Pedersen T.,University of Tromso |
Pedersen T.,Sogn og Fjordane University College |
Ramsvatn S.,University of Tromso |
Nilssen E.M.,University of Tromso |
And 6 more authors.
Regional Studies in Marine Science | Year: 2016
Latitude and temperature have been hypothesized to influence species richness, diversity and trophic control (top-down vs. bottom-up) in marine ecosystems. Ecosystem structures and mass flows of two moderately exploited fjord ecosystems with different temperatures and species diversity were compared. The Ullsfjord and Sørfjord systems (69°-70°N) are located between the relatively simple, low-diversity arctic Barents Sea in the north (71°-80°N) and the more species-rich and temperate North Sea (51°-62°N) in the south. Ullsfjord is the outer part of the fjord system and is deeper, warmer and more diverse than Sørfjord. Ecopath mass-balance models containing 40 ecological groups were developed for Ullsfjord and Sørfjord for the time period 1993-96. To obtain input data, abundance and diet of top-predators, fish, pelagic and benthic invertebrates were investigated. In the more diverse Ullsfjord system, large krill and pelagic shrimps were abundant and lower trophic level groups (TL<3) had the highest keystoneness, suggesting importance of bottom-up control. In contrast, large cod had the highest keystoneness and a large top-down effect as predator on small fishes and the larger crustacean groups in Sørfjord. For the diverse benthic invertebrates, the warmer and faster system (Ullsfjord) had higher mortality rates, shorter life spans and lower biomass (6.3 vs. 9.2 g C m-2) than the colder system (Sørfjord), but production (3.2 vs. 3.6 g C m-2 year-1) was similar in the two systems suggesting bottom-up control of benthic invertebrates. © 2015 Elsevier B.V. All rights reserved. Source
Heymans J.J.,Scottish Association for Marine Science |
Coll M.,CSIC - Institute of Marine Sciences |
Coll M.,Ecopath International Initiative Research Association |
Coll M.,IRD Montpellier |
And 3 more authors.
PLoS ONE | Year: 2014
Background: Ecological attributes estimated from food web models have the potential to be indicators of good environmental status given their capabilities to describe redundancy, food web changes, and sensitivity to fishing. They can be used as a baseline to show how they might be modified in the future with human impacts such as climate change, acidification, eutrophication, or overfishing. Methodology: In this study ecological network analysis indicators of 105 marine food web models were tested for variation with traits such as ecosystem type, latitude, ocean basin, depth, size, time period, and exploitation state, whilst also considering structural properties of the models such as number of linkages, number of living functional groups or total number of functional groups as covariate factors. Principal findings: Eight indicators were robust to model construction: relative ascendency; relative overhead; redundancy; total systems throughput (TST); primary production/TST; consumption/TST; export/TST; and total biomass of the community. Large-scale differences were seen in the ecosystems of the Atlantic and Pacific Oceans, with the Western Atlantic being more complex with an increased ability to mitigate impacts, while the Eastern Atlantic showed lower internal complexity. In addition, the Eastern Pacific was less organised than the Eastern Atlantic although both of these systems had increased primary production as eastern boundary current systems. Differences by ecosystem type highlighted coral reefs as having the largest energy flow and total biomass per unit of surface, while lagoons, estuaries, and bays had lower transfer efficiencies and higher recycling. These differences prevailed over time, although some traits changed with fishing intensity. Keystone groups were mainly higher trophic level species with mostly top-down effects, while structural/dominant groups were mainly lower trophic level groups (benthic primary producers such as seagrass and macroalgae, and invertebrates). Keystone groups were prevalent in estuarine or small/shallow systems, and in systems with reduced fishing pressure. Changes to the abundance of key functional groups might have significant implications for the functioning of ecosystems and should be avoided through management. Conclusion/significance: Our results provide additional understanding of patterns of structural and functional indicators in different ecosystems. Ecosystem traits such as type, size, depth, and location need to be accounted for when setting reference levels as these affect absolute values of ecological indicators. Therefore, establishing absolute reference values for ecosystem indicators may not be suitable to the ecosystem-based, precautionary approach. Reference levels for ecosystem indicators should be developed for individual ecosystems or ecosystems with the same typologies (similar location, ecosystem type, etc.) and not benchmarked against all other ecosystems. © 2014 Heymans et al. Source
Roman J.,University of Vermont |
Estes J.A.,University of California at Santa Cruz |
Morissette L.,M Expertise Marine |
Smith C.,University of Hawaii at Manoa |
And 7 more authors.
Frontiers in Ecology and the Environment | Year: 2014
Baleen and sperm whales, known collectively as the great whales, include the largest animals in the history of life on Earth. With high metabolic demands and large populations, whales probably had a strong influence on marine ecosystems before the advent of industrial whaling: as consumers of fish and invertebrates; as prey to other large-bodied predators; as reservoirs of and vertical and horizontal vectors for nutrients; and as detrital sources of energy and habitat in the deep sea. The decline in great whale numbers, estimated to be at least 66% and perhaps as high as 90%, has likely altered the structure and function of the oceans, but recovery is possible and in many cases is already underway. Future changes in the structure and function of the world's oceans can be expected with the restoration of great whale populations. © The Ecological Society of America. Source
Morissette L.,M Expertise Marine |
Brodie P.F.,Balaena Dynamics Ltd.
Marine Mammal Science | Year: 2014
Marine mammals are an important part of ecosystems, and their trophic role and potential impact have been increasingly studied. One key question is how these large animals interact with fisheries or compete for similar resources. Consequently, some models once used only for fisheries management are now including pinnipeds and cetaceans. However, fish and marine mammals do not share the same ecology and bioenergetics, and complex ecosystem models may not be the best way to assess the impact of pinnipeds or cetaceans in food webs. Indeed, simpler methods based on thermodynamics might give us reasonable answers with limited amounts of data. Here, we present an assessment of two different approaches to assess the trophic role of marine mammals in the northern Gulf of St. Lawrence (Canada): mixed trophic impacts (MTI) based on ecosystem modeling and surface index (SI) impact based on bioenergetics. Our results show that while modeling represents a good way of getting a holistic view of the role of marine mammals in ecosystems, trophic impact estimates based on fundamental thermodynamics principles can also give us answers requiring less data. The body surface area approach presented here might provide a practical tool for ecologists, who are not necessarily ecosystem modelers, to study this issue. © 2014 Society for Marine Mammalogy. Source