Harbouring the enemy

Kelp holdfasts protect juvenile sea urchins from predatory crabs

Colette Feehan, Fiona T.Y. Francis, Robert E. Scheibling

Research output: Contribution to journalArticleResearchpeer-review

1 Citation (Scopus)

Abstract

Predation is an important agent of post-settlement mortality of sea urchins that is mediated by the availability and suitability of spatial refuges, particularly during the vulnerable juvenile stage. In laboratory and field caging experiments, we show that holdfasts of a dominant kelp, Saccharina latissima, provide a spatial refuge for juvenile sea urchins Strongylocentrotus droebachiensis (<20 mm, test diameter) from crabs Cancer borealis and C. irroratus, considered to be the dominant predators of sea urchins in kelp-bed ecosystems in the northwestern Atlantic. In treatments with individual crabs of either species, the presence of holdfasts reduced predation on juvenile sea urchins by 20 to 30% compared to treatments with no refuge. Crabs consumed juveniles (from 5 to 19 mm) in each of three 5 mm size classes in proportion to their abundance, regardless of treatment. In kelp beds in St. Margarets Bay, Nova Scotia, Canada, the number of juvenile sea urchins per holdfast ranged from 0.3 to 0.9, with juveniles in holdfasts accounting for twothirds of the total urchin population density at one site. Up to 4 juveniles occurred within a single holdfast, and there was a significant positive relationship between juvenile size (but not number) and holdfast volume. Small adult sea urchins were not found within holdfasts in kelp beds and rarely occupied holdfasts presented to them in laboratory cages. Our findings indicate an ontogenetic shift in sea urchin-kelp interactions, whereby kelp facilitates recruitment of its major grazer.

Original languageEnglish
Pages (from-to)149-161
Number of pages13
JournalMarine Ecology Progress Series
Volume514
DOIs
StatePublished - 1 Jan 2014

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Echinoidea
macroalgae
crab
crabs
refuge
Cancer borealis
predation
Cancer irroratus
sea
Nova Scotia
cancer
population density
cages
Canada
predator
predators
mortality
ecosystems
ecosystem

Keywords

  • Cancrid crab
  • Kelp bed
  • Predation
  • Sea urchin
  • Spatial refuge
  • Strongylocentrotus droebachiensis

Cite this

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title = "Harbouring the enemy: Kelp holdfasts protect juvenile sea urchins from predatory crabs",
abstract = "Predation is an important agent of post-settlement mortality of sea urchins that is mediated by the availability and suitability of spatial refuges, particularly during the vulnerable juvenile stage. In laboratory and field caging experiments, we show that holdfasts of a dominant kelp, Saccharina latissima, provide a spatial refuge for juvenile sea urchins Strongylocentrotus droebachiensis (<20 mm, test diameter) from crabs Cancer borealis and C. irroratus, considered to be the dominant predators of sea urchins in kelp-bed ecosystems in the northwestern Atlantic. In treatments with individual crabs of either species, the presence of holdfasts reduced predation on juvenile sea urchins by 20 to 30{\%} compared to treatments with no refuge. Crabs consumed juveniles (from 5 to 19 mm) in each of three 5 mm size classes in proportion to their abundance, regardless of treatment. In kelp beds in St. Margarets Bay, Nova Scotia, Canada, the number of juvenile sea urchins per holdfast ranged from 0.3 to 0.9, with juveniles in holdfasts accounting for twothirds of the total urchin population density at one site. Up to 4 juveniles occurred within a single holdfast, and there was a significant positive relationship between juvenile size (but not number) and holdfast volume. Small adult sea urchins were not found within holdfasts in kelp beds and rarely occupied holdfasts presented to them in laboratory cages. Our findings indicate an ontogenetic shift in sea urchin-kelp interactions, whereby kelp facilitates recruitment of its major grazer.",
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Harbouring the enemy : Kelp holdfasts protect juvenile sea urchins from predatory crabs. / Feehan, Colette; Francis, Fiona T.Y.; Scheibling, Robert E.

In: Marine Ecology Progress Series, Vol. 514, 01.01.2014, p. 149-161.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Harbouring the enemy

T2 - Kelp holdfasts protect juvenile sea urchins from predatory crabs

AU - Feehan, Colette

AU - Francis, Fiona T.Y.

AU - Scheibling, Robert E.

PY - 2014/1/1

Y1 - 2014/1/1

N2 - Predation is an important agent of post-settlement mortality of sea urchins that is mediated by the availability and suitability of spatial refuges, particularly during the vulnerable juvenile stage. In laboratory and field caging experiments, we show that holdfasts of a dominant kelp, Saccharina latissima, provide a spatial refuge for juvenile sea urchins Strongylocentrotus droebachiensis (<20 mm, test diameter) from crabs Cancer borealis and C. irroratus, considered to be the dominant predators of sea urchins in kelp-bed ecosystems in the northwestern Atlantic. In treatments with individual crabs of either species, the presence of holdfasts reduced predation on juvenile sea urchins by 20 to 30% compared to treatments with no refuge. Crabs consumed juveniles (from 5 to 19 mm) in each of three 5 mm size classes in proportion to their abundance, regardless of treatment. In kelp beds in St. Margarets Bay, Nova Scotia, Canada, the number of juvenile sea urchins per holdfast ranged from 0.3 to 0.9, with juveniles in holdfasts accounting for twothirds of the total urchin population density at one site. Up to 4 juveniles occurred within a single holdfast, and there was a significant positive relationship between juvenile size (but not number) and holdfast volume. Small adult sea urchins were not found within holdfasts in kelp beds and rarely occupied holdfasts presented to them in laboratory cages. Our findings indicate an ontogenetic shift in sea urchin-kelp interactions, whereby kelp facilitates recruitment of its major grazer.

AB - Predation is an important agent of post-settlement mortality of sea urchins that is mediated by the availability and suitability of spatial refuges, particularly during the vulnerable juvenile stage. In laboratory and field caging experiments, we show that holdfasts of a dominant kelp, Saccharina latissima, provide a spatial refuge for juvenile sea urchins Strongylocentrotus droebachiensis (<20 mm, test diameter) from crabs Cancer borealis and C. irroratus, considered to be the dominant predators of sea urchins in kelp-bed ecosystems in the northwestern Atlantic. In treatments with individual crabs of either species, the presence of holdfasts reduced predation on juvenile sea urchins by 20 to 30% compared to treatments with no refuge. Crabs consumed juveniles (from 5 to 19 mm) in each of three 5 mm size classes in proportion to their abundance, regardless of treatment. In kelp beds in St. Margarets Bay, Nova Scotia, Canada, the number of juvenile sea urchins per holdfast ranged from 0.3 to 0.9, with juveniles in holdfasts accounting for twothirds of the total urchin population density at one site. Up to 4 juveniles occurred within a single holdfast, and there was a significant positive relationship between juvenile size (but not number) and holdfast volume. Small adult sea urchins were not found within holdfasts in kelp beds and rarely occupied holdfasts presented to them in laboratory cages. Our findings indicate an ontogenetic shift in sea urchin-kelp interactions, whereby kelp facilitates recruitment of its major grazer.

KW - Cancrid crab

KW - Kelp bed

KW - Predation

KW - Sea urchin

KW - Spatial refuge

KW - Strongylocentrotus droebachiensis

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U2 - 10.3354/meps10983

DO - 10.3354/meps10983

M3 - Article

VL - 514

SP - 149

EP - 161

JO - Marine Ecology Progress Series

JF - Marine Ecology Progress Series

SN - 0171-8630

ER -