Extinction Risk and Bottlenecks in the Conservation of Charismatic Marine Species

The oceans face a biodiversity crisis, but the degree and scale of extinction risk remains poorly characterized. Charismatic species are most likely to gar- ner greatest support for conservation and thus provide a best-case scenario of the status of marine biodiversity. We summarize extinction risk and diagnose impediments to successful conservation for 1,568 species in 16 families of marine animals in the movie Finding Nemo. Sixteen percent (12–34%) of those that have been evaluated are threatened, ranging from 9% (7–28%) of bony fishes to 100% (83–100%) of marine turtles. A lack of scientific knowledge impedes analysis of threat status for invertebrates, which have 1,000 times fewer conservation papers than do turtles. Legal protection is severely deficient for sharks and rays; only 8% of threatened species in our analysis are protected. Extinction risk among wide-ranging taxa is higher thanmost terrestrial groups, suggesting a different conservation focus is required in the sea

Historical Reconstruction Reveals Recovery in Hawaiian Coral Reefs

Coral reef ecosystems are declining worldwide, yet regional differences in the trajectories, timing and extent of degradation highlight the need for in-depth regional case studies to understand the factors that contribute to either ecosystem sustainability or decline. We reconstructed social-ecological interactions in Hawaiian coral reef environments over 700 years using detailed datasets on ecological conditions, proximate anthropogenic stressor regimes and social change. Here we report previously undetected recovery periods in Hawaiian coral reefs, including a historical recovery in the MHI (∼AD 1400–1820) and an ongoing recovery in the NWHI (∼AD 1950–2009+). These recovery periods appear to be attributed to a complex set of changes in underlying social systems, which served to release reefs from direct anthropogenic stressor regimes. Recovery at the ecosystem level is associated with reductions in stressors over long time periods (decades+) and large spatial scales (>103 km2). Our results challenge conventional assumptions and reported findings that human impacts to ecosystems are cumulative and lead only to long-term trajectories of environmental decline. In contrast, recovery periods reveal that human societies have interacted sustainably with coral reef environments over long time periods, and that degraded ecosystems may still retain the adaptive capacity and resilience to recover from human impacts

Long-term assessment of California kelp forests, drivers, and resiliency

Kelp deforestation threatens life-sustaining services to coastal communities worldwide. Reversing this trend requires an understanding of long-term anthropogenic stressors from global warming, shoreline development, and trophic loss. By georeferencing early 20th century kelp canopy surveys along the eastern US Pacific, we extend reference timelines for the entire mainland coast of California by 60+ years (1911-2016) to discover a nearly 80% overall decline. Using Random Forest models, we find climate warming outweighed all key drivers of regional century-scale losses, but recovery of sea otters as predators of kelp grazing invertebrates corresponded with the only absolute gains in surface canopy. This century-scale perspective identifies staggering alterations of California’s coastline, stressing the urgency of adopting kelp forests into blue carbon initiatives. Additionally, our results demonstrate the role of otters in increasing natural climate resiliency, underscoring the potential for trophic rewilding to support climate mitigation. Together these findings show the importance of innovative and multifaceted strategies to address climate change – including ocean gardening and wildlife reintroductions – to prevent further broad scale losses in ecosystem benefits to coastal communities

Regional discount rates for comparing historical and contemporary kelp canopy surveys.

Regional mainland examples of (A) historical maps and noted harvestable beds (map images provided from [34], and in the public domain), (B) composite of contemporary (2014–16) CDFW aerial surveys, (C) their reframing at comparable scale (or as harvestable beds), and (D) proportional canopy cover distributions derived from the intersections of (B) and (C) throughout California. The 1911–12 kelp survey represents an effort by the US Department of Agriculture to assess potash resources from California’s summer to fall seaweed canopy. Similarly, during the mid-summer to fall seasonal peak, CDFW periodically conducted annual statewide aerial surveys of kelp canopy from 1989 through 2016. Map base layer provided by ArcGIS Hub (https://hub.arcgis.com/datasets/1612d351695b467eba75fdf82c10884f/explore) with U.S. Census data and licensed as public domain.</p

Century-scale, mainland kelp canopy losses throughout northern and southern regions of California slightly surpassed increases along the central coastline.

Mainland kelp canopy resources depicted by (A) total area (ha), and (B) changes within nearshore habitat (≤ 30m depth) during 1911–12 and 2014–2016 (composite) from (C) the Mexico to Oregon state border (0 to 1620 km) [68]. Canopy area gains along central California nearly offset losses within northern and southern coastal regions (see Table 1). To better visualize broad regional trends, we fit a locally weighted regression (LOESS, span 0.075) to these kelp features. Kelp canopy changes between contemporary and historical surveys are indicated by circles, with gains in blue and losses in red. All measurements reflect peak seasonal abundance in kelp from mid-summer through fall. Southern-central and central-northern region dividing landmarks are Point Conception and Pigeon Point, respectively, with San Francisco Bay, Monterey Bay, Santa Barbara Channel, Los Angeles Basin, and San Diego Bay noted as geographic features. Map base layer provided by ArcGIS Hub (https://hub.arcgis.com/datasets/1612d351695b467eba75fdf82c10884f/explore) with U.S. Census data and licensed as public domain.</p

Potential coastal sources of influence to statewide kelp canopy area.

(A) Sea surface temperature (SST) heat extremes and (B) kelp climate maximum events (≥ 20° C) occurred most frequently throughout the southern or low latitude portion of (H) California. We estimated occurrence of coastal heat extremes by calculating mean-monthly frequency of events (1983–2016) within the 95th percentile of historical SSTs recorded from 1870 to 1919. (C) Hard seafloor substrate (≤ 30-meter depth) is more abundant throughout northern and central coastal regions, nearly the reverse distribution of (D) human population density. (E) Sea otter population densities are greatest within the central portion of the state’s coastline, where recovery is occurring. (F) Monthly and (G, J) annual net primary productivity (NPP) variability distributions are nearly mirror opposites, corresponding with greater seasonality in northern California and longer cycles of extreme climate conditions in the southern coastline. Raw data are indicated by circles and smoothed using a uniform-span, locally weighted regression (LOESS, α = 0.075). During analysis, we used smoothed data to characterize both non static factors (i.e., sea otter, humans) and environmental data derived from coarser scale models (i.e., SST, NPP). Map base layer provided by ArcGIS Hub (https://hub.arcgis.com/datasets/1612d351695b467eba75fdf82c10884f/explore) with U.S. Census data and licensed as public domain.</p

Large-scale SST anomalies and net primary productivity variability corresponded most with overall kelp canopy declines, but sea otter density mitigated statewide losses.

(A) raw, pair-wise comparisons of kelp changes to model factors, and (B) modeled relationships of individual conditional expectations (ICE) from the Random Forest (RF) model outputs for the highest ranked variables (please note the varying y-axis scaling). Predominantly soft seafloor substrate, moderately high temperature heat extreme frequency and NPP variabilities, and densely populated coastlines related most strongly with canopy kelp losses. By contrast, sea otters corresponded with minimal to low declines, or even kelp gains at higher population densities (> 0.03 ha -1). We assigned (C) variable importance rankings from comparative increases in model MSE when each factor was removed. Overall, this six factor RF model explains 71% of variability related to century-scale kelp canopy area changes. (D) Two-way partial dependency plots describe the predicted interactions between impact of selected factors on kelp canopy changes. Here kelp increases with y^, symbolized with cool colors. Among all environmental factors, only sea otters consistently correspond with predicted gains in kelp canopy area.</p

This document provides additional details on the derived quantitative densities and ordinal descriptions of historical kelp beds and calculating carbon stores from kelp biomass.

This document provides additional details on the derived quantitative densities and ordinal descriptions of historical kelp beds and calculating carbon stores from kelp biomass.</p

S1 File -

S1 Data and S2 Data: For both data files, the column headers are defined as follows. “OBJECTID” is a unique polygon identifier associated with the ArcGIS database. For the historical data, “densitycode” refers to the ordinal density categories, where the lowest number, 1, equals the lowest density “very thin” and so forth. “ChartNum” refers to the original chart number listed in Cameron et al 1915. For both files, “kelptype” refers to the dominant species composition, “kelpdensity” is kelp bed density in kg m-2 (see above), “aream2” is the polygon area in m2, “aream2_corr” is the discounted polygon area in m2 (according to density, see Section 1 above), and “location” is either California mainland or Channel Islands. “kelpwetmass”, “mt_C”, and “mt_CO2” are all calculated columns of each polygon’s total wet mass, dry C biomass, and CO2 equivalents; respectively, where the unit is mt = 1000 kg. For the contemporary file, “year” is the calendar year of the survey, “kelpbed” is the assigned bed number, and “class_name” is whether the surveyed kelp bed canopy was at the surface or just below (subsurface). (ZIP)</p

Statewide and regional changes in California kelp over the last century.

At the state level, the total area (-6.9%), carbon biomass (+5.3%), and social costs (+5.3%) of harvestable kelp beds (see Methods) were not considerably different from 1910–1912 to 2014–2016 surveys. These trends, however, obscure stark regional differences that encompass a dramatic shift of California kelp over this period. In central California, kelp increased 57.6%, growing 19.7 km2 and adding an estimated 145.6 kt CO2. In all other regions kelp declined. Most notably, northern California saw 63% declines in kelp amounting to an estimated 8.1 km2 and 63.2 kt CO2 lost. The overall decline in kelp canopy area with a simultaneously estimated increase in kelp carbon biomass over time highlights regional differences in species composition and associated bed density and carbon content. The estimated social cost of kelp carbon follows the biomass trends, and in both periods exceeds $US 100M.</p