Disturbance to Marine Benthic Habitats by Trawling and Dredging: Implications for Marine Biodiversity

Abstract

▪ Abstract The direct effects of marine habitat disturbance by commercial fishing have been well documented. However, the potential ramifications to the ecological function of seafloor communities and ecosystems have yet to be considered. Soft-sediment organisms create much of their habitat's structure and also have crucial roles in many population, community, and ecosystem processes. Many of these roles are filled by species that are sensitive to habitat disturbance. Functional extinction refers to the situation in which species become so rare that they do not fulfill the ecosystem roles that have evolved in the system. This loss to the ecosystem occurs when there are restrictions in the size, density, and distribution of organisms that threaten the biodiversity, resilience, or provision of ecosystem services. Once the functionally important components of an ecosystem are missing, it is extremely difficult to identify and understand ecological thresholds. The extent and intensity of human disturbance to oceanic ecosystems is a significant threat to both structural and functional biodiversity and in many cases this has virtually eliminated natural systems that might serve as baselines to evaluate these impacts.

Mediation of macronutrients and carbon by post-disturbance shelf sea sediment communities

“…The presence of these species, in particular the spatangoid Echinocardium cordatum, offers an explanation for the enhanced [NH 4 -N] observed in noncohesive sediment communities that have experienced a high frequency of fishing activity. Based on our findings, a naïve hypothesis would be that the frequency of physical disturbance (here, bottom fishing) is less important for biogeochemical cycling in cohesive sediments than it is in noncohesive sediments, but in the absence of a comparable fully functional ecosystem such a conclusion is premature (Thrush and Dayton 2002). Indeed, even a low frequency of disturbance can cause significant changes to the biotic and abiotic components of the system and it is possible that intensive fishing disturbance can cause a reduction of [NO 3 -N] that relates to over-mobilisation of sediment, increased microbial activity, and net loss of N from the sediments (Bertics et al 2010, Laverock et al 2011).…”

“…Whilst the susceptibility of benthic communities and habitat integrity to perturbation associated with bottom fishing activity has long been established (Thrush and Dayton 2002;Jones 1992), evaluations of the longer term effects of restructured post-disturbance communities inhabiting altered sedimentary conditions on biogeochemical processes have been less prominent (Lambert et al 2014). Cohesive shelf sediments have been considered to be particularly important areas for biogeochemical activity owing to the presence of elevated concentrations of organic matter and living biomass, contributing an estimated 44% of global denitrification and [40% of total organic matter burial (Muller-Karger et al 2005;Seitzinger et al 2006;Middleburg and Levin 2009).…”

Assessment of goods and services, vulnerability, and conservation status of European seabed biotopes: a stepping stone towards ecosystem-based marine spatial management

“…The biotope is also sensitive to continental-marine organic matter input (Mojtahid et al, 2009). High disturbance could be caused by dredging activities or by trawling (Thrush & Dayton, 2002). Megafauna play a significant role in bio-turbation, and as detailed earlier it is these organisms which are most vulnerable to trawling activity.…”

Towards a meaningful assessment of marine ecological impacts in life cycle assessment (LCA)

“…The primary response of benthic organisms to a physical disturbance is often severe damage or mortality (Bolam and Rees, 2003;Kaiser et al, 2006;Collie et al, 2000). Particularly impacted are sedentary organisms and filter feeders, such as anemones, soft corals and bivalve species (Kaiser et al, 2002;Widdicombe and Austen, 2001;Thrush and Dayton, 2002;Smit et al, 2008). This can result in a number of changes in benthic communities, including loss of habitatstructuring species, substantial decline in taxon abundance, and changes in species richness (Kaiser et al, 2002;Thrush and Dayton, 2002;Hiddink et al, 2006).…”