Can These Prehistoric Sea Creatures Survive Climate Change?

4 days ago 7

by Manipadma Jena (bhubaneswar, india,)
Thursday, May 29, 2025
Inter Press Service

BHUBANESWAR, India,, May 29 (IPS) - While a rise in temperature brings an uncertain future for the olive ridley sea turtles, the efforts of international conservation organizations that ban the trade in turtle meat, leather, and shells; the Indian government; coast guards; and village volunteers, including fishermen, have made a huge difference in ensuring their continued existence. Even young village children are eager to do their bit to make sure the turtles survive.In November, tens of thousands of male olive ridley sea turtles (Lepidochelys olivacea) start congregating on just five kilometers of nearshore in Odisha in eastern India. They wait for the females of the species to arrive.

The survival of these prehistoric sea species has largely depended on suitable pairing and mating. However, research findings from around the world indicate that, in the long term, there may be a limited number of males at these mating sites compared to an overwhelming number of females.

Several studies find hatchling sex ratios skewed toward females due to rising sand temperatures brought on by climate change.

Pregnant ridleys dig flask-shaped nests around 18 inches deep and lay large clutches of up to 120 to 150 eggs into them. Covering the nest with sand using their flippers, they leave the eggs to incubate for 45 to 55 days under the sand. The tiny hatchlings scramble out on their own, waiting for the surface sand to cool at night. They make a dash in the direction of the sea by detecting the brighter horizon, which is the reflection of the moon and starlight on water.

As sea turtles have temperature-dependent sex determination, an increase in incubation temperatures at nesting beaches may result in the medium to extreme feminization of some populations, say scientists.

It’s a girl! Many More Times

A study spread over 15 years on nesting olive ridleys on Odisha rookeries in April reported the hatchling sex ratio at Rushikulya was found to be 71 percent female on average and as high as over 90 percent some years.

Gahirmatha and Rushikulya in Odisha are two of the world’s largest nesting sites for Olive Ridleys, with other similar-sized rookeries found only in Mexico and Costa Rica.

“Between 2009 and 2020 (11 years), most years had female-biased sex ratios, with the highest female proportions recorded in 2011 and 2020,” Kartik Shanker, faculty at the Centre for Ecological Sciences at Bengaluru’s Indian Institute of Science (IISc) and lead researcher of the study by Dakshin Foundation, told Inter Press Service.

Sea turtle eggs can only successfully incubate within a narrow thermal range (25 to 35° Celsius), with incubation above the thermal threshold resulting in hatchlings with higher morphological abnormalities and lower hatching (the proportion of eggs that hatch to produce hatchlings) success.

The pivotal incubation temperature, approximately 29° Celsius or around the midpoint of this thermal range, produces a 1:1 sex ratio. Temperatures above the pivot will produce mainly female hatchlings, while those below produce mainly males, according to another study. Although a perfect 1:1 ratio in a single nest is rare, nests taken together often average out.

Even small increases at the upper range of incubation temperatures can negatively affect hatching success. For example, an increase from 30°C to 31°C mean incubation temperature can decrease hatching success by up to 25 percent, finds another study.

The International Union for Conservation of Nature (IUCN) reports females accounting for an extreme 99 percent of newly hatched turtles on some nesting beaches among the green sea turtles.

“Although conservationists hold a 50:50 sex ratio as normal, however, depending on a tropical or temperate geographical location, even a 60:40 or 70:30 ratio can be expected,” Muralidharan Manoharakrishnan, Lead-Marine Species at World Wildlife Fund (WWF-India), told IPS.

“However, if an extreme female bias is found for 5 to 10 contiguous nestings, this is cause for alarm and mitigating action has to be initiated,” he cautioned.

Kai a 3-year-old green sea turtle is released back into the turquoise waters of the Indian Ocean off Kenya’s coast after hospitalization. With rising temperatures, will more hatchlings be born not in the wild but under monitored environs? Photo Credit: Manipadma Jena/IPS

Hotter Climate Also = Abnormal Hatchlings

Current changes in climatic conditions, at least over the past two decades compared to the previous decades, are the latest threat sea turtles face. This, scientists fear, can potentially result in a population collapse in the long term.

The fear is because climate change impacts not just a skewed sex ratio but more serious repercussions. Studies have shown that prolonged warm periods can decrease reproductive frequency and lower hatching success owing to decreased rates of egg fertilization.

Furthermore, higher temperatures accelerate embryo development, reducing the incubation period and limiting embryo growth time. This result is smaller hatchlings, hatchlings with higher abnormalities like faulty locomotor performances and lower energy storage ability, which can seriously compromise their ability to survive predators and travel longer distances to forage and nest.

Other Threats for the Already Vulnerable Sea Turtles

But global warming is only the latest of threats. Sea turtles over the past decades have been under a range of negatively impacting man-made pressures. These threats in their ocean and coastal habitats include unintentional capture in fishing gill nets, mainly bottom trawler nets. Coastal development for ports, tourism, and human habitat and growing beach erosion and sand extraction reduce the nesting habitat.

While poaching for turtle flesh and eggs has reduced drastically, thanks to awareness among local communities around nesting sites, light pollution around these is growing owing to unfettered coastal development. Artificial lights confuse hatchlings that are wired to move towards the sea following the rising sun on the horizon. Instead of scrambling towards the sea, they move towards land following these light sources, resulting in huge mortality.

To put it into perspective, it is believed that only one olive ridley hatchling survives to reach adulthood for every 1,000 hatchlings that enter the sea waters.

Olive Ridleys, the Most Abundant, but for How Long?

Olive ridleys inhabiting tropical and subtropical waters in the Pacific, Atlantic, and Indian Oceans are considered the most abundant of all marine turtle species in the world.

In 2008, the IUCN, which classifies species according to their risk of extinction, declared the ridley as vulnerable based on an estimated global population decline of approximately 30 percent. It says they are considered to be facing a high risk of extinction in the wild, although several scientists differ, including IISc’s Shanker, who thinks olive ridleys are doing well for themselves as of now.

While most research on the global warming impact on sea turtles has been conducted in the northwest Atlantic and Mediterranean regions, where loggerhead and green turtles predominantly nest, the Dakshin study is one of the first on climate impacts on olive ridleys.

The olive ridley turtle is a small-to medium-sized reptile, distinguished by its olive-colored, heart-shaped, hard upper shell. Adults measure between 60 and 70 cm in shell length and weigh around 35 to 50 kilograms. This species is known for its arribada (meaning arrival in Spanish) nesting behavior, where thousands of females simultaneously gather at specific beaches to lay eggs. This distinct mass nesting, although unique in nature, is what also makes them particularly vulnerable to human-induced habitat and environmental changes, including global warming.

Despite challenges, the Bengaluru-based non-profit Dakshin’s report finds olive ridley and leatherback turtles are going strong in India’s coastal region.

"Olive ridleys are thriving; their nest count has increased over the years from 25,000 to 50,000 nests a season in the early 2000s to over 150,000 in the last decade and over 400,000 in some past years," it said.

"Nests at Rushikulya have shown a higher hatching success than other mass nesting beaches around the world over the last decade," according to the non-profit.

Comprehensive impact of climate change on all species of sea turtles and suggested mitigation strategies. Extracted from open-access study by Nikolaos Simantiris

“We have only studied ridleys in Odisha so far... The process is time- and effort-intensive. Dead hatchlings have to be collected and stored in formalin. Lab work, that of dissections and study of primary reproductive organs, is done to determine the sex of hatchlings. We then use mathematical models to predict the sex ratio during each nesting, based on when exactly it occurred,” Kartik Shanker explained.

With additional temperature data, they aim to employ embryo growth models to examine the long-term trends in sex ratios, thus arriving at more exact research findings.

However, sea turtle populations have to be tracked for decades to determine reliable population data. These reptilians are long-lived and late-maturing species and, hence, changes in their demography take place over several years.

Community Proves Its Help Is Key to Turtle Conservation

On the Rushikulya nesting sands this February, a record 800,000 nests in two tranches were counted, according to Shanker. Sections of the beach were packed so thick with turtles there was barely any place to walk, volunteers said. That the prehistoric creatures are thriving, at least at this time, a large part of the credit goes to community-driven conservation.

Even though the government has ‘no fishing zones’ enforced around nest sites and pays fishermen for not fishing during those four months when turtles are active, and international conservation organizations ban trade in turtle meat and its leather and shell, it is the integrated actions of non-profits, the Indian government, coast guards, and village volunteers, including fishermen, that have made the huge difference. Even young village children are eager to do their bit.

Local volunteers ensure hatchlings are released into the sea safely; they monitor arriving turtle numbers and after fencing off the nesting sites, they take turns keeping watch day and night for around two months alongside government forest guards. While sustained awareness generation has kept humans from eating the turtle eggs that were a large-scale trade in the 1970s, dogs and birds pose a major threat to eggs and hatchlings.

This feature is published with the support of Open Society Foundations.

IPS UN Bureau Report

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