Assessment and management of cumulative impacts in California's network of marine protected areas
Introduction
Marine ecosystems worldwide face increasing anthropogenic stressors, including climate change, pollution, habitat degradation, invasive species and overfishing (Knowlton and Jackson, 2008). Around the world, marine protected areas (MPAs) have been established to address the impacts from some of these stressors in the coastal environment (e.g., Guidetti et al., 2014, Agardy et al., 2003). Typically, MPA goals are focused on reducing fisheries-related mortality to maintain or enhance biodiversity. Although impacts from fishing have decreased within many MPAs (Lester et al., 2009, Aburto-Oropeza et al., 2011), the species and habitats in most MPAs remain exposed to other stressors (Hazen et al., 2013, Maxwell et al., 2013), which are not often known or quantified. Moreover, the cumulative impact of multiple stressors has been challenging to quantify and address (Crain et al., 2008). Further adding to this challenge, coastal managers working with limited resources must prioritize their efforts to mitigate the suite of stressors and their impacts (Strain et al., 2014). Here, we use available data on stressors to California coastal ecosystems and estimates of ecosystem vulnerability to estimate the impacts of single stressors as well as the cumulative impact of multiple stressors on each MPA within California's MPA network. Our overarching goal is to demonstrate how quantifying stressors that have the greatest impacts and mapping cumulative impacts within a network of California's coastal MPAs can inform prioritization of management efforts.
Cumulative impacts to MPAs arise from stressors that occur across a range of spatial scales. Climate stressors, including ocean acidification and sea surface temperatures, are increasing globally, and these subtle changes at the global scale are leading to large impacts to local marine communities (Doney et al., 2012). For example, ocean acidification is leading to reduced calcification and growth rates of pelagic phytoplankton, zooplankton and benthic invertebrates (Fabry et al., 2008). These changes can have both direct effects on populations, and indirect effects on community composition and ecosystem function (Kroeker et al., 2010, Kroeker et al., 2013). In addition, rising temperatures have caused some marine species to shift towards higher latitudes, which could result in the range of some protected species shifting beyond of the stationary boundaries of the MPAs, undermining their efficacy (Maxwell et al., 2013; Reviewed in Harley et al., 2006). More locally, ocean-based stressors, such as shipping, ocean pollution, and species invasions, are causing changes in the effectiveness of MPAs. For example, the invasive alga, Caulerpa taxifolia, is migrating into marine reserves in the Mediterranean, smothering existing habitat and replacing native seagrasses, potentially reducing the value of these reserves for the species they are intended to protect (Bax et al., 2003). Many MPAs are subject not only to climate and ocean-based stressors, but also to land-based stressors, such as nutrients and pollutants, arriving via river runoff or through urban waste-water outfall sites and commercial development (Diaz and Rosenberg, 2008).
Moreover, there is evidence that climate stressors can enhance the effect of other environmental impacts. For example, increased nutrient loads have been found to act synergistically with ocean acidification to affect dominance of algae species (turfs or crusts) in rocky marine systems and, similarly, have been found to accelerate the shift in subtidal rocky reefs from kelp forest canopy to turf species (Russell et al., 2009). Likewise, increased exposure to inorganic polycyclic aromatic hydrocarbons pollutants (PAHs) does not significantly impact mortality of crab larvae. However, in the presence of both UV radiation and high PAH exposure, crab larvae face high mortality (Peachey, 2005). Thus, understanding if and where these stressors and their impacts are overlapping and positively correlated may prove informative for managing across suites of human activities and stressors.
To realize the full range of benefits that networks of MPAs are capable of producing, managers must reduce and mitigate multiple stressors and their impacts, both on the MPAs themselves and on the surrounding ecosystems (Alvarez-Romero et al., 2011). Ideally, management efforts to reduce and mitigate multiple stressors and their impacts would be based on a clear understanding of which activities produce which stressors, which stressors produce the greatest impacts, and where impacts are occurring in coastal systems and MPAs. Tracing a stressor back to the activities that produced it can be difficult, as many stressors are diffuse in the environment and may come from several different activities (McCarty and Munkittrick, 1996). For example, excess nutrients can impact ecosystems by producing toxic algal blooms and oxygen depletion zones that lead to mortality or toxicity in shellfish (see review by Smith and Schindler, 2009); however, pinpointing the nutrient source may be complicated because nutrients may be discharged from a number of non-point and point sources, including sewage outfalls, agriculture and forestry activities, and coastal development. In addition, the vulnerability of habitats and species to the cumulative stressors entering their environment is often unknown, making it difficult to estimate the full impact of specific activities or stressors. This type of information will help to address the challenge of managing multiple impacts and can provide managers an opportunity to prioritize which stressors and activities to manage, which areas and MPAs to target, and what kinds of management and industry partnerships are needed to address stressors acting at local-, regional- and global-scales.
More than a decade ago, the state of California enacted the Marine Life Protection Act (California Fish and Game Code Sections 2850–2863) in response to concerns about human impacts to coastal ecosystems, requiring the redesign, designation, and implementation of a statewide network of marine protected areas (MPAs) stretching along the entire coast of California (Carr et al., 2011, Gleason et al., 2013). The MPA network is intended to advance multiple goals including (a) protecting the diversity of marine life, (b) protecting the structure and function of marine ecosystems, and (c) helping to sustain, conserve, and rebuild marine life populations ( Kirlin et al., 2013, California Fish and Game Code of Regulations, 2015). The designation of the MPA network in California specifically addresses fishing as a stressor, but managers must also consider the suite of stressors that cumulatively impact the coastal area (Gleason et al., 2013).
The California Current Cumulative Impacts Model was recently developed to estimate spatial patterns of human activities in California's nearshore marine waters, identify some of the key stressors associated with these activities and, using expert judgment, assess the vulnerability of key habitat types to the identified stressors (Halpern et al., 2009, Teck et al., 2010). The model combines data on the spatial patterns of stressors and habitats, and their vulnerability scores, to estimate and map cumulative impacts. To enhance understanding of cumulative impacts to California's MPAs, we applied the California Current Cumulative Impacts Model to map climate, land-based, and ocean-based stressors, calculate the vulnerability of habitats within MPAs, and measure the cumulative impacts to these habitats. Using the results from this analysis, we quantify where cumulative impacts occur across the MPA network, indicate where impacts are the most intensely concentrated, identify the greatest impacts to habitats within MPAs, and specify which of these impacts co-occur in MPAs. Furthermore, we demonstrate how managers can implement this approach to prioritize management efforts that address cumulative impacts to nearshore MPAs and potentially enhance MPA effectiveness.
Section snippets
Study area
To map impacts to habitats in California's MPAs, we first compiled a spatial data set of MPAs based upon current California regulations from the California Department of Fish and Wildlife (DFW). We included all MPAs and special closures as of December 19, 2012 (Table 1) in the North, North Central, Central and South MLPA regions (California Fish and Game Code Title 14, Section 632). These regions were defined during the MLPA planning process to designate the complete state-wide network of MPAs (
Data & analysis
To assess cumulative impacts to habitats in California's MPAs, we adapted the California Current Cumulative Impacts Model (Halpern et al., 2009) to (1) model climate, land and ocean-based stressor scores in each MPA, (2) assess vulnerability of the habitat types found in each MPA using vulnerability weights developed by Teck et al. (2010), and (3) measure the cumulative impact on habitats in each MPA based on their vulnerability to anthropogenic stressors.
Cumulative impacts in California's MPAs
Across the California coast, we compared the mean cumulative impact scores and the climate-, land- and ocean-based impact scores in each MLPA region for each MPA and the habitats in those MPAs (Fig. 1). Of the 96 assessed MPAs, all were likely to be impacted by ocean acidification and UV radiation increases, and 61% of them by sea surface temperature changes (i.e., change in the number of anomalously high values). Acidification was a significantly greater impact than all other impacts; second
Discussion
Identifying and mitigating impacts to the network of MPAs in California is central to the effective functioning of the network in meeting its goal of conserving and recovering coastal marine species and ecosystems. Using recently developed methods for modeling cumulative impacts to coastal ecosystems we found widespread climate impacts to be some of the greatest across California's MPA network. However, land and ocean impacts, which are likely to have cumulative and interactive effects, may be
Acknowledgements
Resources Legacy Fund (RLF) for prompting and funding this work as part of a larger project looking at policies that regulate these various cumulative impacts. Matt Armsby, JD (RLF), Dr. Mary Gleason (The Nature Conservancy), and Dr. Ben Halpern all provided key feedback in the development of this manuscript.
References (37)
- et al.
Marine invasive alien species: a threat to global biodiversity
Mar. Policy
(2003) - et al.
Designing a network of marine protected areas in California: achievements, costs, lessons learned, and challenges ahead
Ocean Coast. Manag.
(2013) - et al.
California's Marine Life Protection Act Initiative: supporting implementation of legislation establishing a statewide network of marine protected areas
Ocean Coast. Manag.
(2013) - et al.
Human impacts and ecosystem services: insufficient research for trade-of evaluation
Ecosyst. Serv.
(2015) The synergism between hydrocarbon pollutants and UV radiation: a potential link between coastal pollution and larval mortality
JEMBE
(2005)- et al.
Eutrophication science: where do we go from here?
Trends Ecol. Evol.
(2009) - et al.
Large recovery of fish biomass in a no-take marine reserve
PLoS ONE
(2011) - et al.
Integrated land sea conservation planning: the missing links. Annual Review of Ecology
Evol. Syst.
(2011) - et al.
Dangerous targets? Unresolved issues and ideological clashes around marine protected areas
Aquat. Conserv.
(2003) - California Fish and Game Code of Regulations, Title 14, Section 632: Natural Resources, Division 1: Fish and Wildlife...
Knowledge through partnerships: integrating marine protected area monitoring and ocean observing systems
Front. Ecol. Environ.
Interactive and cumulative effects of multiple human stressors in marine systems
Ecol. Lett.
Spreading dead zones and consequences for marine ecosystems
Science
Climate change impacts on marine ecosystems
Annu. Rev. Mar. Sci.
Impacts of ocean acidification on marine fauna and ecosystem processes
ICES J. Mar. Sci. J. du Conseil
Designing marine reserve networks for both conservation and fisheries management
PNAS
Large-scale assessment of Mediterranean marine protected areas effects on fish assemblages
PLoS ONE
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2021, Science of the Total EnvironmentCitation Excerpt :Such patterns obviously had practical implications. For instance, CEAs focusing on habitats within marine protected areas suggested that CC-related stressors had the most intense impacts, supporting that mitigation actions at the MPA scale should be a high priority, at least for shallow habitats, no matter how challenging it is (Mach et al., 2017; Rodríguez-Rodríguez et al., 2015). The response of ecosystems to the combined effects of CC and LS was complex to assess, and only 58.6% of studies at ecosystem level teased apart the effect of CC and LS.
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Present address: Hopkins Marine Station, Stanford University, 120 Ocean View Blvd, Monterey, CA 93950, USA.
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Present address: Monterey Bay Aquarium, 886 Cannery Row, Pacific Grove, CA 93940, USA.