Towards a framework for assessment and management of cumulative human impacts on marine food webs

Abstract

Effective ecosystem-based management requires understanding ecosystem responses to multiple human threats, rather than focusing on single threats. To understand ecosystem responses to anthropogenic threats holistically, it is necessary to know how threats affect different components within ecosystems and ultimately alter ecosystem functioning. We used a case study of a Mediterranean seagrass (Posidonia oceanica) food web and expert knowledge elicitation in an application of the initial steps of a framework for assessment of cumulative human impacts on food webs. We produced a conceptual seagrass food web model, determined the main trophic relationships, identified the main threats to the food web components, and assessed the components' vulnerability to those threats. Some threats had high (e.g., coastal infrastructure) or low impacts (e.g., agricultural runoff) on all food web components, whereas others (e.g., introduced carnivores) had very different impacts on each component. Partitioning the ecosystem into its components enabled us to identify threats previously overlooked and to reevaluate the importance of threats commonly perceived as major. By incorporating this understanding of system vulnerability with data on changes in the state of each threat (e.g., decreasing domestic pollution and increasing fishing) into a food web model, managers may be better able to estimate and predict cumulative human impacts on ecosystems and to prioritize conservation actions

Impact of anthropogenically created canopy gaps on wave attenuation in a Posidonia oceanica seagrass meadow

“…Moorings using anchors (anchoring) and fixed weights moorings (mooring) are one of the main causes of anthropogenic disturbances within seagrass meadows (Walker et al 1989, Hastings et al 1995, Montefalcone et al 2008, Boudouresque et al 2012, Demers et al 2013, Giakoumi et al 2015. Gaps caused by trawling and the anchoring of large boats have been found along the Mediterranean coast (Francour et al 1999, Leriche et al 2006) and nearshore mooring scars can increase the loss of sedimentary organic carbon stores (Serrano et al 2016).…”

Seascape ecology in Posidonia oceanica seagrass meadows: Linking structure and ecological processes for management

“…Human activities, such as coastal development, trawling, anchoring, fish farms, are well known to directly modify P. oceanica meadow structure at all depths (Boudouresque et al, 2009;Giakoumi et al, 2015), but such effects are less evident within the 35-43 m bathymetric range (Pasqualini et al, 1998). As in the case of naturally-occurring patches of the seagrass, patches resulting from anthropogenic activities can be clearly identified at a large spatial scale according to their size and shape Clabaut et al, 2014;Pasqualini et al, 1999).…”

Advancing marine conservation in European and contiguous seas with the MarCons Action

“…The understanding of biological invasion processes and their impacts on native marine biodiversity and ecosystems, as well as the quantification and mapping of the impacts of invasive alien species, are considered as prerequisites for the prioritization of conservation management actions (Blackburn et al 2011. Biological invasions are being widely disregarded when planning for conservation in the marine environment, although their explicit consideration can significantly alter spatial conservation priorities (Giakoumi et al 2016). Additional management actions aimed at prevention as well as the mitigation of the impact of invasive species are required at all levels.…”

“…Another important issue that has been largely overlooked by the scientific community is how to account for biological invasions in marine conservation planning (Giakoumi et al 2016). This globally important threat to biodiversity, often facilitated by climate change, needs to be mitigated through specific conservation actions.…”