14 -The Tidelands Rocky Shores, Soft-Substratum Shores, Marshes, Mangroves, and Estuaries

1. 14 -The TidelandsRocky Shores, Soft-Substratum Shores, Marshes, Mangroves, and Estuaries Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton ©Jeffrey S. Levinton 2001

2. ZONATION -universal feature of rocky shores, also true of soft sediments but not as distinct (3-dimensional nature, owing to presence of burrowing organisms and others within the sediment)

3. Example of zonation on rocky shore, along a gradient of wave exposure on a site in the United Kingdom

4. 2 SPATIAL GRADIENTS: • Vertical • Horizontal - changing wave exposure

5. Vertical gradient • Heat Stress, Desiccation • Gas Exchange - dissolved oxygen • Reduced feeding time • Wave shock • Biological interactions - competition, predation

6. Heat Stress/Desiccation • Varies on small spatial scales • Body size, shape are both important - reduction of surface area/volume reduces heat gain and water loss • Evaporative cooling and circulation of body fluids aids in reduction of heat loss • Well sealed exoskeletons aid in retarding water loss (acorn barnacles, bivalves)

7. Vertical Gradients • Higher intertidal organisms more resistant to heat and desiccation stress than lower intertidal organisms

8. Vertical Gradients 2 • Higher intertidal organisms more resistant to heat and desiccation stress than lower intertidal organisms • Higher intertidal animals have less time to feed. Sessile forms therefore grow more slowly than lower intertidal organisms

9. Vertical Gradients 3 • Higher intertidal organisms more resistant to heat and desiccation stress than lower intertidal organisms • Higher intertidal animals have less time to feed. Sessile forms therefore grow more slowly than lower intertidal organisms • Mobile carnivores can feed only at high tide, usually feed more effectively at lower tide levels, which are immersed a greater proportion of the day

10. Oxygen consumption • Intertidal animals usually cannot respire at time of low tide

11. Oxygen consumption 2 • Intertidal animals usually cannot respire at time of low tide • Respiratory organs (gills of polychaetes, bivalves) must be moist to acquire oxygen, and therefore are usually withdrawn at low tide

12. Oxygen consumption 3 • Intertidal animals usually cannot respire at time of low tide • Respiratory organs (gills of polychaetes, bivalves) must be moist to acquire oxygen, and therefore are usually withdrawn at low tide • Some animals greatly reduce metabolic rate at time of low tide

13. Oxygen consumption 4 • Intertidal animals usually cannot respire at time of low tide • Respiratory organs (gills of polychaetes, bivalves) must be moist to acquire oxygen, and therefore are usually withdrawn at low tide • Some animals greatly reduce metabolic rate at time of low tide • Some high intertidal animals can respire from air (e.g., some mussels) even at low tide, as long as air is not too dry

14. Pacific sand bubbler crab, Scopimera inflata, has membrane on each leg (shaded green), which exchanges gas from air into arterial blood

15. Wave shock 1 • Abrasion - particles in suspension scrape delicate structures

16. Wave shock 2 • Abrasion - particles in suspension scrape delicate structures • Pressure - hydrostatic pressure of breaking waves can crush compressible structures

17. Wave shock 3 • Abrasion - particles in suspension scrape delicate structures • Pressure - hydrostatic pressure of breaking waves can crush compressible structures • Drag - impact of water can exert drag, which can pull organisms from their attachments to surfaces, erode particles from beaches and carry organisms from their burrows or living positions

18. Causes of Vertical Zonation 1 • Physiological tolerance of different species at different levels of the shore

19. Causes of Vertical Zonation 2 • Physiological tolerance of different species at different levels of the shore • Larval and adult preference - larvae may settle at time of high tide at high levels, mobile organisms have a series of behavioral responses that keep them at certain levels of shore

20. Causes of Vertical Zonation 3 • Physiological tolerance of different species at different levels of the shore • Larval and adult preference - larvae may settle at time of high tide at high levels, mobile organisms have a series of behavioral responses that keep them at certain levels of shore • Competition - species may be capable of excluding others from certain levels of the shore

21. Causes of Vertical Zonation 4 • Physiological tolerance of different species at different levels of the shore • Larval and adult preference - larvae may settle at time of high tide at high levels, mobile organisms have a series of behavioral responses that keep them at certain levels of shore • Competition - species may be capable of excluding others from certain levels of the shore • Predation - mobile predators more effective usually on the lower shore: affects distributions of vulnerable prey species

22. A rocky shore in the U.K. At the time of low tide on hot dry days, the gastropod Nucella lapillus retreats into the crack where it is moist and cool. Note the areas cleared of mussels adjacent to the cracks.

23. Beaches and Wave Action • Exposed beaches - strong erosion and sediment transport • Difficult environment for macrobenthos to survive and maintain living position • Swash riding - means of moving up and down with rising and falling tide - maintain position in wet but relatively non-eroded tidal level

24. Swash Riding - found in Mole Crab Emerita, some species of the bivalve Donax

25. The mole crab, Emerita talpoida, burrowing into an exposed beach in North Carolina

26. Interspecific Interactions and Zonation • Why are there vertical zones, with dominance often of single sessile species within a zone?

27. Interspecific Interactions and Zonation 2 • Why are there vertical zones, with dominance often of single sessile species within a zone? • Possible explanations: (1) Differences in tolerance of species at different tidal heights (2) Competitive interactions (3) other factors

28. Investigation by Field Manipulation Experiments • Classic experiments of Joseph Connell • Studied factors controlling vertical zonation by selective inclusion and exclusion of hypothesized interacting species

29. Rocky Shores of Scotland - Key Species in Connell’s study • Chthamalus stellatus - acorn barnacle, ranging from subtropical latitudes to northern British isles • Semibalanus balanoides - acorn barnacle, ranging from Arctic to southern British isles, overlapping in range with C. stellatus • Nucella lapillus - carnivorous gastropod, drills and preys on barnacles

30. Connell Field Experiment • transplant newly settled Chthamalus to all tidal levels • caged some transplants, excluded Nucella • allow Semibalanus to settle and cleaned Semibalanus cyprids off some rocks

31. Results of Connell Experiment • Chthamalus survival poorer in presence of Semibalanus • Chthamalus survival decreased where Semibalanus grew the fastest • Chthamalus survival increased in high intertidal due to its resistance to desiccation

32. Conclusions from Connell Experiments • Predation important in lower intertidal • Biological factors control lower limit of species occurrence • Physical factors control upper limit • Community structure a function of very local processes (larval recruitment not taken into account as a factor)

33. Desiccation Chthamalus MHW spring MHW neap Mean tide MLW neap MLW spring Competition Chthamalus Semibalanus Semibalanus Wave Shock Predation Physical factors Interspecific effects Adult density Settlement of cyprids

34. Mytilus “byssing” Nucella Nucella lapillus

35. Dense population of the barnacle Semibalanus balanoides

36. Soft Sediments • Zonation not as distinct as on rocky shores • Competition - demonstrated by experiments

37. Mud Flat Field Experiments by Sarah Woodin • burrowing Armandia brevis versus tube builders • Cage placed on sediment with top screen: tube builders settled on screen, Armandia burrowed through and reached higher densities than when screen was absent and tube builders settled directly in sediment and established tubes

38. Soft Sediments - Vertical Stratification • Dominant species found at different levels below sediment-water interface • Experimentally reduce density of deep-dwelling clams, remaining individuals grow faster - demonstrates effect of density • Removal of shallow dwelling species of bivalves has no effect on growth of deeper-dwelling species

39. Occurrence of various bivalves at different burrowing depths in a sand flat in southern California

40. Predation and Species Interactions • Predators reduce prey density • Prey species compete • Conclude: predation may promote coexistence of competing prey species

41. Field Experiment of Robert Paine • Rocky shores of outer coast of Washington State • Principle predator - starfish Pisaster ochraceus • Pisaster preys on a wide variety of sessile prey species, including barnacles, mussels, brachiopods, gastropods

43. Pacific coast starfish Pisaster ochraceus, flipped over Left: eating a mussel, Right: eating barnacles

44. Mussel bed, Tatoosh Island, Washington

45. Paine Experiment and Results 1 • Removal of Pisaster ochraceus

46. Paine Experiment and Results 2 • Removal of Pisaster ochraceus • Successful settlement of recruits of mussel Mytilus californianus

47. Paine Experiment and Results 3 • Removal of Pisaster ochraceus • Successful settlement of recruits of mussel Mytilus californianus • Other species greatly reduced in abundance, Mytilus californianus became dominant

48. Paine Experiment and Results 4 • Removal of Pisaster ochraceus • Successful settlement of recruits of mussel Mytilus californianus • Other species greatly reduced in abundance, Mytilus californianus became dominant • Conclude: Pisaster ochraceus is a keystone species, a species whose presence has strong effects on community organization mediated by factors such as competition and predation

49. Larval Recruitment Exerts Strong Effects1 • Results from manipulative experiments usually depend upon steady recruitment of larvae of competing species

50. Larval Recruitment Exerts Strong Effects 2 • Results from manipulative experiments usually depend upon steady recruitment of larvae of competing species • What if recruitment is variable?