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

4. 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)

5. Zonation claimed to be universal in mid- and high-latitude rocky shores, but there often are exceptions (a) a black lichen zone (b) a periwinkle (littorine gastropod) zone with sparse barnacles (c) a barnacle-dominated zone either overlapping with mussel-dominated zone or with mussels below (d) a zone dominated variously, but usually by seaweeds

6. 2 SPATIAL GRADIENTS: • Vertical • Horizontal - changing wave exposure

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

8. Vertical gradient • Heat stress, desiccation • Gas exchange - dissolved oxygen • Reduced feeding time • Wave shock • Biological interactions - competition, predation

9. 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)

10. Heat Stress/Desiccation • Stress can be measured in terms of energy budgets • Heat shock proteins can be used to assay temperature stress, higher intertidal species produce fewer HSP than low intertidal species when stressed with high temperature • Heat shock proteins interact with seasonal acclimation; summer acclimated mussels produce less HSP at a higher threshold temperature than winter acclimated mussels

11. Tidepool, Tatoosh Island, Washington State, anemones, corals live in moister microhabitats; barnacles and mussels are better protected against desiccation and live in drier microhabitats

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

13. Vertical Gradients Cell stability (ciliary function) is retained at higher temperatures for higher intertidal gastropod species of genus Nerita

14. Vertical Gradients Mobile species can move to appropriate level of the intertidal zone. The contribution of behavioral responses of the high-intertidal gastropod Littorina neritoides to the regulation of its vertical position on rocky shores.

15. Oxygen Consumption • 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 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

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

17. Wave Shock • 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. Swash riders: move up and down to maintain burrowing position in moist sand, as tide rises and falls; includes some bivalves, burrowing mole crab Emerita

19. Causes of Vertical Zonation • 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 juveniles/adults 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 • Behavior - selective movement

20. Interspecific Competition - Space Limiting Within and Between Species

21. Predation - mobile carnivores are more effective lower in the intertidal 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

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

23. Interspecific Interactions and Zonation • 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) predation changes with tidal level

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

25. 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

26. Connell Field Experiment • Transplanted newly settled Chthamalus to all tidal levels • Caged some transplants, excluded Nucella • Allowed Semibalanus to settle and cleaned newly settled Semibalanus off some rocks

27. 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

28. 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)

29. 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

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

31. 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

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

33. Rocky shore food web studied by Robert Paine See Paine, R. T. 1966, American Naturalist

34. Paine Experiment and Results • 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

35. Starfish tend to aggregate on the lower part of the shore and predation is concentrated lower down; starfish aggregate near new mussel recruits.

36. Pisaster ochraceus, concentrated at bottom of mussel bed

37. Disturbance as a Factor in Intertidal Community Structure • Disturbances are physical events that influence the distribution and abundance of organisms • Disturbances may reduce abundance of competing species • Disturbances may therefore allow coexistence of competitively inferior species or may allow colonization of species adapted to disturbance

38. Postelsia palmaeformis, the palm seaweed, invades rocks that have been severely disturbed by storms; spores are released and travel just a few centimeters from the plant, allowing local spread of a colonizing individual Blanchette, C.A. 1996, J. Exp. Mar. Biol. Ecol. 197:1-14

39. Spatial Scale of Disturbance Is Crucial in Subsequent Colonization Events • A very small scale disturbance in a mussel bed might just result in the mussels moving and sealing off the opened patch • Larger patches might be colonized by other species, and the patch might last many months or even indefinitely • Therefore, spatial scale of disturbance might affect the spatial pattern of dominance of species, creating a mosaic of long-lived patches

40. Spatial Scale Matters • Cannot extrapolate all interactions at small scales to large scales • Alternative stable states at some large spatial scale • Thus large patches created by disturbance may be qualitatively different than small scale interactions - outcomes may be different

41. Disturbance and spatial scale: events following the opening of a small and large patch in a Pacific coast mussel bed See Suchanek,T.H. 1981 Oecologia 50: 143-152

42. Larval Recruitment Exerts Strong Effects • Results from manipulative experiments usually depend upon steady recruitment of larvae of competing species • What if recruitment is variable? • Competitively superior species might not take over, owing to low rates of recruitment • Recruitment might be reduced if currents are not favorable, high water flow results in flushing of larvae from inshore habitates, poor year for phytoplankton results in poor year for success of plankton-feeding larvae

43. The effects of variation of tidal flushing on larval recruitment in a semienclosed coastal area, such as a bay

44. Settlement rate of the barnacle Semibalanus balanoides in different years (dots) as a function of flushing time of Narragansett Bay, Rhode Island. High rainfall = high flushing rates

45. Water Flow and Community Structure

46. Soft Sediment Intertidal • Higher intertidal species burrow more deeply • Zonation not as distinct as on rocky shores • Water retention reduces vertical desiccation and temperature stress gradients

47. The depth of burrowing is deeper in the intertidal, where exposure to desiccation and temperature variation at the sediment surface is greatest

48. Soft Sediment Competitive Interactions Mud Flat Field Experiments by Sarah Woodin • Burrowing Armandia brevis versus tube builders • Topless cage - with and without top screen • Results: with screen, tube builder larvae settle on screeen, Armandia burrows through and settle on bottom; without screen - Armandia and tube builders settle. --> Armandia less dense in bottom without screen • Interpretation: Space is limiting

49. Saccoglossus bromophenolosus Some burrowing species produce Br-poisons, discourages settlement of other species

50. 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