Increased connectivity and depth improve the effectiveness of marine reserves

Abstract

Marine reserves are a key tool for the conservation of marine biodiversity, yet only ~2.5% of the world's oceans are protected. The integration of marine reserves into connected networks representing all habitats has been encouraged by international agreements, yet the benefits of this design has not been tested empirically. Australia has one of the largest systems of marine reserves, providing a rare opportunity to assess how connectivity influences conservation success. An Australia‐wide dataset was collected using baited remote underwater video systems deployed across a depth range from 0 to 100 m to assess the effectiveness of marine reserves for protecting teleosts subject to commercial and recreational fishing. A meta‐analytical comparison of 73 fished species within 91 marine reserves found that, on average, marine reserves had 28% greater abundance and 53% greater biomass of fished species compared to adjacent areas open to fishing. However, benefits of protection were not observed across all reserves (heterogeneity), so full subsets generalized additive modelling was used to consider factors that influence marine reserve effectiveness, including distance‐based and ecological metrics of connectivity among reserves. Our results suggest that increased connectivity and depth improve the aforementioned marine reserve benefits and that these factors should be considered to optimize such benefits over time. We provide important guidance on factors to consider when implementing marine reserves for the purpose of increasing the abundance and size of fished species, given the expected increase in coverage globally. We show that marine reserves that are highly protected (no‐take) and designed to optimize connectivity, size and depth range can provide an effective conservation strategy for fished species in temperate and tropical waters within an overarching marine biodiversity conservation framework.

Effects of human footprint and biophysical factors on the body‐size structure of fished marine species

“…Combined, these results stress the importance of geographic areas subjected to low levels of human footprint in the surrounding seascape (Cinner et al 2013(Cinner et al , 2018 as spatial refuges for large-bodied individuals across multiple ecosystem configurations. Our results also suggest that well-designed NTMR networks (Knott et al 2021, Goetze et al 2021 and areas that remain relatively unaltered by humans provide useful reference points against which target levels of large-bodied fish indicators can be assessed (Stuart-Smith et al 2017;McClanahan et al 2019). This will boost the understanding of the potential benefits of protecting large-bodied fishes for conserving trophic links (Dulvy et al 2004;Mumby et al 2006) and contribute to the recovery of local stocks through larval supply (Le Port et al 2017;Andrello et al 2017;Marshall et al 2019).…”

“…For large-bodied individuals (>90th percentile of the body-size distribution) and individuals >MLS, probability of occurrence and relative abundance was best predicted by gradients of human gravity, depth, and seascape relief. The NTMRs were strong predictors of the abundance of legal-size fishes, but had weak support for predicting the probability of occurrence of large fishes, highlighting potential limitations in NTMR coverage and design (Edgar et al 2018;Goetze et al 2021). In contrast, models for sublegal individuals were weak, but consistently featured positive relationships with environmental predictors, including mean and variance in SST.…”

“…), a species that displays high residency and territoriality and responds strongly to NTMR protection and direct catch or effort control measures (Hopf et al 2016). The variable response across regional species groups highlights potential limitations in the design of NTMR networks around Australia where fisheries management measures are in place (Edgar et al 2018;Goetze et al 2021), such as gaps in NTMR coverage across the biogeographic extent of occurrence of species groups we analyzed (Roberts et al 2021). Multiple intrinsic factors can also influence the biodiversity benefits of NTMRs, such as the size, age, level of compliance, connectivity of the zones, and the level of exploitation in the surrounding seascape (Claudet et al 2008;Edgar et al 2014;Cinner et al 2018).…”

“…For instance, in our synthesis, there was an uneven representation of the size of NTMRs across the human gravity gradient; small (<10 km 2 ) NTMRs were overrepresented in areas of high human gravity, whereas the largest NTMRs (>100 km 2 ) exclusively occurred in areas of low to intermediate human gravity. Gains in ecological and societal benefits may exist in establishing representative networks of NTMRs, including large NTMRs in areas with high human gravity (Cinner et al 2018(Cinner et al , 2020 that cover broad-depth ranges (Goetze et al 2021).…”

Ecological connectivity of the marine protected area network in the Baltic Sea, Kattegat and Skagerrak: Current knowledge and management needs

“…A number of studies do, however, investigate the effect of connectivity on MPAs performance, mainly in tropical regions (e.g. Ortodossi et al 2019 ; Steneck et al 2009 ; Goetze et al 2021 ) or incorporate connectivity in conservation prioritisation by identifying and studying connectivity between nursery and adult habitats in tropical seascapes (e.g. Weeks 2017 ).…”