Lecture 9 –INTERTIDAL ZONATIONBIOLOGICAL FACTORS

reproductive mode

competition larval settlement

predation

survival

grazing

BIOLOGICAL FACTORS

1. Grazing

-growth of Laminaria- zone ends abruptly

Why?

1. Grazing

Experiment done in New South Wales, Australia

Underwood (1980 Oecologia 46:201)

Used exclusion cages

1- Open 2 - Fence 3 - Roof 4 - Cage

Grazers excluded Grazers excludedGrazers inGrazers in

Normal ShadeShadeNormal

1- Open 2 - Fence 3 - Roof 4 - Cage

Grazers excluded Grazers excludedGrazers inGrazers in

Normal ShadeShadeNormal

No growth or recruitment

Recruitment but poor growth

No growth or recruitment

Recruitment and growth to nearly adult size

Therefore - upper limit dictated by exposure + grazers

2. PredationPisaster ochraceous on Mytilus californianus

R. Paine

2. PredationPisaster ochraceous on Mytilus californianus

2. PredationPisaster ochraceous on Mytilus californianus

Time (Years)

0 2 4 6 8 10

Height above chart datum

1.5

1.0

0.5

Pisaster removal begins Pisaster removal ends

3. Competition

Chthalamus Semibalanus

3. Competition

Millport, Isle of Cumbrae

3. Competition

EHWS

MTL

ELWS

Chthalamus zone

Semibalanus zone

3. Competition

EHWS

MTL

ELWS

Chthalamus zone

Semibalanus zone

Remove Semibalanus

3. Competition

EHWS

MTL

ELWS

Chthalamus zone

Semibalanus zone

Remove Chthalamus

3. Competition

Lifted Smothered Crushed ??

100

50

0

Source of Mortality

3. Competition

MHWS

MTL

MHWN

MLWN

MLWS

Larval settlement Effects of physical factors Competition

Chthamamus

Semibalanus

Distribution of Semibalanus and Chthalamus

Wethey 1983. Biol.Bull. 165:330

Semibalanus

Chthalamus

Wethey 1983. Biol.Bull. 165:330

Nahant, Mass.No Chthalamus

Guilford & Horse Island, Conn.Semibalanus & Chthalamus coexist

Distribution of Semibalanus and Chthalamus

Perc

ent c

over

by

each

spe

cies

100

50

100

50

100

50

Tidal Height

MHWN MLWN

Vertical-North

Vertical-West

10º Slope-South

ChthalamusSemibalanus

Wethey 1983. Biol.Bull. 165:330

Distribution of Semibalanus and Chthalamus

100

50

100

50

ChthalamusSemibalanus

Drip

DryPe

rcen

t cov

er b

y ea

ch s

peci

es

Tidal Height

MHWN MLWN

Wethey 1983. Biol.Bull. 165:330

Distribution of Semibalanus and Chthalamus

Wethey 1983. Biol.Bull. 165:330

Perc

ent c

over

by

each

spe

cies

Tidal Height

MHWN MLWNChthalamusSemibalanus

Increasing sun exposure

Distribution of Semibalanus and Chthalamus

Wethey 1983. Biol.Bull. 165:330Tidal Height

MHWN MLWN

Vertical-North

Vertical-West

10º Slope-South

ChthalamusSemibalanus

Set

tlem

ent d

ensi

ty (

no.

/cm

2

1.0

0.5

2.0

1.0

1.0

0.5

Distribution of Semibalanus and Chthalamus

4. Larval Settlement

Generalized life cycle for marine invertebrates

Dispersing larva (planktonic)

settle

juvenileadult

egg

4. Larval Settlement

Larval settlement Final distribution pattern

happens because of

1. Indiscriminate settlementand high mortality

2. Discriminate settlementand low mortality

4. Larval Settlement

Flustrellidra lives on Ascophyllum

Distribution of Bryozoans

Hurlbut 1991. J.Exp. Mar. Biol. Ecol. 147:103

4. Larval Settlement

Hurlbut ‘91 - Distribution of Bryozoans

Alcyonidium

Chondrus

FucusRock

Geukensia

Hurlbut 1991. J.Exp. Mar. Biol. Ecol. 147:103

4. Larval Settlement

Hurlbut 1991. J.Exp. Mar. Biol. Ecol. 147:103

4. Larval Settlement

Hurlbut ‘91 - Distribution of Bryozoans

FlustrellidraAscophyllum

Hurlbut 1991. J.Exp. Mar. Biol. Ecol. 147:103

4. Larval Settlement

Results

Flustrellidra

- larvae selectively settle on Ascophyllum- greater survivorship on Ascophyllum

Alcyonidium

-larvae show preferential settlement on Fucus and Chondrus - most adult colonies occur on rock

Hurlbut 1991. J.Exp. Mar. Biol. Ecol. 147:103

Summary

Observed distribution andabundance

temperaturedesiccation ice

wave exposure

reproductive modecompetition

larval settlementpredationsurvival

grazing