Ecosystem features determine seagrass community response to sea otter foraging

Hessing‐Lewis, Margot; Rechsteiner, Erin U.; Hughes, Brent B.; Tinker, M. Tim; Monteith, Zachary L.; Olson, Angeleen M.; Henderson, Matthew Morgan; Watson, Jane C.

doi:10.1016/j.marpolbul.2017.09.047

Cited by 19 publications

(39 citation statements)

References 70 publications

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“…). BC's Central Coast is a geographically complex coastline, with a suite of nearshore habitats, including eelgrass meadows of varying sizes and attributes (Table ) (Hessing‐Lewis et al ). With low human population density and sparse land‐based development, this area provides an opportune setting for obtaining regional estimates of eelgrass carbon storage with a focus on ecological and biophysical drivers rather than human disturbance.…”

Section: Methodsmentioning

confidence: 99%

Reduced water motion enhances organic carbon stocks in temperate eelgrass meadows

Prentice

Hessing‐Lewis

Sanders‐Smith

et al. 2019

Limnology & Oceanography

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Organic carbon (OC) storage in coastal vegetated ecosystems is increasingly being considered in carbon financing and climate change mitigation strategies. However, spatial heterogeneity in these “blue carbon” stocks among and within habitats has only recently been examined, despite its considerable implications. Seagrass meadows have potential to store significant amounts of carbon in their sediments, yet studies comparing sediment OC content at regional and meadow scales remain sparse. Here, we collected sediment cores from six temperate eelgrass (Zostera marina) meadows on the coast of British Columbia, Canada, to quantify sediment OC stocks, accumulation rates, and sources, and to examine local and regional drivers of variability. Sediment OC content was highly variable—across all sites, stocks in the top 0–5 cm ranged from 83 to 1089 g OC m−2, while the 15–20 cm stocks exhibited a 24‐fold difference, from 59 to 1407 g OC m−2. Carbon accumulation rates ranged from 4 to 33 g OC m−2 yr−1. Isotopic mixing models revealed that sediment OC was primarily terrestrial carbon (41.3%) and canopy‐forming kelps (33.3%), with a smaller contribution of eelgrass (25.3%). Here, we show that regional variability in OC content exceeds meadow‐scale variability. This result is likely driven by landscape factors, most notably relative water motion, representing a more dominant control on seagrass OC accumulation than meadow‐scale factors such as canopy complexity. These findings elicit caution when scaling up seagrass meadow OC content and demonstrate that measures of the hydrodynamic environment could improve estimates of carbon storage in temperate soft sediment habitats.

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Section: Methodsmentioning

confidence: 99%

Reduced water motion enhances organic carbon stocks in temperate eelgrass meadows

Prentice

Hessing‐Lewis

Sanders‐Smith

et al. 2019

Limnology & Oceanography

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“…The shoreline complexity of the central coast allows for a diverse matrix of nearshore marine habitats within this seascape (Hessing‐Lewis et al. ). Similar to other northern‐latitude coastlines, mixed patches of seagrass, kelp forest habitats ( N. luetkeana and/or Macrocystis pyrifera ), and sand habitats are common elements of this region.…”

Section: Methodsmentioning

confidence: 99%

“…based on long‐term monitoring of the Choked Passage seagrass food web (Hessing‐Lewis et al. ) and established trophic relationships in temperate seagrass food webs (Appendix , ; Hughes et al. ).…”

Section: Methodsmentioning

confidence: 99%

Nearshore seascape connectivity enhances seagrass meadow nursery function

Olson

Hessing‐Lewis

Haggarty

et al. 2019

Ecological Applications

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Diverse habitats composing coastal seascapes occur in close proximity, connected by the flux of materials and fauna across habitat boundaries. Understanding how seascape connectivity alters important ecosystem functions for fish, however, is not well established. For a seagrass‐dominant seascape, we predicted that configuration and composition of adjacent habitats would alter habitat access for fauna and trophic subsidies, enhancing nursery function for juvenile fish. In an extensive Zostera marina seagrass meadow, we established sites adjacent to (1) highly complex and productive kelp forests (Nereocystis luetkeana), (2) unvegetated sand habitats, and (3) in the seagrass meadow interior. Using SCUBA, we conducted underwater observations of young‐of the‐year (YOY) rockfish (Sebastes spp.) recruitment across sites. Using generalized linear mixed effects models, we assessed the role of seascape adjacency relative to seagrass provisions (habitat complexity and prey) on YOY recruitment. YOY rockfish collections were used to trace sources of allochthonous vs. autochthonous primary production in the seagrass food web, via a δ13C and δ15N isotopic mixing model, and prey consumption using stomach contents. Overall, seagrass nursery function was strongly influenced by adjacent habitats and associated subsidies. Allochthonous N. luetkeana was the greatest source of energy assimilated by YOY rockfish within seagrass sites. In seagrass sites adjacent to N. luetkeana kelp forests, YOYs consumed higher quality prey, which corresponded with better body condition relative to sites adjacent to sand. Moreover, kelp forest adjacency enhanced YOY rockfish recruitment within the seagrass meadow, suggesting that habitat complexity is a key seascape feature influencing the nursery function of nearshore habitats. In general, to promote seascape connectivity, the conservation and restoration of nursery habitats should prioritize the inclusion of habitat mosaics of high structural complexity and productivity. We illustrate and emphasize the importance of using a seascape‐level approach that considers linkages among habitats for the management of important nearshore ecosystem functions.

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“…Our analyses of foraging ecology and niche space variation in sea otters involved several steps. First, we used established analytical methods to quantify diet composition (i.e., frequency of occurrence representation of various prey taxa and size classes in sea otter diets), rate of energy gain, and diet diversity from observational foraging data (Hessing‐Lewis et al, ; Tinker, Bentall et al, ; Tinker et al, ). We then combined foraging data for each occupation area with environmental parameters (habitat, depth) and analyzed the multivariate data set using nonmetric multidimensional scaling analysis (nMDS) to examine whether there were groupings that correlated with occupation area or sex class.…”

Section: Methodsmentioning

confidence: 99%

“…We used direct observations of foraging behaviour combined with a Monte Carlo algorithm to analyze sea otter foraging data (Hessing‐Lewis et al, ; Tinker, Bentall et al, ; Tinker et al, ). Prey functional groups were defined by both taxa and size class (Table ) and were limited to prey that comprised at least 5% of overall diets by frequency of occurrence.…”

Section: Methodsmentioning

confidence: 99%

Sex and occupation time influence niche space of a recovering keystone predator

Rechsteiner

Watson

Tinker

et al. 2019

Ecology and Evolution

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Predators exert strong effects on ecological communities, particularly when they re‐occupy areas after decades of extirpation. Within species, such effects can vary over time and by sex and cascade across trophic levels. We used a space‐for‐time substitution to make foraging observations of sea otters (Enhydra lutris) across a gradient of reoccupation time (1–30 years), and nonmetric multidimensional scaling (nMDS) analysis to ask whether (a) sea otter niche space varies as a function of occupation time and (b) whether niche space varies by sex. We found that niche space varied among areas of different occupation times. Dietary niches at short occupation times were dominated by urchins (Mesocentrotus and Strongylocentrotus spp; >60% of diets) in open habitats at 10–40 m depths. At longer occupation times, niches were dominated by small clams (Veneroida; >30% diet), mussels (Mytilus spp; >20% diet), and crab (Decapoda; >10% diet) in shallow (<10 m) kelp habitats. Diet diversity was lowest (H′ = 1.46) but energy rich (~37 kcal/min) at the earliest occupied area and highest, but energy poor (H′ = 2.63, ~9 kcal/min) at the longest occupied area. A similar transition occurred through time at a recently occupied area. We found that niche space also differed between sexes, with bachelor males consuming large clams (>60%), and urchins (~25%) from deep waters (>40 m), and females and territorial males consuming smaller, varied prey from shallow waters (<10 m). Bachelor male diets were less diverse (H′ = 2.21) but more energy rich (~27 kcal/min) than territorial males (H′ = 2.54, ~13 kcal/min) and females (H′ = 2.74, ~11 kcal/min). Given recovering predators require adequate food and space, and the ecological interactions they elicit, we emphasize the importance of investigating niche space over the duration of recovery and considering sex‐based differences in these interactions.

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Ecosystem features determine seagrass community response to sea otter foraging

Cited by 19 publications

References 70 publications

Reduced water motion enhances organic carbon stocks in temperate eelgrass meadows

Reduced water motion enhances organic carbon stocks in temperate eelgrass meadows

Nearshore seascape connectivity enhances seagrass meadow nursery function

Sex and occupation time influence niche space of a recovering keystone predator

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