Morphometry and growth of a Bivalve : the common cockle, Cerastoderma edule in the Bay of Somme

Type Poster
Date 2008-09
Language English
Author(s) Bellamy Elise, Mahe KeligORCID, Lefebvre AlainORCID
Meeting Physiomar, 1-4 Septembre 2008, Brest, France
Abstract Cockle (Cerastoderma edule) growth has not been studied a lot yet and the current approach of counting external ridges in order to make age estimation is limited. Nevertheless, growth is a key parameter for the monitoring of bivalve populations, which are heavily exploited in French estuaries. This morphometric study is based on the analysis of cockles shells collected in the Bay of Somme. This site, which has an area of 70 km², is located in the eastern Channel in the north of France, and is one of the most important French cockles fields.

This analysis is part of a study of the dynamic of cockles stocks in the Bay of Somme, which shows sharp inter-annual abundance fluctuations. High-resolution pictures analysis were performed with the TNPC software (Digital Processing for Calcified Structures) on both valves in order to measure the following parameters : length, width and area, with a 1.10-4 millimeter accuracy. Also, the weight of each valve was measured too with a 0.1 mg precision.

Crossed analysis of these four parameters allow quantifying the difference which may exist between left and right valves. In a second time, internal increments census after thin slicing and polishing allow estimating cockles age with a resolution of a day at least.

After age validation through the internal increments, the statistical modeling (GLM), based on external morphometric data, will be calibrated. This will enable to avoid having to study increments in the future.
Furthermore, the coupling of a growth study with environmental parameters acquisition at an adequate frequency could supply some clues to the strong abundance variations of cockles, noticed in the Bay of Somme, and so, will constitute a tool for management in this sector.
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Bellamy Elise, Mahe Kelig, Lefebvre Alain (2008). Morphometry and growth of a Bivalve : the common cockle, Cerastoderma edule in the Bay of Somme. Physiomar, 1-4 Septembre 2008, Brest, France.