Prioritising seascape connectivity in conservation using network analysis

Capturing twenty years of change in ecosystem services provided by coastal Massachusetts habitats

Accounting for ecosystem services across expansive and diverse landscapes presents unique challenges to managers tasked with navigating and synthesizing the social-ecological dynamics of varied stakeholder interests and ecological functions. One approach to this challenge is through expert based matrices that provide valuations for specific service-habitat combinations. In this study, we combine a literature review with local expert input to build an ecosystem service capacity matrix for the Massachusetts Bays National Estuary Partnership (MassBays). We then apply this matrix to a custom conglomerate land cover data set and a habitat connectivity analysis to assess the spatial and temporal dynamics in select ecosystem services of coastal habitats across MassBays from 1996 to 2016. In 1996, saltmarsh was the primary provider of coastal ecosystem services, representing roughly 60% of the total service capacity. More specifically, high elevation saltmarsh was top-ranked, followed by tidal flats, seagrass, low elevation saltmarsh and unclassified saltmarsh. This distribution of service provisioning varied considerably among the five regions of MassBays, reflecting the unique habitat mixes and local expert valuations of each. Although saltmarsh dominated the overall production of services, seagrass and tidal flats drove 97% of the service changes that occurred from one year to the next. From 1996 to 2016, MassBays lost 50% of its seagrass cover and gained 20% more tidal flats, resulting in a 5% overall loss in ecosystem services. Again, this varied among the five regions, with Cape Cod losing as much as 12% of a given service while the Upper North Shore gained 4% in services overall. We bootstrapped the analysis to provide a range of probable outcomes. We also mapped the changes in service production for each of the sixty-eight embayments. This analysis will aid local managers in accounting for ecosystem services as they develop management plans for their represented stakeholders.

Comparing spatial conservation prioritization methods with site- versus spatial dependency-based connectivity

Larval dispersal is an important component of marine reserve networks. Two conceptually different approaches to incorporate dispersal connectivity into spatial planning of these networks exist, and it is an open question as to when either is most appropriate. Candidate reserve sites can be selected individually based on local properties of connectivity or on a spatial dependency-based approach of selecting clusters of strongly connected habitat patches. The first acts on individual sites, whereas the second acts on linked pairs of sites. We used a combination of larval dispersal simulations representing different seascapes and case studies of biophysical larval dispersal models in the Coral Triangle region and the province of Southeast Sulawesi, Indonesia, to compare the performance of these 2 methods in the spatial planning software Marxan. We explored the reserve design performance implications of different dispersal distances and patterns based on the equilibrium settlement of larvae in protected and unprotected areas. We further assessed different assumptions about metapopulation contributions from unprotected areas, including the case of 100% depletion and more moderate scenarios. The spatial dependency method was suitable when dispersal was limited, a high proportion of the area of interest was substantially degraded, or the target amount of habitat protected was low. Conversely, when subpopulations were well connected, the 100% depletion was relaxed, or more habitat was protected, protecting individual sites with high scores in metrics of connectivity was a better strategy. Spatial dependency methods generally produced more spatially clustered solutions with more benefits inside than outside reserves compared with site-based methods. Therefore, spatial dependency methods potentially provide better results for ecological persistence objectives over enhancing fisheries objectives, and vice versa. Different spatial prioritization methods of using connectivity are appropriate for different contexts, depending on dispersal characteristics, unprotected area contributions, habitat protection targets, and specific management objectives. Comparación entre los métodos de priorización de la conservación espacial con sitio y la conectividad espacial basada en la dependencia.

Mapping oysters on the Pacific coast of North America: A coast-wide collaboration to inform enhanced conservation

To conserve coastal foundation species, it is essential to understand patterns of distribution and abundance and how they change over time. We synthesized oyster distribution data across the west coast of North America to develop conservation strategies for the native Olympia oyster (Ostrea lurida), and to characterize populations of the non-native Pacific oyster (Magallana gigas). We designed a user-friendly portal for data entry into ArcGIS Online and collected oyster records from unpublished data submitted by oyster experts and from the published literature. We used the resulting 2,000+ records to examine spatial and temporal patterns and made an interactive web-based map publicly available. Comparing records from pre-2000 vs. post-2000, we found that O. lurida significantly decreased in abundance and distribution, while M. gigas increased significantly. Currently the distribution and abundance of the two species are fairly similar, despite one species being endemic to this region since the Pleistocene, and the other a new introduction. We mapped the networks of sites occupied by oysters based on estimates of larval dispersal distance, and found that these networks were larger in Canada, Washington, and southern California than in other regions. We recommend restoration to enhance O. lurida, particularly within small networks, and to increase abundance where it declined. We also recommend restoring natural biogenic beds on mudflats and sandflats especially in the southern range, where native oysters are currently found most often on riprap and other anthropogenic structures. This project can serve as a model for collaborative mapping projects that inform conservation strategies for imperiled species or habitats.

Estimating benthic trophic levels to assess the effectiveness of marine protected area management

Designating and managing marine protected areas (MPAs) can mitigate many ocean threats. Banning fishing activities within MPAs enhances the robustness of food-web dynamics and thus increases trophic resilience. Ecosystem function indicators, such as mean trophic level, are increasingly applied in conservation management. Stable isotope analysis is a common tool in trophodynamic studies as it provides information about food sources and trophic level within food webs. In contrast to the traditional top-down approaches in conservation management (mainly for fisheries), this study focuses on bottom-up responses to protection according to the target species in regional small-scale fisheries. The present study aimed to examine how MPA status affects trophodynamics in the rocky reefs of the Illas Atlánticas Marine-Terrestrial National Park (Galicia, NW Spain). Results showed no differences between inside and outside the MPA in species stable isotopic signatures or trophic level. However, these results should be considered with caution due to some limitations in the study design (small number of sites per location, biogeographic differences associated with the island nature of the MPA, or seasonal variability). Nevertheless, the lax fishing management, the lack of proper implementation (the MPA was established in 2002 without a management plan until 2019), and the small size of the studied MPA may result in ineffective conservation outcomes that could have been reflected in the stable isotopic content of the food web. The large number of "paper park" MPAs existing worldwide are not only detrimental to the perception of marine protection, but also provide poor protection of marine ecosystems. Subject to further studies accounting for both environmental and management factors on stable isotope signatures, trophic interactions can form a cost-effective tool for monitoring MPA effectiveness.

Species dispersal along rivers and streams may have variable importance to metapopulation structure

The ability to prioritize habitats that have spatially varied contributions to species persistence can produce synergistic benefits for regional conservation efforts. However, conservation in spatially diverse landscape-networks requires considering dispersal asymmetry in the context of ecological connectivity and metapopulation persistence. By developing an approach based on metapopulation theory, this study prioritized the importance of habitat (as determined by the habitat quality and spatial position in networks) on metapopulation structure in mountainous streams. As a case study, we examined dispersal via overland and instream networks in a riverine mayfly Rhithrogena sp. cf. japonica in a mountain range of Southwest China. Compared to flow velocity, water depth, and instream nutrient-levels, water temperature was a key factor in determining local habitat suitability for R. sp. cf. japonica. Higher water temperature was linked to poor habitat suitability. Instream pathways were the main dispersal corridors compared with overland movement between tributaries for this mayfly. In basins on the east aspect of this mountain range, either monotonically increasing (i.e., never decreasing) or unimodal (i.e., with a single peak) patterns demonstrated the importance of riverine habitats that occur along elevational gradients. However, the importance of habitat appeared to show no definite patterns with elevation on the west aspect. In terms of metapopulation structure, local quality of habitat contributed more to the regional importance of habitat than its spatial position in the networks. The framework presented highlights that the importance of riverine habitats may be quite variable in species having directional dispersal networks across the fluvial landscape in mountainous areas. Results from this framework can serve as the basis to apply a mechanistic understanding to managing and protecting native populations through regional restoration actions.

Non-reef habitats in a tropical seascape affect density and biomass of fishes on coral reefs

Nonreef habitats such as mangroves, seagrass, and macroalgal beds are important for foraging, spawning, and as nursery habitat for some coral reef fishes. The spatial configuration of nonreef habitats adjacent to coral reefs can therefore have a substantial influence on the distribution and composition of reef fish. We investigate how different habitats in a tropical seascape in the Philippines influence the presence, density, and biomass of coral reef fishes to understand the relative importance of different habitats across various spatial scales. A detailed seascape map generated from satellite imagery was combined with field surveys of fish and benthic habitat on coral reefs. We then compared the relative importance of local reef (within coral reef) and adjacent habitat (habitats in the surrounding seascape) variables for coral reef fishes. Overall, adjacent habitat variables were as important as local reef variables in explaining reef fish density and biomass, despite being fewer in number in final models. For adult and juvenile wrasses (Labridae), and juveniles of some parrotfish taxa (Chlorurus), adjacent habitat was more important in explaining fish density and biomass. Notably, wrasses were positively influenced by the amount of sand and macroalgae in the adjacent seascape. Adjacent habitat metrics with the highest relative importance were sand (positive), macroalgae (positive), and mangrove habitats (negative), and fish responses to these metrics were consistent across fish groups evaluated. The 500-m spatial scale was selected most often in models for seascape variables. Local coral reef variables with the greatest importance were percent cover of live coral (positive), sand (negative), and macroalgae (mixed). Incorporating spatial metrics that describe the surrounding seascape will capture more holistic patterns of fish-habitat relationships on reefs. This is important in regions where protection of reef fish habitat is an integral part of fisheries management but where protection of nonreef habitats is often overlooked.

A multi-scale, integrative modeling framework for setting conservation priorities at the catchment scale for the Freshwater Pearl Mussel Margaritifera margaritifera

The identification and prioritization of sites for conservation actions to protect biodiversity in lotic systems is crucial when economic resources or available areas are limited. Challenges include the incorporation of multi-scale interactions, and the application of species distribution models (SDMs) to rare organism with multiple life stages. To support the planning of conservation actions for the highly endangered Freshwater Pearl Mussel Margaritifera margaritifera (FPM), this paper aims at developing an ecohydrological modeling cascade including a hydrological model (SWAT) and a hydraulic model (HEC-RAS). Building on hydrology and hydraulics, Random Forest models for potential risk to juveniles due to sand accumulation, SDMs for adults habitat niche, and a landscape connectivity assessment of dispersal potential were developed. The feasibility of such models integration was tested in the Aist catchment (630 km²) in Austria. The potential FPM habitat and the sand accumulation risk for the whole catchment were predicted with good accuracy. Results show that while the potentially suitable habitats for adults FPM cover 34% of the river network, only few habitat patches can maximize the dispersal potential (4% of the river network) and even less are showing limited impact of accumulations (3.5% of river network). No habitat patch that meets all the three criteria is available, suggesting approaches that target the patch-specific critical life stage-factors are promising for conservation.

Global trends in protected area connectivity from 2010 to 2018

Connectivity of protected areas (PAs) is needed to ensure the long-term persistence of biodiversity and ecosystem service delivery. The Convention on Biological Diversity agreed in 2010 to have 17% of land covered by well-connected PA systems by 2020 (Aichi Target 11). We here globally assess, for all countries, the trends in terrestrial PA connectivity every other year from 2010 to 2018 using the ProtConn indicator, which quantifies how well the PA systems are designed to support connectivity. The percentage of protected connected land (ProtConn) has increased globally from 6.5% in 2010 to 7.7% in 2018. Oceania experienced the largest recent increase in PA connectivity, whereas Asia is the only content with a lower ProtConn in 2018 than in 2010. Globally, the relative increase in the percentage of protected connected land (ProtConn) is nearly twice that of the percentage of land under protection (PA coverage), due to clear improvements in the design of PA systems for connectivity in many regions. The connectivity of the PA networks has become more dependent on the permeability of the unprotected landscape matrix in between PAs and on the coordinated management of adjacent PAs with different designations and of transboundary PA linkages. The relatively slow recent increase in PA connectivity globally (2016-2018) raises doubt as to whether connectivity targets will be met by 2020, and suggests that considerable further action is required to promote better-connected PA systems globally, including the expansion of the PA systems to cover key areas for connectivity in many countries and regions.

Spatially explicit network analysis reveals multi-species annual cycle movement patterns of sea ducks

Conservation of long-distance migratory species poses unique challenges. Migratory connectivity, that is, the extent to which groupings of individuals at breeding sites are maintained in wintering areas, is frequently used to evaluate population structure and assess use of key habitat areas. However, for species with complex or variable annual cycle movements, this traditional bimodal framework of migratory connectivity may be overly simplistic. Like many other waterfowl, sea ducks often travel to specific pre- and post-breeding sites outside their nesting and wintering areas to prepare for migration by feeding extensively and, in some cases, molting their flight feathers. These additional migrations may play a key role in population structure, but are not included in traditional models of migratory connectivity. Network analysis, which applies graph theory to assess linkages between discrete locations or entities, offers a powerful tool for quantitatively assessing the contributions of different sites used throughout the annual cycle to complex spatial networks. We collected satellite telemetry data on annual cycle movements of 672 individual sea ducks of five species from throughout eastern North America and the Great Lakes. From these data, we constructed a multi-species network model of migratory patterns and site use over the course of breeding, molting, wintering, and migratory staging. Our results highlight inter- and intra-specific differences in the patterns and complexity of annual cycle movement patterns, including the central importance of staging and molting sites in James Bay, the St. Lawrence River, and southern New England to multi-species annual cycle habitat linkages, and highlight the value of Long-tailed Ducks (Calengula haemalis) as an umbrella species to represent the movement patterns of multiple sea duck species. We also discuss potential applications of network migration models to conservation prioritization, identification of population units, and integrating different data streams.

An approach to incorporating inferred connectivity of adult movement into marine protected area design with limited data

Marine protected areas (MPAs) are important conservation tools that can support the resilience of marine ecosystems. Many countries, including Canada, have committed to protecting at least 10% of their marine areas under the Convention on Biological Diversity's Aichi Target 11, which includes connectivity as a key aspect. Connectivity, the movement of individuals among habitats, can enhance population stability and resilience within and among MPAs. However, little is known about regional spatial patterns of marine ecological connectivity, particularly adult movement. We developed a method to assess and design MPA networks that maximize inferred connectivity within habitat types for adult movement when ecological data are limited. We used the Northern Shelf Bioregion in British Columbia, Canada, to explore two different approaches: (1) evaluating sites important for inferred regional connectivity (termed hotspots) and (2) assessing MPA network configurations based on their overlap with connectivity hotspots and interconnectedness between MPAs. To assess inferred connectivity via adult movement, we used two different threshold distances (15 and 50 km) to capture moderate home ranges, which are most appropriate to consider in MPA design. We applied graph theory to assess inferred connectivity within 16 habitat and depth categories (proxies for distinct ecological communities), and used novel multiplex network methodologies to perform an aggregated assessment of inferred connectivity. We evaluated inferred regional connectivity hotspots based on betweenness and eigenvector centrality metrics, finding that the existing MPA network overlapped a moderate proportion of these regional hotspots and identified key areas to be considered as candidate MPAs. Network density among existing MPAs was low within the individual habitat networks, as well as the multiplex. This work informs an ongoing MPA planning process, and approaches for incorporating connectivity into MPA design when data are limited, with lessons for other contexts.

Simulating urban expansion and its impact on functional connectivity in the Three Gorges Reservoir Area

Understanding the impact of urban expansion on functional connectivity is significant to biodiversity conservation. Particularly, in the Three Gorges Reservoir Area (TGRA, Southwest China), the urban land has rapidly expanded to provide settlements for an enormous population of TGRA migrants. However, the consequence of future land-use changes to the functional connectivity of the local habitat network has rarely been studied. To extend this knowledge, this paper proposes a framework that integrates a novel cellular automata (CA) simulation model and ecological network analysis, taking the TGRA as the study area, to predict how different urban expansion scenarios might affect functional connectivity for a nationally protected species, the leopard. The least-cost path modeling is used, and a set of connectivity indicators are adopted to evaluate functional connectivity. The results show that, the population-growth-based urban expansion maintains a higher connectivity than the business-as-usual and fast-urban-growth scenarios. In addition, the connectivity loss due to urban expansion can be offset by the reforestation efforts of the Green-for-Grain Project. Finally, we identify habitat patches that act as key connectivity providers, and suggest that those patches be prioritized for protection to avoid significant connectivity loss.

Managing birds of conservation concern on sandy shores: How much room for future conservation actions is there?

Resource limitations often prevent the active management required to maintain habitat quality in protected areas. Because restrictions in access or allowable public activities are the sole conservation measure in these locations, an important question to consider is whether species of conservation concern truly benefit from parcels that are shielded from human disturbance. Here, we assess the conservation benefit of protecting birds from human recreation on over 204 km of sandy beaches by (a) estimating the total area of beach-nesting bird habitat that has been created by conservation protections; (b) quantifying the change in nesting habitat extent should further conservation protections be implemented; and (c) providing data to inform future protected area expansion. We use a maximum entropy species distribution modeling approach to estimate the extent and quality of suitable habitat for four beach-nesting bird species of conservation concern under the existing management regime and compare it to scenarios in which the entire study area is either unprotected of fully protected from human disturbance. Managing humans has dramatic conservation returns for least terns and piping plovers, creating extensive nesting habitat that otherwise would not exist. There is considerable scope for conservation gains, potentially tripling the extent of nesting areas. Expanding conservation footprints for American oystercatchers and black skimmers is predicted to enhance the quality of existing nesting areas. The work demonstrates the utility of modeling changes in habitat suitability to inform protected area expansion on ocean beaches and coastal dunes.

Seascape genetics and biophysical connectivity modelling support conservation of the seagrass Zostera marina in the Skagerrak-Kattegat region of the eastern North Sea

Maintaining and enabling evolutionary processes within meta-populations are critical to resistance, resilience and adaptive potential. Knowledge about which populations act as sources or sinks, and the direction of gene flow, can help to focus conservation efforts more effectively and forecast how populations might respond to future anthropogenic and environmental pressures. As a foundation species and habitat provider, Zostera marina (eelgrass) is of critical importance to ecosystem functions including fisheries. Here, we estimate connectivity of Z. marina in the Skagerrak-Kattegat region of the North Sea based on genetic and biophysical modelling. Genetic diversity, population structure and migration were analysed at 23 locations using 20 microsatellite loci and a suite of analytical approaches. Oceanographic connectivity was analysed using Lagrangian dispersal simulations based on contemporary and historical distribution data dating back to the late 19th century. Population clusters, barriers and networks of connectivity were found to be very similar based on either genetic or oceanographic analyses. A single-generation model of dispersal was not realistic, whereas multigeneration models that integrate stepping-stone dispersal and extant and historic distribution data were able to capture and model genetic connectivity patterns well. Passive rafting of flowering shoots along oceanographic currents is the main driver of gene flow at this spatial-temporal scale, and extant genetic connectivity strongly reflects the "ghost of dispersal past" sensu Benzie, 1999. The identification of distinct clusters, connectivity hotspots and areas where connectivity has become limited over the last century is critical information for spatial management, conservation and restoration of eelgrass.

Protected area connectivity: Shortfalls in global targets and country-level priorities

Connectivity of protected areas (PAs) is crucial for meeting their conservation goals. We provide the first global evaluation of countries' progress towards Aichi Target 11 of the Convention on Biological Diversity that is to have at least 17% of the land covered by well-connected PA systems by 2020. We quantify how well the terrestrial PA systems of countries are designed to promote connectivity, using the Protected Connected (ProtConn) indicator. We refine ProtConn to focus on the part of PA connectivity that is in the power of a country to influence, i.e. not penalizing countries for PA isolation due to the sea and to foreign lands. We found that globally only 7.5% of the area of the countries is covered by protected connected lands, which is about half of the global PA coverage of 14.7%, and that only 30% of the countries currently meet the Aichi Target 11 connectivity element. These findings suggest the need for considerable efforts to improve PA connectivity globally. We further identify the main priorities for improving or sustaining PA connectivity in each country: general increase of PA coverage, targeted designation of PAs in strategic locations for connectivity, ensuring permeability of the unprotected landscapes between PAs, coordinated management of neighbouring PAs within the country, and/or transnational coordination with PAs in other countries. Our assessment provides a key contribution to evaluate progress towards global PA connectivity targets and to highlight important strengths and weaknesses of the design of PA systems for connectivity in the world's countries and regions.

Designing connected marine reserves in the face of global warming

Marine reserves are widely used to protect species important for conservation and fisheries and to help maintain ecological processes that sustain their populations, including recruitment and dispersal. Achieving these goals requires well-connected networks of marine reserves that maximize larval connectivity, thus allowing exchanges between populations and recolonization after local disturbances. However, global warming can disrupt connectivity by shortening potential dispersal pathways through changes in larval physiology. These changes can compromise the performance of marine reserve networks, thus requiring adjusting their design to account for ocean warming. To date, empirical approaches to marine prioritization have not considered larval connectivity as affected by global warming. Here, we develop a framework for designing marine reserve networks that integrates graph theory and changes in larval connectivity due to potential reductions in planktonic larval duration (PLD) associated with ocean warming, given current socioeconomic constraints. Using the Gulf of California as case study, we assess the benefits and costs of adjusting networks to account for connectivity, with and without ocean warming. We compare reserve networks designed to achieve representation of species and ecosystems with networks designed to also maximize connectivity under current and future ocean-warming scenarios. Our results indicate that current larval connectivity could be reduced significantly under ocean warming because of shortened PLDs. Given the potential changes in connectivity, we show that our graph-theoretical approach based on centrality (eigenvector and distance-weighted fragmentation) of habitat patches can help design better-connected marine reserve networks for the future with equivalent costs. We found that maintaining dispersal connectivity incidentally through representation-only reserve design is unlikely, particularly in regions with strong asymmetric patterns of dispersal connectivity. Our results support previous studies suggesting that, given potential reductions in PLD due to ocean warming, future marine reserve networks would require more and/or larger reserves in closer proximity to maintain larval connectivity.

Node self-connections in network metrics

Zamborain-Mason et al. (Ecol. Lett., 20, 2017, 815-831) state that they have newly proposed network metrics that account for node self-connections. Network metrics incorporating node self-connections, also referred to as intranode (intrapatch) connectivity, were however already proposed before and have been widely used in a variety of conservation planning applications.