Beaches and Barrier IslandsMARS 345030 October 2012Beachesare dynamic intertidal habitatsA Beach Requires: Waves A supply of unconsolidated sedimenterosion from uplandssediment deposited by riversCobble BeachesLocal ErosionConditions that set up wavesHigh windConstant directionLong fetch orAlternative source of waves – ship trafficWaves transport potential energy as displacement of the sea surface away from mean sea levelCrestTroughWave feels bottom (moves sand) at D<L/2Wave breaks at D<1.3 HWavelength, LWave height, HWater depth = DCircular pathElliptical pathDeep Water WaveShallow Water WaveDeep Water WaveSand bar traps water delivered by waves, occasional breaks in the sand bar leave openings for “rips” that let it escape“Rip Currents”http://lrm.nt.gov.au/__data/assets/image/0003/20991/nt_diagram.jpgDuring hurricanes there can be net onshore flow of surface waters over a wide area, If this happens over a shallow wide continental shelf, there is no exit channel Water piles up against the shore: storm surgeMinimal storm surge on small islands, deep continental shelvesSTORM SURGEhttp://www.wx-pilot.com/wp-content/uploads/surgebulge_COMET.jpgLow pressure at the center of the storm is a factor, tooEffects of Waves1. Extend upper limit of intertidal area (splashing)2. Mix gases into water (e.g. O2, N2)3. Mechanical effects – determines how securely animals “attach”4. Determines particle sizeBoulders and cobblesgravel (>2 mm)sand (0.062 – 2 mm)silt (<0.062 mm)Sandy Beaches (0.062 – 2 mm)Wave EnergyParticle Size coarse fineSlope steep gradualStability unstable stableWater retention low higherOxygen high lowOrganic matter low higherHigh LowHigh EnergyLow Energyhigh energy low energyHighly mobileSedentary infaunaOxygen penetrationSandy Beach (Sand flat) Mud flatEpifauna low or none, moderatemotile organismsMacroinfauna suspension feeders, depositfeeders,no permanent burrows permanent burrows Meiofauna some moreFood web detritus-based detritus-basedControls of organism distributionI. Physical factorsWavesParticle typeTidesZonation occurs on the beach, tooControls of organism distributionI. Physical factorsa. Wavesb. Particle Typec. TideII. Biological factorsa. Predation & HerbivoryTidal and Lunar Rhythmshttp://www.vims.edu/~jeff/Pugnax.jpghttp://www.nrdc.org/water/conservation/hbyear/images/july1.jpghttp://www.vims.edu/~jeff/fiddler.htmTidal rhythms: Fiddler crabs (Uca pugnax)Casts of burrowsTidal rhythms: Fiddler crabs (Uca pugnax)High tide on home beachCrab activityNight time in the aquariumhttp://www.research.noaa.gov/spotlite/archive/images/hcrabs.jpgTidal rhythms: Horseshoe crabs (Limulus polyphemus)http://www.agpix.com/catalog/AGPix_MiPi14/large/AGPix_MiPi14_1408_Lg.jpghttp://research.myfwc.com/images/gallery/20060621_084242_18352.JPGTidal rhythms: Horseshoe crabs (Limulus polyphemus)Ellinger et al. 2006 JEMBEActivity corresponds to tidal cyclehttp://www.glaucus.org.uk/ShoreCrabsDSCF0882E.jpgSemilunar rhythms: Green shore crab (Carcinus maenas) moulting behaviorNaylor 2001 Earth, Moon & PlanetsPercent moultingwithin 24 hr of captureTideMoon phasehttp://www.shallowwaterangler.com/flyfishing/050426b.jpghttp://coris.noaa.gov/glossary/epitoky_186.jpghttp://www.kidsbiology.com/Lunar rhythms: Pacific Palolo worm (Eunice viridis)http://www.coralcoe.org.au/news_stories/indigenous/images/4.jpgLunar rhythms: Pacific Palolo worm (Eunice viridis)Naylor 2001 Earth, Moon & PlanetsLunar rhythms: Pacific Palolo worm (Eunice viridis)Worms spawningDate of Moon in 3rdQuarterLunar months vs solar yearshttp://www.ryanphotographic.com/images/JPEGS/Epitokes%20and%20diver%20Belize%20copy.jpgLunar rhythms: Pacific Palolo worm (Eunice viridis)http://www.coralcoe.org.au/news_stories/indigenous/imagegallery.htmlLunar rhythms: Pacific Palolo worm (Eunice viridis)What cues rhythms?Magnetic field?*Many factors: mechanical agitation thought to be most common on beacheshttp://gosoutheast.about.com/od/photoswebcamspodcasts/ig/Beautiful-Beaches-of-the-SE/A-Sunrise-at-the-Beach---NC.htmBarrier IslandsA Consequence of BeachesSapeloTybeeSt. SimonsOssabawBarrier Islands a dominant feature of the East and Gulf coasts of the US2,686 miles of beach!Typical structure:Beach, barrier island, salt marsh, uplandBertness3 million years bp15,000 years bpNowSea Level FluctuationsGray’s Reef was dry land~40 milesRelict Sand Dune Complexes From Last High Stand of Sea LevelThree series of sand dune featuresBarrier Islands are Dynamic Landformshttp://www.geosci.unc.edu/faculty/glazner/Images/Coastlines/barrier.htmlABABBarrier Islandswaleshttp://w3.salemstate.edu/~lhanson/gls214/gls214_barrier_isl.htmOverwashed during severe