Impacts on the ocean food chain: implications for native biodiversity, seafood & tourism industries
General Context (from MBIE contract)
Climate change will drive non-uniform variation in ocean conditions (e.g., sea surface temperature, salinity, acidification, CO2, nutrients, light availability), resulting in impacts to phytoplankton production at the base of the oceanic food web and the distribution of different marine organisms. This modelling will explore the potential implications for marine fisheries, ecosystem services, native biodiversity, carbon sequestration and Maori customary fishing.
Case Study Area
The Oceans Case Study will provisionally focus on the entire New Zealand Economic Exclusion Zone (EEZ) and extended continental shelf:
The boundaries for New Zealand’s extended continental shelf confirmed by the United Nations Commission (Source; Land Information New Zealand)
Note: the Oceans Case Study does not consider coastal areas, and so excludes impacts on aquaculture, invasive species, land-ocean interactions and aesthetic values/tourism.
Potential Impacts of Climate Change
Marine Biota in the EEZ are influenced by a variety of drivers and stressors that are altering in response to climate change:-
- Warming of surface and sub-surface water
- Increased stratification of surface waters
- Changes in wind-driven mixing and currents
- Ocean acidification
- Changes in nutrient supply
- Changes in light availability
- Decrease in oxygen availability
Potential Implications of Climate Change
Most marine organisms have optimal temperature ranges, and warming of water and alteration of currents associated with climate change will result in change in the distribution of pelagic and benthic organisms, and potentially decline in abundance and distribution. Warming and change in current flow may also result in an increase presence of sub-tropical water and potentially invasive species in the EEZ.
Warming and associated stratification may alter nutrient supply to surface ocean waters, which will influence phytoplankton productivity, distribution and biomass. This will impact the marine foodchain through changes in quantity and quality of organic matter that supports prey species for fish.
Ocean acidification will have a variety of impacts on different biotic groups, particularly carbonate-forming organisms such as particular planktonic groups and cold-water corals. This has food chain and biodiversity implications, and may also affect other ecosystem services such as carbon sequestration.
Oxygen depletion in sub-surface waters may influence the depth distribution of different marine organisms
There is currently limited understanding of the net effect of the change of individual drivers and their interactive effects in response to climate change; however predicting the impact at the base of the food chain, on habitat-forming species and fisheries, biodiversity and ecosystem services is essential for guiding long-term environmental and resource (sustainable fisheries, extractive industries, and tourism) management. Discussions with stakeholders have directed the case study research to establishing the overall climate-related trends in a variety of physical and chemical variables to determine the impact on three biotic groups:
- Phytoplankton and primary production
- Cold water corals
- Major commercial fisheries
Projections from a suite of Earth System Models show significant changes in the open-ocean around New Zealand by the end of the 21st Century:
- Most of the ocean properties assessed are highly sensitive to future CO2 emissions, with the high emission scenario (RCP8.5) yielding the largest projected changes.
- Mean sea surface temperature will increase by 2.5oC, and exceed 3oC in the north Tasman Sea. Decreases in surface chlorophyll-a, nitrate, phosphate and pH accompanied by shallowing of the surface layer.
- Projected changes in wave height are relatively small, with the largest increases (<+4%) in Subantarctic waters south of NZ, and decreases (-5%) on the Chatham Rise Region.
- Surface water nutrient concentrations will decline, particularly in the eastern Chatham Rise region, with a decrease in nitrate by ~9% under RCP8.5. Conversely dissolved iron is projected to increase Subtropical water.
- The pH of surface water will decline by 0.33 under RCP8.5, with the resulting pH (7.77), and associated rate of change in pH, being unprecedented in the last 25 million years. Subantarctic surface pH will fall below the current pH minimum around 2030, with acidification creating corrosive conditions for organisms with carbonate shells in Subantarctic surface waters.
- Primary Production in surface waters will decline by an average 6% from the present day under RCP8.5, with Subtropical waters, experiencing the largest decline.
- The decrease in particle flux from the surface to the seabed, of 9-12% by 2100, indicates that carbon sequestration will decline in the open ocean around New Zealand.
- Changes in particle flux will alter the food available for fish. A decline in particle flux was identified for all 38 species (including 30 commercial species), ranging from 2.2 to 24.6% by 2100. The largest decline in particle flux occurs in areas occupied by the northern spiny dogfish, gemfish, frostfish and tarakihi, and lowest decline in areas occupied by black oreo, barracouta, southern blue whiting and blue warehou.
- Climate change will not significantly lower dissolved oxygen in the mid-water around NZ, but the depth at which carbonate dissolves will become progressively more shallow. This will contribute to a decline in suitable habitat for cold water corals in New Zealand waters, and impact deep-sea ecosystems and biodiversity. The Chatham Rise may provide temporary refugia, which should be considered in spatial management of marine protected areas.
- The regional variation of the impact of climatic change in New Zealand waters needs to be considered in management and policy decisions. For example, regions that are most sensitive to climate change include Subantarctic waters south of 50oS and the eastern Chatham Rise, which support important fisheries, and Subtropical waters north-east of NZ.
Click here to download the RA2 Marine Case Study Synthesis Report.