Climate change disrupts core habitats of marine species

Climate change will bring about significant distributional reorganization of marine life with a net range loss of core habitat for the majority of marine species, a new study led by researchers at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven (AWI) and co-authored by the AquaMaps Team—Rainer Froese, Cristina Garilao, Kristin Kaschner, Kathleen Kesner-Reyes predicts.

With the increasing demands for marine natural resources, understanding how these changes in species composition will affect marine life in the future is critical for conservation management. For this purpose, authors of the study ‘Climate change disrupts core habitats of marine species’ published in Global Change Biology analyzed predictions of a multiparameter habitat suitability model covering the global projected ranges of >33,500 marine species from climate model projections under three CO2 emission scenarios (RCP2.6, RCP4.5, RCP8.5) for the year 2100.

Species turnover maps showing changes in marine species composition between the beginning and the end of the 21st century under three Representative Concentration Pathways.

Results show that the majority of species will experience net range loss of their core habitat under the three CO2 scenarios modelled. Under the high emission scenario (RCP 8.5), many species’ core habitat areas will decline, resulting in a net loss of 50% of the core habitat areas for nearly half of all marine species in 2100. As a result of continuing distributional reorganization of marine life, equatorial gaps will appear for a great majority (88%) of marine species with cross-equatorial ranges. Changes in spatial dynamics of habitat use, novel or irregular trophic interactions and reduced effective population sizes are ecological implications of distributional gaps.

“This assessment of potential substantial loss of suitable habitat has so far been overlooked in global scale studies, and this study of changes in habitat suitability may illustrate ecological change better than trends in latitudinal range shifts,” according to the authors of the study.

The study implies that the ecological consequences of the depicted contractions, disruptions, or shifts are likely to have far-reaching effects on marine biodiversity. 

Many habitat-forming species, including kelp, seagrass, and corals, are among the organism groups with very high potential range size contractions and may seriously compromise habitat conditions for many more associated species that depend on food or shelter that these habitat-forming species provide.

The equator and the subtropics are predicted to see the greatest species losses, which are expected to be especially noticeable in the Caribbean Sea, eastern Mediterranean, Red Sea, and Indo-Pacific region.

Some areas will see rapid compositional reorganization much sooner than 2100. With high emissions, projections show dramatic changes in the polar regions, as well as parts of the Mediterranean and Red Sea, by 2050.

Outcomes of the research also indicate that significant alterations in trophic dynamics and the structure of the food web can result from the loss or invasion of apex predators, which are crucial top-down food web regulators in the ocean. 

More than 65% of all fish top predator species in the data set will expand their ranges to new ecoregions under the strong mitigation scenario (RCP2.6). This proportion of species increases to 92% under RCP8.5.

Under RCP4.5 and 8.5, 1% and 14% (respectively) of marine ecoregions could lose more than half of their current fish top predator species due to shifting ranges.

Top predator species turnover in the polar regions is expected to be higher than average. Changes in habitat suitability in the Arctic are projected to favor more frequent fish top predator invasion, whereas areas in the Antarctic are expected to experience loss, gain, or replacement of current fish top predator species assemblages.

“This fundamental spatial and structural reorganization of marine life necessitates renewed efforts to expand the area, connectivity, and integrity of our oceans while decreasing the number of threatened marine species,” the authors conclude. “They also highlight the importance of putting into action dynamic management plans and global partnerships in order to effectively mitigate climate change and pursue biodiversity conservation. In particular, the UN Convention on Biological Diversity (CBD/COP/15/1/Add.3; and the “30×30” target (expand protected areas to cover 30% of the planet’s land and sea by 2030), can be extremely useful political frameworks for achieving these objectives.”

Overall, the study underscores that the degree of spatial and structural reorganization of marine life, as well as the repercussions for ecosystem functionality and conservation efforts, will be strongly influenced by the realized greenhouse gas emission pathway.

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