The Faroes ecoregion foodweb structure differs between the shelf and oceanic areas, with the former more diverse and better understood. The main species making up the different foodweb trophic levels have been listed in the previous sections. Both the shelf and oceanic foodwebs are influenced by the interannual variability of the Subpolar Gyre extent, which has an impact on the primary production and, hence, knock-on effects on all trophic levels.
Bottom-up control dominates the status of foodweb trophic levels. For instance, there is a positive relationship between primary production and 0-group abundance of sandeel and other fish larvae (cod, haddock, and Norway pout; figures 10d and 10f). The primary production effect propagates through population recruitment and individual growth of cod and haddock. Sandeel and 0-group Norway pout are key species in these foodweb interactions, and their abundances correlate to those of cod, haddock, and guillemots both temporally and spatially.
Top-down forces also operate. A large abundance of 0-group fish has the potential to graze down and thus regulate the biomass of large-sized zooplankton during late June on the shelf. The biomass of benthic crustaceans has increased in synchrony with a decrease in demersal fish (cod and haddock) suggesting predation release on the plateau.
Benthic productivity is known, in part, to be determined by the amount of phytoplankton reaching the seabed, which positively correlates with haddock and flatfish biomass. The relevance of this benthopelagic coupling is further supported by the long-lived bivalve Arctica islandica, whose growth negatively correlates with the zooplankton abundance in summer.
An important knowledge gap associated with the foodweb functioning is related to krill. At the Faroe Plateau level (200–300m) stomach content analysis identified krill as an important food source for saithe (up to 20%), while their dynamics are unknown.
Trends in non-indigenous species
Seven non-indigenous species have been detected in the ecoregion with the pink salmon (Oncorhynchus gorbuscha) being the most recent species found in 2019. The abundance of pink salmon has increased recently by several orders of magnitude in the adjacent ecoregion (Norwegian Sea), and the species may have local effects from grazing on fish larvae and other fish prey in coastal areas.
Temporal trends in non-indigenous species remains a knowledge gap.
