Brenda Konar

Do trophic cascades affect the storage and flux of atmospheric carbon? An analysis of sea otters and kelp forests

We combine data collected from the past 40 years to estimate the indirect effects of sea otters (Enhydra lutris) on ecosystem carbon (C) production and storage across their North American range, from Vancouver Island to the western edge of Alaskas Aleutian Islands. We find that sea otters, by suppressing sea urchin (Strongylocentrotus spp) populations, allow kelp (Order Laminariales) ecosystems to develop with a net primary productivity (NPP) of 313–900 grams C per square meter per year (g C m−2 yr−1) and biomass density of 101–180 grams C per square meter (g C m−2). In the absence of sea otters, these areas would have an NPP of 25–70 g C m−2 yr−1 and biomass density of 8–14 g C m−2. Over an ecosystem area of approximately 5.1 × 1010 m2, the effect of sea otter predation on living kelp biomass alone represents a 4.4-to 8.7-teragram increase in C storage. At 2012 prices (US

Global patterns of kelp forest change over the past half-century

47 per ton of C), this stored C would be valued at US

Rhodolith bed: a newly discovered habitat in the North Pacific Ocean

205 million–

Competitive dominance among sessile marine organisms in a high Arctic boulder community

408 million on the European Carbon Exchange. Although questions re...

Large-scale spatial distribution patterns of echinoderms in nearshore rocky habitats

Significance Kelp forests support diverse and productive ecological communities throughout temperate and arctic regions worldwide, providing numerous ecosystem services to humans. Literature suggests that kelp forests are increasingly threatened by a variety of human impacts, including climate change, overfishing, and direct harvest. We provide the first globally comprehensive analysis of kelp forest change over the past 50 y, identifying a high degree of variation in the magnitude and direction of change across the geographic range of kelps. These results suggest region-specific responses to global change, with local drivers playing an important role in driving patterns of kelp abundance. Increased monitoring aimed at understanding regional kelp forest dynamics is likely to prove most effective for the adaptive management of these important ecosystems. Kelp forests (Order Laminariales) form key biogenic habitats in coastal regions of temperate and Arctic seas worldwide, providing ecosystem services valued in the range of billions of dollars annually. Although local evidence suggests that kelp forests are increasingly threatened by a variety of stressors, no comprehensive global analysis of change in kelp abundances currently exists. Here, we build and analyze a global database of kelp time series spanning the past half-century to assess regional and global trends in kelp abundances. We detected a high degree of geographic variation in trends, with regional variability in the direction and magnitude of change far exceeding a small global average decline (instantaneous rate of change = −0.018 y−1). Our analysis identified declines in 38% of ecoregions for which there are data (−0.015 to −0.18 y−1), increases in 27% of ecoregions (0.015 to 0.11 y−1), and no detectable change in 35% of ecoregions. These spatially variable trajectories reflected regional differences in the drivers of change, uncertainty in some regions owing to poor spatial and temporal data coverage, and the dynamic nature of kelp populations. We conclude that although global drivers could be affecting kelp forests at multiple scales, local stressors and regional variation in the effects of these drivers dominate kelp dynamics, in contrast to many other marine and terrestrial foundation species.

Spatial relationships between polychaete assemblages and environmental variables over broad geographical scales

Abstract Rhodoliths are unattached calcareous red algae that form extensive beds. Although rhodolith beds are widely distributed in temperate and tropical areas, a recent discovery in the North Pacific Ocean represents a significant northward extension of known rhodolith distribution. This bed, located in Prince William Sound, Alaska, is composed of one rhodolith species, Phymatolithon calcareum, with two reproductive states, tetrasporangial and gametangial. A characteristic feature of this bed is that cryptofaunal chitons were the most abundant associated invertebrate species. Comparisons with P. calcareum populations in other regions showed that Prince William Sound thalli are smaller in many measurable anatomical features.

Patterns of Spatial Variation of Assemblages Associated with Intertidal Rocky Shores: A Global Perspective

In most hard substrate environments, space is a limiting resource for sessile organisms. Competition for space is often high and is a structuring force within the community. In the Beaufort Sea’s Boulder Patch, crustose coralline red algae are major space occupiers. This research determined if coralline algae were competitively dominant over other sessile organisms. To test this hypothesis, overgrowth was documented in terms of “winners” and “losers” on the contact borders between different species. Crustose corallines occurred in over 80% of the observed interactions but were only winners in approximately half of them. Most frequently, bryozoans, tunicates, and sponges were superior competitors over crustose corallines, while at the same time these invertebrate groups were among the least abundant space occupiers.

Lacuna vincta (Mollusca, Neotaenioglossa) herbivory on juvenile and adult Nereocystis luetkeana (Heterokontophyta, Laminariales)

This study examined echinoderm assemblages from nearshore rocky habitats for large-scale distribution patterns with specific emphasis on identifying latitudinal trends and large regional hotspots. Echinoderms were sampled from 76 globally-distributed sites within 12 ecoregions, following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). Sample-based species richness was overall low (<1–5 species per site), with a total of 32 asteroid, 18 echinoid, 21 ophiuroid, and 15 holothuroid species. Abundance and species richness in intertidal assemblages sampled with visual methods (organisms >2 cm in 1 m2 quadrats) was highest in the Caribbean ecoregions and echinoids dominated these assemblages with an average of 5 ind m−2. In contrast, intertidal echinoderm assemblages collected from clearings of 0.0625 m2 quadrats had the highest abundance and richness in the Northeast Pacific ecoregions where asteroids and holothurians dominated with an average of 14 ind 0.0625 m−2. Distinct latitudinal trends existed for abundance and richness in intertidal assemblages with declines from peaks at high northern latitudes. No latitudinal trends were found for subtidal echinoderm assemblages with either sampling technique. Latitudinal gradients appear to be superseded by regional diversity hotspots. In these hotspots echinoderm assemblages may be driven by local and regional processes, such as overall productivity and evolutionary history. We also tested a set of 14 environmental variables (six natural and eight anthropogenic) as potential drivers of echinoderm assemblages by ecoregions. The natural variables of salinity, sea-surface temperature, chlorophyll a, and primary productivity were strongly correlated with echinoderm assemblages; the anthropogenic variables of inorganic pollution and nutrient contamination also contributed to correlations. Our results indicate that nearshore echinoderm assemblages appear to be shaped by a network of environmental and ecological processes, and by the differing responses of various echinoderm taxa, making generalizations about the patterns of nearshore rocky habitat echinoderm assemblages difficult.

Current Patterns of Macroalgal Diversity and Biomass in Northern Hemisphere Rocky Shores

This study examined spatial relationships between rocky shore polychaete assemblages and environmental variables over broad geographical scales, using a database compiled within the Census of Marine Life NaGISA (Natural Geography In Shore Areas) research program. The database consisted of abundance measures of polychaetes classified at the genus and family levels for 74 and 93 sites, respectively, from nine geographic regions. We tested the general hypothesis that the set of environmental variables emerging as potentially important drivers of variation in polychaete assemblages depend on the spatial scale considered. Through Morans eigenvector maps we indentified three submodels reflecting spatial relationships among sampling sites at intercontinental (>10000 km), continental (1000–5000 km) and regional (20–500 km) scales. Using redundancy analysis we found that most environmental variables contributed to explain a large and significant proportion of variation of the intercontinental submodel both for genera and families (54% and 53%, respectively). A subset of these variables, organic pollution, inorganic pollution, primary productivity and nutrient contamination was also significantly related to spatial variation at the continental scale, explaining 25% and 32% of the variance at the genus and family levels, respectively. These variables should therefore be preferably considered when forecasting large-scale spatial patterns of polychaete assemblages in relation to ongoing or predicted changes in environmental conditions. None of the variables considered in this study were significantly related to the regional submodel.

Influence of taxonomic resolution and morphological functional groups in multivariate analyses of macroalgal assemblages

Assemblages associated with intertidal rocky shores were examined for large scale distribution patterns with specific emphasis on identifying latitudinal trends of species richness and taxonomic distinctiveness. Seventy-two sites distributed around the globe were evaluated following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). There were no clear patterns of standardized estimators of species richness along latitudinal gradients or among Large Marine Ecosystems (LMEs); however, a strong latitudinal gradient in taxonomic composition (i.e., proportion of different taxonomic groups in a given sample) was observed. Environmental variables related to natural influences were strongly related to the distribution patterns of the assemblages on the LME scale, particularly photoperiod, sea surface temperature (SST) and rainfall. In contrast, no environmental variables directly associated with human influences (with the exception of the inorganic pollution index) were related to assemblage patterns among LMEs. Correlations of the natural assemblages with either latitudinal gradients or environmental variables were equally strong suggesting that neither neutral models nor models based solely on environmental variables sufficiently explain spatial variation of these assemblages at a global scale. Despite the data shortcomings in this study (e.g., unbalanced sample distribution), we show the importance of generating biological global databases for the use in large-scale diversity comparisons of rocky intertidal assemblages to stimulate continued sampling and analyses.