Our Warming Ocean

Dr Anjani Ganase discusses the latest findings as scientists investigate the impacts of warmer temperatures in the ocean

 

1.     Mangrove and coral reef restoration efforts offer major returns on investment

 Sea-level rise is happening rapidly and threatens low-lying countries. Many small island states in the Caribbean and the Pacific have millions of people living along coasts. While some governments have begun prepping for sea-level rise through hard engineering and the construction of sea walls, pumps and overflows, scientists propose that restoration of coastal and marine habitats offers better long-term protection. Coral reefs, mangroves and sand dunes act as natural defences to the impact of coastal flooding, stabilise the coastline, and can provide major returns on investment. Even if restoration amounts to some 100,000 USD (which is the case on many coral reefs), the benefits of the ecological restoration outweigh the cost with respect to coastal protection. The restored habitats continue to grow, and investment in mitigation can result in other benefits which produce returns over long periods, say 30 years. In some countries where ecological solutions have been carried out, additional benefits, such as buffering the impacts of storm water pollution, have added to the long-term protection of coastlines. While many countries have emergency funds allocated for climate disaster recovery, much more should be dedicated to general conservation of marine habitats. There is the opportunity to align interests in conservation of coastal habitats with those of protection and flood reduction. Hybrid solutions using hard structures to support or ramp up coastal habitats (semi-natural defences) have also proved to be effective for the short to mid-term.

2.     Baleen whales are changing migratory patterns because of seasonal shifts related to temperature

 Phenology refers to the timing of recurring biological events, such as mating, flowering etc. In Cape Cod Bay, three species of migratory whales - right, humpback and fin whales- congregate for spring feeding. Using over twenty years of movement data of these baleen whales within the Bay along with long-term sea surface temperature data, scientists from the New England Aquarium were able to show shifts in the regional use of the gulf over time because of a warming ocean. As spring temperatures are reached earlier, they noted the earlier arrivals and departure of the humpback and right whales. They also observed the relocation of habitat by the fin whales within the bay; these feed on certain plankton species which have also been altered by thermal changes. As the bay is heavily utilised by commercial vessels, such changes in the migratory patterns and habitat use in the bay may have significant consequences on the conservation and management of the marine mammals.

 

Polar bears in North-East Greenland by Andreas Preußer, Trier, Germany

3.     Newly discovered sub-population of Greenland Polar Bears is adapting to changing environment and climate.

Polar bears are considered to be marine mammals; they spend extensive amounts of their lives roaming the Arctic sea ice hunting for seals. Polar bears are capable of swimming long distances in the ocean to get to patches of sea ice, but as climate change has resulted in less sea ice, polar bears have suffered significantly from this habitat loss and loss of food. Scientists have recently discovered a subpopulation of polar bears living in southeast Greenland that do not rely on sea ice; they hunt along the coastal edges of glaciers.  This population is genetically distinct from the other polar bears because of hundreds of years of isolation owing to the surrounding steep mountains that make access difficult even for the scientists to observe this population. Scientists also relied on the local hunting communities to gain information on the movements of bears in the region. The scientists learned that the polar bears only had access to sea ice for four months of the year for hunting seals, where they would drift on sea ice rafts over 120 miles south along the currents then swim to the nearest coastal area and walk back north to their fjord. For the remainder of the year, they hunt along the freshwater glaciers close to their homes. While this population was generally smaller in size, the discovery presents insights into the ways in which polar bears are adapting to climate change. 

 

Artist impression of ancient coral reefs by Heinrich Harder (1920).

4.     Ancient coral reefs expanded into tropical ocean space, but where might modern corals migrate in a time of rapid climate change?

 While present-day coral reefs are limited to tropical and sub-tropical regions, a look back in time revealed that coral reefs occupied a larger geographic space during the Mesozoic - Paleogene era (252 to 23 million years ago). Scientists relate the broader latitudinal distribution (up to 45 degrees north) to a combination of warmer climate and the orientation of the continents that supported large shallow water areas which were conducive for coral reef development. As the tectonic plates shifted and the climate cooled over eons, coral reef biodiversity began to concentrate in the tropical areas. In this present era, given the human-induced changes in the earth’s temperature as a result of carbon emissions, scientists are not convinced that most of the coral communities can migrate quickly enough to adapt to rapidly rising temperatures. The climate is warming over the recent hundred years, as opposed to over millions of years, and many coral species will be lost. While some corals are already being observed at higher latitudes, these corals will compete with native and temperature sensitive benthic communities, largely made up of algal communities such as kelp forests, which are the major habitat providers to crucial marine communities in temperate regions; this may further contribute to significant native biodiversity loss.

5.     Warmer oceans mean hungrier predators

 Through pole-to-pole experiments, scientists have discovered that there is greater pressure from predation in the tropical oceans of the world because of greater appetite. Such appetites peak in the tropical Pacific and Atlantic regions with warmer waters. Scientists present fish predators with squid as food and quantified the amount eaten across latitudes. Tropical areas consistently resulted in lower remaining biomass.  Warmer water temperatures increase the metabolism of fish resulting in increased activity and feeding to supplement the energy use. Such appetites may have consequences on the rest of the marine food web and may result in the reduction or dominance of certain prey populations with cascading consequences on the composition of marine communities and food webs.

 

References

Beck, Michael W., et al. "Return on investment for mangrove and reef flood protection." Ecosystem Services 56 (2022): 101440.

Guerry, A. D., et al. "Protection and restoration of coastal habitats yield multiple benefits for urban residents as sea levels rise." npj Urban Sustainability 2.1 (2022): 1-12.

Laidre, Kristin L., et al. "Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st-century sea-ice conditions." Science 376.6599 (2022): 1333-1338.

Jones, Lewis A., et al. "Climatic and tectonic drivers shaped the tropical distribution of coral reefs." Nature Communications 13.1 (2022): 1-10.

Pendleton, Daniel E., et al. "Decadal‐scale phenology and seasonal climate drivers of migratory baleen whales in a rapidly warming marine ecosystem." Global Change Biology (2022).