José Luis Acuña- University of Oviedo, Spain

1. Fakinggiants: Theevolution of highclearancerates in jellyfishes José Luis Acuña-University of Oviedo, Spain Angel López-Urrutia, SpanishInstitute of Oceanography, Gijón, Spain Sean Colin, Roger Williams University, US

2. Whygelatinous? -ProbablyNOTto be untasty and transparent and evade predation: Manypredatorsloveeatingjellies. Manyjellieslive in thedeepocean, wherebeingseenisNOTanissue. Many of thosejelliesGZ are bioluminiscent. -Jellyfishesmusthavesometrickto endure lowfood: They do NOT use lipids They do NOTmigrate in time Theywithstandprolongueddegrowth -A possibilityisthatlarge, waterladdenbodiesallowforlargefood capture surfaces (e.g. Harbison 1992). -A cost-benefitanalysis of theirpredationmechanismsupportsthis idea.

3. Fishes and jellyfishes are cruisingpredators… Modifiedfrom Kiørboe 2008 adaptedfrom Kiørboe 2008 U S’ -Fishesremovepreyfrom a volumewhich can be calculated as thevisuallyperceptivesurface times theswimmingvelocity. -Jellyfishesswimtoforcethewater in front of thebell (in the figure, in red) toflowaccrossthebellmargin, where a pressuredrop causes thewatertorotate in a vortexaroundthetentacles, whereprey capture occurs(in the figure, in green). Wewillassumethat: Volumecleared=βVolumePerturbed orelse Clearancerate=βSU -Whereβis a searchefficiencyexpressingthe ratio of volumeclearedtovolumeperturbed. -Intuitively, β>>1 in fishesbut <1 in jellyfishes. Isthis true?

4. …withwidelydifferentsearchingefficiencies. Clearancerate=βSU -We can solvetheaboveequationfor β and combine itwith publishedmeasurements of clearancerates, S and U toarrive at estimates of β. β=Clearancerate/SU

5. Thuswe can applyWare’s (1978) cost-benefitmodel TOTAL RESPIRATION Grossenergyobtainedbypredation - Net Energyavailable forproduction - Metaboliccost of swimming = Basal respiration Acuña, López-Urrutia and Colin 2011 Foodassimmilationefficiency (Uye & Shimauchi 2005) Basal respiration Waterdensity Preyconcentration Dragcoefficient (Mc. Henry & Jed 2003) Searchingefficiency Energyconversioncoefficient Propulsiveefficiency Sahin et al.2009 Bell cross-surface Daniel 1983 Swimmingvelocity

6. Thuswe can applyWare’s (1978) cost-benefitmodel... 300 -Thecostsincrease as the cube of theswimmingvelocity P=100 μg C/L -Thebenefitsincreaseonlylinearly. 200 -The basal respirationisconstast. -Benefits-costsgenerate a dome-shaped curve. costs, benefitsRb (mg C/day) P=50 μg C/L 100 -Ifwesubtractthe basal respiration, the curve isslightlyshifteddownwards. P=25 μg C/L P=12.5 μg C/L P=6,1 μg C/L -Thereisanoptimalforagingvelocityforwhichthescopeforgrowthismaximum. 0 -Theslope of thebenefitfunctiondecreaseswith P. Thisshiftsthe H functiontotheleftand theoptimumvelocitybecomesslower. Thisis Ware’sbasicprediction. 80 40 benefits-costs (mg C/day) H (mg C/day) -However, weknowthatjellyfishes do notadjusttheirswimmingvelocities (e.g. Titelman & Hanson 2006). 0 -Whatkind of fixedswimmingvelocityshould be favoredby natural selection in this case? -40 30 0 10 20 30 -Theoneallowing net benefitwithlessprey. Swimmingvelocity, U (cm/s)

7. ...toanalyzetheevolution of structureinstead of behavior. -When H isplottedagainstlogP and logU, the 0-growthisoclinereaches a global minimumwhichalsocorrespondsto a single, and slow, global optimalswimmingvelocity H(mg C d-1) Uopt Ureal -Aurelia’s actual velocityisslightlyslower, and remainswithintheregionwheredegrowthrates are mild. -Reducingthebellsurface, i.e. byeliminatingtheexcesswaterfromthebody, allowsfor a fasterglobal Uopt, butbringstheisocline up, causingstarvation at higherfoodconcentrations -Last, increasingβ has no effectonUopt, althoughitlowersthethreshold, makingthesistem more effective and lesssensitivetooptimization. Thisisthefishstrategy -Hereweproposethatjellyfisheshaveevolvedfrom B to A (increasing S), whilefisheshaveevolvedfrom B to C (increasingβ).

8. So are they so good at clearingprey? Not more butnotlessthanfishes -In a carbonbasisJellyfishesclear and respire just as much as fishes. -However, bothjellyfishes and fishesclear 10 times as much as theirputativeprey, thecrustaceans. -Whatisgoingonhere?

9. ¿Son las medusas capaces de procesar mayores volúmenes de agua? Somehelpfromterrestrialecology -In terrestrialsystems, predatorshaveonly 10% of preybiomassthantheirprey. Thisiswhythey use anarea 10 times largerthantheirprey -Forthatverysamereason, weshouldexpectthat, in aquaticsystems, predatorsshould use a volume ten times largerthantheirprey. 3rdtrophiclevel 2ndtrophiclevel 1sttrophiclevel BIOMASS

10. ¿Son las medusas capaces de procesar mayores volúmenes de agua? Wrap up -As predators, bothjellyfishes and fishessufferpreydilution. -Thefishstrategy: increaseβ. -Thejellyfishstrategy: increaseS. -This has probablyhad a cost in terms of swimmingvelocity, from a potential of tens of centimeters per secondtojust a fewcentimeters per second. -Thisisnot a widerange, butitisessential: itenvelopesthetypicalrange of turbulentvelocities in theupperoceanlayer. -Thus, thisisprobablywhyjellyfishes are countedamongtheplanktonnot necton, and whytheydependonoceancurrents and frontsfor sex encounter and torecruitintobenthos. -However, thistrick has allowedjellyfishtobear up in thecompetitivegame, and toreplacetheirfishcompetitorswhenoverfished. THANKYOU