Modelling growth and reproduction of the Pacific oyster Crassostrea gigas: Advances in the oyster-DEB model through application to a coastal pond

Abstract

A bio-energetic model, based on the DEB theory exists for the Pacific oyster Crassostrea gigas. Pouvreau et al. [Pouvreau, S., Bourles, Y., Lefebvre, S., Gangnery, A., Alunno-Bruscia, M., 2006. Application of a dynamic energy budget model to the Pacific oyster, C. gigas, reared under various environmental conditions. J. Sea Res. 56, 156–167.] successfully applied this model to oysters reared in three environments with no tide and low turbidity, using chlorophyll a concentration as food quantifier. However, the robustness of the oyster-DEB model needs to be validated in varying environments where different food quantifiers reflect the food available for oysters, as is the case in estuaries and most coastal ecosystems. We therefore tested the oyster-DEB model on C. gigas reared in an Atlantic coastal pond from January 2006 to January 2007. The model relies on two forcing variables: seawater temperature and food density monitored through various food quantifiers. Based on the high temperature range measured in this oyster pond (3–30 °C), new boundary values of the temperature tolerance range were estimated both for ingestion and respiration rates. Several food quantifiers were then tested to select the most suitable for explaining the observed growth and reproduction of C. gigas reared in an oyster pond. These were: particulate organic matter and carbon, chlorophyll a concentration and phytoplankton enumeration (expressed in cell number per litre or in cumulative cell biovolume). We conclude that when phytoplankton enumeration was used as food quantifier, the new version of oyster-DEB model presented here reproduced the growth and reproduction of C. gigas very accurately. The next step will be to validate the model under contrasting coastal environmental conditions so as to confirm the accuracy of phytoplankton enumeration as a way of representing the available food that sustains oyster growth.

Introduction

Energetic budget models have been widely applied to bivalves in aquaculture, especially for assessing the carrying capacity of coastal systems (e.g. Héral, 1993, Dowd, 1997, Bacher et al., 1998, Duarte et al., 2003, Grant et al., 2003). Such models are based on ecophysiological modelling that details the physiological processes and energetics of an organism in response to environmental fluctuations. Most energetic models of bivalves are net production models (e.g. Ross and Nisbet, 1990, Raillard et al., 1993, Smaal and Widdows, 1994, Barillé et al., 1997, Campbell and Newell, 1998, Grant and Bacher, 1998, Scholten and Smaal, 1998, Ren and Ross, 2001, Hawkins et al., 2002, Gangnery et al., 2003) based on the Scope for Growth (SFG) concept (Bayne and Newell, 1983). Dynamic energy budget (DEB) models are a different type of energetic model that describes the rates at which organisms assimilate and utilise energy for maintenance, growth and reproduction. DEB modelling has also been applied to various bivalves (e.g. Van Haren and Kooijman, 1993, Ren and Ross, 2005, Cardoso et al., 2006, Pouvreau et al., 2006). The DEB theory is based on physical and chemical assumptions for individual energetics (Kooijman, 1986, Kooijman, 2000), whereas the energetics in SFG models are empirically-based using allometric relationships (Lika and Nisbet, 2000, Nisbet et al., 2000, Van der Meer, 2006).

DEB theory has recently been more specifically applied to the Pacific oyster Crassostrea gigas (e.g. Van der Veer and Alunno-Bruscia, 2006). Pouvreau et al. (2006) validated the DEB model for this species reared in various different environments and concluded that the model could be applied in many ecosystems where C. gigas is cultured. Our study aims to refine the initial version of the oyster-DEB model by Pouvreau et al. (2006) and to test the updated version under new environmental conditions in an Atlantic oyster pond. More precisely, this paper describes how effects of temperature on physiological processes have been modified and improved in the model, compared with the extended Arrhenius relationship proposed by Van der Veer et al. (2006). Model simulations were performed using a number of food quantifiers to identify those most suitable for predicting the growth of C. gigas. In the initial oyster-DEB model by Pouvreau et al. (2006), chlorophyll a concentration (chl-a) was the only food quantifier tested. Although chl-a is often used to estimate the phytoplankton biomass available for filter-feeders, there are many sources of discrepancies when using chl-a: (1) quantity of chl-a per phytoplankton cell varies a great deal over the year (Llewellyn et al., 2005), (2) the chl-a measured includes inputs from many sources, e.g. from macroalgae and river detritic particles containing both labile and refractory components, toxic algae, and picoplankton such as Chlorophyta flagellates, which are not retained or assimilated by C. gigas (Barillé et al., 1993, Dupuy et al., 2000b). Moreover, chl-a is a photosynthetic pigment and not a nutritive compound for filter-feeders. We therefore tested additional food quantifiers: particulate organic matter (POM), particulate organic carbon (POC) and, for the first time to our knowledge, phytoplankton enumeration expressed both in cell number per litre and in cumulative biovolume of cells. This assessment aimed to determine the most relevant quantifier to explain oyster growth and reproduction throughout the year.