Zooplankton IIDistributions in the SeacopepodsSeasonal CyclesphytoplanktonTemperate North AtlanticTemperate North Pacificphytopl. zoopl.Spring bloom:Chl. a = 1 mg/m3PP = 250 mg C/m2/dmostly diatoms(some picoplankton)phytopl. zoopl.Spring bloom:Chl. a = 0.3-0.4 mg/m3PP = 550 mg C/m2/ddiatomsmostly copepodscopepodsmicrozooplankton (flagellates)mostly picoplanktonThe micrograzer hypothesishttp://www.reefkeeping.com/issues/2004-02/rs/index.phpReproductive CyclesPhased to lunar cycle, tides,Day-night cycleryanphotographic.comPolychaete epitokes - Palolo Wormbrucechard.blogspot.comHypotheses to explain vertical migration:1. Predator avoidance (from visual predators)2. Horizontal position change (vertical current shear = new food patch)3. Energy conservation (cooler at depth)4. Avoidance of light damageZooplankton Vertical Migrationup at nightdown during dayhttp://www.teara.govt.nz/EarthSeaAndSky/SeaLife/Plankton/1/ENZ-Resources/Standard/3/en#breadcrumbtophttp://upload.wikimedia.org/wikipedia/commons/1/1f/Krill_swarm.jpgRed Krill (Munida gregaria, ‘squat lobster’), swarm beached in NZ. These are meroplankton, the adults are benthic like Spiny Lobstershttp://www.niwascience.co.nz/ncabb/abb/2003-04/seeking2_large.jpg/viewSalp swarm. Have been reported to cover 100,000 sq km (~40,000 sq mi)Why swarm?1. May help reduce predation – a swarm looks like a much larger animal than an individual krill – discourage predators2. May be part of mating activity3. Growth rate exceeds dispersion rate4. Other…Atkinson et al. (2004). Nature 432, 100-103. Long-term decline in krill stock and increase in salps within the Southern Ocean1926-20031926-20031997-2003Long-term average abundances around AntarcticaChlorophyllKrillSalpsKrill DeclinedSalps MaintainKrill are Ice-dependentSalps are not – no relationship with ice coverShort-lived, high growth ratesLong lived (2+ years), slow growth rate• Ice coverage has declined – change in circulation patterns• Alternate hypothesis – overfishing of krill stocks• Salps have low food value• Consequences for krill-dependent foodweb –whales, penguins, sealseutrophic:higher in nutrientslarger phytoplanktonlarger zooplanktonoligotrophic:low in nutrientspicoplankton dominatesmaller zooplanktonupwelling:higher in nutrientslarger phytoplanktonlarger zooplanktonConditions change dramatically along the “Merry-go-Round”Western Boundary CurrentUpwellingColdWarmwarm core ringcold core ringWarm color = warm waterCross sectionMixing and vertical transport along isopycnals provides nutrients, stimulates phytoplankton growth, food for zooplankton and fish that are also abundnat around these structuresIsopycnal = surface of equal densityWarm color = high chlorophyllHigh nutrient, low lightHigh light, usually low nutrientsairsea-www.jpl.nasa.gov/.../ocean_eddies.htmlLow chlHigh chlcoldwarmTIMEbottom featuresconvergenceInternal waves in a stratified water column break over shallow bank, causing mixing, surface convergencesbottom featureslocal topographyestuary creek frontsAlldredge and Hamner 1980high in zooplanktonlee sidezooplankton types on lee sideTidal shear and water mass boundaries, subduction, just like a warm or cold front in the atmospherehttp://po.gso.uri.edu/color/publications/LineInSea.pdfbottom featureslocal topographyestuary creek frontsLangmuir cellsConsequences of Patchiness1. Makes sampling difficult2. Attracts predators3. Provides protection from predators4. Complicates foodweb models5. May make it possible for large mobile predators to live at allPhytoplankton Patchiness sensed by a
View Full Document
Unlocking...