Changes in productivity, including risk of spread of invasive species.

Key drivers
Temperature
Ocean Circulation
Extreme weather events
What has happened

Changes in phytoplankton primary production have been observed in the SAOT’s. For example, in 2006 warming and changes in currents boosted primary production in the northern part of the Falklands Conservation Zone.

In the cooler shallow seas around Tristan and the Falklands, kelp forests are particularly important primary producers and provide suitable habitat for many of the islands’ species. 

Kelp forests may be particularly vulnerable to climate change, although there is no recent conclusive evidence of ocean warming induced Kelp loss in the South Atlantic. This could be a result of slower warming rates, unreported changes or lower monitoring effort. Giant Kelp, found in Tristan, has an upper temperature range of 20°C. Temperatures at Tristan da Cunha’s northern islands (Tristan, Nightingale and Inaccessible islands) are already close to this and there is anecdotal evidence of kelp fronds disintegrating in summer. 

Kelp in the Falkland Islands may be more stable than other kelp habitats across the world, as the forests do not experience the same strong winter storms that affect frond biomass in other high latitude areas.

CONFIDENCE LEVEL
LOW

Low evidence, low agreement

There are many other factors that drive variation in productivity (e.g., short-term oceanographic variability or other anthropogenic pressures) and given the lack of detailed study of these in the SAOT’s observations must be treated with a low confidence.

What could happen

Further changes in temperature and extreme weather events are likely to exacerbate the current challenges facing kelp in the SAOT’s. This is likely to further impact on primary production and as a result alterations to the community structures of marine organisms. There may also be impacts on the habitat’s ability to take up and sequester CO2 from the atmosphere.

Each of the SAOTs is concerned about impacts of Invasive Alien Species (IAS) and how they could be further exacerbated by climate change. The role of climate change in new marine invasions is unclear, but changing temperatures, currents and weather patterns may open new pathways for species to arrive. It may also create conditions that facilitate the establishment and prevalence of these IAS, which in many cases out compete native species. 

St Helena has seen an increase in abundance of sea grapes, which can reproduce by fragmentation. An increase in storm events or changes in currents, alongside increasing sea temperatures could facilitate the spread of this species. It is difficult to predict what effect this might have on other primary producers and the wider ecosystem, though some impacts on Atlantic fisheries have already been observed. Kelp is also vulnerable to impacts from IAS such as invasive macroalgae or turf-forming algae which could begin to out compete native species in Tristan and the Falklands.

Accidental introduction of the house mouse to Gough Island in the Tristan Archipelago has impacted the populations of the Tristan albatross, Atlantic petrel great shearwater, and MacGullivray’s Prion as they prey on chicks and eggs. Changes in climate are predicted to make conditions more favourable for the mouse population which could further exacerbate their impact on native species.

CONFIDENCE LEVEL
LOW

Low evidence, medium agreement

There is very little monitoring and data to be able to model and predict how local-scale changes will affect primary productivity. The role of climate change in the spread of IAS is unclear, however comparisons can be drawn from other parts of the world.