Demographic changes in Pleistocene sea turtles were driven by past sea level fluctuations affecting feeding habitat availability

Abstract

Pleistocene environmental changes are generally assumed to have dramatically affected species’ demography via changes in habitat availability, but this is challenging to investigate due to our limited knowledge of how Pleistocene ecosystems changed through time. Here, we tracked changes in shallow marine habitat availability resulting from Pleistocene sea level fluctuations throughout the last glacial cycle (120–14 thousand years ago; kya) and assessed correlations with past changes in genetic diversity inferred from genome‐wide SNPs, obtained via ddRAD sequencing, in Caribbean hawksbill turtles, which feed in coral reefs commonly found in shallow tropical waters. We found sea level regression resulted in an average 75% reduction in shallow marine habitat availability during the last glacial cycle. Changes in shallow marine habitat availability correlated strongly with past changes in hawksbill turtle genetic diversity, which gradually declined to ~1/4th of present‐day levels during the Last Glacial Maximum (LGM; 26–19 kya). Shallow marine habitat availability and genetic diversity rapidly increased after the LGM, signifying a population expansion in response to warming environmental conditions. Our results suggest a positive correlation between Pleistocene environmental changes, habitat availability and species’ demography, and that demographic changes in hawksbill turtles were potentially driven by feeding habitat availability. However, we also identified challenges associated with disentangling the potential environmental drivers of past demographic changes, which highlights the need for integrative approaches. Our conclusions underline the role of habitat availability on species’ demography and biodiversity, and that the consequences of ongoing habitat loss should not be underestimated.

Overview of Effect of Plastic Waste Pollution on Marine Environment

“…An important example of the role of sea turtles in the marine ecosystem is tropical sea turtles (hawksbills), which feed on a type of sea sponge that grows among coral reefs. With this type of feeding, turtles prevent excessive growth of this marine sponge and thus protect coral reefs from suffocation and death due to excessive growth of this sponge [20]. Plastic reaches the turtles through random feeding, as turtles sometimes do not differentiate between food and plastic, especially that plastic, which is very similar to turtle food [21].…”