OYSTER PRODUCTION IN A MAN-MADE SALTWATER CREEK SYSTEM IN THE NETHERLANDS

Introduction

In the Netherlands traditionally two main sites are used for oyster production: Lake Grevelingen and the Eastern Scheldt. Production in these systems have their challenges as food availability is low and competition high in the Eastern Scheldt, while in Lake Grevelingen water quality issues arise occasionally. The sector is therefore looking for additional cultivation sites. Recently a man-made saltwater creek system was constructed as a new nature reservation area in the Southwestern part of the Netherlands. Within the 300 ha area approx. 30 ha is designated for aquaculture activities. In 2020 first experiments focusing on the oyster production potential within the area started. As growth of oyster is dependent on the environmental circumstances (Barillé et al., 1997; Bernard et al., 2011; Cognie et al., 2003; Palmer et al., 2021) the system characteristics were also investigated.

Methodology

The Waterdunen area, a man made saltwater creek, is located near Groede, The Netherlands. The creek system is fed by North sea water through culverts that dampen the tide. The system is exposed to a tidal curve of approx. 1.2 m. At the end of the 3.2 km creek system a 7.500 m2 experimental location has been developed. At the inlet of this area three paddlewheels are able to increase the flow through of oxygen rich water.

System characteristics were investigated using continuous data loggers (water temperature, dissolved oxygen, chlorophyll, turbidity and flow velocity). Furthermore every three weeks water samples were analyzed for microalgae abundancy during the period December 2020-August 2021.

Growth of the Pacific cupped oyster (Crassostrea gigas) at different live stages (oyster spat of 14mm, half-grown oysters of 32.5g and commercial size oysters of 60.3g) was assessed using three oyster cultivation methodologies (off bottom and bags with an inundation time of 16 h. and bags with an inundation time of 12 h.). The growth of oyster spat was assessed every three weeks using measurements of the length of 300 individuals per treatment. Growth of the half-grown and commercial size oyster was assessed using total weight, tissue weight and condition index (AFNOR) every six weeks for 90 individuals per treatment. In addition the growth of on bottom European flat oysters (Ostrea edulis, 52.5g) were also assessed using the same measurements and sample size. Mortality of all oyster groups was evaluated over time by counting dead individuals.

Results

Preliminary results show relatively high chlorophyll content within the water system (3.3 – 16.7 µg L-1 December – March) as compared with the main cultivation sites in the Netherlands (0.51 – 4.1 µg L-1  and 0.48 – 11.6 µg L-1 December – March for Lake Grevelingen and Eastern Scheldt respectively (Rijkswaterstaat, 2021)). Due to the low water column and tidal curve temperature fluctuations can be fast (water temperature of 6.5˚C at 6 February 2021 and 0.5˚C at 12 February 2021).

A clear effect of inundation time on the growth and mortality of all oyster groups was found. Highest growth occurred in the oysters that had the longest inundation time (while these groups showed lowest mortality. Pacific cupped oyster spat started growing within the winter months while half-grown and commercial size Pacific cupped oysters started showing growth in spring. In all cases growth was mainly related to the chlorophyll content in the water. The European flat oysters did not shown any growth and high mortality was found in this group, most likely due to high turbidity in the water column.

References

Barillé, L., Prou, J., Héral, M., & Razet, D. (1997). Effects of high natural seston concentrations on the feeding, selection, and absorption of the oyster Crassostrea gigas (Thunberg). Journal of Experimental Marine Biology and Ecology, 212(2), 149–172.

Bernard, I., de Kermoysan, G., & Pouvreau, S. (2011). Effect of phytoplankton and temperature on the reproduction of the Pacific oyster Crassostrea gigas: Investigation through DEB theory. Journal of Sea Research, 66(4), 349–360. https://doi.org/10.1016/j.seares.2011.07.009

Cognie, B., Barillé, L., Massé, G., & Beninger, P. G. (2003). Selection and processing of large suspended algae in the oyster Crassostrea gigas. Marine Ecology Progress Series, 250, 145–152.

Palmer, S. C. J., Barillé, L., Kay, S., Ciavatta, S., Buck, B., & Gernez, P. (2021). Pacific oyster (Crassostrea gigas) growth modelling and indicators for offshore aquaculture in Europe under climate change uncertainty. Aquaculture, 532, 736116. https://doi.org/10.1016/j.aquaculture.2020.736116

Rijkswaterstaat. (2021). Veldparameters-OW (Expert)—Rijkswaterstaat Waterinfo. Waterinfo. https://waterinfo.rws.nl/#!/kaart/Veldparameters-OW/(massa)Concentratie___20chlorofyl-a___20in___20Oppervlaktewater___20ug___2Fl