Geoscience Reference
In-Depth Information
dissipative.beaches.(Defeo.and.McLachlan.2005)..The.autecological.predictions.of.
the.habitat.harshness.hypothesis.were.not.supported.empirically.for.two.Uruguayan.
species.by.Defeo.et.al..(2003).who.suggested.(p..352).that.“biotic.mechanisms.could.
be. of. utmost. importance. in. dissipative. beaches.”. This. conclusion. is. supported. by.
studies. that. have. suggested. or. demonstrated. the. effects. of. competition. in. the. yel-
low.clam.
Mesodesma mactroides
.(Braziero.and.Defeo.1999).and.the.density-related.
effects.on.burrowing.in.
Donax
.spp..(McLachlan.1998;.Dugan.et.al..2004)..In.addi-
tion,. predation. (by. shore. birds,. onuphid. polychaetes,. and. ghost. crabs). and. trophic.
cascades.may.be.inluential..For.example,.on.a.southern.California.beach,.the.quan-
tity. of. macrophyte. wrack. was. signiicantly. correlated. with. the. species. richness,.
abundance,.and.biomass.of.wrack-associated.fauna.and.the.abundance.of.predators.
such.as.shore.birds.(Dugan.et.al..2003)..Furthermore,.upward.cascading.reductions.
can.occur.if.poorly.designed.beach.nourishment.interventions.suppress.macrofaunal.
recovery.(Peterson.et.al..2006).
Consequently,.both.physical.and.biological.factors.play.ecological.roles.on.sandy.
beaches,. although. the. relative. importance. of. various. factors. and. mechanisms. in.
explaining.distributional.patterns.may.vary.with.beach.type.and.is.uncertain..This.
knowledge.deicit.hinders.attempts.to.predict.the.effects.of.events.such.as.climate.
change.on.beach.ecosystems..This.is.further.complicated.by.the.existence.of.strong.
linkages.between.beaches.and.adjacent.habitats.
HABITAT LINKAGES
Sandy. beaches. have. functional,. ecological. linkages. to. adjacent. ecosystems,. espe-
cially.sand.dunes.and.the.surf.zone.(Brown.and.McLachlan.1990)..Indeed,.they.are.
sometimes.considered.a.single.ecological.unit.(James.2000a).or.a.single.geomorphic.
unit. termed. the. “littoral. active. zone”. in. which. the. exchange. of. sand. and. organic.
matter.is.particularly.important.(Short.and.Hesp.1982;.McLachlan.and.Brown.2006)..
Beaches.are.also.linked.to.estuaries.in.terms.of.sediments,.nutrients,.and.shared.spe-
cies.(Schoeman.and.Richardson.2002;.Sherman.et.al..2002;.Gladstone.et.al..2006)..
In.addition,.nutrient-rich.groundwater.lows.through.beaches.from.terrestrial.aqui-
fers.to.the.sea.
Trophic.links.are.particularly.important.because.beaches,.being.unstable,.have.no.
large.attached.plants.to.provide.food.for.animals..Instead,.much.primary.production.
is.imported.via.surf-zone.phytoplankton,.stranded.macrophytes,.carrion,.and.terres-
trial.vegetation.(Koop.et.al..1982;.Dugan.et.al..2003)..Phytoplankton.are.consumed.
by.beach-dwelling.ilter-feeders,.and.stranded.vegetation/detritus.is.fragmented.by.
small.invertebrates..Plant.fragments.and.the.nutrient-rich.feces.of.these.invertebrate.
consumers.are.decomposed.by.beach.bacteria,.and.nutrients.are.transported.back.to.
the.sea.to.fuel.primary.production.(McLachlan.et.al..1981)..For.example,.the.feces.
of.the.ilter-feeding.bivalve.
Donax serra
.generate.up.to.24%.of.the.nutrients.used.
by.phytoplankton.blooms.(McLachlan.et.al..1981)..Consequently,.the.trophic.links.
among.the.surf.zone,.kelp.beds,.rocky.shores,.and.beaches.can.be.strong.(Soares.et.
al..1997)..Links.also.exist.with.estuaries,.which.provide.a.trophic.subsidy.to.beach.
invertebrates.(Schlacher.and.Connolly.2009)..For.example,.estuarine.discharge.can.
inluence.the.abundance.of.bivalve.mollusks.on.beaches.
(
Donn.1987;.Schoeman.and.
