Using ecological trajectories to track long‐term taxonomic and functional changes in benthic shallow soft‐bottom communities (Bay of Saint‐Brieuc, English Channel)

Abstract

1. Taxonomic and functional trajectories of benthic assemblages were studied in shallow soft-bottom sediments in the bay of Saint-Brieuc (Western English Channel). Changes were assessed at different spatial and temporal scales using a macrobenthic dataset based on 38 stations sampled in 1987 and 2019, coupled with data from one station sampled annually between 2005 and 2019 as part of the European Water Framework Directive monitoring programme. 2. Taxonomic trajectories indicated 1) changes in the structure and distribution of benthic assemblages, 2) an homogenization of the assemblages, and 3) significant functional shifts. 3. Fishing activities and nutrient enrichment are probably strong drivers of the observed changes, as suggested by the higher mortality rate of fragile, flexible, tubiculous and burrowing species, and the increase in the abundance of opportunistic species in the assemblages. Certain populations of macroinvertebrates seem jointly controlled by climate change and by the aforementioned local factors of disturbance. 4. The Community Trajectory Analysis framework appears as a new and interesting method to track ecological changes in marine ecosystems by measuring change with respect to a baseline state, to help define ecological recovery (station returning to the initial ecological state) and departure (station presenting increased changes over time), and to analyse trajectory similarity. 5. According to the degradation of habitat over time, we identify the need for the implementation of knowledge-based conservation strategies, especially within Natura 2000 sites.

Stomach content and stable isotope analyses provide complementary insights into the trophic ecology of coastal temperate bentho-demersal assemblages under environmental and anthropogenic pressures

“…In 2019, the benthic macrofauna was dominated by molluscs, annelids and crustaceans (Sturbois et al, 2021a). Knowledge concerning subtidal fishes in the study area are rare and old.…”

“…Despite bordering the National Nature Reserve of the bay of Saint-Brieuc and partially belonging to the Natura 2000 "Baie de Saint-Brieuc-Est" site (European Union network, FR5300066), the study area is exposed to a number of anthropogenic pressures including mussel culture and scallop dredging (Sturbois et al, 2021b(Sturbois et al, , 2021a. Mussels are farmed on wooden poles (312 ha; Figure 1) in the north-eastern part of the intertidal area and on ropes in the western part of the study area.…”

“…Mussels are farmed on wooden poles (312 ha; Figure 1) in the north-eastern part of the intertidal area and on ropes in the western part of the study area. The sea bed is exposed to long-term scallop dredging (Sturbois et al, 2021a).…”

“…In the bay of Saint-Brieuc (Western English Channel), fish communities that use the intertidal area at high tide have been studied in relation to salt marsh (Laugier, 2015;Sturbois et al, 2016) and green tides (Le Luherne et al, 2016). Despite a recent update of the benthic macrofauna knowledge in the subtidal area belonging to the "Baie de Saint-Brieuc -Est" Natura 2000 site and neighbouring the National Nature Reserve of the bay of Saint-Brieuc (Sturbois et al, 2021a), data on bentho-demersal fish and cephalopods are rare and old (Gully, 1981;Le Dean and Moreau, 1981). The marine protected areas did not prevent this shallow subtidal area under a megatidal regime from different anthropogenic activities (Shellfish farming, eutrophication, invasive species) and the bay has been supporting intense bottom fishing (mostly scallop dredging) for decades.…”

“…The marine protected areas did not prevent this shallow subtidal area under a megatidal regime from different anthropogenic activities (Shellfish farming, eutrophication, invasive species) and the bay has been supporting intense bottom fishing (mostly scallop dredging) for decades. This fishing pressure has affected benthic habitats (Sturbois et al, 2021a) ACCEPTED MANUSCRIPT / CLEAN COPY and may have potential impacts on fish and cephalopod communities of the marine protected area.…”