COSM

Nest Morphology

Loggerhead Nest Morphology

Loggerhead Sea Turtle nests can be classified by their complexity, position on the beach, and surface conditions found after nesting. Classification allows one to define commonalities in nest morphology and begin to understand their genesis. In the SCISTCP we have classified nests for many years according to this scheme.

Two levels of complexity are recognized:

Simple Nests — in which the turtle crawls onto the beach, excavates her body pit in loamy sand facing shoreward, deposits her eggs, and exits as she covers by rotating 180o either over her egg chamber or by making a loop shoreward of the nest, forming an elliptical covering pit with entrance and exit crawlways at opposite ends of the nest.

Complex Nests — in which the turtle crawls onto the beach, often multiple times, wanders about, excavates her body pit in firm sand facing virtually any direction, deposits her eggs, and exits as she covers by rotating around over her egg chamber forming an elliptical covering pit with entrance and exit crawlways on the ocean side of the nest.

Four positions on the beach are recognized:

Dune Nests — The turtle nests on the front, top, or behind the first sand dunes on the beach; body pits are deep due to dry surface sand and subtle stratigraphic layering masks the position of the egg chamber.

Backbeach Nests — The turtle nests at, or above, the spring high tide line, often in, or below, fresh or old wrack mats, and/or in heavy mineral layers.

Washover nests — The turtle nests on a washover fan; nests are deposited in laminated sands and egg chambers are often placed in damp, or wet sand susceptible to inundation and being washed out or buried by accreting ephemeral sand dunes.

Forebeach Nests — The turtle nests above high tide level on a neap tide; nest is deposited below spring high tide line level and will be inundated by spring high tides and storm tides; beach is very firm and often wet below, eggs are deposited in shallow egg chambers barely covered by covering behavior.

Two surface conditions are recognized:

Obstructed Nests — The turtle often encounters obstructions (wrack, grasses, exposed or buried logs, buried soils or peat) as she attempts to dig her body pit or egg chamber; often resulting in wandering crawlways, multiple attempts to dig egg chambers, chaotic behaviors and resulting in complex nests, clutches of eggs often placed in “odd” places (outside the nest beneath the wrack mat, beneath clumps of grass, beneath and alongside logs), and thin bioturbated covering layers.

Unobstructed Nests — The turtle encounters no significant obstructions to nesting; resulting in elliptical nests with clearly defined entrance and exit crawlways, flipper scarps, and a hummocky bioturbated surface covering layer.

A glossary of terms is provided for your ease of learning in this section as is a diagramatic nest sketch.

dnr_loggerhead_nest_morphology

Diagram of Loggerhead nest morphology (Courtesy of GaDNR).

nstmap

Diagram of matrix of morphologic elements around and within a Loggerhead nest. Note that the body pit and egg chamber are covered by the stirred-up (bioturbated) sand of the covering pit.

Nests are three-dimensional structures, so to understand them they could be trenched to expose the layering (stratigraphy) in a vertical view. This technique of visualization is common in Geology because geologists often see structures in vertical faces or diagrams.

nest_cross_section

A vertical trench along a line through line x-y on the map view of “morphologic elements” above right would show the stirred-up (bioturbated) sand of the covering pit overlying that filling the body pit and neck of the egg chamber. This disturbed sand overlies the still firm, laminated sand of the active backbeach.

Last updated: 12/11/2014

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