Dynamic Energy Budget (DEB) parameters for ensis directus

In this report a Dynamic Energy Budget (DEB) model for razor clams (Ensis directus) is presented. A DEB model is a generic model describing growth and development of individual organisms as a function of environmental conditions. The DEB model for Ensis directus is based on the standard DEB model. The species specific primary DEB parameters are estimated with the Add_my_pet procedure, using literature data and the results of laboratory experiments with Ensis directus. The performance of the model is demonstrated by theoretical model experiments with varying environmental conditions. In following projects, the model will be used to predict and quantify the effects of sand mining on the shellfish community in the Dutch coastal zone. For this purpose the functional response of the model should be adapted so that the combined effect of changing phytoplankton and suspended sediment concentration on the uptake rate can be simulated

Freshwater immersion as a method to remove Urosalpinx cinerea and Ocinebrellus inornatus from mussel seed

A simple experiment to test whether immersion in freshwater for ≤24 hours would kill two oyster drills, Urosalpinx cinerea and Ocinebrellus inornatus was conducted to test the proposal of using freshwater to rid mussel seed of the drills before translocation from the Oosterschelde to the Wadden Sea. Freshwater failed to kill any individuals of either species, but did cause them to detach from the substratum for the entire time of immersion. Immersion in freshwater is therefore not recommended as a method to control the drills. Rinsing in freshwater may be an option to remove the drills without killing them, but has no guarantee of 100 % success. Further investigation may result in the development of other treatment options

Relating a DEB model for mussels (Mytilus edulis) to growth data from the Oosterschelde : trace-back analysis of food conditions

In this study, the food conditions for mussels are estimated at different locations within the Oosterschelde. In 2014, 2015 and 2016, mussels with a uniform size were placed in baskets at the borders of commercial culture plots distributed over the Oosterschelde. Each month, a subsample was taken from each basket to measure growth (shell length and individual weight) of the mussels. The results show a variation in growth performance, both in shell length as in flesh weight, between the different locations. A model approach was used to translate the spatial differences in growth to spatial differences in food conditions. A Dynamic Energy Budget (DEB) model was fitted to the data in order to trace-back the food conditions. During this fitting, the food correction factor (ψψ) was optimized. ψψ can be interpreted as an indication of the food conditions (algae concentration, quality, current velocity) at that specific location in comparison to the average food conditions in the whole Oosterschelde. The results show that there is a spatial, but also year-to-year variation in food conditions within the Oosterschelde. Locations with the best food conditions were Neeltje Jans N in 2015 and Hammen 9, Dortsman and Krabbenkreek in 2016. Growth of the mussels in the baskets in 2014 was lower than in 2015 and 2016. This is probably caused by the larger size of the mussels that were used in 2014 and the fact that the growth of mussels reduces with size. In contravention to the expectations, there was no clear pattern in growth conditions from the western part of the Oosterschelde to the eastern and northern part. For example, the growth of the mussels at the two locations in the northern part of the Oosterschelde (Krabbenkreek and Viane) where ralatively good compared to the other locations. In practice, however, mussel farmers use the culture plots in the northern part mainly for storage of seed and halfgrown mussels. Possibly the mussels in the baskets perform better in this area than on the bottom culture plots. The DEB model is a good tool to trace-back the food conditions from the measured growth data. The parameters for blue mussel, that is used for the DEB model should be updated. The parameters are presently based on historical data, whereas new data are available

Risk analysis on the import of mussels from the Limfjord and the Isefjord (Denmark) to the Oosterschelde

This report is the result of a risk analysis on the introduction of exotic non-indigenous species – species that have their origin outside the North Atlantic Continental Shelf region – with the import of bottom culture mussels from the Isefjord and the Limfjord (Denmark) into the Oosterschelde. Based on available literature data and expert judgement, the target species are identified and the risks of these species are assessed semiBquantitively. It is concluded that the risk of introducing exotic non-indigenous species into the Oosterschelde with the import of mussels from the Isefjord and the Limfjord is low

DEB model for cockles (Cerastoderma edule) in the Oosterschelde

The natural and cultured shellfish populations in the Oosterschelde are of considerable biological and economical interest. The hydromorphology of the Oosterschelde is continuously changing and adapting in response to natural anthropological and climatological changes. In view of these changes and of possible future developments in the region, questions arise with regard to the impact on the system’s carrying capacity for shellfish populations. Dynamic shellfish models can help to answer these questions. In this study, a Dynamic Energy Budget (DEB) model for cockles (Cerastoderma edule) in the Oosterschelde estuary is presented

High risk exotic species with respect to shellfish transports from the Oosterschelde to the Wadden Sea

This study presents the results of a literature review on 11 exotic marine species that are present in the Oosterschelde and could potentially be introduced into the Wadden Sea with shellfish transfers. Ten of the species result from a previous risk study, where they were identified as the species posing the highest risk. The Japanese oyster drill, that was recently observed in the Oosterschelde was also included in this study. The species discussed in the present study are: colonial tunicates Didemnum sp and Botrylloides violaceus the American oyster drill (Urosalpinx cinerea) and the Japanese oysterdrill (Ocinebrellus inornatus), the copepods Myticola orientalis and M. ostreae, the colonial bryozoan Smittoidea prolifica, Marteilia refringens and the macroalgae Gracilaria vermiculophylla, Polysiphonia senticulosa and Undaria pinnatifida. Four of these species (Gracilaria vermiculophylla, Undaria pinnatifida, Didemnum vexillum and Botrylloides violaceus) have recently been observed in the Wadden Sea. Some of these species are known pest species and could have an impact on the Wadden Sea ecosystem and/or the shellfish culture. The information that is collected in this study can be used to get a more realistic estimation of the risks compared to the risk assessment study of 2008 which was based on a worst-case approach. Moreover, the results can be used in the development of mitigating measures to reduce the risks of introducing these exotic species with the shellfish transfer from the Oosterschelde to the Wadden Sea

Introduction, establishment and expansion of the Pacific oyster Crassostrea gigas in the Oosterschelde (SW Netherlands)

The Pacific oyster Crassostrea gigas was first introduced as an exotic species by oyster farmers in 1964 in the Oosterschelde estuary (SW Netherlands). The initial phase is not well documented but first natural spatfall was recorded in 1975. Excessive spatfall occurred in 1976 and this is considered the start of the expansion phase of the wild oysters. Oyster beds in intertidal and subtidal areas of the Oosterschelde estuary have been growing since. The development in the intertidal area has been reconstructed by using aerial photography, validated by ground truth in 2000¿2002. In the subtidal areas extensive oyster beds have been detected by using side scan sonar; on hard substrates along the dikes coverage with oysters up to 90% locally has been recorded by scuba diving surveys. Expansion has also occurred into adjacent water bodies including the Wadden Sea. By forming resistant reefs the oysters induce structural changes in the ecosystem. It is concluded that bed area is still expanding while decrease of the fraction live animals may indicate adjustment of the stock size to the local conditions

Bepaling bestand op de mosselpercelen in de Waddenzee najaar 2008

A total stock of 30 million kg (net fresh weight) was estimated to be present at the culture plots in the Western part of the Wadden Sea in autumn 2008. The total stock could be divided into 12 million kg seed mussels and 16 million kg consumption mussels. In the same period in 2007 the total stock was 35 million kg. Most of the mussels in 2008 were present near Terschelling at the locations Oosterom, Balgen, Meep and Kabelgat. Seed mussels are mainly present at Meep and Balgen, while consumption mussels are mainly present at, Kabelgat en Oostero