Non-living Compartments Research Articles

From Marine Metacommunities to Meta-ecosystems: Examining the Nature, Scale and Significance of Resource Flows in Benthic Marine Environments

The metacommunity framework has been readily applied to coastal benthic marine environments to examine how larval dispersal affects the dynamics of patchily distributed communities. Transitioning to a meta-ecosystem perspective requires knowledge of interactions between living and non-living compartments occurring across scales in these environments. Here, we synthesize and analyze evidence of non-living resource flows in coastal benthic marine environments. Our objectives are to establish the types of benthic ecosystems that are coupled by resource flows, the spatial scale and directionality of the couplings, and the magnitude of resulting subsidization of recipient organisms. We find that resource flows commonly couple different types of coastal benthic ecosystems and can occur bidirectionally between ecosystems. Our quantitative synthesis yields a frequency distribution of resource flow distance, which suggests they frequently couple ecosystems across smaller distances than larval dispersal and that the probability of resource flows coupling benthic ecosystems decreases exponentially with distance between ecosystems. The magnitude of subsidization of recipient organisms also decreases with distance from the source of the resource flow. Our findings reveal that considering ecosystem heterogeneity and the respective scales of different types of spatial flows will be an important component of extending the marine metacommunity framework to meta-ecosystems. We propose an avenue for integrating ecosystem heterogeneity into meta-ecosystem theory, based upon general differences in functioning across coupled ecosystems revealed by our synthesis, and we argue for the development of a hierarchical meta-ecosystem theory.

Seasonal dynamics and stoichiometry of the planktonic community in the NW Mediterranean Sea: a 3D modeling approach

The 3D hydrodynamic Model for Applications at Regional Scale (MARS3D) was coupled with a biogeochemical model developed with the Ecological Modular Mechanistic Modelling (Eco3M) numerical tool. The three-dimensional coupled model was applied to the NW Mediterranean Sea to study the dynamics of the key biogeochemical processes in the area in relation with hydrodynamic constraints. In particular, we focused on the temporal and spatial variability of intracellular contents of living and non-living compartments. The conceptual scheme of the biogeochemical model accounts for the complex food web of the NW Mediterranean Sea (34 state variables), using flexible plankton stoichiometry. We used mechanistic formulations to describe most of the biogeochemical processes involved in the dynamics of marine pelagic ecosystems. Simulations covered the period from September 1, 2009 to January 31, 2011 (17 months), which enabled comparison of model outputs with situ measurements made during two oceanographic cruises in the region (Costeau-4: April 27-May 2, 2010 and Costeau-6: January 23-January 27, 2011).

Effect of invasive species on the structure and function of the Sylt-Rømø Bight ecosystem, northern Wadden Sea, over three time periods

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 462:143-161 (2012) - DOI: https://doi.org/10.3354/meps09837 Effect of invasive species on the structure and function of the Sylt-Rømø Bight ecosystem, northern Wadden Sea, over three time periods Dan Baird1,*, Harald Asmus2, Ragnhild Asmus2 1Department of Botany and Zoology, Stellenbosch University, 7600 Stellenbosch, South Africa 2Alfred Wegener Institute for Polar and Marine Research, Wattenmeer Station, Station Sylt, 25992 List, Sylt, Germany *Email: danbaird@sun.ac.za ABSTRACT: Three quantitative energy flow models have been constructed for the Sylt-Rømø Bight representing the stocks and flows in the ecosystem during 1995, 2007 and 2010. The 1995 model consists of 59 compartments, while the 2007 and 2010 models have 63 compartments each. The 4 additional compartments in the 2007 and 2010 models are 2 native barnacle species Semibalanus balanoides and Balanus crenatus and 2 invasive species namely the Pacific oyster Crassostrea gigas and the Australasian barnacle Austrominius modestus. Oyster and A. modestus biomass increased from virtually zero in 1995 to 15 and 1.3 gC m−2, respectively, in 2007, and then subsequently decreased to 0.6 and 0.12 gC m−2, respectively, in 2010. Reasons for the increases in oysters and A. modestus are related to climate change which favored strong recruitment of the invasive species during unseasonably warm summers, and the subsequent decline to weak recruitment of the invasive species and an unseasonably cold 2009/2010 winter. We used ecological network analysis (ENA) to quantify ecosystem structure and function through analyses of energy (or carbon) transfer between living and non-living compartments in each of the 3 network models. Results from ENA show an increase in most of the system attributes, but a decline in number of cycles, the trophic efficiency, the ascendency ratios, and relative redundancy from 1995 to 2007; these are ascribed to the impact of the invasive species on system organization and function. Following the dramatic decline of the invasive species from 2007 to 2010 most of the system attributes decreased. The variance in the biomass and associated flows of other compartments in addition to that of the invasive species has also played a role in the changes in system attributes and function. KEY WORDS: Ecosystem function · Alternate ecosystem states · Invasive species · Crassostrea gigas · Austrominius modestus · Food web models · Ecological network analysis · Northern Wadden Sea Full text in pdf format Supplementary material PreviousNextCite this article as: Baird D, Asmus H, Asmus R (2012) Effect of invasive species on the structure and function of the Sylt-Rømø Bight ecosystem, northern Wadden Sea, over three time periods. Mar Ecol Prog Ser 462:143-161. https://doi.org/10.3354/meps09837 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 462. Online publication date: August 21, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Lower trophic levels and detrital biomass control the Bay of Biscay continental shelf food web: Implications for ecosystem management

The Bay of Biscay (North-East Atlantic) has long been subjected to intense direct and indirect human activities that lead to the excessive degradation and sometimes overexploitation of natural resources. Fisheries management is gradually moving away from single-species assessments to more holistic, multi-species approaches that better respond to the reality of ecosystem processes. Quantitative modelling methods such as Ecopath with Ecosim can be useful tools for planning, implementing and evaluating ecosystem-based fisheries management strategies. The aim of this study was therefore to model the energy fluxes within the food web of this highly pressured ecosystem and to extract practical information required in the diagnosis of ecosystem state/health. A well-described model comprising 30 living and two non-living compartments was successfully constructed with data of local origin, for the Bay of Biscay continental shelf. The same level of aggregation was applied to primary producers, mid-trophic-levels and top-predators boxes. The model was even more general as it encompassed the entire continuum of marine habitats, from benthic to pelagic domains. Output values for most ecosystem attributes indicated a relatively mature and stable ecosystem, with a large proportion of its energy flow originating from detritus. Ecological network analysis also provided evidence that bottom-up processes play a significant role in the population dynamics of upper-trophic-levels and in the global structuring of this marine ecosystem. Finally, a novel metric based on ecosystem production depicted an ecosystem not far from being overexploited. This finding being not entirely consistent over indicators, further analyses based on dynamic simulations are required.

The consequences of the aggregation of detritus pools in ecological networks

Ecological networks are quantitative, graph-based descriptions of ecosystems, consisting of compartments (trophospecies and nutrient pools) that exchange fluxes of nutrients or energy. Previous research pointed out how the model's design is a crucial task that can heavily influence analyses results, and how merging compartments for the purpose of comparing two or more different ecosystems can significantly alter the indices on which the comparison is based. All these works have been focused on the aggregation of trophospecies, whereas networks may comprise several nutrient compartments that may be lumped as well, either for lack of information or for comparison constraints. We show how the aggregation of these non-living compartments can have a greater influence on network analysis results than trophospecies clustering. This problem should on the one hand encourage modelers to make an effort to test the possible effects of aggregations, and on the other show how the role of non-living compartments could be very important in determining network dynamics.

Energy flow of a boreal intertidal ecosystem, the Sylt-Rømø Bight

A detailed energy flow model consisting of 56 living and 3 non-living compartments was assembled for the intertidal area of the Sylt-Romo Bight. The model depicts the biomass of each com- partment, carbon flow between the components, imports and exports, as well as an energy budget for each. The food web was analysed by means of network analysis which showed that about 17% of the total daily flow through the system is recycled through a complex cycling structure consisting of 1197 cycles. The cycling network indicated that about 99% of the recycling involves 2 to 3 compartments, with sediment bacteria and particulate organic carbon (POC) participating in most instances. Input/output analyses indicated that phytoplankton production in the Bight does not satisfy the demands of filter-feeders on an annual average basis so that about 160 mgC m -2 d -1 of phytoplank- ton have to be imported. We compared several dimensionless system level indices, such as inter- nalised and normalised A/DC (ascendancy/development capacity) ratios, calculated for the Bight with those of other marine and estuarine ecosystems on a global basis. These comparisons showed that energy is rather inefficiently transferred within the Bight at a mean trophic efficiency index of 2.61%, and that most of the system level indices are lower than those of other coastal ecosystems. However, higher values were obtained for flow diversity and food web connectance compared to other systems. This study has revealed the Bight to be a highly complex system whose energy pathways appear to be sensitive to external perturbations.

Network analysis of the northern Benguela ecosystem by means of netwrk and ecopath

Two software packages are available to analyze ecosystems and to compute ecosystem variables: netwrk 4.2a and ecopath 4.0. A flow model of the northern Benguela ecosystem was used to compare the outputs from these two packages. The northern Benguela ecosystem is a sub-system of the Benguela upwelling ecosystem off the coast of Southern Africa. The food web used in this study consists of 24 compartments, of which 22 were living and two were non-living compartments. netwrk is a DOS-based package constructed in ‘FORTRAN’ by R.E. Ulanowicz, University of Maryland, in the late 1980s (updated in 1999 — version 4.2a), while ecopath is a Windows-based package written in ‘Visual Basic’ that uses the same methodologies as netwrk but whose algorithms have been programmed based on the original descriptions with some differences in interpretation. There are fundamental differences between the input methodologies of the two packages, which leads to differences in their output. netwrk takes the respiration of primary producers into consideration, while ecopath does not. This leads to various discrepancies in the calculation of throughput and all the parameters related to it, such as the ascendency and development capacity. In most cases, the differences are small enough that the interpretation of the results would bring the modeler to the same qualitative conclusion using ecopath or netwrk. However, the mixed trophic impacts, Lindeman spine, primary production required and Finn Cycling Index, are markedly different for the two models. It is concluded that consolidating these models would be of enormous value to ecosystem analysis.

A carbon flow model and network analysis of the northern Benguela upwelling system, Namibia

A carbon flow model was constructed of the northern Benguela upwelling ecosystem. The model consists of 22 living and two non-living compartments, depicting the biomass of each compartment and the rates of exchange between them. The only primary producer in this system is phytoplankton, whilst bacteria, heterotrophic microflagellates and microzooplankton form part of the microbial loop. Primary consumers include mesozooplankton, macrozooplankton and jellyfish, while the fish community consists of anchovy, pilchard, lanternfish, gobies, horse mackerel, hake, snoek, benthic feeding fish and other carnivorous fish. The top consumers are seabirds and seals. The primary production–zooplankton–pelagic fish–demersal fish energy flow pathway appears to dominate in this system, with jellyfish, pilchard and horse mackerel being the most important planktivores. Jellyfish appears to be an important component in the system due to its high biomass and consumption of about 10% of the primary production. Hake is the most important secondary consumer. The carbon flow model was analyzed by means of network analysis, and the results show a total system throughput of about 88897 mg C m −2 day −1, a development capacity of 38 041 mg C m −2 day −1, an ascendancy value of 17 313 mg C m −2 day −1, that about 7% of the total system throughput is recycled on a daily basis, and that the internal relative ascendancy is about 44%. These results were compared to similar data from other systems such as the southern Benguela and the Peruvian upwelling systems.

Analysis of ecosystem structure and function: extended path and flow analysis of a steady-state oyster reef model

An analysis of the extended path and flow structure of a six compartment steady-state oyster reef model was conducted. The extended path and flow structure were analyzed in the context of a refined canonical path classification system based on the systems theory methods of environ and network unfolding analyses. A computer implementation of an operational path classification system facilitated investigation of a finite portion (path length ≤17 arcs) of the direct and indirect path structure of the oyster reef model. Important results of the path structure analysis include: (1) few simple paths and large numbers of compound paths enumerated; (2) dominance of path numbers by subsequent passage terminal cycle paths; (3) structural evidence in support of feedback control in ecosystems; (4) results provide evidence by analogy to support the hypothesis of network homogenization first described using the systems analysis methods of environ analysis and network unfolding; (5) constancy of the pattern of origin–destination path counts with increasing path length; (6) importance of nonliving compartments in the extended path structure of ecosystems. Simultaneous path and flow analysis of the oyster reef model assessed the flow contributions of the fundamental path categories for this model using a modification of a path-based network unfolding method. First passage paths contribute most of the flow; however, multiple passage cyclic paths also provide a large (22%) flow contribution. Because of cycling in the system, the numerous long paths in the extended path structure of this ecosystem model are significant in its function as represented by the flows. These results provide microscopic evidence for the macroscopic results of environ analysis that implicate cycling as a key ecosystem attribute in the mechanisms of holistic system determination. The principles enunciated here for a model with a low cycling index (11%) carry over to, and would be even more significant for, models with high cycling indexes. These results also serve to form a link between the extended structure of food webs and their functioning as represented by energy-matter flows. The present analysis demonstrates that extended path structure, and the component articulation from which it is generated, have significant consequences for ecosystem function.

Carbon Budget and Network Analysis of a High-energy Beach/Surf-zone Ecosystem

A carbon budget, compiled for a high-energy beach/surf-zone ecosystem in South Africa, consists of 14 living and two non-living compartments, namely dissolved organic carbon and suspended particulate organic carbon. The living compartments constitute three trophic assemblages; the microbial loop, the interstitial system and the macrofauna. The food web budget was subjected to network analysis to assess the status of the system. Input–output analysis indicated that the microbial loop is the most important trophic assemblage in this system, with the interstitial assemblage second in importance. Lindeman trophic analysis estimated that detritivory amounts to 868 mgC m −2day −1and the detritivory:herbivory ratio is 13:1. Biogeochemical cycle analysis concluded that this system is not under any anthropogenic stress, having a nexus with 48 cycles, three 24-cycle nexuses, a single cycle including 11 compartments, and only seven single-cycle nexuses. Based on global systems’ properties, this ecosystem has a high normalized internal ascendency (A i:C i) which suggests that it is well organized and stable. The system possesses significant internal stability and resistance, a feature that is expected from a physically controlled environment. The relative ascendency (A:C) of this system falls well within the range of relative ascendencies for other systems, being higher than most estuaries but lower than upwelling systems, bays and seas. Overall, this ecosystem is perceived to be unstressed and mature, with the physical control exerted on it providing significant internal stability.

Energy Flow in the Kromme Estuarine Ecosystem, St Francis Bay, South Africa

An energy flow network was constructed for the Kromme estuary, South Africa. Extensive data, collected on this estuary, were used to calculate the energetics of each of the 27 compartments identified in this system. The model consists of three non-living and 24 living compartments. The non-living compartments were dissolved organic carbon (DOC), suspended and sediment particulate organic carbon (POC), while the living compartments consisted of four plant groups, three bacterial groups and 17 animal groups. The animals range from meiofauna to macrofauna and fish. Biomass of all compartments were estimated in mg C m −2and exchanges in mg C m −2day −1. It was found that the main primary producers are the marsh halophytes and macrophytes. It seems that although the salt marshes cover only 38% of the Kromme estuary, the marsh halophytes contribute 78% of the total primary production, making it the most important producer in this estuary. Less than 10% of the halophyte production enters the grazing food-chain, with the remainder being broken down to sediment detritus. This indicates that the sediment detritus, as well as the animals that feed on it, forms the most important part of this food-web.

A comparison of whole-community and ecosystem approaches (biomass size distributions, food web analysis, network analysis, simulation models) to study the structure, function and regulation of pelagic food webs

A step-by-step procedure for investigating the structure, function and regulation of pelagic communities as an entirety is suggested which proceeds along gradients of increasing requirements for data and knowledge, and of growing understanding of ecosystem functioning. It comprises methodologies based on biomass size distributions, followed by food web analysis, network analysis and dynamic simulation models. The different approaches are compared with respect to data requirements, theoretical foundations, operational problems, time and computational effort, and the different types of information they provide on food web structure and dynamics. These ideas are illustrated with data from Lake Constance. Biomass size distributions provide a structural and energetic food web analysis based only on measurements of abundances and body sizes, and a few general assumptions mainly on size relationships of metabolic activities and trophodynamics. Food web analysis considers binary webs depicting qualitatively trophic links between species or trophic guilds and provides profound information about the food web structure. Mass-balanced flow diagrams (trophic webs) take into account the magnitude of flows between living and non-living compartments, and provide comprehensive descriptions of fluxes and cycling of matter and the trophic food web structure when evaluated by network analysis. These three static approaches are contrasted with tactical dynamic simulation models depicting interaction webs and representing unique possibilities of studying the dynamic nature, spatio-temporal organization, direct and indirect cause-effect relationships, and impact of physical forcing. However, these capabilities are only achievable on the expenditure of a very large research effort.