University of Southampton OES Undergraduate Falmouth Field Course 2016 - Group 3 databank and initial findings.
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Phytoplankton
The phytoplankton samples taken from offshore stations were quite variable. A lot of samples did not have phytoplankton present. This was due to the excessive presence of Lugols used to dye the cells. The bottles used already had the dye in them, but in varying quantities so the amount of water sample needed to be added was variable and unknown. Chaetoceros was the most frequently occurring, with a maximum at Station 34, at a depth of 18.4m. Other species were present at other depths and stations, but in low numbers.
The phytoplankton data is unreliable and not much can be extracted from it. One can assume that Chaetoceros is a more resilient species and did not disintegrate after exposure to too much Lugols.
Station 33
Two nets were towed vertically for ten metres each - one from a depth of 20m and
a second from a depth of 10m, which correspond to samples A and B respectively. Sample
A was the furthest offshore and was subsequently found to have the greatest number
of zooplankton of any sample, accounting for over 17% of all individuals identified
across all sites. This sample also had the highest number of copepods, hydromedusae,
siphonophores and echinoderms. The deeper trawl had more than three-fold the number
of individuals per m-3 than the shallower trawl, however the ratios of organisms
to each other was reasonably consistent 
between the sites, with siphonophorae dominating
both depths. Relative abundances of hydromedusae and copepoda were also similar at
both depths, albeit with greater abundance observed deeper in the water column.
Sample B was found to have nearly an order of magnitude more photosynthetically active radiation than the deeper Sample A. This is accompanied by nearly a magnitude of order more copepods identified in Sample A than Sample B. This is expected as copepods are negatively phototropic (Clarke, 1934; Huntley & Brooks, 1982). There is also a peak in fluorescence between 10 and 20m depth, possibly indicating phytolplankton that the zooplankton may be grazing on.
Copepod vertical distribution is predominantly affected by light and food availability, as gradients for other factors such as temperature or salinity are too gradual to be observed by such small organisms (Clarke, 1934) (Huntley & Brooks, 1982). When food supply is greater, zooplankton are able to dive deeper in the day
Station 34
As with the first station, two nets (Samples C & D) were trawled upwards for ten metres from 20m and 10m respectively. As the second-closest site to the shore (but further away from the estuary than Station 38, the closest to shore), this station showed the lowest abundance of individuals from both trawls combined. Sample D (the shallower trawl) had the (joint-) second lowest total abundance of any site. Significantly less organisms were found there, possibly due to a lack of phytoplankton at the depths sampled which in turn resulted from the increased levels of PAR.
Station 35
No net deployment.
Station 36
Only one trawl was carried out at this site as it was too shallow to perform two 10m trawls. Sample E had one of the lowest total abundances and showed a similar assemblage of organisms to Sample D. This is expected as there was less than a kilometer between the sites and both samples were taken over similar depth ranges.
Station 37
A wider variety of species was identified at this station, and both samples had some of the highest total abundances per m-3. The greatest volume of water was also sampled here (Sample F – 4.91m-3) as well as the greatest depth (25m to surface). The shallow trawl (Sample G) found the second highest total abundance of all samples. A fairly extended and consistent peak in fluorescence was observed from roughly 10 to 25m, which may explain the increased abundance of organisms and the similarity in total abundance between the two samples at this site.
Station 38
This station showed the greatest change in abundances with depth, with 19 individuals identified per m-3 in Sample H (the deeper trawl) and only three in Sample I. This is accompanied by a clear difference in average fluorescence across the depths at which these trawls were carried out (Sample H – 0.11, Sample I – 0.07). Siphonophorae made up over 50% of the zooplankton in the deeper layer.
General Trends
Siphonophorae were the most common organism, accounting for a third of all zooplankton identified. In all sites where they were found, siphonophores were more common in the deeper layer than the upper layer.
Copepods tended to be found in areas of lower PAR ~5.00x102 and below 10m depth.
In terms of biogeography, assemblages could roughly be grouped in to two distinct clades – a northern clade consisting of stations 33, 37 and 38; and a southern clade of stations 34 and 36.
Offshore sampling - Phytoplankton
Offshore sampling - Zooplankton
Navigate to: Pontoon sampling
Fig 28. Copepod zooplankton (ERA Biotech 2016)
References
Batistić, M., Lučić, D., Carić, M., Garić, R., Licandro, P. and Jasprica, N., 2013. Did the alien calycophoran
Muggiaea atlantica outcompete its native congeneric M. kochi in the marine lakes of Mljet Island (Croatia)?. Marine Ecology, 34(s1), pp.3-13.
ERA Biotech, (2016). [online] Marinebiotech.eu. Available at: http://www.marinebiotech.eu/c/images/thumb/1/15/Calanus_finmarchicus.jpg/250px-Calanus_finmarchicus.jpg [Accessed 1 Jul. 2016].
University of British Columbia, (2016). [online] Eoas.ubc.ca. Available at: https://www.eoas.ubc.ca/research/phytoplankton/diatoms/centric/chaetoceros/images/full/C_didymus_40xDIC_1_full. jpg [Accessed 1 Jul. 2016].
Zooplankton Online, (2016). [online] Zpkonline.com. Available at: http://zpkonline.com/~bjohnson/wp-content/uploads/2013/07/margelopsis_male_or_juv_thumb.jpg [Accessed 1 Jul. 2016].
Fig 30. Siphonopohore zooplankton (Batistić et al. 2013)