Samenvatting

This study originates from an increasing demand for seaweed cultivation. HZ University of Applied Sciences, together with farmers, under the umbrella “Living Lab Schouwen Duiveland” will conduct a field study to assess the possibilities for introducing brown seaweed cultivation at or near existing mussel line culture sites and to find which processes may positively or negatively impact production as a result from this combination. Therefore, the current scientific states of shellfish and seaweed integrated multitrophic aquaculture (IMTA) are explored in the present study.
With this literature review and analysis, elaborations on biological, chemical, and physical processes derived from a multitrophic aquaculture setup with macroalgae- and shellfish populations are provided, integrated and applied. How they may affect each other’s environment and thus productivity draws an idea of the positive and negative aspects of combining macroalgae and shellfish. With elaboration on different feedback loops and their subcategories, the severity of advantages and disadvantages in a multitrophic aquaculture system are determined through a collection of different studies. The collected references and the obtained insights from this literature review may yield a general framework for the proposed field studies on multitrophic aquaculture with Mytilus edulis (Linnaeus, 1758) and Saccharina latissima ((Linnaeus) C.E.Lane, C.Mayes, Druehl & G.W.Saunders, 2006) hanging cultures in Lake Veere, the Eastern Scheldt and the North Sea later this year.

Overall, the interactions between S.latissima and M.edulis prove beneficial for both production and the environmental quality near the poly culture sites. Key parameters found include oxygen cycling, nutrient cycling, carbon cycling, biofouling, light availability, and water movement. In short, it was found that the direct effects of seaweeds cultivation on shellfish cultures include output of oxygen, both decreasing benthic nutrient fluxes and providing temporary refuge from ocean acidification. On the other hand, seaweeds decrease current velocity, causing shifts in supply of seston and settlement potential of epiphytes but also competing with algae for inorganic nutrients. Looking at the positive direct impact of III shellfish cultures on seaweed cultivation, it was found that they enhance light availability trough algae consumption and inorganic nutrient availability through waste output but also consume epiphytes before settlement on seaweed blades. The additional inorganic nutrients from shellfish waste however may induce algae blooms, diminishing light availability and in periods of nutrient shortage, they indirectly compete for inorganic nutrients with seaweed through algae consumption.

For an S.latissima and M.edulis poly-cultivation setup, it is important that specific impacts are allowed to influence both cultures. This can be ensured by integrating S.latissima in close proximation to M.edulis long-lines, oriented on main current direction for optimal transport of nutrient and seston fluxes. Yet, there should be some room between the separate longlines as direct contact of S.latissima blades and M.edulis cultivation lines can induce mechanical stress on both species.

Through the discussion section, it seems recommendable to measure and/or monitor several parameters during the pilot study. Important parameters include oxygen concentrations, nutrient concentrations, current velocity, current direction, S.latissima blade quality/ nutrient contents, M.edulis meat quality/ nutrient contents and shell quality, M.edulis ammonia output, carbon concentration/ calcite saturation/ pH, irradiance (water transparency), chlorophyll-a and M.edulis filtration rates. It may also be interesting to monitor and identify epiphyte settlement on the cultivation system and cultured species.