MEPS 535:117-128 (2015)  -  DOI: https://doi.org/10.3354/meps11400

ABSTRACT: An experimental trial to mitigate dredging impact was undertaken within Falmouth Harbour, UK, removing a surface layer of dead maerl for storage on a barge and allowing the channel to be deepened before re-laying the maerl. The resilience (resistance and recovery) of the habitat and faunal assemblage to this disturbance was assessed. Six sites each had 2 conditions—a manipulated treatment area where maerl (25 m² plots, top 0.3 m) was removed, stored on a barge and re-laid by backhoe dredger and a control area—which were cored at 0 (before), 5 and 44 wk after re-lay. PERMANOVA was used to test for differences between condition and time using a 2-factor design. Results should not be extrapolated to live maerl habitats or to large, long-lived fauna that may live within them. Following the mechanical disturbance, the maerl matrix structure was altered through loss of fine sediment from the lower half of cores (>10 cm). There was also a significant reduction in the number of taxa and abundance of infauna and a change in the assemblage composition. By Week 44, however, no such significant differences were evident, indicating that the infauna was in a state of recovery. The only response variable showing recovery was annelid biomass. The trial demonstrated that removing and re-laying the top 0.3 m of maerl habitat is technically feasible, and whilst some differences in the habitat structure following re-laying were evident, this did not affect the habitat quality enough to prevent recolonisation of infauna.

KEY WORDS: Marine protected area · Recovery · Anthropogenic impact · Ecosystem impact · Dredging mitigation · Marine biodiversity · Habitat complexity