Marine Fish biodiversity loss in the Pacific Islands under climate change / by Francisco Blaha

A lot of discussions are "out there" on the impact of climate change on fisheries. I should be posting more about this topic (and I will!). Is a difficult topic to grasp, yet the key message I find again and again is that "change is inevitable" and we need to figure out how to deal with it.

  Maps of projected Maximum Catch Potential (MCP) during different periods.  (a) Mean MCP for the 1980–2000 reference period. (b) Change in MCP during 2040–2060 and 2080–2100 under Representative Concentration Pathways (RCPs) 2.6 and 8.5 in comparison to the reference period.

Maps of projected Maximum Catch Potential (MCP) during different periods. (a) Mean MCP for the 1980–2000 reference period. (b) Change in MCP during 2040–2060 and 2080–2100 under Representative Concentration Pathways (RCPs) 2.6 and 8.5 in comparison to the reference period.

This paper read quite worryingly, yet I have not enough knowledge to provide fair criticism, yet I suppose that the reviewers of Marine Policy have done that. I quote some aspects out of an entry of the Nereus Program webpage and the paper itself. Read it and I leave it up to you to make your own conclusions.

The paper highlights state:

  • Under the RCP 8.5 scenario, tropical Pacific temperature will rise by ≥ 3 °C by 2100.
  • This is accompanied by declines in dissolved oxygen, pH, and net primary production.
  • This will lead to local extinctions of up to 80% of marine species in some regions.
  • 9 of 17 Pacific Island entities experience ≥ 50% declines in maximum catch potential.
  • Impacts can be greatly reduced by mitigation measures under the RCP 2.6 scenario.

The Pacific Islands region is the warmest of the global ocean. It’s also an area where there is less seasonal variability — it more or less feels like summer all year. Because there are no drastic seasons, the animals in the tropical Pacific may find changing conditions to be more of a shock.

The authors examined the effects of climate change on more than a thousand species, including those that live on reefs and those that live in open-water habitats. Both groups underwent declines in local biodiversity, but the rates of decline were higher for the open-water species.

These changes would be detrimental to Pacific Islanders, who are highly dependent on marine species for food, economic opportunities, and cultural heritage. Additional threats come from sea level rise and increasing major storms. Also, these are often developing countries with less resources available for societal adaptations to climate change.

Conclusions
Changing environmental conditions are anticipated to alter the marine environment surrounding PICTs in a multitude of ways. Increases in SST and declines in surface oxygen, pH, and NPP are projected throughout this region with these impacts accelerating throughout the 21st century, especially under the RCP 8.5 scenario.

Under RCP 2.6, these physical and biogeochemical changes are projected to be similar, albeit less severe. Together these changes in temperature, pH, oxygen, and NPP alter the ecological niches available to commercially important fishes and invertebrates. This results in high levels of local species extinction under both climate change scenarios as species either move towards more suitable habitats or as abundance potentially drops among species that are not capable of migrating.

The species that become locally extinct are not replaced by as many new species moving into the area because relatively few species are adapted to the novel environmental conditions projected to occur in the western tropical Pacific by the end of the 21st century. When taken together, these factors result in a decline in MCP that exceeds 50% across much of the tropical Pacific under the RCP 8.5 scenario. Climate mitigation measures can serve to drastically improve this projected outcome, with fewer areas experiencing large decreases in MCP under RCP 2.6.

 Graves in Majuro

Graves in Majuro