Beach profile monitoring for marine turtle nesting areas.

By Charlotte de Fontaubert, Heidi Hertler, Aaron Henderson, and Anela Akiona

The Turks & Caicos Islands (TCI) are an archipelago of about forty limestone islands. Most of the land habitat is scrub lands. The mangrove forests, seagrass ecosystems, salt flats and coral reefs that line the coast are among the most biologically productive coastal tropical systems, functioning as both nurseries and refuge from predators. Scattered between these coastal ecosystems and limestone cliffs are white sand, isolated beaches, proven to be ideal for turtle nesting.

Near shore coral reefs are extremely productive, supporting most of the TCI economy, either through fisheries or tourism, along with resident and transient marine turtles. TCI waters support regionally significant foraging aggregations of green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles, and, to a lesser extent, loggerhead (Caretta caretta) turtles, all species which have been designated as endangered or critically endangered by the International Union for the Conservation of Nature (IUCN). They are also listed under Annex I of the Convention on International Trade in Endangered Species (CITES), and while this listing protects these species from international trade between parties to CITES, they are still harvested throughout the Caribbean, largely for domestic consumption. Marine turtles utilize a variety of habitats throughout their lives including sandy beaches, coral reefs, seagrass beds, and other shallow nearshore foraging areas.
Sea turtles are one of the most ancient groups of animals. They are primarily found in warm and temperate waters around the world. Many migrate over 1,000 miles from feeding grounds to nesting beaches, the same beaches from where they were born. Female green turtles mate every two to four years, usually in June through September; while female hawksbills breed every two years, usually in April through November. Sand temperature determines the sex of the turtle, where below 30ºC is predominantly male and above is predominately female. Hatchlings emerge at night from buried nests to make their way to the sea. Turtles feed on jellyfish, seaweed, crustaceans (crabs and shrimp), sponges, and algae, all of which are abundant around the Turks & Caicos Islands.
Whilst the full extent of the impacts of climate change on marine and coastal ecosystems is hard to predict in any significant detail, many of these impacts have already been observed and felt, globally and in the Turks & Caicos. For instance, sea-surface temperatures have increased, sea-level has measurably risen, current pattern changes have been documented, and even water pH balance has changed as a result of ocean acidification. These impacts are of great concern for the survival of marine turtles.
Temperature profoundly influences many aspects of marine turtle life behavior and distribution, from adults’ distribution to sex ratios of hatchlings. Elevated sea surface temperature and changes in precipitation affect turtle growth rate, nesting periodicity and onset of nesting season, incidence of disease, and change predator distribution and prey abundance. Sea-level rise affects beach erosion pattern and size, thus reducing nesting site option and success. Altered strengths and locations of sea-surface currents affect migration patterns and alter distribution of juveniles.
It is within this context that the School for Field Studies Centre for Marine Resource Studies (SFS CMRS) has launched an innovative project, funded in part by the Curtis and Edith Munson Foundation and supported locally by Ambergris Cay, to monitor changes in the profile of beaches where marine turtles are known to nest. In addition, SFS CMRS carries out a capture and tag program focusing on site fidelity (areas used by individuals) and growth rates. The project follows an innovative yet very simple and inexpensive methodology, which was originally developed by the World Wildlife Fund (WWF) with a view to encourage the collection of consistent, comparable, and reliable data on marine turtle nesting beaches throughout the world. The methodology is relatively labor-intensive; however, the tools used are quite cheap and easy to procure, thus ensuring the possible adoption of this methodology in the most basic settings. Led by the Centre Director, Dr. Heidi Hertler, and Research Fellow, Dr. Charlotte de Fontaubert, the project has been implemented with a series of interns and students participating in the SFS study abroad program. The beach profiles can be compared throughout the year to account for seasonal variations, and over time, as the impacts of climate change become more acutely felt.
Nine beaches historically or currently used as turtle nesting sites on the Caicos Banks are regularly visited. Beach profiles are measured to monitor change in beach area and erosion and accretion patterns over time. Beach characteristics include beach width, slope, and characteristics, and shading. Temperature loggers were installed near potential nesting sites to monitor changes in temperature annually and to collect long-term data. SFS CMRS is also monitoring weather conditions, including rain, temperature, and solar radiation.
The project methodology requires the researchers to measure the distance and angles between different segments of each beach, all the way up to the vegetation line and down to the watermark. A beach typically has a backshore, foreshore, and nearshore and all these areas are carefully measured. Two different techniques are always used in parallel, the so-called Emery and Abney methods. The Emery method requires two people to hold measured poles and to extend a transect line and a simple line equipped with a level, and to measure both the distance and the height difference between the poles. This provides useful three-dimensional data about the beach. The sand characteristics are made up of temperature, color, particle size, and moisture content. All affect the rate at which heat is exchanged between the surface and the turtle nest. Beach temperatures vary among beaches and seasonally. The average temperature of beaches associated with an undeveloped coast is greater than near developed coast. Orientation of the beach plays a role in this and further investigation is underway. We are also discovering that all beaches are not the same with respect to sand grain size.
We are continuing to investigate other variables that will impact turtle nesting success now and in the future. Once all the data have been collected, covering at least two full years, the results of this research will be aggregated with those of sister projects around the world, thus allowing for comparison of the situation in the Turks & Caicos to that in other, far away areas where marine turtles nest and even in different oceans.
In addition to our beach profiling, Dr. Aaron Henderson leads SFS CMRS staff and students on surveys of the marine turtle population around South Caicos. Turtles are captured, measured, and, if not already, tagged with flipper and Passive Integrated Transponder (PIT) tags. Turtle movement is also tracked using Lotek Lat1400 tags from which we can determine in what environments they roam, i.e. banks, shallow reefs, or deep reefs. DNA samples also help to understand better the local population.
Maintaining healthy habitats for marine turtles in a changing climate can have ecological, social, and economic benefits. Healthy ecosystems provide protection for additional species and continue to supply resources to coastal communities. Understanding the impacts on the natural resources of the TCI make us better equipped to help sustain marine populations dependent on them.