Green sea turtle [photo credit: Papahanaumokuakea National Monument]

(CN) – Sea turtle populations in Pacific coral reefs are increasing, according to a study that reveals the positive results of environmental protection efforts around the world and gives researchers information to protect these turtles from the effects of global changes.

Researchers from the U.S. National Oceanic and Atmospheric Administration’s Pacific Islands Fisheries Science Center recorded numbers of threatened and endangered sea turtles for 13 years at 53 sites across four regions of the U.S. islands in the Pacific as part of a larger study of other marine life, according to a research article released Wednesday by PLOS ONE.

The sites were located between islands, atolls and reefs in American Samoa, the Hawaiian Archipelago, the Mariana Archipelago and the Pacific Remote Island Area complex. Each site was observed every two or three years in April, using a boat towing two scuba divers 49 feet underwater who recorded the species and numbers of turtles within sight.

Researchers observed two species specifically, the green and the hawksbill turtles. Green sea turtles greatly outnumbered hawksbill across the survey area, providing further evidence of the need to protect the endangered hawksbill.

Historically hawksbills were exploited for their tortoiseshell, and study authors say the creatures are also at risk due to “highly-threatened coral reef habitat on which they depend for sponges and invertebrate prey.” In most parts of the Pacific hawksbill turtles are scarce, but the study noted there were significant numbers of hawksbill in American Samoa.

A hawksbill turtle swims in off the coast of Saba, Netherlands Antilles. (Aquaimages via Wikipedia)

The news is even better for green sea turtles, who were present in relatively high numbers at some sites and showed population increases overall. These higher numbers can be attributed to global efforts to protect sea turtles and their habitat, and the research confirms “extensive management protections can yield positive conservation results.”

Researchers have regularly visited sea turtle breeding grounds for observation and monitoring, but until now have not had access to comprehensive in-water surveys where turtles spend the majority of their time.

“This study represents one of the largest sea turtle population surveys ever conducted, filling critical gaps on in-water abundance and drivers of population density. Across the tropical Pacific several locations held impressive densities of sea turtles, and in all regions densities were driven by bottom-up forces like ocean temperatures and productivity and top-down forces such as human impacts,” said article co-author Sarah Becker of the Monterey Bay Aquarium in California in a statement.

In the future, the authors say it would be helpful for researchers to sample across seasons instead of one month, and also track seasonal temperature changes and document corresponding shifts in sea turtle populations.

The study notes that “if documented rates of warming continue,” some cooler areas like the Hawaiian Islands might see an increase in sea turtle populations while warmer waters might surpass the ideal temperature for turtles to thrive, and see numbers decline.

“Understanding the relationships between turtle populations and environmental drivers will help managers predict and protect turtle populations given rapid global change,” the authors wrote.

Strict enforcement of laws protecting sea turtles provides one path to protecting and increasing their population, but environment may be a limiting factor and additional research is needed.

The news was not all good for marine creatures, however. A second study issued Wednesday led by Rutgers University found global warming hits sea creatures the hardest, with twice as many disappearing from their habitats as land-dwelling species.

Study authors looked at worldwide research on nearly 400 species, and found many more marine creatures live on the edge of dangerously high temperatures and – unlike land animals – don’t have forests, shaded areas or underground to escape the heat.

“We find that, globally, marine species are being eliminated from their habitats by warming temperatures twice as often as land species,” said lead author Malin Pinsky, an associate professor at Rutgers University-New Brunswick, in a statement. “The findings suggest that new conservation efforts will be needed if the ocean is going to continue supporting human well-being, nutrition and economic activity.”

Looking historically, the researchers noted ancient extinctions have often been concentrated at specific latitudes or in areas where climate changed rapidly.

“Understanding which species and ecosystems will be most severely affected by warming as climate change advances is important for guiding conservation and management,” the study authors wrote.