Modelling food web interactions, variation in plankton production, and fisheries in the western English Channel ecosystem

Abstract

To explore the contributions that fishing, trophic interactions and plankton production make to explanations of the observed variation of higher trophic (principally fish) levels in the western English Channel ecosystem, Ecosim simulations were run from 1973 to 1999 using the most complete data set yet assembled. The results indicate that a bottom-up mechanism plays an important role in the system production. Inclusion of a primary producer biomass forcing term, estimated from empirical data, improved the goodness of fit of the model estimates to the available biomass data by about 25% compared to fitting using only the series of fishing mortalities. Model fitting was further improved by changing the so-called vulnerability parameters, causing an overall improvement of 62% in explained variation. Incorporating the new vulnerability values, the model was used to estimate a primary production anomaly function to replace the primary producer biomass forcing in driving the model simulations. In this scenario, the model estimated a series of values for primary producer abundance that approximated the empirical data, but gave lower estimates than were observed towards the end of the period. This version also gave a better fitting to the zooplankton abundance data and generally improved the fitting to all functional groups. KEY WORDS: Ecopath · Climate change · Ecosystem approach · English ChannelResale or republication not permitted without written consent of the publisher

Body size‐dependent responses of a marine fish assemblage to climate change and fishing over a century‐long scale

“…This could have been directly through reduced thermal physiological stress and faster growth rates, or indirectly through enhanced prey availability and reduced vulnerability to predators by thermal influences on behaviour (Hurst, 2007). These results imply a significant component of bottom-up forcing of the Western English Channel fish community structure, consistent with modelling results from this ecosystem (Araú jo et al, 2006). Many of the larger species in our study area are piscivorous top predators that exert influence on abundance of prey populations, and it is possible that removal of these ecologically important fish may have released the smaller section of the assemblage from topdown control and resulted in the observed rapid shifts in relation to climatic variability.…”

Temporal variability in total, micro- and nano-phytoplankton primary production at a coastal site in the Western English Channel

“…In coastal waters, this goal is particularly challenging as a result of optical signatures heavily influenced by non-biological particles (Sathyendranath et al, 1989;Tilstone et al, 2005), physically complex waters (e.g. Sharples et al, 2001) as well as an inherent lack of long-term observations required to distinguish natural variations from anthropogenic-driven changes in the underlying phytoplankton dynamics (Araujo et al, 2006;Le Quere et al, 2003). Temporal variability in primary production is ultimately driven by a complexity of facets operating across a range of scales, notably temperature (Harding et al, 1986), nutrients (Kyewalyanga et al, 1998), turbulence (Lewis et al, 1984) and irradiance intensity (Cote and Platt, 1984), as well as biological factors such as community structure (Cote and Platt, 1984) and physiological state (Platt and Sathyendranath, 1993), which together are strongly regulated in coastal systems by the physical structure of the water column (e.g.…”

“…Size-class based approaches to estimate primary production have been developed in an effort to better predict temporal and spatial variability relevant to ecosystem and biogeochemical scale processes (Hirata et al, 2009;Kameda and Ishizaka, 2005). A major advance in understanding community drivers of production is the partitioning of primary production into different size groups (Sieburth et al, 1978), which has also been aided by analysis of ocean colour models of size fractionated production (Brewin et al, 2010b) and ecosystem models (Araujo et al, 2006). Specific models of size-fractionated primary production have now been developed for both open ocean (Uitz et al, 2008) and coastal waters (Barnes et al, 2014); however, sufficient data sets still do not exist to fully understand which factors govern the seasonal and inter-annual variability in production for different size fractions (Uitz et al, 2008) and efforts to predict carbon transfer through coastal food webs thus remain exceptionally limited (Bauer et al, 2013).…”

An end-to-end coupled model ROMS-N2P2Z2D2-OSMOSE of the southern Benguela foodweb: parameterisation, calibration and pattern-oriented validation

“…In the current modelling landscape, there is a limited but increasing choice of existing mechanistic models for assessing the effects of both fishing and environment (Fulton 2010). Applications of the ecosystem model Ecopath with Ecosim (Walters et al 1997) have started to address the effects of both fishing and climate change in a more explicit way (Araújo et al 2006;Field et al 2006;Mackinson 2009), but as the trophic control of interactions between species is fixed (through vulner ability coefficients), this model is probably not flexible enough to address the effects of important changes in climate and fishing drivers that may induce shifts in foodweb structure.…”