Mediterranean coastal ecosystems provide various valuable ecosystem goods and services; however, they are vulnerable to ecological degradation due to a dramatic increase in resource use and environmental stress. Disentangling the effects of multiple human interventions on coastal ecosystems requires whole description of food web interactions using quantitative tools. A mass balance Ecopath model has been developed here for Saronikos Gulf, a naturally oligotrophic Mediterranean coastal ecosystem with a long history of human interventions. Our main focus was to describe the structure and functioning of the ecosystem, investigate the trophic interplay among the various compartments of the food web under the impact of mixed multi-gear fisheries, and to quantify resilience related emergent ecosystem properties. To this end, we reviewed a large amount of local and regional biological information which was integrated in 40 functional groups covering all trophic levels, while fishing activities were described with 7 fleets. The model shared characteristics of both productive (e.g., high amount of flows) and oligotrophic systems (e.g., low biomass accumulation) and presented typical features of Mediterranean ecosystem functioning, such as the importance of detritus as an energy source, strong benthic-pelagic coupling and the dominance of the pelagic compartment in terms of total production and consumption. Trophic forcing in the ecosystem of Saronikos Gulf was complex with both top-down and bottom-up drivers being important. Zooplankton was the central nexus between basal resources and higher trophic levels, while top predators such as hake, squids and anglerfish were identified as keystone species presenting a significant overall effect on the food web via direct and indirect trophic interactions. Ecological indicators depicted a moderately complex food-web of a large and immature ecosystem with its strengths in reserve being affected by environmental degradation. Additionally, exploitation indices classified fishing activities in Saronikos Gulf as unsustainable, affecting several target groups, including high trophic level species. However, the morphological and bathymetric complexity of Saronikos Gulf seems to function as a natural ecological reserve for the ecosystem by providing nursery grounds to various species (e.g., hake, small pelagic fishes) and supporting important fish stocks for local fisheries.

An Ecopath with Ecosim (EwE) modeling approach was used to explore the ecological structure of the largest lake in Greece (Lake Trichonis). Until the mid-1990s, the lake was receiving a high level of pollution and the fishing pressure was intense, while since the early 2000s, fisheries and other human pressures gradually declined. Nowadays, the lake’s fisheries mainly target Atherina boyeri due to the absence of market demand for the other fish species in the lake, resulting in a low overall fisheries pressure on the fish stocks. The model was built with data collected through: (a) field samplings, (b) in-depth targeted interviews of professional fishermen and (c) historical archive information. The model considered 22 functional groups, while fishing activities were represented by three classes according to the used gears. The outputs of the model revealed that the ecosystem is dominated by low trophic level species (also identified as keystone species), indicating the significance of bottom-up control in the regulation of food web processes. Ecological indicators depicted that the lake’s ecosystem is mature and resilient to external disturbances. The methodological approach used in this study was shown to be helpful for studies addressing ecosystem structure, in particular with limited data availability.

Introduction: Current manifestations of anthropogenic stressors on coastal ecosystems have intensified the need for a more profound understanding of trophic interactions, particularly under the ongoing climate change that is triggering the rewiring of food webs globally.Methods: Herein, we present the development of an Ecopath model for the Eastern Ionian Sea (EIS; Central Mediterranean) in 1998-2000, the parameterization and fitting of the dynamic module Ecosim to biomass and catch data from 2000 to 2020, and future projections of the ecosystems’ responses to a set of single and multiple stressor scenarios for the period 2021-2080. The 21 simulations consisted of two levels of climate change and total and gear-specific fishing effort reduction. We estimated the cumulative impact of multiple stressors on ecosystem dynamics, with emphasis on stressor interactions (synergistic vs. antagonistic) and addressed the response of ecological indicators estimated in broad functional groups (e.g. trophic guilds, pelagic and demersal resources), to identify those that best track perturbation-induced shifts.Results: The EIS is a moderately complex oligotrophic ecosystem, where exploitation indices classified fishing activities as sustainable, yet some stocks remain overexploited (e.g., hake, cuttlefish). The integration of trophic interactions, climate warming, fishing activity, and primary production enhanced the model's accuracy, indicating that both anthropogenic exploitation and environmental factors have historically shaped ecosystem dynamics. Future simulations highlighted that the high-baseline carbon emission scenario (RCP8.5) intensified ecosystem changes, compared to the scenario of moderate carbon mitigation (RCP4.5) after 2050. Moreover, antagonistic stressor interactions that persisted throughout the projection period under combined RCP4.5 scenarios shifted to synergistic by the latter half of the century (2080) under RCP8.5, resulting in negative effects on the biomass of most functional groups and raising serious concerns for future stock sustainability, as synergistic effects of stressors may non-linearly increase adverse impacts on ecosystems. Indicators showed that multiple stressors led to less abundant, less diverse, and lower trophic level benthivore communities, while piscivores were particularly vulnerable to warming, supporting projections of top-predator declines.Discussion: Our findings emphasize the urgency of utilizing the window of opportunity until 2050 to integrate climate-adaptive measures into fisheries management in order to prevent future declines of Mediterranean marine resources.