EcologicalInteractions

James L. Bodkin and M. Tim Tinker

PreyDirectEffects

IndirectEffects

Urchins large, & abundant, Kelps rare

Sea Otters Rare or Absent

Urchins small & Kelps abundant

Sea Otters Abundant

MACROPHYTES and ECOSYSTEM  STRUCTURE & FUNCTION

• Structural complexity

• Habitat diversity• Species diversity• Refugia• Complementary 

production• Food web 

subsidies• Hydrodynamics• Carbon 

sequestration• Primary 

production

vonBiela et al. 2015Most carbon in muscle of these fish derived from macro algae, in some locations up to 90%

Similar work demonstrates importance of kelp derived carbon in other nearshore taxa (invertebrates, fishes, birds, mammals) as well as export of kelp‐derived carbon to offshore food webs

Dunton et al. 1987, Duggins et al. 1989  Bustamante and Branch 1996, Fredrickson et al. 2003, Estes et al. 2004,  Reisewitz et al. 2006 ..…….

Indirect effects on fish

Ecological Interactions: Nearshore Mixed Sediment Habitats 

• Sheltered  Shores• Macrophyte production (understory kelps and eel grass)

• Sediment excavations/disturbance• Altered abundance & size classes of infaunal bivalves

• Modified filtration rates

• Exposed Shores• Perhaps the most under‐studied of the sea otter habitats

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Edible Biomass (g wet wt./

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Sea Otter Density

Post Pre

Biomass of Clam Prey Species at Glacier Bay Sites With Increasing Sea Otter Density

Summary Ecological Interactions, SEAK• Current status of sea otters and nearshore marine ecosystems 

are an artifact of human activities over 250 years• Direct effects of otter predation can include maintenance of  

abundance, sizes, and biomass of prey• Indirect effects of reduced herbivory documented across many 

habitats following the removal of sea urchins• Restoration of kelp forests & other

macrophytes have ecosystem level effects related to habitat and increased primary production  

• Our understanding of long term direct & indirect effects of sea otterrecovery are still incomplete

Sea Otters and Ecological Interactions,California

San Nicolas Sub-tidal sites

Spatial variation in predators and prey

San Nicolas, North Side (low otter effect)Otter effect Otter effectFrequent crashes

of urchin pop’n.s…most likelydisease driven

No relationship between otters and urchins

San Nicolas West End (high otter effect)

Strongylocentrotus franciscanus Strongylocentrotus putpuratus

West end site 1 West end site 1

Otter effect Otter effect

Red urchins start to decline by mid 1990s

Purple urchinsabundant until early 2000s

Kenner, M.C. and M.T. Tinker 2018. Stability and change in kelp forest habitats at San Nicolas Island. Western Naturalist. 78(4): 1-11

What about other coastal habitats, such as estuaries?

Another Opportunistic Experiment:Elkhorn Slough

©Keith Ellenbogen

Sea otter colonization of Elkhorn Slough

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1980 1985 1990 1995 2000 2005 2010 2015 2020

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 Otters

Sea otters in Elkhorn Slough

Trophic Impacts to Estuarine food webs: early stages (1990s – 2010)

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Cancercrab

clam small un-idcrab

mussel worm smallcrustacean

shore crab star sand crab snail kelp crab sand dollar

Pro

porti

on o

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al b

iom

ass

cons

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Diet Composition 1999-2010

Top-down effects: Sea otters reduced the overall biomass and size of crabs

Hughes, B. B., R. Eby, E. Van Dyke, M. T. Tinker, C. I. Marks, K. S. Johnson, and K. Wasson. 2013. Recovery of a top predator mediates negative eutrophic effects on seagrass. Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1302805110

Trophic Cascade in Sea Grass Habitat

Hughes, B. B., R. Eby, E. Van Dyke, M. T. Tinker, C. I. Marks, K. S. Johnson, and K. Wasson. 2013. Recovery of a top predator mediates negative eutrophic effects on seagrass. Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1302805110

600% Increase in Seagrass Biomass!!

Trophic Impacts to Estuarine food webs: later stages (2012– 2015)

Sea otter diets in upper estuary

Otter Exclusion Procedural Control

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Otter Exclusion Control

Cra

b de

nsity

cha

nge

*tra

p-1

P < 0.05

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Otter Exclusion Control

Abo

vegr

ound

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mas

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-2

P < 0.05

Reduction in burrowing healthier marsh

Conclusions: Sea otter ecosystem effects vary between coastal habitatsKelp forests• primary productivity, species diversity,

enhanced nursery habitat for fish, shoreline stability, carbon fixation, etc.

Seagrass:• Sea otters reduce crab populations,

facilitating grazers in seagrass beds• Positive effects for eelgrass resilience.Salt marsh:• Sea otters reduce burrowing crabs,

healthier pickleweed• Appear to reduce bank erosion &

marsh loss (ms. in prep)

Ginny L. Eckert Juneau Center, College of Fisheries and Ocean Sciences,

University of Alaska Fairbanks

S E A O T T E R S A N D F I S H E R I E S ,S O U T H E A S T

A L A S K A

Photo credit: Deborah Mercy

Geoduck clam density

Hoyt 2015Before After

Without Sea otters

With Sea otters

Photo credit: Phillip Collaç

California sea cucumber,Parastichopus californicus

Dungeness crab,Cancer magister

Geoduck clam,Panopea generosa

Red sea urchin, Strongylocentrotus 

franciscanus

Pinto abaloneHaliotus kamtchatKanaWhat are 

sea otters eating?

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ENES

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clam

snai

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p

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Prey type (grouped)

cont

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to d

iet (

biom

ass)

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RED

SEA

UR

CH

IN

GEO

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CK

CLA

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CA

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KIN

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fish

mus

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scal

lop

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r mol

lusk

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umbe

r

wor

m

Sea otter diets

n= 699 bouts from 6,117 dives 

46% of diet commercially important

Hoyt 2015

NW Dall Island

cont

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to d

iet

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RAB

clam

s

mus

sels

clam

s

snai

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p

Oth

er c

ucum

bers

Oth

er

wor

m

ABAL

ON

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Oth

er m

ollu

sks

crab

s

Urc

hin

(gre

en)

star

fish

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EN

ES

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B

Coronation Island

cont

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ion

to d

iet

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Geographic differences in diet

Hoyt 2015

Hoyt 2015

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0.25

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0.75

1.

0. 7.5 15. 22.5 30.

Commercial con

tribution to diet

Maximum observed density (otters km‐2)

Commercial contribution as a log‐linear function of density

NW Dall Island (99% red sea urchins)

Photo Credit: Enrique R.  Aguirre Aves

Sea Otter by Victor Tumuluk (Hydaburg)

Photo Credit: Enrique R. Aguirre Aves

Ibarra in progress

H U M A N S - S E A O T T E R S - B U T T E R

C L A M S

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1‐10 21‐30 41‐50 61‐70 81‐90 101‐110 121‐130

Freq

uency (%

)

Length (mm)

No Sea Otters or Humans

Clam size distribution without sea otters

Ibarra in progress

Clam size distribution with sea otters

Only Sea Otters

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Freq

uency (%

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Length (mm)

Ibarra in progress

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Freq

uency (%

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Length (mm)

Sea Otters & Humans

Clam size distribution with sea otters & humans

Ibarra in progress

Sea otters and humans• Commercial species in diet greatest early after colonization: long‐established populations supported by clams

• Effect on subsistence clam populations, both abundance and size structure

• Coexistence will be challenging: must account for spatial structure of sea otter populations, and dynamic nature of diet and interactions

T H A N K S

Photo credit: Deborah Mercy

Zac HoytSean LarsonSonia N. IbarraWendel W. RaymondStephen J. Langdon Sunny RiceVerena GillTim Tinker

Alaska Sea Grant, North Pacific Research BoardSoutheast Alaska Regional Dive Fishery AssociationNational Science Foundation