Nearly 20 per cent of species found in 21 of 51 UNESCO World Heritage marine sites have reached or exceeded their living thermal limits, according to an analysis by Down To Earth (DTE).
The UN body’s new report, Engaging Communities to Safeguard Ocean Life, indicated that warming oceans may make many species vulnerable and force them to live outside their known thermal ranges, raising concerns on their protection.
The DTE analysis found 881 of the 4,406 species mapped by the report have reached or breached their thermal limits. The list includes 342 species of fish, 135 species of algae and 76 species of molluscs that reside in different parts of the world’s oceans.
The list also includes five species of mammals and seven species of sharks such as lesser sandshark, Whitespotted eagle ray, Caribbean reef shark, Southern stingray, Krefft’s ray, Lemon shark and yellow stingray.
Among mammals, Atlantic bottlenose dolphin, West Indian manatee, southern elephant seal, True’s beaked whale and Crabeater seal are residing in areas located in an unsuitable temperature range.
UNESCO developed a standardised eDNA non-invasive sampling method to map ocean life and create an inventory of marine biodiversity in 21 of its 51 World Heritage marine sites.
About 53 per cent of species (consisting of 474 species) living in thermal limit range are from the Belize Barrier Reef Reserve systems, as per UNESCO data.
The Coiba National Park and its Special Zone of Marine Protection in Panama ranked second, with 26.6 per cent of its species living in thermal limits. It was followed by Everglades National Park in the US, with 24.4 per cent of its species exposed to unsuitable water temperatures.
The Banc d’Arguin National Park in Mauritania saw 23.9 per cent of species living in thermal limits that they have reached or breached.
These areas are mainly in the North Atlantic Ocean and North Pacific Ocean.
Besides, the Sundarbans in the Bay of Bengal recorded 19.8 per cent of species living in exceeding thermal limits.
“The metric we used represents the thermal limit of a species, calculated based on its current distribution. As ocean temperatures rise, many species will find themselves living beyond this limit in certain areas,” said Silas Principe, a researcher (species distribution modeler) at Ocean Biodiversity Information System (OBIS).
Principe added that this does not necessarily mean the species will face local extinction, but the possibility cannot be denied. The information indicates that these species are living in increased stress in these regions.
“Such stress could, for example, negatively affect their reproductive capacity. Some species may adapt or migrate to more suitable conditions, but others may not,” he explained.
The researcher said species living in the tropical regions have not encountered high temperatures in recent times and it remains uncertain as to what extent they will be able to adapt.
“This type of prediction highlights the urgency of meeting emission reduction targets to ensure the best possible climate outcomes,” Principe said.
At present, the global sea surface temperature (SST) is roughly 1 degrees Celsius higher than 140 years ago, according to National Oceanic and Atmospheric Administration.
The warmest future climate scenario or SSP 8.5 (best estimate projected warming of 4.4°C by the end of the century), means a ‘business-as-usual’ scenario, where emissions continue to increase at the present rate and humanity does not make enough efforts to reduce greenhouse emissions.
Fanny Douvere, head of UNESCO’s World Heritage Marine Programme, stated during the release of the report that climate disruption and ocean warming is shifting marine species into cooler and deeper waters from their natural habitats.
Ocean heat content has impacted all the six major oceans since 1998. But the most significant warming has been in the southern oceans, a study led by Saurabh Rathore, a postdoctoral researcher at L’OCEAN, Sorbonne University, Paris had said.
The IPCC’s Climate Change 2022: Impacts, Adaptation and Vulnerability already observed North Atlantic right whales moving northwards due to warming waters in the ocean and decrease in food availability.
The whale is known to feed in the Canadian provinces of New Brunswick and Nova Scotia which are believed to be abandoned as fish, lobsters, oysters and crabs are migrating towards suitable waters, marine ecologist Andrea Buchholz told DTE.
Similarly, warming waters have compelled white-beaked dolphins found in cooler North Atlantic waters to move north-west from the southern areas during 1991-2017.
The exposure to high temperature stress also impacts reproduction of mammals. Female sperm whales are unable to conceive at their known rates due to warm waters.
High temperatures also affect survival rates of mammals and increase stress levels. As species migrate for new suitable waters, they become more vulnerable to new pathogens.
Warming oceans also affect water movement, impacting oxygen levels between the surface waters and deeper waters that naturally circulates, providing nutrients to marine species.
These changes can alter species behaviour. For instance, bacteria which use oxygen as fuel switch to nitrate, eventually releasing nitrogen gas and impacting water and atmosphere characteristics, a study ‘Ocean Acidification: From Knowledge to Action’, published in 2012, said.