Northern Kelp Crab (Pugettia Producta)

Kelp Crabs Eat Kelp. And Lots Else?

Katie Dobkowski*, Kasey Cordova, Declan Farr, Bryce O’Brien, Megan Dethier, Helen Berry Bull Kelp Forests – Ecologically Important Nearshore Habitats (Possible) Kelp Consumers Northern kelp crabs, Pugettia producta

Photos courtesy of Dr. KenSe bens, Dr. Stephanie Crofts, and WSU Beachwatchers Feeding Exprmts Nereocystis Laboraty FedingExp iments n=7 -

Macroalga #1 11

Macroalga #2 “Buffet - Style” choi (same snumberofcb to alowrndmpig

Nereocystis for adjustmen) Controls n=7

Macroalga #1 - 11

Macroalga #2 P. producta elects to eat bull kelp over other species of macroalgae

A) x B)

yy yy Adjusted Mass Lost (g) 0 5 10 15 20 0 5 10 15 20

NAS NUC

C) D)

x x

x y y yy Adjusted Mass Lost (g) 0 5 10 15 20 0 5 10 15 20

NUM N Sm Af Pugettia producta, the Northern Kelp Crab

Nereocystis Alaria Saccharina Costaria Ulva Lacuna

Bull Kelp Winged Kelp Sugar Kelp Seersucker Sea Lettuce Snail

Organism photos courtesy of Sound Water Stewards Laboratory Feeding Experiments Choice and No Choice “Pairwise” Comparisons

What crabs CAN eat: Paired What crabs CHOOSE to eat: No Choice Experiments Paired Choice Experiments

Nereocystis stipe Nereocystis stipe

Nereocystis blade

Nereocystis blade Do kelp crab preferences vary with bull kelp life stage? Adults Only Juveniles Only

a) Choice: p<0.00001 b) Choice, p=0.002

F eeding Rate (g k elp/g cr ab/hr) * * 0.000 0.005 0.010 0.015 0.000 0.005 0.010 0.015

c) No Choice: p=0.002 d) No Choice, p=0.008

* F eeding Rate (g k elp/g cr ab/hr) 0.000 0.005 0.010 0.015 0.000 0.005 0.010 0.015

Blade Stipe Blade Stipe

Food Type Food Type No – blades preferred in both juvenile and adult feeding experiments Do kelp crabs chose to consume bull kelp stipes or blades?

Blades Only Stipe Only

a) Choice b) Choice, p=0.01

* F eeding Rate (g k elp/g cr ab/hr) 0.000 0.005 0.010 0.015 0.000 0.005 0.010 0.015

No Choice No Choice F eeding Rate (g k elp/g cr ab/hr) 0.000 0.005 0.010 0.015 0.000 0.005 0.010 0.015

AdultBladeJuvenileBlade AdultStipeJuvenileStipe

Food Type Food Type Blades preferred BUT can eat stipes – if offered ONLY stipes, prefer juvenile stipe to adult stipe. Do kelp crabs eat Sargassum?

Photos by Kasey Cordova YES – and lots of other foods too. Do kelp crabs eat Sargassum if the morphology effect is removed? Choice

No Choice YES – and may even prefer to consume Sargassum “jello” over bull kelp “jello”?!? How high are kelp crab densities in bull kelp beds? Cr abs/10m x 1 m tr ansect ANOVA

F2,9=1.429

01234567 p=0.289

CattlePoint EagleCove WhiteSign

Site

It likely varies by where in the Salish Sea you are looking! Photo by Dr. Megan Dethier Northern kelp crabs eat:

• Bull kelp • Preferred over many other macroalgae in choice trials • Both adult and juvenile stages • Blades preferred • Snails • Consumed in feeding experiments • Present in gut content analysis • Sargassum • Consumed fresh (found in gut content analysis) • As “jello” (effect of morphology removed) Future Directions

• Survey additional sites around the Salish Sea to quantify variation in kelp crab density and gut contents • Habitat and diet – match or mismatch? • Nereocystis/other kelp species • Sargassum • Complete additional choice and no choice laboratory feeding experiments • “Jello” made with freeze-dried (not fresh) Sargassum • Intact fresh Sargassum Questions?