1. Lecture 9 –
INTERTIDAL ZONATION
BIOLOGICAL FACTORS

2. BIOLOGICAL FACTORS grazing competition larval settlement survival
reproductive mode
predation

3. 1. Grazing
-growth of Laminaria
- zone ends abruptly
Why?

4. 1. Grazing
Experiment done in New South Wales, Australia

5. Underwood (1980 Oecologia 46:201)
Used exclusion cages
1- Open
2 - Fence
3 - Roof
4 - Cage
Grazers in
Grazers excluded
Grazers in
Grazers excluded
Normal
Normal
Shade
Shade

6. Therefore - upper limit dictated by exposure + grazers
1- Open
2 - Fence
3 - Roof
4 - Cage
Grazers in
Grazers excluded
Grazers in
Grazers excluded
Normal
Normal
Shade
Shade
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

8. 2. Predation
Pisaster ochraceous on Mytilus californianus
R. Paine

9. 2. Predation
Pisaster ochraceous on Mytilus californianus

10. 2. Predation Pisaster ochraceous on Mytilus californianus
Pisaster removal begins
Pisaster removal ends
1.5
Height above chart datum
1.0
0.5
Time (Years)

11. 3. Competition
Chthalamus
Semibalanus

12. 3. Competition
Millport, Isle of Cumbrae

13. 3. Competition
EHWS
Chthalamus zone
MTL
Semibalanus zone
ELWS

14. 3. Competition Remove Semibalanus EHWS Chthalamus zone MTL
Semibalanus zone
ELWS

15. 3. Competition Remove Chthalamus EHWS Chthalamus zone MTL
Semibalanus zone
ELWS

16. 3. Competition
100 50
Lifted Smothered Crushed ??
Source of Mortality

17. 3. Competition Chthamamus Semibalanus MHWS MHWN MTL MLWN MLWS
Larval settlement
Effects of physical factors
Competition

18. Semibalanus Chthalamus Distribution of Semibalanus and Chthalamus
Wethey Biol.Bull. 165:330

19. Distribution of Semibalanus and Chthalamus
Nahant, Mass.
No Chthalamus
Guilford & Horse Island, Conn.
Semibalanus & Chthalamus coexist
Wethey Biol.Bull. 165:330

20. Distribution of Semibalanus and Chthalamus
100 50
Vertical-North
100 50
Vertical-West
Percent cover by each species
100 50
10º Slope-South
Chthalamus
Semibalanus
MHWN
MLWN
Tidal Height
Wethey Biol.Bull. 165:330

21. Distribution of Semibalanus and Chthalamus
100 50
Drip
Percent cover by each species
100 50
Dry
Chthalamus
Semibalanus
MHWN
MLWN
Tidal Height
Wethey Biol.Bull. 165:330

22. Distribution of Semibalanus and Chthalamus
Increasing sun exposure
Percent cover by each species
Chthalamus
Semibalanus
MHWN
MLWN
Tidal Height
Wethey Biol.Bull. 165:330

23. Distribution of Semibalanus and Chthalamus
1.0
0.5
Vertical-North
2.0
1.0
Settlement density ( no./cm2
Vertical-West
1.0
0.5
10º Slope-South
Chthalamus
Semibalanus
MHWN
MLWN
Tidal Height
Wethey Biol.Bull. 165:330

24. Generalized life cycle for marine invertebrates
4. Larval Settlement
Generalized life cycle for marine invertebrates
Dispersing larva (planktonic)
egg
settle
juvenile
adult

25. 4. Larval Settlement Larval settlement Final distribution pattern
happens because of
1. Indiscriminate settlement
and high mortality
2. Discriminate settlement
and low mortality

26. 4. Larval Settlement Distribution of Bryozoans
Flustrellidra lives on Ascophyllum
Hurlbut J.Exp. Mar. Biol. Ecol. 147:103

27. 4. Larval Settlement Hurlbut ‘91 - Distribution of Bryozoans Chondrus
Geukensia
Alcyonidium
Rock
Fucus
Hurlbut J.Exp. Mar. Biol. Ecol. 147:103

28. 4. Larval Settlement
Hurlbut J.Exp. Mar. Biol. Ecol. 147:103

29. 4. Larval Settlement Hurlbut ‘91 - Distribution of Bryozoans
Flustrellidra
Ascophyllum
Hurlbut J.Exp. Mar. Biol. Ecol. 147:103

30. larvae selectively settle on Ascophyllum
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 J.Exp. Mar. Biol. Ecol. 147:103

31. Observed distribution and
Summary
desiccation
ice
temperature
wave exposure
reproductive mode
grazing
competition
larval settlement
survival
predation
Observed distribution and
abundance