Population dynamics and secondary production of the cockle Cerastoderma edule (L.) in a backbarrier tidal flat in the Wadden Sea

Abstract

SUMMARY: The population biology of the bivalve Cerastoderma edule was studied by monthly sampling from April 1994 to September 1995 at Neuharlingersieler Nacken, a backbarrier tidal flat near Spiekeroog island (East Frisian Wadden Sea, North Sea). Four stations located along a tidal gradient from 56 to 80% immersion time were established in order to analyse cockle growth, mortality and production. The highest densities were recorded at the beginning of the study (1000-1250 ind. m -2 ) with an intense and progressive decrease through 1995. A spatial distribution pattern was observed during summer 1994, with juveniles (3-12 mm long) being found in the high intertidal whereas adults occurred along the middle and lower intertidal. Based on growth increment data from tagging-recapture experiments, the parameters of the von Bertalanffy growth curve were estimated to be: asymptotic length L ∞ = 40 mm, and growth constant K = 0.404 y -1 . A growth ring was formed in summer (July-August 1994). Annual somatic production ranged between 38.16 and 59.33 g AFDW . m -2 . y -1 . Total mortality ranged between Z = 0.52 year -1 and Z = 3.03 year -1 . The distribution of the population was affected by passive displacements of juvenile cockles from the upper part of the intertidal toward lower zones in combination with high mortality at the station farthest from the coast, probably resulting from mussels overlying.Key words: Cerastoderma edule, cockle, growth, mortality, biomass, production, Wadden Sea.-Se ha estudiado la dinámica de la población del bivalvo Cerastoderma edule en Neuharlingersieler Nacken, una zona intermareal de la isla de Spiekeroog (mar del Norte), realizando muestreos mensuales entre abril de 1994 y septiembre de 1995. Al objeto de analizar su crecimiento, mortalidad y producción se establecieron cuatro estaciones a lo largo de un gradiente mareal, dispuestas en fondos sumergidos entre el 56 y el 80% del tiempo. Al inicio del estudio se registraron las densidades más elevadas (1000-1250 ind. m -2 ), produciéndose una disminución intensa y progresiva a lo largo de 1995. En el verano de 1994 se observó que los juveniles (3-12 milímetros de longitud) estaban localizados en la zona superior del intermareal mientras que los adultos ocupaban las zonas más bajas. En base a los datos de incrementos del crecimiento obtenidos en experiencias de marcado y recaptura, se estimaron los siguientes parámetros de la función de crecimiento de von Bertalanffy: longitud asintótica L ∞ = 40 mm y la constante de crecimiento K = 0,404 año -1 . Se observó la formación de un anillo de crecimiento entre julio y agosto de 1994. La producción somática anual osciló entre 38,16 y 59,33 g PSLC m -2 . año -1 . La mortalidad total osciló entre Z = 0,52 año -1 y Z = 3,03 año -1 . La distribución de la población se vió afectada por movimientos pasivos de los juveniles desde la zona superior del intermareal hacia las zonas más bajas y por una elevada mortalidad en la estación más alejada de la costa, posiblemente ocasionada por el establecimiento...

Population dynamics of the invasive Pacific oyster Crassostrea gigas during the early stages of an outbreak in the Wadden Sea (Germany)

“…Most studies on the population dynamics of marine invertebrates are carried out for non invasive populations, for example the bivalves Aequipecten opercularis (L.) from the western English Channel (Heilmayer et al 2004), Donax serra from Namibian sandy beaches (Laudien et al 2003) and from the Wadden Sea Cerastoderma edule (Ramón 2003) and Mytilus edulis (Munch-Petersen and Kristensen 2001). Only the studies of Diederich (Diederich et al 2005;Diederich 2006) give the opportunity for a detailed comparison of the population dynamic of the invasive Pacific oyster in the East Frisian Wadden Sea.…”

“…In comparison to the above mentioned non invasive populations, the population growth constant of the Pacific oyster from the Wadden Sea (range K = 0.3-0.99 year -1 ) is in the range of native natural occurrence populations: K = 0.604 year -1 for the population of Aequipecten opercularis (L.) from the western English Channel (Heilmayer et al 2004), K = 0.274 year -1 for the population of Donax serra from Namibian sandy beaches (Laudien et al 2003) and K = 0.404 year -1 for the Cerastoderma edule population from the Wadden Sea (Ramón 2003) and K = 0.243-0.902 year -1 for the Mytilus edulis population (Munch-Petersen and Kristensen 2001). Thus, the Pacific oyster population in the Wadden Sea can be described as a population which can be viable.…”

“…Calculated (with FiSAT II) over the 3 years of our investigation, total mortality was Z = 1.19-3.16 year -1 and thus in the range of other mussel populations in the Wadden Sea, e.g. Cerastoderma edule with Z = 0.52-3.03 year -1 (Ramón 2003) and Mytilus edulis with a mean annual mortality of Z = 0.84 year -1 (Munch-Petersen and Kristensen 2001). In contrast to the higher mortality of M. edulis during the first years, the mortality of the oyster population we found increased with the years.…”

Modelling of common European cockle Cerastoderma edule fishing grounds aimed at sustainable management of traditional harvesting

“…Fluctuation in the speed of growth led, in these examples, to an alternation of wide and narrow growth zones. Reading annual rings remains difficult, however, since variations in growth during the same year lead to the possible formation of extra stria [33,34]. For each winter ring observed, the SL of the cockle was measured (anteroposterior axis; Fig.…”

“…The modelling of the cockle growth can be adjusted to the model by von Bertalanffy [35], which is generally used to compare mollusc growth rates [33]. The parameters of the von Bertalanffy growth model were estimated by an iterative non-linear leastsquares method [36].…”