Assessing Benthic Responses to Fishing Disturbance Over Broad Spatial Scales That Incorporate High Environmental Variation

Abstract

Marine benthic habitats are modified by a number of human-related disturbances. When these disturbances occur at large scales over areas of high environmental variability, it is difficult to assess impacts using metrics such as species richness or individual species distributions because of varying species-specific responses to environmental drivers (e.g., exposure, sediment, temperature). Impact assessment can also be problematic when assessed at broad spatial scales because of regional heterogeneity of species pools. Even when effects on individual species can be detected, it is difficult to upscale from individual species to ecosystem scale effects. Here, we use a functional group approach to assess broad scale patterns in ecological processes with respect to fishing and environmental drivers. We used data from field surveys of benthic communities from two large, widely separated areas in New Zealand's EEZ (Chatham Rise and Challenger Plateau). We assigned 828 taxonomic units (most identified to species) into functional groups related to important ecosystem processes and likely sensitivity to, and recovery from, fishing disturbance to the seafloor. These included: opportunistic early colonists; substrate stabilisers (e.g., tube mat formers); substrate destabilisers; shell hash-creating species; emergent epifauna; burrowers; and predators and scavengers. Effects of fishing disturbance on benthic functional composition were observed, even at this broad spatial scale. Responses varied between functional groups, with some being tolerant of fishing impacts and others showing rapid declines with minimal fishing effort. The use of a functional group approach facilitates assessment of impacts across regions and species, allowing for improved generalisations of impacts to inform management and decision making.

Effects of Benthic Protection Extent on Recovery Dynamics of a Conceptual Seafloor Community

“…Three functional groups, substrate destabilizers (FG 4), late colonizers -emergent epifauna (FG 6), and late colonizersburrowers (FG 7), showed the least tolerance to disturbance (as also observed in an empirical study using functional groups to investigate the benthic responses to fishing disturbance by Lundquist et al, 2018). The large and immediate declines in presence of these functional groups within the seafloor disturbance model at low to moderate rates of disturbance (e.g., >10% disturbance), imply sensitivity to disturbance as evidenced throughout the literature for these functional groups (Turner et al, 1999;Jennings et al, 2001;Thrush et al, 2001).…”

“…in New Zealand (Lundquist et al, 2013(Lundquist et al, , 2018. The FGs range from early to late colonists, surface dwellers to burrowers, substrate stabilizers to de-stabilizers, scavengers, predators and filter feeders; biological traits and life history determine how sensitive each FG will be to physical disturbance of the seafloor and how FGs interact within the model ( Table 1).…”

“…Locally and seasonally restricted dispersal, limited mobility and late maturity (Grigg, 1977;Gordon et al, 2010), thus likely to be the most sensitive to perturbation (Lundquist et al, 2018) 7…”

“…However, many studies have demonstrated that species loss is not random and that species with particular biological traits have different disturbance-recovery dynamics (Pearson and Rosenberg, 1978;Thrush et al, 2006;Sciberras et al, 2018). Specific combinations of biological traits (functional groups) have also been used to derive indicators of, or sensitivity to, stressors, predict ecosystem functions and services and predict recovery dynamics of specific species (de Juan et al, 2007;Ellis et al, 2017;Hewitt et al, 2018;Lundquist et al, 2018). Functional group approaches facilitate evaluation of general predictions about seafloor communities without the need to model each species individually and enable comparisons over large scales (e.g., different regions), despite differences in species composition, to determine the impact of environmental drivers or disturbance (e.g., Bremner et al, 2003;Tillin et al, 2006;de Juan et al, 2007de Juan et al, , 2009Lundquist et al, 2018).…”

Vulnerability of Demersal Fish Assemblages to Trawling Activities: A Traits-Based Index

“…Some of these historical declines belong to the class of cartilaginous fishes Chondrichthyes (Damalas et al, 2015), widely recognized to be negatively affected by fishing due to life-history strategies characterized by slow growth, late maturity, long life spans and low fecundity (e.g., Foster et al, 2014;Henriques et al, 2014). Sessile invertebrates that are highly susceptible to trawling and are known to be declining in fishing grounds, like sponges or cnidarians (Lundquist et al, 2018) were not recorded within our study areas. Would these have been recorded, they would have been classified as highly vulnerable according to our index scores, as these taxonomic groups are generally characterized by very high catchability, high resistance, and low resilience.…”