The Role of Pre-Existing Disturbances in the Effect of Marine Reserves on Coastal Ecosystems: A Modelling Approach

Abstract

We have used an end-to-end ecosystem model to explore responses over 30 years to coastal no-take reserves covering up to 6% of the fifty thousand square kilometres of continental shelf and slope off the coast of New South Wales (Australia). The model is based on the Atlantis framework, which includes a deterministic, spatially resolved three-dimensional biophysical model that tracks nutrient flows through key biological groups, as well as extraction by a range of fisheries. The model results support previous empirical studies in finding clear benefits of reserves to top predators such as sharks and rays throughout the region, while also showing how many of their major prey groups (including commercial species) experienced significant declines. It was found that the net impact of marine reserves was dependent on the pre-existing levels of disturbance (i.e. fishing pressure), and to a lesser extent on the size of the marine reserves. The high fishing scenario resulted in a strongly perturbed system, where the introduction of marine reserves had clear and mostly direct effects on biomass and functional biodiversity. However, under the lower fishing pressure scenario, the introduction of marine reserves caused both direct positive effects, mainly on shark groups, and indirect negative effects through trophic cascades. Our study illustrates the need to carefully align the design and implementation of marine reserves with policy and management objectives. Trade-offs may exist not only between fisheries and conservation objectives, but also among conservation objectives.

Ocean Futures Under Ocean Acidification, Marine Protection, and Changing Fishing Pressures Explored Using a Worldwide Suite of Ecosystem Models

“…Similarly, if MPAs are too large, economic benefits may be diminished. Unintended effects such as displaced effort or trophic cascades have been suggested by many modeling studies of MPAs, for instance by Walters et al (1999), and more recently by Savina et al (2013) who found negative impacts on prey fish when MPAs promoted shark recovery in a study of New South Wales, Australia. Here we test the assertion by Fulton et al (2015) that MPAs perform best in terms of specific objectives related to species recovery, but that they can lead to tradeoffs across species and ecological objectives such as biodiversity and economic equity.…”

Marine reserves can enhance ecological resilience

“…Harvest (or bycatch) of both predators and prey, such that harvest release can outweigh predation increase in prey T: (Baskett 2006, Kellner et al 2010, Micheli et al 2004a, Savina et al 2013, Takashina et al 2012) E: (Mumby et al 2006, Shears et al 2012 Weakened…”

Improving the spatial allocation of marine mammal and sea turtle biomasses in spatially explicit ecosystem models

“…The sophistication of EwE with Ecospace and Atlantis allows these modeling approaches to tackle a wide number of EBFM issues, including MPA effectiveness (e.g. Salomon et al 2002, Martell et al 2005, Savina et al 2013, Olsen et al 2018, the consequences of bycatch reduction measures (e.g. Fulton et al 2007, Walters et al 2010, Morzaria-Luna et al 2012, 2013, and management strategy evaluations integrating ecosystem considerations (e.g.…”