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 Laboratory Feeding Experiments “Buffet- Style” choice Feeding Experiments Controls n=7-11 n=7-11 (same as number of crabs to allow random pairing for adjustment) 1 2 1 2 s s # # i # # i t t a a a a g g g g l l l l cys cys a a a a o o o o r r r r c c c c Nereo Nereo Ma Ma Ma Ma P. producta elects to eat bull kelp over other species of macroalgae A) x B) 20 20 x 15 15 yy yy Adjusted Mass Lost (g) 10 10 5 5 0 0 NAS NUC C) D) x x 20 20 15 15 x y y yy Adjusted Mass Lost (g) 10 10 5 5 0 0 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 0.015 0.015 ab/hr) elp/g cr 0.010 0.010 eeding Rate (g k F * * 0.005 0.005 0.000 0.000 c) No Choice: p=0.002 d) No Choice, p=0.008 0.015 0.015 ab/hr) elp/g cr * 0.010 0.010 * eeding Rate (g k F 0.005 0.005 0.000 0.000 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 ab/hr) 0.015 0.015 elp/g cr 0.010 0.010 * eeding Rate (g k F 0.005 0.005 0.000 0.000 No Choice No Choice ab/hr) 0.015 0.015 elp/g cr 0.010 0.010 eeding Rate (g k F 0.005 0.005 0.000 0.000 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? ansect abs/10m x 1 m tr Cr 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?.