GROUP
Plymouth Field Course 2019
4
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OFF-SHORE
Plankton
Zooplankton:
Figure 1: Almost half of the zooplankton in the sample taken from the water at Station C25 (Figure 1) were adult copepods (3028.6 individuals m-3). In addition, copepod nauplii (1221.2 individuals m-3) contributed almost 15% to the total zooplankton. Appendicularians, cladocerans, decapod larvae, cirripede larvae, polychaete larvae and hydromedusae formed a moderate amount, while chaetognaths and echinoderm larvae made up a small amount of the total zooplankton count.
Figure 2: Approximately 50% of the total zooplankton count in the sample taken from Station C27 (Figure 2) were adult copepods (1786.6 individuals m-3). The next largest contribution was from appendicularians (675.65 individuals m-3), followed by cladocerans (434.8 individuals m-3), copepod nauplii (239.3 individuals m-3) and cirripede larvae (141.6 individuals m-3). There were also minor contributions from polychaete larvae, echinoderm larvae, decapod larvae, gastropod larvae and hydromedusae.
Figure 3: Over 75% of the total zooplankton count from the sample taken at Station C28 (Figure 3) were adult copepods (7122 individuals m-3). Appendicularians (1076 individuals m-3) contributed the second largest quantity. Copepod nauplii (291 individuals m-3) and chaetognaths (261.5 individuals m-3) contributed a moderate amount, while decapod larvae, cirripede larvae, fish larvae, polychaete larvae and gastropod larvae contributed minor amounts.
Rollover figures to see captions
Phytoplankton:
Station C25: The highest phytoplankton abundance (57 cells) was found at 15.5m, corresponding to the depth of the thermocline at that station. The most abundant genus at this station was the diatom genus Chaetocerous, with a peak of 29 cells counted in the 15.5m sample. Dinoflagellates of the genus Ceratium were the second most abundant and were present at every sampling depth as well as being the dominating species at the surface (12 cells per sample). Diatoms were dominant in the community close to the seabed.
Station C26: At station C26 the highest abundance of phytoplankton cells was registered at depth 4.3m, two orders of magnitude higher than the deeper samples. The community was dominated by diatom genera, with Guinardia as the most abundant (244 cell/10ml). At intermediate depth, Chaetocerous individuals were the most abundant (7 cells), while close to the seafloor Coscinodiscus were the most abundant (4 cells).
Station C27: At station C27 the highest phytoplankton concentration was registered along the transect and the diatoms Chaetocerous were the most abundant genus. The peak abundance occurred at depth 4.2m, with a community composed almost exclusively of Chaetocerous individuals (732 cells per sample) with Mesodinium rubrum making up 2% of the phytoplankton sampled. The sample taken at 14.2 m was still dominated by Chaetocerous, two orders of magnitude higher than the other diatom genera recorded. At 22.9m no Chaetocerous individuals were present, the community was dominated by the genus Coscinodiscus but was overall one order of magnitude lower in phytoplankton number. The sample in proximity of the seabed is missing because the niskin bottle did not close correctly when fired.
Station C28: At station C28 the lowest abundance of phytoplankton was recorded. The 29.4m sample contained the highest phytoplankton number (19 cells/ 10ml), which coincided with the deep chlorophyll maximum registered with the CTD. At that depth, Pseudo-nitzchia was the most abundant genus despite being absent from both the surface and the deep sample.