COSM

Forebeach Nests

Loggerhead Forebeach Nests

Forebeach nests are those dug by the turtle in sand deposited on the forebeach, the area below the spring high tide line and above low tide. The forebeach, comprised of firm, packed sand, forms as sand is washed in and out and along the shoreline.

During neap tides, the high tide line is located well out on the forebeach, exposing the upper forebeach to solar heating. Nesting turtles sense the temperature difference as they crawl from wet sand on the lower forebeach onto the solar heated sand on the upper forebeach, triggering their nesting behavior and often causing nesting below the spring high tide line. Forebeach nests are therefore in a position where they will be inundated by the next spring tide set and the eggs will be drowned. Forebeach sand is firmly packed and difficult to dug; tending to have very shallow body pits, very shallow egg chambers, and limited covering pits.

The fine grained sand of the forebeach is often lightly banded with ghostly laminations consisting of heavy mineral and quartz layers, making sedimentary structures difficult to see and the egg chamber discontinuity very difficult to see. Because of their location, these nests must be relocated if they are to hatch.

Forebeach nests are generally deposited during neap tides when the turtle triggers crossing the lower high tide line present on those tides.

97-072ret

Nest [97-072] was deposited at grid location 1.8 km on South Beach about 2 m in front of a 30 cm erosional scarp. Relocation was necessary to insure a hatch. The egg chamber was situated in the top of a 28 cm heavy mineral bed. The nest was trenched twice to study its stratigraphy and to sample the sediment.

There will be no emergence of hatchlings from forebeach nests left in place, the eggs will be blackened by reduction in anaerobic conditions and smell sulfurous.

Egg Chamber Black Eggs Washed 665

A forebeach nest that was not moved in the early part of our learning cycle was deposited on the upper forebeach slightly below the Spring High Tide Line. A storm moved a wedge of sand onto the upper foreshore and backbeach resulting in deposition of an additional 20 cm of laminated sand and drowning of the eggs. Assessment of the hatch of this nest showed no hatch due to drowning by inundation. Normally these eggs would also be blackened by reduction.

Last updated: 7/27/2016

Sea Turtle Program at St. Catherines Island • (912) 478-1744 • jgaskin@georgiasouthern.edu