Emodnet-Arctic

Abundance of three most abundant species of phytoplankton expressed as time series

Summary:
This sub-challenge was quite hard to solve, due to the following reasons:

  • The study area is quite broad and is home to many different types of (eco-)systems, which makes it unwise to generalize the three most abundant species of phytoplankton.
  • Even in small geographical areas the most abundant species may change year to year, so what is one year the most abundant species may the next year not be the most abundant species anymore.
  • Most studies seem to focus on either zooplankton or primary production in the broader sense of the word, mostly focusing on chlorophyll concentrations and not on individual species.
  • The data which is available is quite spread out both on a temporal an spatial level, is presented in different formats and need different levels of processing.
  • There seem to be gaps in both time and space of monitored areas in the arctic when it comes to individual species of phytoplankton. The data found was not up-to-date.

Results:
The definition of plankton is a group of organisms in aquatic environments which are carried along by ocean currents without the means to swim against them. Phytoplankton are the ‘flora’ plankton, or microalgae, and contain chlorophyll for photosynthesis. Primary production in oceans can be measured through chlorophyll concentrations, however this does not distinguish between different species of phytoplankton. Dinoflagellates and diatoms are the two most common classes of phytoplankton.

In the Arctic area, phytoplankton are essential for primary production and serve as the base of the marine food web. Both the presence of nutrients and light availability limit primary production, giving the Arctic area a distinct seasonal character. Upwelling of warm nutrient-rich Atlantic Water is one of the key factors driving primary production.

As described in Hallegraeff (2010): “Climate change confronts marine ecosystems with multifactorial stressors, such as increased temperature, enhanced surface stratification, alteration of ocean currents, intensification or weakening of nutrient upwelling, stimulation of photosynthesis by elevated CO2, reduced calcification from ocean acidification, and changes in land runoff and micronutrient availability”. Because climate change does not affect the phytoplankton habitat in a singular way, it is difficult to predict the response of the phytoplankton community. For example, the winter sea-ice decline creates favourable conditions for upwelling, creating in turn favourable conditions for phytoplankton (Falk-Petersen et al., 2015). Other studies however indicate a less favourable condition for phytoplankton through freshening of the water by melting ice (Coupel et al., 2015). Larsen et al. (2014) indicate the decreased sea-ice as associated with earlier phytoplankton blooms. It is clear that the declining sea-ice extent in the Arctic area is contributing to shifts in primary production (Frey, Moore, Cooper, & Grebmeier, 2015; Logvinova, Frey, Mann, Stubbins, & Spencer, 2015). In 2011, NOAA published a map showing the change in primary productivity, based on a study by Arrigo & van Dijken (2015), see Figure 1.

The higher ocean temperatures create an increasingly stratified water column, inhibiting nutrient rich waters to mix with nutrient depleted waters. Amounts of larger phytoplankton such as diatoms are predicted to be reduced as they need more nutrients to survive, in comparison to smaller phytoplankton such as cyanobacteria (Lindsey & Scott, 2010). However, in the polar regions the reduced mixing will keep the plankton closer to the surface (and sunlight), creating favourable conditions for an increase in plankton (Hallegraeff, 2010).

Changes primary production fig 1 // changes-primary-production-fig1.png (567 K)
Figure 1: Changes in primary production between 1998 and 2000. Browns show declines, while greens show increases. Increases in primary production were greatest in the eastern Arctic Ocean, mirroring the areas of greatest sea ice loss in the Kara and East Siberian seas (source: Arrigo & van Dijken 2011 and NOAA 2011).

As can be seen on Figure 1, the primary production varies in the entire Arctic area. To answer the question of this sub-challenge, it was decided to not focus on the entire area but to take a smaller area as an example. The Kara sea was chosen as it seems to have had a change in primary production over the years, and phytoplankton on species level is available. As the three most abundant species of phytoplankton tend to fluctuate over the years, it was chosen to focus on species groups.

Data was downloaded from COPEPOD (The Coastal & Oceanic Plankton Ecology, Production & Observation Database - An online database of plankton abundance, biomass, and composition data compiled from a global assortment of cruises, projects, and institutional holdings, it was created by NOAA's National Marine Fisheries Service). The data was selected on coordinates roughly edging the Kara Sea (Longitude between 50 and 100, Latitude between 70 and 80), grouped on species groups and averaged per year to create time series. The following graphs were the results:

Data monitoring cruises fig 2 // data-monitoring-cruises-fig2.png (63 K)

Figure 2: Data from monitoring cruises in the Kara Sea area, downloaded from NOAA and sorted on species groups. The units on the y-axis are #/mL.

As can be seen in the above graph, as well as read in the text, diatoms and dinoflagellates seem to be the most abundant species groups in this area.

Diatom data COPEPOD fig 3 // diatom-data-copepod-fig3.png (77 K)

Figure 3: Diatom data from COPEPOD, selected on coordinates roughly edging the Kara Sea (Longitude between 50 and 100, Latitude between 70 and 80), grouped on species groups, averaged per year.

Dinoflagellate data COPEPOD fig 4 // dinoflagellate-data-copepod-fig4.png (63 K)

Figure 4: Dinoflagellate data from COPEPOD, selected on coordinates roughly edging the Kara Sea (Longitude between 50 and 100, Latitude between 70 and 80), grouped on species groups, averaged per year.


From the Biological Atlas of the Arctic Seas 2000: Plankton of the Barents and Kara Seas - physical and biological data for the region extending from the Barents Sea to the Kara Sea during 158 scientific cruises for the period 1913 - 1999, phytoplankton data per cruise in Kara and Barents sea, the Kara sea data was downloaded. The most abundant species in this dataaset were: Fragilaria spp, Thalassiosira spp, Chlorophycota spp, Nitzschia spp and Melosira spp. These species groups can also be seen in the data from COPEPOD.


References:
For this sub-challenge, the following sources were used: