jump to 45,000 cells/L at 21.8m. Silicon concentration shows a similar trend between 1.31m and 14.13m, where it rises from 2.09µmol/L to 2.33µmol/L. However, whereas the number of diatoms increases between 14.13m and 21.8m, the silicon concentration decreases between the same depths, falling from 2.33µmol/L to 2.22µmol/L.

Figure OB.9: Abundance of diatom species with silicon concentration at different depths within the water column at Station 1 (G11).

Phytoplankton Vs. Nitrate Station 1 (G9)

As shown in figure B.10 nitrate concentration shows an overall increase between 1.2m-41m whilst numbers of phytoplankton show an overall decrease. There is an initial increase of nitrate in surface waters, from 0.6139µmol/L to 4.2776µmol/L between 1.2m-15m. Numbers of phytoplankton also increase from 19,000 cells/L to 23,000 cells/L between these depths. A decrease in nitrate concentration occurs whilst an increase in numbers of phytoplankton is observed between 15m-27m. Nitrate concentration peaks at 4.2776µmol/L at a depth of 15m whilst a peak in phytoplankton numbers is observed at 27m at a number of 50,000 cells/L.

Figure OB.10: Abundance of total phytoplankton with nitrate concentration at different depths within the water column at Station 1 (G9).

Phytoplankton Vs. Nitrate Station 2 (G9)

At station 2 both nitrate concentration and numbers of phytoplankton decrease in shallower waters (5.8m-16.4m). Between 16.4m-32.5m nitrate concentration increased from 2.5µmol/L to 5.5 µmol/L and the number of phytoplankton increased from 1000 cells/L to 36,000 cells/L. Nitrate concentration peaked at a depth of 5.8m at 13.5µmol/L whereas number of phytoplankton peaked at a depth of 32.5m at 36,000 cells/L.

Figure OB.11: Abundance of total phytoplankton with nitrate concentration at different depths within the water column at Station 2 (G9).

Phytoplankton Vs. Nitrate Station 1 (G11)

As shown in figure B.12 nitrate concentration increases from 0.664µmol/L to 14.1494µmol/L between 1.3m-14.1m. The number of phytoplankton also increased between these depths from 3,200 cells/L to 12,000 cells/L. The number of phytoplankton continues to increase to a depth of 21.8m whilst nitrate concentration decreased from 14.1494µmol/L to 3.5652µmol/L between 14.1m-21.8m.