Growth performance and condition of oysters (Crassostrea gigas and Ostrea edulis) farmed in an offshore environment (North Sea, Germany)

Abstract

Aquaculture production plays an increasingly important role to meet the global demand for aquatic products and expands continuously. Most mariculture organisms are produced in coastal areas, where space is scarce and user conflicts exist. For extensive cultures farming off the coast at offshore sites could be a solution to eliminate these problems and facilitate further expansion of environmentally sustainable aquaculture. The aim of this study was to examine the biological adequacy of two candidate species for ostreiculture, the Pacific oyster Crassostrea gigas and the European flat oyster Ostrea edulis. Growth rates, condition and mortality in offshore environments were investigated by transferring oyster spat of both species to 4 different sites in 2004 and 2007. Samples were taken every six to eight weeks from April to October and length, width, height and dry mass were measured as well as the Condition Index (CI = dry mass meat •100/dry mass shell) was calculated. Results show that both oyster species grow successfully in a high-energy environment. Mean growth rates are similar to those measured in individuals from coastal habitats (wild banks and cultures) and the CI shows seasonal variation in both species. The survival rate for both species was N 99% in 2007. However, in the previous trial in 2004 a high mortality rate was observed for O. edulis at one single site at the end of the experiment. Differences were observed in the increase of shell length and dry mass between sites and size classes. Taking these results into account site-selection criteria for different offshore locations are presented. We conclude that offshore cultivation of oysters will be successful if site-selection criteria are examined carefully when choosing a location for offshore aquaculture.

The German Case Study: Pioneer Projects of Aquaculture-Wind Farm Multi-Uses

“…Bernadette Pogoda) located on the seabed of coastal seas. In general, growth rates were similar to those of oysters from nearshore coastal areas (Pogoda et al 2011). This documents that offshore-cultivated oysters are able to achieve a "normal" or "natural" growth performance.…”

“…Results of these studies clearly elucidated that all three bivalve species grow successfully under exposed conditions in offshore environments (e.g. Buck 2007;Brenner et al 2012;Pogoda et al 2011Pogoda et al , 2013. As the "multi-use" of offshore wind farms for aquaculture installations will facilitate the further expansion of environmentally friendly and sustainable aquaculture, most test sites of the described cultivation experiments were conducted in North Sea areas of two offshore wind farms (OWF): "Butendiek" (in operation since 2015) and "Nordergründe" 1 (currently under construction in late 2016, Fig.…”

“…11.15b). Thicker shells and a very compact appearance indicate that these animals strongly invested energy in shell growth to withstand the strong currents as well as to prevent shell abrasion (Newkirk et al 1995;Pogoda et al 2011). This emphasizes the importance of a detailed and thorough site selection prior to the start of offshore oyster cultivation or any aquaculture operation in general (see Pogoda et al 2011).…”

“…All three species are classified as extractive species in aquaculture and are therefore ideal candidates for offshore cultivation with IMTA concepts. They reduce nutrient emissions of higher trophic species by filter-feeding and require low maintenance as they do not require additionally feed (Pogoda et al 2011).…”

Offshore and Multi-Use Aquaculture with Extractive Species: Seaweeds and Bivalves

“…Mussels (Mytilus edulis) and oysters (Ostrea edulis) were successfully cultivated in and in the vicinity of the wind farms Nordergründe (17 nautical miles off Bremerhaven) and Butendieck (ODAS, 14 nautical miles off the Island of Sylt), as well as in North-South and West-East transects crossing all potential wind farms in the German Bight (Brenner et al 2007;Buck 2007Buck , 2017Buck et al 2006b). Health conditions with regard to infestations of macro-parasites, fitness and growth performance for both species were excellent (Pogoda et al 2011(Pogoda et al , 2012(Pogoda et al , 2013Brenner et al 2007Brenner et al , 2012Brenner et al , 2014. Various technical solutions to connect submerged infrastructures to a windmill foundation or to deploy it centrally into a wind farm area were worked out (Buck 2007;Buck et al 2006b, see also Chap.…”