Modelling survival and connectivity of <i>Mnemiopsis leidyi</i> in the south-western North Sea and Scheldt estuaries

Abstract

Abstract. Three different models were applied to study the reproduction, survival and dispersal of Mnemiopsis leidyi in the Scheldt estuaries and the southern North Sea: a highresolution particle tracking model with passive particles, a low-resolution particle tracking model with a reproduction model coupled to a biogeochemical model, and a dynamic energy budget (DEB) model. The results of the models, each with its strengths and weaknesses, suggest the following conceptual situation: (i) the estuaries possess enough retention capability to keep an overwintering population, and enough exchange with coastal waters of the North Sea to seed offshore populations; (ii) M. leidyi can survive in the North Sea, and be transported over considerable distances, thus facilitating connectivity between coastal embayments; (iii) under current climatic conditions, M. leidyi may not be able to reproduce in large numbers in coastal and offshore waters of the North Sea, but this may change with global warming; however, this result is subject to substantial uncertainty. Further quantitative observational work is needed on the effects of temperature, salinity and food availability on reproduction and on mortality at different life stages to improve models such as used here.

Observing and modelling phytoplankton community structure in the North Sea

“…The designation of specific accessory pigments to algal taxonomic groups of different size, e.g. fucoxanthin and peridinin for large-cell diatoms and dinoflagellates, has been widely established in the biological oceanographic literature (Uitz et al, 2006(Uitz et al, , 2008. The equations used to estimate the contribution of pico-phytoplankton (0-2 µm), nano-phytoplankton (2-20 µm) and micro-or net phytoplankton (> 20 µm) were later modified by Hirata et al (2008Hirata et al ( , 2011 and Brewin et al (2010).…”

“…Pelagic and benthic aerobic and anaerobic bacteria are also included. The pelagic module includes a number of processes in addition to those included in the oceanic version presented by Vichi et al (2007) to make it suitable for temperate shelf seas: (i) a parameterization for diatoms allowing growth in spring, (ii) enhanced transparent exopolymer particles (TEP) excretion by diatoms under nutrient stress, (iii) the associated formation of macro-aggregates consisting of TEP and diatoms, leading to enhanced sinking rates and a sufficient food supply to the benthic system especially in the deeper offshore areas (Engel, 2000), (iv) a Phaeocystis functional group for improved simulation of primary production in coastal areas (Peperzak et al, 1998;Ruardij et al, 2005), (v) a new resuspension module for inorganic fine SPM that responds to combined currents and surface waves, and uses a concentrationdependent settling velocity for improved simulation of the under-water light climate (van der Molen et al, 2017), and (vi) resuspension of particulate organic material, in proportion to the resuspended inorganic SPM and the relative concentrations of organic and fine inorganic matter in the sea bed. The model includes a three-layer benthic module comprising 53 state variables, which enables it to resolve a high level of detail of benthic processes and benthic-pelagic coupling.…”

“…It solves the 3-D partial differential equations for conservation of mass, momentum, salt, and heat. The ERSEM-BFM (European Regional Seas Ecosystem Model -Biogeochemical Flux Model) version used here is a development of the model ERSEM III (see Baretta et al, 1995;Ruardij and van Raaphorst, 1995;Ruardij et al, 1997Ruardij et al, , 2005Vichi et al, 2003Vichi et al, , 2004Vichi et al, , 2007van der Molen et al, 2013van der Molen et al, , 2014, and describes the dynamics of the biogeochemical fluxes within the pelagic and benthic environment. The ERSEM-BFM model simulates the cycles of carbon, nitrogen, phosphorus, silicate, and oxygen, and allows for variable internal nutrient ratios inside organisms, based on external availability and physiological status.…”

“…Larger cells such as diatoms are consumed directly by copepod grazers, giving a higher transfer of energy and ultimately impacting commercial fish stocks (Jennings and Collingridge, 2015). As the physical structure of the North Sea becomes increasingly well understood due to advances in hydrodynamic modelling (van Leeuwen et al, 2015) and availability of long-term observations (Greenwood et al, 2010;Núñez-Riboni and Akimova, 2015), the potential to predictively model plankton population structure and distribution increases as well.…”

“…This demand for detailed information applies to the North Sea, with users and policy makers requiring information about topics including eutrophication and nutrient ratios (Skogen et al, 2014), productivity in relation to fisheries (Chassot et al, 2007), harmful and nuisance algal blooms (Blauw et al, 2010;Kurekin et al, 2014), water clarity (Dupont and Aksnes, 2013;Capuzzo et al, 2015), biodiversity (Brandsma et al, 2013), effects of climate change (van der Wakelin et al, 2015a), effects of trawling (Allen and Clarke, 2007; , and impacts of marine renewable energy generation (van der Molen et al, 2014. In particular, indicators of Good Environmental Status (GES) are required in the context of the Marine Strategy Framework Directive (MSFD; Borja et al, 2013).…”