Loggerhead sea turtle (Caretta caretta) microbiome: insight into endozoic and epizoic communities (TurtleBIOME)
Funding: Croatian Science Fund (HRZZ): Installation Research Grants (UIP-05-2017)
Project duration: 01. 03. 2018. – 28. 02. 2023. (60 months)
Project leader: Sunčica Bosak, PhD, Assistant professor
Project number: UIP-2017-05-5635
Funding (HRZZ): 1.943.840,00 HRK (260.918,00 EUR)
Co-funding (PMF): 361.800,00 HRK (48.892,00 EUR)
Project web page: http://www.turtlebiome.biol.pmf.hr/
The microbiome of animals and plants has become increasingly regarded as a vital system, key to the survival and fitness of their host. The microbial communities throughout the host’s body, and specifically within the gut, give their hosts support with symbiotic functions, like aiding the immune system or protecting from pathogens. Furthermore, the evolution of hosts is currently viewed through the paradigm of holobiont, describing the plant/animal together with the organisms living within or on their surface. Sea turtles are fascinating, large, long-lived, widely distributed marine vertebrates, but highly susceptible to human disturbance in marine ecosystems and consequently among the most endangered species in the world. We propose a study that would allow us to obtain the very first description of sea turtle microbial biodiversity by studying the microbiome of Mediterranean subpopulation of loggerheads occurring in the Adriatic Sea. Due to long-term conservation efforts, the Mediterranean subpopulation of loggerhead sea turtles shows an overall population increase and is considered as Least Concern on the IUCN Red List. Hence, we believe that this stable Mediterranean subpopulation offers a unique opportunity to study both healthy, numerous population and individuals that are recovering in sea turtle rehabilitation centers.
Turtles are famously known for their shells, with the upper carapace harboring a complex community of epibionts such as macroalgae and invertebrates. Some of these organisms require the animal substrate to live and develop and are thus exclusively epizoic and depending entirely on their hosts. Recent exciting findings show that sea turtles also harbor unique and abundant communities of diatoms – one of the most important groups of photosynthetic microorganisms present in almost all aquatic habitats. Sea turtle-associated diatoms show the ability to colonize the surface of animal tissues, both skin and carapace and new species/genera have been described worldwide from all sea turtle species. In spite of their importance and essential role in the host animal physiological functions, there are huge knowledge gaps on the sea turtle holobiont. Very little is known about microbes inhabiting sea turtle intestines and with no reports describing sea turtle epibiotic bacteria. TurtleBIOME project contribution will be to provide a clear, complete and detailed image of the microbial composition of the surface biofilm and the gut microbiome of loggerhead sea turtles. We will achieve this goal by pairing state-of-the-art culture-independent molecular approach, e.g. new generation sequencing (NGS) of bacterial and fungal components of the micro-community and single cell PCR amplification of diatoms, with classical approach of diatom cultivation and light and electronic microscope observations of biofilm components. The added value of this research is that we propose to analyze and characterize the microbiome of different individuals stranded or accidentally caught in the eastern coast of Adriatic Sea in cooperation with the Marine Turtle Rescue Centre in Pula, Croatia.
We believe that our Adriatic study will address the current gaps in the literature and general knowledge about microbes, sea turtles, and their close associations. The proposed study will provide baseline data on the composition of loggerhead microbiome that might be integrated with the existing information about sea turtle behavior, their migration routes, and foraging habitats thus contributing to long-term plans for sea turtle protection. This investigation may open many new avenues for further research into co-evolution and biogeography of microbial epi- and endobionts and their hosts, their physiological ability to thrive in these extreme habitats, as well as their capacity to function as ecological indicators of sea turtle behaviour and health. Similar approach could be used to monitor and protect other large marine vertebrates such as dolphins or whales in the rapidly changing world we live in.
Photo credit: Marinko Babić