A comparison of community and trophic structure in five marine ecosystems based on energy budgets and system metrics

As part of the international MENU collaboration, energy budget models for five marine ecosystems were compared to identify differences and similarities in trophic and community characteristics across ecosystems. We examined the Gulf of Maine and Georges Bank in the Northwest Atlantic Ocean, the combined Norwegian/Barents Seas in the Northeast Atlantic Ocean, and the eastern Bering Sea and the Gulf of Alaska in the Northeast Pacific Ocean. Comparable energy budgets were constructed for each ecosystem by aggregating information for similar species groups into consistent functional groups across all five ecosystems. Several ecosystem metrics (including functional group production, consumption, and biomass ratios, ABC curves, cumulative biomass, food web macrodescriptors, and network metrics) were examined across the ecosystems. The comparative approach clearly identified data gaps for each ecosystem, an important outcome of this work. Commonalities across the ecosystems included overall high primary production and energy flow at low trophic levels, high production and consumption by carnivorous zooplankton, and similar proportions of apex predator to lower trophic level biomass. Major differences included distinct biomass ratios of pelagic to demersal fish, ranging from highest in the Norwegian/Barents ecosystem to lowest in the Alaskan systems, and notable gradients in primary production per unit area, highest in the Alaskan and Georges Bank/Gulf of Maine ecosystems, and lowest in the Norwegian ecosystems. While comparing a disparate group of organisms across a wide range of marine ecosystems is challenging, this work demonstrates that standardized metrics both elucidate properties common to marine ecosystems and identify key distinctions for fishery management

A bioenergetics-based population dynamics model of Pacific herring (Clupea harengus pallasi) coupled to a lower trophic level nutrient-phytoplankton-zooplankton model: Description, calibration, and sensitivity analysis

We describe an approach to dynamically couple a fish bioenergetics-based population dynamics model to the NEMURO lower trophic level nutrient–phytoplankton–zooplankton model. The coupled models, denoted NEMURO.FISH and configured for Pacific herring (Clupea harengus pallasii) on the west coast of Vancouver Island, are capable of simulating the daily dynamics of the lower trophic levels and the daily average weight and numbers of individual herring in each of 10 age classes over multiple years. New recruits to the herring population are added each June based on either constant recruitment or dynamic recruitment generated from an environmental Ricker spawner–recruitment relationship. The dynamics of the three zooplankton groups in the NEMURO model determine the consumption rate of the herring; herring consumption affects the zooplankton, and egestion and excretion contribute to the nitrogen dynamics. NEMURO was previously calibrated to field data for the West Coast Vancouver Island. Thirty-year simulations of herring growth and population dynamics were performed that used repeated environmental conditions for the lower trophic levels of NEMURO and historical environmental variables for the herring spawner–recruit relationship. Herring dynamics were calibrated to the west coast of Vancouver Island such that the coupled models reasonably duplicated observed herring weights-at-age and total herring biomass. Additional 30-year simulations under constant recruitment with herring coupled and uncoupled from NEMURO clearly showed the effects of the feedback mechanism between the two models and also showed that herring have small to moderate effects on their prey. Monte Carlo uncertainty analysis showed the importance of feeding- and respiration-related parameters to predicted individual and population herring growth. The utility of theNEMURO.FISH framework for improving our understanding of climate change effects on marine ecosystem dynamics is discussed

Introduction : ICES Symposium on 'The Influence of Climate Change on North Atlantic Fish Stocks', May 2004

An ICES Symposium on The Influence of Climate Change on North Atlantic Fish Stocks was held in Bergen, Norway, from 11 to 14 May 2004. The Symposium, sponsored by the ICES/GLOBEC Working Group on Cod and Climate Change (WGCCC) as part of their synthesis activities, was convened to address the issue of climate variability and its impact on cod and other fish stocks in the North Atlantic. It followed 11 years after the first WGCCC-sponsored ICES Symposium on Cod and Climate (ICES, 1994) in Reykjavík, Iceland, which was convened to gather together the then current knowledge of the influence of climate variability on cod. The 2004 Symposium was timely because of the recent declines and collapses of some important commercial fish stocks in the North Atlantic, declines in which environmental influences are believed to have played a role. In addition, there has been growing concern about the effects of anthropogenically induced climate change on fish populations, especially in light of the general warming throughout the North Atlantic during the later 1990s (see Turrell et al., 2003) and into the present decade