Geoscience Reference
In-Depth Information
Variation. among. beaches. allows. them. to. be. classiied. morphodynamically. into.
relective.and.dissipative.beaches.(Short.and.Wright.1984),.although,.in.reality,.there.
is. a. continuum. between. the. two. extremes. with. most. beaches. being. intermediate.
(Short. 1999).. Relective. beaches. are. narrow. and. steep. with. waves. breaking. at. the.
shoreline.. Consequently,. they. lack. a. surf. zone. (the. subtidal. area. where. breaking.
waves.approach.the.beach.face),.and.the.swash.zone.(where.broken.waves.advance.
up. the. beach. face. and. retreat. as. backwash). is. narrow. and. energetic.. The. sand. is.
coarse.with.little.organic.matter.and.is.well.drained.and.oxygenated..By.compari-
son,. dissipative. beaches. are. wide. and. lat. with. an. extensive. surf. zone,. iner. sand,.
abundant.organic.matter,.and.a.wide,.low-energy.swash.zone.that.gives.ilter-feed-
ers.greater.access.to.planktonic.food..Their.vertical.chemical.gradients.are.steeper.
(McLachlan.and.Turner.1994).and.most.organisms.live.in.the.oxygenated.layer.near.
the. surface.. Relective. and. dissipative. beaches. are. more. common. in. tropical. and.
temperate.regions,.respectively.(McLachlan.and.Brown.2006).
Not.only.do.these.habitat.features.provide.the.ecological.setting,.some.also.pro-
mote. the. vulnerability. of. beaches. to. climate. change.. For. example,. the. instability.
of.the.sand.facilitates.the.predicted.erosion,.desiccation.may.be.worsened.by.tem-
perature.increases,.and.lower.water.pH.may.affect.both.calcareous.sediments.and.
calcium-dependent.species.
BIOTA AND ECOLOGY
Contrary. to. popular. belief,. sandy. beaches. are. not. ecological. deserts. but. support.
hundreds. of. species. (McLachlan. and. Brown. 2006).. A. few. of. these. are. large. and.
mobile.and.use.the.beach.or.dunes.for.nesting.and.feeding.(e.g.,.seabirds.and.turtles).
or.are.opportunistic.visitors.(e.g.,.bears.and.kangaroos)..Most.species,.however,.are.
small.and.inconspicuous..Some,.such.as.ocypodid.ghost.crabs,.talitrid.sandhoppers,.
and. wrack-dependent. isopods,. amphipods,. and. insects,. inhabit. the. upper. beach..
Others,.the.great.majority,.live.intertidally.beneath.the.sand.surface..They.include.
primary-producing,. microscopic. algae. (mostly. episammic. and. epipelic. diatoms),.
decomposers.(bacteria.and.fungi),.and.invertebrates.(mostly.nematodes,.crustaceans,.
polychaetes,.and.mollusks)..The.invertebrates.are.often.grouped.on.the.basis.of.size,.
the. meiofauna. being. less. than. half. a. millimeter. long,. the. macrofauna. larger.. The.
former.occupy.interstitial.spaces.between.sandgrains.and.comprise.far.more.species.
than. the. macrofauna. (Brown. 2001).. Feeding. types. include. scavengers,. predators,.
and.deposit-.and.ilter-feeders.
Sandy-beach.species.exhibit.physiological,.morphological,.and.behavioral.adap-
tations. to. the. habitat. (Brown. and. McLachlan. 1990).. These. include. orientation.
mechanisms.(Scapini.2006),.mobility.and.burrowing,.and.rhythmic.tidal.migrations.
(Enright. 1961;. Forward. 1986;. Hacking. 1996;. Jones. et. al.. 1998).. The. life. histories.
of.many. macrofaunal. species.are.metamorphic.with.planktonic,.dispersive.larvae..
Exceptions. include. peracarid. crustaceans,. a. factor. that. may. inluence. their. ability.
to.migrate.as.climate-change.pressures.take.effect..In.addition,.many.species.have.
calcium-based. exoskeletons. and. their. ability. to. adapt. or. acclimate. to. reduced. pH.
imposed.by.climate.change.is.unknown.
