Monitoring the resilience of a no take marine reserve to a range extending species using benthic imagery

Abstract

Global climate change is driving the redistribution of marine species and thereby potentially restructuring endemic communities. Understanding how localised conservation measures such as protection from additional human pressures can confer resilience to ecosystems is therefore an important area of research. Here, we examine the resilience of a no-take marine reserve (NTR) to the establishment of urchin barrens habitat. The barrens habitat is created through overgrazing of kelp by an invading urchin species that is expanding its range within a hotspot of rapid climate change. In our study region, a multi-year monitoring program provides a unique time-series of benthic imagery collected by an Autonomous Underwater Vehicle (AUV) within an NTR and nearby reference areas. We use a Bayesian hierarchical spatio-temporal modelling approach to estimate whether the NTR is associated with reduced formation of urchin barrens, and thereby enhances local resilience. Our approach controls for the important environmental covariates of depth and habitat complexity (quantified as rugosity derived from multibeam sonar mapping), as well as spatial and temporal dependence. We find evidence for the NTR conferring resilience with a strong reserve effect that suggests improved resistance to the establishment of barrens. However, we find a concerning and consistent trajectory of increasing barrens cover in both the reference areas and the NTR, with the odds of barrens increasing by approximately 32% per year. Thus, whereas the reserve is demonstrating resilience to the initial establishment of barrens, there is currently no evidence of recovery once barrens are established. We also find that depth and rugosity covariates derived from multibeam mapping provide useful predictors for barrens occurrence. These results have important management implications as they demonstrate: (i) the importance of monitoring programs to inform adaptive management; (ii) that NTRs provide a potential local conservation management tool under climate change impacts, and (iii) that technologies such as AUVs and multibeam mapping can be harnessed to inform regional decision-making. Continuation of the current monitoring program is required to assess whether the NTR can provide long term protection from a phase shift that replaces kelp with urchin barrens.

Towards transboundary networks of climate-smart marine reserves in the Southern California Bight

“…Represent habitat attributes (e.g., steepness, rugosity) known to favour the biomass recovery of species 102 that enhance the resilience of ecosystems to adapt to climate change 103 . Examples include predatory species that stabilize sea urchin populations, allowing giant kelp to persist 7,103 .…”

“…Areas with high cumulative impacts (e.g., coastal development, pollution, runoffs) are likely degrading ecosystem health, fisheries productivity, and resilience to climate change (reviewed by Green, et al 9 ), preventing marine reserves from producing the expected benefits 9, 10 . However, these are general recommendations since reducing overfishing inside marine reserves, combined with restoration actions and other management strategies that directly address those threats, can build resilience 3, 5, 7 to threats not directly managed by marine reserves and contribute to the recovery of degraded areas. Therefore, the decision to protect or restore highly threatened areas requires cost-benefit analysis on a site-specific basis 91 and other considerations such as ecological connectivity.…”

“…Marine reserves can rebuild the biomass of overfished species 1 , conserve biodiversity 2 , and enhance the resilience and adaptive capacity of ecosystems to climate impacts [3][4][5][6][7] . However, delivering large-scale benefits requires networks of marine reserves that are functionally interconnected, and are large enough to protect the underlying biophysical processes that maintain species distribution and composition 8 .…”

Regional estimates of a range‐extending ecosystem engineer using stereo‐imagery from ROV transects collected with an efficient, spatially balanced design

“…rodgersii into Tasmania is relatively recent, and initial monitoring efforts have reported urchin densities substantially lower than found in their native range of New South Wales (e.g. Perkins et al., 2020) as this species gradually increases its range and abundance within Tasmanian waters. Likewise, our results demonstrated a significant decline in abundance and barren cover from the northern locations (GIMR and Butlers Point) to the most southern region of the Tasman Peninsula, following the spatial pattern observed in previous studies (e.g.…”

“…Terrain attributes that have been previously found to influence urchin distribution (i.e. Perkins et al., 2020) were kept as explanatory variables in the analysis.…”