Hard Substrate Hard Substrate CommunitiesCommunities

Hard substrate = rocks, old shells, Hard substrate = rocks, old shells, pilings, jetties, piers, pilings, jetties, piers,

docksdocks

Intertidal – perhaps best know Intertidal – perhaps best know marine marine communitycommunity

TidesTides = periodic rise and fall of = periodic rise and fall of sea sea levellevel

• Caused by gravitational attraction of Caused by gravitational attraction of sun and moon sun and moon and and centrifugal force centrifugal force generated by the rotation of the generated by the rotation of the earth-moon system around the sunearth-moon system around the sun

• Periodicity of 24 hours, 50 minutesPeriodicity of 24 hours, 50 minutes

• gravitational attraction: sun and gravitational attraction: sun and moon pull at the Earth’s oceans, moon pull at the Earth’s oceans, causing a tidal bulgecausing a tidal bulge

• the tidal influence of the Moon is the tidal influence of the Moon is about twice that of the Sunabout twice that of the Sun

• Two classifications of tide based on the Two classifications of tide based on the orientation of the Sun and Moon. orientation of the Sun and Moon.

• Spring tide Spring tide : Sun, Moon and Earth are all in : Sun, Moon and Earth are all in a line (full or new moon), Sun and Moon act a line (full or new moon), Sun and Moon act together to create one large tidal bulge, together to create one large tidal bulge, and causes the greatest tidal differences and causes the greatest tidal differences because the. because the.

• Neap tideNeap tide: Sun and Moon are at right : Sun and Moon are at right angles from each other (quarter moon angles from each other (quarter moon phase), when the, smaller tidal bulge. phase), when the, smaller tidal bulge.

• distance of Moon: 50K km difference. distance of Moon: 50K km difference. perigee (nearest), the gravitational pull is perigee (nearest), the gravitational pull is ~40% greater than at apogee (farthest). ~40% greater than at apogee (farthest).

• Approximately two high tides and Approximately two high tides and two low tides each daytwo low tides each day

• when it is high tide at one coastal when it is high tide at one coastal location, it is low tide along a location, it is low tide along a different coast a quarter of the way different coast a quarter of the way around the Earth. around the Earth.

• Bay of Fundy, eastern Minas Basin, Bay of Fundy, eastern Minas Basin, on the - Moon near perigee @ spring on the - Moon near perigee @ spring tide, HT up to 16 meters above LT. tide, HT up to 16 meters above LT.

• The geogr. location, shape of the The geogr. location, shape of the shoreline, water depth key reasons shoreline, water depth key reasons for tidal variations.for tidal variations.

Result of the tides –Result of the tides –

• Exposure in the air for periods every Exposure in the air for periods every dayday– Greater temperature differencesGreater temperature differences– Desiccation/water loss – time of Desiccation/water loss – time of

exposure changes as tide advancesexposure changes as tide advances– Intense solar radiationIntense solar radiation

WavesWaves

• Mechanical effectMechanical effect

• Creates a “splash zone”Creates a “splash zone”

• Mixing – chemicals, dissolved gases, Mixing – chemicals, dissolved gases, suspended particlessuspended particles

Salinity changesSalinity changes

• Rainfall, freshwater runoffRainfall, freshwater runoff

• Tidal pools – evaporation exceeds Tidal pools – evaporation exceeds precipitationprecipitation

BarnaclesBarnacles

BarnaclesBarnacles

Mytilus californianusMytilus californianus

Nucella (Thais)Nucella (Thais)

LimpetsLimpets

Starfish - Starfish - PisasterPisaster

Sea AnemonesSea Anemones

TunicatesTunicates

BryozoansBryozoans

Sea UrchinsSea Urchins

AlgaeAlgae

Adaptations – OrganismsAdaptations – Organisms

1.1. Minimize water loss/desiccation Minimize water loss/desiccation during exposureduring exposure

• Hide out in most crack, crevice, under Hide out in most crack, crevice, under algaealgae

• Tolerate tissue desiccation, rehydrate at Tolerate tissue desiccation, rehydrate at high tidehigh tide

• Structural behavioral modifications – Structural behavioral modifications – close up, clamp down, mucus, gills in close up, clamp down, mucus, gills in cavitycavity

Adaptations – OrganismsAdaptations – Organisms

2.2. Minimize thermal stressMinimize thermal stress• Large size, surface/volume ratioLarge size, surface/volume ratio• Light/heat reflectionLight/heat reflection• Evaporative coolingEvaporative cooling

Adaptations – OrganismsAdaptations – Organisms

3.3. Avoid destruction in waves Avoid destruction in waves• Attach to substrateAttach to substrate• Thicker shellsThicker shells• Clamp to substrateClamp to substrate

4.4. Salinity stress Salinity stress

Conspicuous horizontal Conspicuous horizontal banding, or zonation of banding, or zonation of

organismsorganisms

Stephenson & Stephenson Stephenson & Stephenson 19491949

universal scheme to describeuniversal scheme to describe• SupralittoralSupralittoral – splash zone – splash zone

– Littorina Littorina (periwinkle), encrusting lichens (periwinkle), encrusting lichens and algaeand algae

• MidlittoralMidlittoral – barnacle and mussels – barnacle and mussels zonezone

• Infralittoral Infralittoral – algae and more diverse – algae and more diverse mix of animalsmix of animals

• SublittoralSublittoral – subtidal zone – subtidal zone

Why?Why?

1.1. Period of submergence – “critical Period of submergence – “critical tidal level” (Doty 1945)tidal level” (Doty 1945)

2.2. Desiccation – sets upper limits to Desiccation – sets upper limits to organismsorganisms

• north vs south-facing slopesnorth vs south-facing slopes• irregularitiesirregularities

3.3. Thermal stressThermal stress

4.4. SunlightSunlight

Joseph Connell 1961Joseph Connell 1961

Coast of Scotland:Coast of Scotland:

Chthamalus Chthamalus stellatusstellatus

Balanus Balanus balanoidesbalanoides

Thais lapillusThais lapillus (now (now NucellaNucella))

Robert Paine 1966Robert Paine 1966

• Observed structure of the food web in rocky Observed structure of the food web in rocky intertidal from Washington to Costa Ricaintertidal from Washington to Costa Rica

• Washington – predatory starfish Washington – predatory starfish PisasterPisaster and and NucellaNucella, the drill – lots of diversity, the drill – lots of diversity

• Costa Rica – no starfish, the drill Costa Rica – no starfish, the drill NucellaNucella is is the top predator – less species diversitythe top predator – less species diversity

• What was going on??What was going on??

• Went back to Washington and experimentedWent back to Washington and experimented

Paine’s experiments:Paine’s experiments:

• Removed starfish from rocks and Removed starfish from rocks and observed resultsobserved results

• With Pisaster ~ 15 speciesWith Pisaster ~ 15 species• Without ~ 8 species (plots dominated by Without ~ 8 species (plots dominated by

Mytilus, Mytilus, the best competitor for space)the best competitor for space)

• Pisaster - “Pisaster - “Keystone speciesKeystone species” – indirectly ” – indirectly controls the structure of whole controls the structure of whole communitycommunity

Connell in California (1970)Connell in California (1970)

• Balanus glandulaBalanus glandula (like (like ChthamalusChthamalus))

• Balanus cariosusBalanus cariosus

• Refuge in space (Refuge in space (Balanus glandulaBalanus glandula))

• Refuge in size (Refuge in size (Balanus cariosus)Balanus cariosus)

Paul Dayton 1971Paul Dayton 1971

Space is key – processes involved in Space is key – processes involved in getting, keeping, and using spacegetting, keeping, and using space

• Physical stress – desiccation, etc.Physical stress – desiccation, etc.

• Physical disturbance – waves, drift logsPhysical disturbance – waves, drift logs

• Predation – biological disturbancePredation – biological disturbance

• CompetitionCompetition

• Natural deathNatural death

Dayton’s experiments:Dayton’s experiments:

• Fucus – Fucus – whip effectwhip effect on barnacles vs on barnacles vs protection from desiccationprotection from desiccation– Treatment = removalTreatment = removal of of FucusFucus

• Limpets – eat algae; disturb and/or eat Limpets – eat algae; disturb and/or eat barnaclesbarnacles– Treatment = “dog dishes” to exclude limpetsTreatment = “dog dishes” to exclude limpets

• ThaisThais – drills mussels and barnacles – drills mussels and barnacles– Treatment = cages to excludeTreatment = cages to exclude

• PisasterPisaster – eats mussels and barnacles, etc. – eats mussels and barnacles, etc.– Treatment = removalTreatment = removal

Dayton’s conclusions:Dayton’s conclusions:

• Sessile marine organisms compete for Sessile marine organisms compete for spacespace

• Three levels of “biological disturbance”Three levels of “biological disturbance”– Grazing by limpetsGrazing by limpets– Predation by Predation by Thais/NucellaThais/Nucella– Predation by Predation by PisasterPisaster

• Pattern in nature = mosaic of Pattern in nature = mosaic of disturbance and recovery; disturbance disturbance and recovery; disturbance maintains patchiness, keeps diversity maintains patchiness, keeps diversity highhigh

Impact of Connell, Paine, and Impact of Connell, Paine, and Dayton’s work on field of Dayton’s work on field of ecologyecology• Shift in thinking about how communities Shift in thinking about how communities

are organizedare organized

• Earlier view – competitive dominant has Earlier view – competitive dominant has broadest niche, diversity the result of broadest niche, diversity the result of specialization to avoid competitionspecialization to avoid competition

• New view – dominants often less New view – dominants often less abundant, inferior competitors can have abundant, inferior competitors can have broader niche, predators and disturbance broader niche, predators and disturbance create diversity by preventing competitioncreate diversity by preventing competition

Rocky Intertidal ParadigmRocky Intertidal Paradigm1.1. Upper limits of distribution are primarily Upper limits of distribution are primarily

determined by physical factorsdetermined by physical factors2.2. Lower limits of distribution are primarily Lower limits of distribution are primarily

determined by biological interactions (competition determined by biological interactions (competition for space and predation)for space and predation)

3.3. Predation or physical disturbance can prevent Predation or physical disturbance can prevent competitive exclusion (enhancing species diversity) competitive exclusion (enhancing species diversity) by keeping superior competitors at low densitiesby keeping superior competitors at low densities

4.4. In benign physical environments, predation is most In benign physical environments, predation is most important in determining community compositionimportant in determining community composition

5.5. In harsh physical environments, predation intensity In harsh physical environments, predation intensity is reduced and competition is most important in is reduced and competition is most important in determining community compositiondetermining community composition

Exceptions and Limitations of Exceptions and Limitations of RIPRIP1.1. Upper limits of distribution are primarily Upper limits of distribution are primarily

determined by physical factorsdetermined by physical factors

2.2. Lower limits of distribution are primarily Lower limits of distribution are primarily determined by biological factors (competition for determined by biological factors (competition for space and predation)space and predation)

• Starvation restricts upper reachesStarvation restricts upper reaches

• Larval settlement determines the limits of Larval settlement determines the limits of distributiondistribution

-- -- shorter period of inundation means reduced probability shorter period of inundation means reduced probability of settlement in upper reachesof settlement in upper reaches

-- larvae chose where they settle-- larvae chose where they settle

-- adult larval interactions affect settlement patterns -- adult larval interactions affect settlement patterns

Exceptions and Limitations of Exceptions and Limitations of RIPRIP4.4. In benign physical environments, predation is most In benign physical environments, predation is most

important in determining community compositionimportant in determining community composition

5.5. In harsh physical environments, predation intensity is In harsh physical environments, predation intensity is reduced and competition is most important in reduced and competition is most important in determining community compositiondetermining community composition

• Assumes prey have a greater physical tolerance than Assumes prey have a greater physical tolerance than predator, can find refuges in spacepredator, can find refuges in space

• Variations in recruitment determine the level of competitionVariations in recruitment determine the level of competition

• Importance of predator selectivity and competitive hierarchyImportance of predator selectivity and competitive hierarchy

• In same environment, both predation and competition are In same environment, both predation and competition are important, both for different life stagesimportant, both for different life stages