Comparing Apples to Oranges: Common Trends and Thresholds in Anthropogenic and Environmental Pressures across Multiple Marine Ecosystems

Abstract

Ecosystem-based management (EBM) in marine ecosystems considers impacts caused by complex interactions between environmental and anthropogenic pressures (i.e., oceanographic, climatic, socio-economic) and marine communities. EBM depends, in part, on ecological indicators that facilitate understanding of inherent properties and the dynamics of pressures within marine communities. Thresholds of ecological indicators delineate ecosystem status because they represent points at which a small increase in one or many pressure variables results in an abrupt change of ecosystem responses. The difficulty in developing appropriate thresholds and reference points for EBM lies in the multidimensionality of both the ecosystem responses and the pressures impacting the ecosystem. Here, we develop thresholds using gradient forest for a suite of ecological indicators in response to multiple pressures that convey ecosystem status for large marine ecosystems from the US Pacific, Atlantic, sub-Arctic, and Gulf of Mexico. We detected these thresholds of ecological indicators based on multiple pressures. Commercial fisheries landings above approximately 2-4.5 t km −2 and fisheries exploitation above 20-40% of the total estimated biomass (of invertebrates and fish) of the ecosystem resulted in a change in the direction of ecosystem structure and functioning in the ecosystems examined. Our comparative findings reveal common trends in ecosystem thresholds along pressure gradients and also indicate that thresholds of ecological indicators are useful tools for comparing the impacts of environmental and anthropogenic pressures across multiple ecosystems. These critical points can be used to inform the development of EBM decision criteria.

Characterizing and comparing marine fisheries ecosystems in the United States: determinants of success in moving toward ecosystem-based fisheries management

“…These include tracking ratios such as the exploitation index (landings to biomass), areal landings, landings to productivity, total revenue relative to biomass, revenue relative to productivity, and total employments relative to biomass; and ensuring that they do not fall below specific thresholds (c.f., Mace 1994;Botsford et al 1997;Murawski 2000;Horan et al 2011;McClanahan et al 2011;Large et al 2013Large et al , 2015. For example, Samhouri et al (2010), Large et al (2015) and Tam et al (2017a) showed for multiple systems that an exploitation index above 15% represented a threshold not to be exceeded, which had resulted in a tipping point in ecosystem status. Our findings show that exploitation rates for the Gulf of Mexico have approached or exceeded 15% and have remained closer to 10% for the Mid-Atlantic and New England regions.…”

“…Comparative marine ecosystem studies have high value (Vasconcellos et al 1997;Hunt and Megrey 2005;Megrey et al 2009;Murawski et al 2009). By comparing consistent, common data across systems, clear patterns can and have emerged (Link et al 2012;Murphy et al 2013;Tam et al 2017a). Furthermore, lessons learned from structured case study analysis can highlight strengths and successes, and conditions thereof, warranting application elsewhere.…”

“…But more so, sluicing these data to develop integrative indicators that illuminate what constitutes the criteria for successful fisheries management and acceptable fisheries ecosystems remains a challenge, and goal, that is still sorely needed (Rudd 2004;Levin et al 2009;Anderson et al 2015). This has arguably been done for single-species fisheries (Rogers and Greenaway 2005;Nash et al 2016), but rarely as an entire ecosystem (Rogers and Greenaway 2005;Tam et al 2017a). Such ecosystem-level performance metrics have been broadly considered as simply indicators (Samhouri et al 2013;Lockerbie et al 2018), reference points, or thresholds (Fulton et al 2005;Jennings and Dulvy 2005;Link 2005;Link et al 2015;Tam et al 2017b) or status context (Link et al 2002;Coll et al 2016;Slater et al 2017).…”

Capturing threshold responses of marine benthos along gradients of natural and anthropogenic change

“…We investigate the nature of the faunal responses to environmental gradients and determine the extent to which these gradients predict their distribution. Quantifying the shape and magnitude of organisms’ responses allows us to identify community thresholds when a small change in a gradient causes sharp increases or decreases in the occurrence of a range of different types of organisms (Connell et al, 2017; Groffman et al, 2006; Tam et al, 2017). These threshold responses are often exacerbated by species interactions, where the loss or gain of one or more key species may precipitate the loss or appearance of others (e.g.…”

Changing how we approach fisheries: A first attempt at an operational framework for ecosystem approaches to fisheries management

“…There is a significant need for a framework like the one proposed here. Largely because we need to change the mindset when approaching fisheries issues from one of weighing or exploring every potential, optimized outcome to one of identifying workable solutions in the context of such oceanographic, ecological and socioeconomic complexity (Boyd, Lennartz, Glover, & Doney, 2015;Cheung et al, 2010;Fulton et al, 2019;Halpern et al, 2015Halpern et al, , 2008Hilborn, 2011;Hoegh-Guldberg & Bruno, 2010;Jackson et al, 2001;Link, 2018;Link et al, 2012aLink et al, , 2012bLink & Marshak, 2019;Marshall et al, 2017;Micheli, Leo, Butner, Martone, & Shester, 2014;Ruckelshaus, Klinger, Knowlton, & DeMaster, 2008;Tam et al, 2017). We propose the first ever framework to systematically, simultaneously, comparatively and relatively explore population diagnostics that link responses to main causal factors.…”