Kelp ForestsMARS 34501 October 2013Subtidal Environments: Marine environments that lie between the lowest low tides and the edge of the continental shelf.Subtidal:Kelp SystemsSeagrassesHard BottomsCoral ReefsEstuariesUnvegetatedIntertidal:Salt MarshesMangrovesBeachesRocky ShoreKelp EcosystemsSubtidalCharacteristics of Subtidal Environments:Lighted bottomAllows for growth of rooted plants/algaePenetration typically to depths of 20-40 m in coastal systemsModerate environmental variabilitySubtidal not exposed to extreme conditions of intertidalBut more variable than deep seaStrong benthic-pelagic couplingBenthic animals within reach of POC from surface watersKelp Ecosystems: Subtidal environments thathave kelps (brown macroalgae, Phaeophyceae; Laminariales; Laminariaceae) as the dominant primary producersWhere do they occur?Cold temperate WatersL=LaminariaM=MacrocystisMore abundant, further equator-ward along western edges of continentsUpwellingBladeStipeHoldfastPneumatocystNereocystisThe pneumatocyst and similar flotation organs are key to kelp forest development, allows plant to root offshore in deep water while blades to be kept near surface, in the light.Two types of Kelp Ecosystems:Kelp Beds: smaller kelp; blades do not reach the surface. Shallower water, north east coastEx: Laminaria, Fucus, Ascophyllum(last two are intertidal)Kelp Forests: taller kelp; bladesreach to the surface, plants have pneumatocysts, upwelling zones.Ex: Macrocystis, Nereocystis.Resemble terrestrial ‘forests’ Understory of shorter kelpCan be 30 m tallKelp Ecosystems: 3-D structureMostly red algaeRocky substrateLight availability is important: light must penetrate to the rocky bottom to allow young kelp to establish.Temperate systems: maximum of 20-40 m, shallower when turbid.Kelps have no roots: holdfast anchored to rocky substrate.Where do N and P come from? high nutrient water is requiredwind and waves deliver waterexplains distributionNot found in tropical areasAre found where cold currents and upwelling occurWhy?Factors Determining Kelp Distribution:Hard substrateSufficient water movementNutrient-rich waterSufficient lightKelp growth ratesunder optimal conditions: 50 cm d-1for MacrocystisWater MovementMeasures of GrowthPrimary Production in Marine EcosystemsSystem gC/m2/y apples/m2/yOpen ocean <100 1Benthic deep sea* 0 0Coastal upwelling 300 6Kelp Systems 1300 26Tropical forests 1200 24*doesn’t include vents and seepsWhat happens to kelp productivity?1) Herbivores eat it: sea urchins and gastropodsHow much is eaten? 1911 100%1930 50%1960 0%Urchins increased in numbers; sea otters decreased.Did overgrazing by urchins explain the loss of kelps?Changes inkelp areaover time in aCalifornia bed;“urchin barrens”Usually not much; animals feed on detrital kelp and understory kelp.But…Fur hunting;nearly extinctNatural experiment: Sea otter effects on kelp beds?Healthy system: 10% loss to herbivores(Estes and Palmisano 1974)53,0006,000(Estes et al. 1998)1,825 otters y-1Preferred food: sea lions and sealsDecline due to just 3.7 killer whales“Grand Prey Collapse” for Killer Whales?1. Humpback and blue whales2. Harbor seals and sea lions3. Sea ottersPrey preference:(Springer et al. 2003)(Wade et al. 2007)Baleen whalesMultiple orca species?What happens to kelp productivity?1) Herbivores eat it: sea urchins and gastropods2) Converted to detritus (“drift kelp”)Storm surge rips blades from kelpStorm surge rips entire kelp from rocksEntangled blades rip other kelpKelp regenerate quickly if holdfast intactStorm damage most severe during El Nino years…Storm Damage:(Reed et al. 2008)El Nino/Southern Oscillation (ENSO)Normal El NinoUpwelling reduced in summer:NutrientsTemperatureCurrentsAtmospheric PressureSurface CurrentsSpawns major storms along west coast in winterEffects of El Nino years on kelp systems:Pt. Loma, CA: 1982 600 ha1983 40 haWhat happens to kelp productivity?1) Herbivores eat it: sea urchins and gastropods2) Converted to detritusStorm DamageEroding Tips:Growth of kelps occurs at the baseTip is the oldest partBattered tips fray and disintegratePOC and DOC released10%90%Detritivoresand bacteriaStrong El Nino winterOld Kelp(Levinton 2001)Alternate steady states in kelpecosystems?High kelp biomass; lots of detritus, urchins fat and happy: sedentary and under coverStorms or high urchinpopulation, limited food: “barrens”Detritus-basedGrazing-basedKelp Forests•Provide structure•Habitat for many animals•Provide food•Sea otters: “guardians of the