Mabel Nava

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 af-fected 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  thou-sand years ago; kya) and assessed correlations with past changes in genetic diver-sity 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 ma-rine habitat availability during the last glacial cycle. Changes in shallow marine habitat availability correlated strongly with past changes in hawksbill turtle genetic diver-sity, 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 diver-sity rapidly increased after the LGM, signifying a population expansion in response to warming environmental conditions. Our results suggest a positive correlation be-tween Pleistocene environmental changes, habitat availability and species’ demog-raphy, 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 con-sequences of ongoing habitat loss should not be underestimated.

 

KEYWORDS: ddRAD sequencing, demographic change, habitat availability, Pleistocene sea turtles, sea level change

Date
2021
Data type
Scientific article
Theme
Education and outreach
Research and monitoring
Geographic location
Aruba
Bonaire
St. Eustatius
St. Maarten

Population recovery changes population composition at a major southern Caribbean juvenile developmental habitat for the green turtle, Chelonia mydas

Understanding the population composition and dynamics of migratory megafauna at key developmental habitats is critical for conservation and management. The present study investigated whether diferential recovery of Caribbean green turtle (Chelonia mydas) rookeries infuenced population composition at a major juvenile feeding ground in the southern Caribbean (Lac Bay, Bonaire, Caribbean Netherlands) using genetic and demographic analyses. Genetic divergence indicated a strong temporal shift in population composition between 2006–2007 and 2015–2016 (φST=0.101, P<0.001). Juvenile recruitment (<75.0cm straight carapace length; SCL) from the north-western Caribbean increased from 12% to 38% while recruitment from the eastern Caribbean region decreased from 46% to 20% between 2006–2007 and 2015–2016. Furthermore, the product of the population growth rate and adult female abundance was a signifcant predictor for population composition in 2015–2016. Our results may refect early warning signals of declining reproductive output at eastern Caribbean rookeries, potential displacement efects of smaller rookeries by larger rookeries, and advocate for genetic monitoring as a useful method for monitoring trends in juvenile megafauna. Furthermore, these fndings underline the need for adequate conservation of juvenile developmental habitats and a deeper understanding of the interactions between megafaunal population dynamics in diferent habitats.

Referenced in BioNews 31 article "Genetic Testing to Measure Sea Turtle Conservation Success"

Date
2019
Data type
Scientific article
Theme
Education and outreach
Research and monitoring
Geographic location
Bonaire