Beschreibung: Benthic organisms and their bioturbation activities have a profound effect on a multitude of sediment properties. While many studies have already explored benthic impacts at small temporal and spatial scales, little is known on how the small-scale effects accumulate and interactively guide large-scale (km-scale) morphological evolution. Here we firstly summarize the most important processes of benthos affecting sediment stability and then explore existing biomorphodynamic modeling studies both at small- and large-scales. In general, microbenthos (body size 〈0.1 mm) mainly stabilizes sediments while meio- (0.1–1 mm) and macrobenthos (〉1 mm) may stabilize or destabilize sediments. Among all types of sediment, fine-grained fraction (silt and clay) is most sensitive to the impact of benthos. Benthic organisms have the capability to mediate sediment transport and sedimentation patterns beyond their habitats on the long-term and over a large-scale. However, so far, numerical models evaluating benthic impact are limited to explorative studies and have not reached a stage where they can be used for predictive modeling. The barriers hindering a further development of biomorphodynamic models include not only limited understanding of fundamental biological/bio-physical processes affecting morphological development and dynamic feedback loops among them but also a shortage of data for model calibration and confirmation of simulation results. On the other hand, thriving for higher model complexity does not necessarily lead to better performance. Before conducting biomorphodynamic modeling, researchers must figure out which questions can be answered in a meaningful sense with simulation results that can be compared with observations and which level of modeling complexity is sufficient for that purpose.

Beschreibung: The Working Group on Fisheries Benthic Impact and Trade-offs (WGFBIT) develops methods and performs assessments to evaluate benthic impact from fisheries at regional scale, while con- sidering fisheries and seabed impact trade-offs. In this report, new fishery benthic impact assessments (ToR A) are shown out for several sub- regions in (French Mediterranean, Celtic Seas). For other regions, updates of the whole assess- ment or specific steps only were presented. To further standardise the different components of the WGFBIT approach across all (sub-)re- gional assessments, a more detail overview of those components was compiled. These compo- nents were slightly different among those regions, related to variation in data availability, envi- ronmental characteristics and implementation possibilities among the (sub-)regions. In WGFBIT, assessments are sometimes based on trawl or grab data, which are sampling differ- ent components of the seafloor ecosystem and can have consequences on the created sensitivity layer. Therefore, there is looked in more detail how the sensitivity outcome (and layers) can dif- fer due to the use of benthic data gathered with different gears (grab/core, trawl or video). The preliminary comparability analyses are performed on different levels: (1) based on co-located sampling; (2) comparing sensitivity maps of the (sub-) area, based on different gears. There were differences observed in longevity distribution at locations sampled with different gears and dif- ferences in data and models lead also to differences in the sensitivity layers. The WGFBIT seafloor assessment framework is not the only way to assess benthic impacts from physical disturbance. A discussion session was held on how the future workflow on advice that ICES WGFBIT assessment contribute to, will be organized. Marine sediments harbour significant levels of biodiversity that play a key role in ecosystem functions and services such as biogeochemical cycling, carbon storage and the regulation of cli- mate. Through the removal of fauna, changes in physico-chemical nature and resuspension of sediment, bottom trawling may result in significant changes in the ecosystem functioning of shelf seas. An assumption of the current PD model is that high community biomass implies higher ecosystem functioning. However, total community biomass does not necessarily reflect changes in species and functional trait composition which play a key role in regulating ecosystem func- tions. ToR D is working on an improved understanding of the link between species functional effect traits and proxies and processes for specific ecosystem functions to improve our ability to predict the impact of fishing disturbance on benthic ecosystem functioning more accurately. Links between species traits and biogeochemical parameters and the impact of trawling on these links are being explored using multivariate ordination analyses using different fauna and bioge- ochemical datasets collected in the North Sea, Celtic Sea, Kattegat, Baltic Sea and the eastern Mediterranean. Changes due to trawling in the trajectories of species densities over time and the concurrent changes in the bioturbation and bioirrigation potential of communities are being modelled using a combination of data-driven mechanistic model and a biogeochemical model. We report on the different data analysis methods that ToR D members have developed over the last year.

Beschreibung: ICES

Beschreibung: Published

Beschreibung: Refereed