Carrying capacity of Saccharina latissima cultivation in a Dutch coastal bay: a modelling assessment

Abstract

Kelp cultivation receives increasing interest for its high-value products and ecological services, especially in Europe and North America. Before industrial kelp farming in marine ecosystems continue to scale up, evaluation of the site-wide production relative to ecological carrying capacity (CC) of the identified system is essential. For this purpose, a mechanistic kelp model was developed and applied for hypothetical numerical experiments of expanding the farming area in a Dutch coastal bay (the Eastern Scheldt), where cultivation of Saccharina latissima (sugar kelp) is emerging. The kelp model was implemented within a three-dimensional hydrodynamic–biogeochemical model to account for the environmental interactions. The model captured the seasonal growth dynamics of S. latissima, as well as its carbon and nitrogen contents measured at the Eastern Scheldt pilot sites. The model results suggest that expanding the kelp farming area to ∼1–30% of the bay (representing ∼3.4–75 kt harvest dry weight in the 350-km2 bay) had the potential to weaken the spring bloom, and thereby affected the coexisting shellfish culture in the bay. Competition between S. latissima and phytoplankton mostly occurred in late spring for nutrients (dissolved inorganic nitrogen). The ecological CC should be weighed according to these negative impacts. However, the production CC was not reached even when farming ∼30% of the Eastern Scheldt, i.e. harvesting totally 75 kt dry mass, given that the simulated overall S. latissima production kept increasing with the farming activity. Our modelling approach can be applied to other systems for S. latissima cultivation and assist in assessing CC and environmental impacts.

Modelling spatial variability of cultivated Saccharina latissima in a Dutch coastal bay shows benefits of co-cultivation with shellfish

“…These data are used to compare with the model. The sampling and measurement approaches are presented in detail by Jiang et al (2022) and are not repeated here. Note that S. latissima was co-cultivated with blue mussels at Site 2.…”

“…A hydrodynamic-biogeochemical-kelp model was developed for the Eastern Scheldt and part of the adjacent North Sea to simulate the environmental factors and S. latissima growth (Jiang et al, 2022). Tidal elevation, current velocity, temperature, salinity, and other physical variables were solved in the General Estuarine Transport Model (GETM, open-access at https://getm.eu/).…”

“…The individual structural carbon, reserve carbon, and reserve nitrogen are calculated as state variables (in mmol ind -1 ) in the kelp model, sources and sinks of which are dependent on environmental factors calculated in GETM-FABM. Governing equations, variables, and parameters are presented by Jiang et al (2022), and here we review the three key processes (i.e., the structural growth, photosynthesis, and DIN uptake) that are directly influenced by the environment and contribute to the spatial variability of S. latissima growth.…”

“…f(Q), ranging from 0 to 1, quantifies the relative amount of carbon and nitrogen reserves, which is mainly supplied by photosynthesis and DIN uptake. If the nitrogen (carbon) reserve is in relative shortage, f(Q) is calculated based on the ratio of the reserved nitrogen (carbon) to the structural biomass (see details in Jiang et al, 2022).…”

“…In our previous work, we used numerical models to assess the ecological and production carrying capacities of S. latissima cultivation in the Eastern Scheldt, a Dutch tidal bay where S. latissima farming is recently initiated (Jiang et al, 2022).…”