Research Document - 2012/125

Indicators, impacts and recovery of temperate deepwater marine ecosystems following fishing disturbance

By J.M.R. Curtis, K. Poppe, and C.C. Wood

Abstract

This Research Document was prepared to support discussions related to specific terms of reference (ToR objective 2 and 5a) outlined for the National Science Advisory Process Concerning Corals, Sponges, and Hydrothermal Vents in Canadian Waters (DFO 2010):

2. Based on available information, and to the extent possible, provide advice on the susceptibility of corals, sponges, and hydrothermal vents to fishing impacts as well as their potential for recovery once impacted.

5a. When indicators (e.g. spatial extent, abundance, species richness, rareness, etc...) of the ecological function served by corals, sponges, and hydrothermal vents are used, discuss the strengths and weaknesses of these indicators.

We identified primary literature on the impacts of anthropogenic disturbances in temperate deepwater marine ecosystems and their recovery following disturbance. Our search returned 545 papers published from 2000-2009, and 46 of these satisfied our initial screening criteria, notably empirical studies that included a spatial or temporal reference for quantitatively measuring ecosystem responses to anthropogenic activities. Our review did not focus exclusively on impacts of fishing on coral and sponge taxa; we extracted relevant but sparse data on corals and sponges from our database to address ToR objective 2. None of the studies we reviewed addressed hydrothermal vents. To address ToR objective 5a, we summarized the suite of indicators that authors used to measure the responses of populations, communities and ecosystems to anthropogenic disturbances. Across studies, approximately 250 variables were measured to evaluate impacts, and these variables related primarily to the state of invertebrate and vertebrate populations, community structure, ecosystem function, environmental conditions, fisheries, and other threats. Preliminary analysis of published studies indicates that coral and sponge taxa are, on average, more susceptible to fishing impacts than other invertebrate or vertebrate taxa. Compared to reference states, abundances of corals and sponges were 1-57% and 20-91% lower in sites following a single disturbance event. In areas that were repeatedly disturbed, coral and sponge abundances were 19-100% (median = 88.8%) and 22-100% (median = 98.3%) lower compared to reference states. Of sponges and corals that were not removed through fishing, the proportion of dead or damaged organisms following trawling ranged from 23-100% for corals, and 14-67% for sponges. While some studies reported signs of sponge recovery following disturbance (e.g. repair, regrowth, recruitment), few studies provided quantitative or qualitative evidence of coral recovery. However, most (83%) of the studies we reviewed lasted no more than 1 year following disturbance, which made it difficult to quantify the tempo and magnitude of coral and sponge recovery.

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