Hard Substrate Communities

1. Hard Substrate Communities Hard substrate = rocks, old shells, pilings, jetties, piers, docks Intertidal – perhaps best know marine community

2. Tides = periodic rise and fall of sea level • Caused by gravitational attraction of sun and moon and centrifugal force generated by the rotation of the earth-moon system around the sun • Periodicity of 24 hours, 50 minutes

3. gravitational attraction: sun and moon pull at the Earth’s oceans, causing a tidal bulge • the tidal influence of the Moon is about twice that of the Sun

4. Two classifications of tide based on the orientation of the Sun and Moon. • Spring tide : Sun, Moon and Earth are all in a line (full or new moon), Sun and Moon act together to create one large tidal bulge, and causes the greatest tidal differences because the. • Neap tide: Sun and Moon are at right angles from each other (quarter moon phase), when the, smaller tidal bulge. • distance of Moon: 50K km difference. perigee (nearest), the gravitational pull is ~40% greater than at apogee (farthest).

7. Approximately two high tides and two low tides each day • when it is high tide at one coastal location, it is low tide along a different coast a quarter of the way around the Earth. • Bay of Fundy, eastern Minas Basin, on the - Moon near perigee @ spring tide, HT up to 16 meters above LT. • The geogr. location, shape of the shoreline, water depth key reasons for tidal variations.

9. Result of the tides – • Exposure in the air for periods every day • Greater temperature differences • Desiccation/water loss – time of exposure changes as tide advances • Intense solar radiation

10. Waves • Mechanical effect • Creates a “splash zone” • Mixing – chemicals, dissolved gases, suspended particles

11. Salinity changes • Rainfall, freshwater runoff • Tidal pools – evaporation exceeds precipitation

16. Barnacles

17. Barnacles

18. Mytilus californianus

19. Nucella (Thais)

20. Limpets

21. Starfish - Pisaster

22. Sea Anemones

24. Tunicates

26. Bryozoans

27. Sea Urchins

28. Algae

32. Adaptations – Organisms • Minimize water loss/desiccation during exposure • Hide out in most crack, crevice, under algae • Tolerate tissue desiccation, rehydrate at high tide • Structural behavioral modifications – close up, clamp down, mucus, gills in cavity

33. Adaptations – Organisms • Minimize thermal stress • Large size, surface/volume ratio • Light/heat reflection • Evaporative cooling

34. Adaptations – Organisms 3. Avoid destruction in waves • Attach to substrate • Thicker shells • Clamp to substrate 4. Salinity stress

35. Conspicuous horizontal banding, or zonation of organisms

36. Stephenson & Stephenson 1949universal scheme to describe • Supralittoral – splash zone • Littorina (periwinkle), encrusting lichens and algae • Midlittoral – barnacle and mussels zone • Infralittoral – algae and more diverse mix of animals • Sublittoral – subtidal zone

37. Why? • Period of submergence – “critical tidal level” (Doty 1945) • Desiccation – sets upper limits to organisms • north vs south-facing slopes • irregularities • Thermal stress • Sunlight

38. Joseph Connell 1961 Coast of Scotland: Chthamalus stellatus Balanus balanoides Thais lapillus (now Nucella)

40. Robert Paine 1966 • Observed structure of the food web in rocky intertidal from Washington to Costa Rica • Washington – predatory starfish Pisaster and Nucella, the drill – lots of diversity • Costa Rica – no starfish, the drill Nucella is the top predator – less species diversity • What was going on?? • Went back to Washington and experimented

41. Paine’s experiments: • Removed starfish from rocks and observed results • With Pisaster ~ 15 species • Without ~ 8 species (plots dominated by Mytilus, the best competitor for space) • Pisaster - “Keystone species” – indirectly controls the structure of whole community

42. Connell in California (1970) • Balanus glandula (like Chthamalus) • Balanus cariosus • Refuge in space (Balanus glandula) • Refuge in size (Balanus cariosus)

44. Paul Dayton 1971 Space is key – processes involved in getting, keeping, and using space • Physical stress – desiccation, etc. • Physical disturbance – waves, drift logs • Predation – biological disturbance • Competition • Natural death

45. Dayton’s experiments: • Fucus – whip effecton barnacles vs protection from desiccation • Treatment = removalof Fucus • Limpets – eat algae; disturb and/or eat barnacles • Treatment = “dog dishes” to exclude limpets • Thais – drills mussels and barnacles • Treatment = cages to exclude • Pisaster – eats mussels and barnacles, etc. • Treatment = removal

46. Dayton’s conclusions: • Sessile marine organisms compete for space • Three levels of “biological disturbance” • Grazing by limpets • Predation by Thais/Nucella • Predation by Pisaster • Pattern in nature = mosaic of disturbance and recovery; disturbance maintains patchiness, keeps diversity high

47. Impact of Connell, Paine, and Dayton’s work on field of ecology • Shift in thinking about how communities are organized • Earlier view – competitive dominant has broadest niche, diversity the result of specialization to avoid competition • New view – dominants often less abundant, inferior competitors can have broader niche, predators and disturbance create diversity by preventing competition

48. Rocky Intertidal Paradigm • Upper limits of distribution are primarily determined by physical factors • Lower limits of distribution are primarily determined by biological interactions (competition for space and predation) • Predation or physical disturbance can prevent competitive exclusion (enhancing species diversity) by keeping superior competitors at low densities • In benign physical environments, predation is most important in determining community composition • In harsh physical environments, predation intensity is reduced and competition is most important in determining community composition

49. Exceptions and Limitations of RIP • Upper limits of distribution are primarily determined by physical factors • Lower limits of distribution are primarily determined by biological factors (competition for space and predation) • Starvation restricts upper reaches • Larval settlement determines the limits of distribution -- shorter period of inundation means reduced probability of settlement in upper reaches -- larvae chose where they settle -- adult larval interactions affect settlement patterns

50. Exceptions and Limitations of RIP 4.In benign physical environments, predation is most important in determining community composition • In harsh physical environments, predation intensity is reduced and competition is most important in determining community composition • Assumes prey have a greater physical tolerance than predator, can find refuges in space • Variations in recruitment determine the level of competition • Importance of predator selectivity and competitive hierarchy • In same environment, both predation and competition are important, both for different life stages