TY - JOUR
T1 - Harbouring the enemy
T2 - Kelp holdfasts protect juvenile sea urchins from predatory crabs
AU - Feehan, Colette J.
AU - Francis, Fiona T.Y.
AU - Scheibling, Robert E.
N1 - Publisher Copyright:
© Inter-Research 2014.
PY - 2014
Y1 - 2014
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
UR - http://www.scopus.com/inward/record.url?scp=84908701007&partnerID=8YFLogxK
U2 - 10.3354/meps10983
DO - 10.3354/meps10983
M3 - Article
AN - SCOPUS:84908701007
SN - 0171-8630
VL - 514
SP - 149
EP - 161
JO - Marine Ecology Progress Series
JF - Marine Ecology Progress Series
ER -