COSM

Backbeach Nests

Loggerhead Backbeach Nests

Backbeach nests are those dug by the turtle in sand deposited on the backbeach, above spring high tide line, but below, or on, the storm high tide line. The storm high tide line may be represented by a berm or terrace, a scarp or bluff, or washover or washin fan. The area between spring high tide line and storm high tide line is often covered by wrack that forms wrack mats as sand fills the porosity of the mat, producing a tough surface armor on the beach.

 

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Backbeach nests are deposited between Spring High Tide Line and Storm High Tide Line, often a dry area covered by wrack mats from the last storm and/or Spring Tide. This new nest was deposited almost on top of an earlier nest, demonstrating beach fidelity, along the scarped dune ridges of South Beach. A notebook diagram for this nest was presented on the Nest Reading page.

When turtles crawl from the sea and approach the backbeach, they crawl across the latest high tide line, sense the change in temperature change from damp (tidal) sand to warm (solar heated) sand, trigger and nest on the backbeach. Because of wrack mats and other exposed and buried obstructions, these nests are often obstructed. Backbeach nests are therefore highly variable in their position and in the positioning of the egg chamber within them. Backbeach sand is firmly packed and not easily dug; tending to have shallow body pits, shallow egg chambers, and small covering pits.

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Complex, obstructed backbeach nest on South Beach at 4.586 km, nesting in Spartina wrack-mat disoriented the turtle, clutch was found by board at front center, covering pit above board in wrack [Nest 94-088].

Simple, unobstructed backbeach nest on South Beach near Mc Queens Inlet. Teacher-interns are reading and documenting nest before they dig it to validate clutch. [Nest 7/21/00].

The fine-grained sand of the backbeach is almost always strongly banded with abundant laminae of heavy mineral grains alternating with quartz layers of sand, making horizontal sedimentary lamination structures very noticeable and the egg chamber discontinuity easy to see.

 

Discontinuity 94-091 86812

Egg chamber discontinuities in backbeach nests are usually exhibited as discrete bulls-eyes surrounded by the contour-like patterns of the horizontally laminated sand layers of the backbeach facies.

The firm sand of the backbeach, their position near the spring and storm high tide lines, and their lack of elevation generally makes backbeach nests unsuccessful, especially in stormy summers. Backbeach nests are extremely vulnerable to vagrancies of tidal inundation and washout due to storms and by strong storm surges. Backbeach nests are often covered by wrack mats.

Upon emergence of hatchlings, beach slope directly influences the direction hatchlings crawl. Beackbeach obstructions, trees, stumps, or wrack, often slow the hatchlings and make them vulnerable to predation.

Last updated: 7/27/2016

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