FALMOUTH FIELDCOURSE

Group 5

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Biological data

The biology of the water column was tested by counting and identifying the phytoplankton and the zooplankton present at varying depths and locations.

Phytoplankton cell count was measured using a 1ml sample of the 100ml seawater sample collected. This was placed on a Sedgewick rafter cell with engraved squares. The number and species of phytoplankton in 100 squares were counted.

The zooplankton was measured using the a 10ml sample of the 1L sample collected. This was put into a Bogorov chamber and the number and type of zooplankton were counted. These were then converted to the number per volume of water sampled using the following equations.

πr2L = V and (nx100)/V = N

Chlorophyll concentration was measured using a fluorometer. The acetone with filter paper was frozen over night as an alternative to sonicating the sample. Once in the lab the acetone was poured into a tube and the µg/L of acetone was measured using a fluorometer. This was converted to µg/L of seawater using µg/L acetone x (6/100).

The concentration and location of plankton depends on the stratification of the water as this will affect the location of the nutrients.

Above: Chlorophyll analysis in a fluorometer (Photo credit - Eleanor Spencer)

Phytoplankton

Station C4

There may be an outlier in the Nitzchia sp as there appears to be a much larger standard deviation (600,000 phytoplankton cells per litre). Whereas all other species identified are found within similar quantities. This anomaly may be due to human error in identification or counting.

Station C5

There are clear distinctions between the individual depths sampled at location C5 with few species being found at multiple depths. There were only three individual species found at this site (two species at 27.7m and 45.6m and only one species at 7.5m and 27.7m). There was a large amount of diversity observed at 27.7m corresponding to the chlorophyll maximum. However, the largest accumulative number of phytoplankton may be found at 7.5m, where light attenuation is the greatest. The species found here was Rhizosolenia setigera. This environment is perfect for this species, this could explain why they are so abundant here.  

Station C7

Divisions between each depth at station C7 are not clearly defined, with several species found at multiple depths. Three species were found at depths 8.7m and 17.4m. Guinardia flaccida was found at three depths (8.7m, 25.2m and 45.5m).  However, the Largest diversity of species occurred at 17.4m with 8 species being observed and a larger number of phytoplankton found. This would correspond with the chlorophyll maximum found at this depth.

Station C8

There is no clear distinction between depths at this site due to the majority of the species being found at several depths. However, 44.8m was found to have clear separation due to the species found there (Rhizosolenia sp.).  This species may be found at depth as they migrate to over 300m to collect nutrients. An outlier can be observed for Leptocylindrus daricus at 22.1m. This particular species is more commonly found at river lagoon inlets. The anomaly could be consequence of human error, since the deviation (100000 phytoplankton cells per litre) is so large and these spikes cannot be observed in any other species

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Click below for more data from offshore

Click below to see our biological data from the estuary and the pontoon at King Harry Ferry

Chlorophyll

The chlorophyll concentration at station C5 reflects the fluorescence patterns observed in the CTD data collected. The large peak shown at ~20m shows a strong deep chlorophyll maximum, this is the base of the thermocline as seen in the CTD data.

Station C7 chlorophyll concentration shows a strong peak at about 18m, this reflects the deep chlorophyll maximum observed in the CTD fluorescence data.

Chlorophyll concentration at station C8 shows a deep chlorophyll maximum at ~20m, this supports the CTD data.

The lack of time and resources limited our collection of samples for chlorophyll analysis, this therefore restricts our picture of the water column structure. The large error bars shown suggest that the chemical analysis may not have been entirely accurate.

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Zooplankton

Copepoda is the most abundant species throughout all 3 stations analysed for zooplankton offshore. Copepoda are considered to be the most abundant holoplankton species around the world. When comparing  the copepod numbers at stations C5 and C8; the shallower depth of C5 (12-7m) had a lower abundance than the deeper depth (25-18m) with a difference of 150 individuals per metre cubed. However, for station C8 the opposite occurred but with a difference of 500 individuals per metre cubed. At station C5 all other species that were found at both depths have a greater abundance at the shallower depth excluding that of Hydromedusae (Jellyfish).

In station C7, at the depth around the chlorophyll maximum, Copepoda are found in high abundance. Excluding that of station C8 at depth 10-5m where Echinoderm larvae are found to be equal in number to that of Copepoda. Though at this station species diversity is found to be similar for both depths, the species abundance is found to be greater at the shallower depth (10-5m) with the majority of the species found at this depth. Since this location only had one replicate this difference may be considered to be human error.  

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