Estuaries and Intertidal Communities

1. Estuaries and Intertidal Communities Chapters 11 and 12

2. Intertidal Communities • The effects of the tides and the nature of the community depends on the substrate. • Two major types of intertidal communities: • Rocky shore communities • Soft bottom tidal communities

3. Rocky Shore Communities • Occur mostly on active margins. • Most rocky shore inhabitants live on the rock surface- called epifauna. • Low tide- epifauna are exposed to the air. • Emersion time- time spent out of the water. • Emersion time is longer the higher up the intertidal you go.

4. Challenges to epifauna • Water loss- they will dessicate if exposed too long. • Two mechanisms for coping- • Run and hide, or ‘clam up’ • Run and hide- escape to tide pools or hide in crevices • Clam up- protective shell to hold in water.

5. Some Shelled Residents

6. Whelks

7. Cross-Section of Whelk

8. Temperature and salinity • Exposure to the air creates greater changes in temperature and salinity. • Air has greater daily temp. range, and is flooded with fresh water during rains. • Tide pools can experience very large temperature and salinity variations.

9. Feeding strategies • Filter feeders cannot feed at low tide. • must be submerged to filter • often clam up during low tide • Deposit feeders are rare in the rocky intertidal zone – few sediments to “hold” nutrients • Animals higher in the intertidal have less time to feed, often grow more slowly than animals lower in the intertidal.

10. Wave Energy • Incoming waves refract along the shore. • This causes waves to come in parallel to the shore. • Headlands receive the most wave impact. • Bays receive less wave energy.

11. Wave Refraction

12. Wave energy on a coastline

13. Coping with wave energy • Organisms that live on exposed shores must deal with waves. • Strategies: • Holdfasts • Strong attachments • Thick shells • Low Profiles • Flexibility • Finding Shelter

14. Limiting Resources • In rocky intertidal communities, food is abundant. • Space is the greatest limiting factor- all sessile organisms will die if not strongly attached. • Competition for space is intense. • Rocky intertidal zones exhibit vertical zonation- distinct bands at different heights.

15. Vertical Zonation on Rocky Shores • Upper intertidal- lichens, cyanobacteria, and periwinkles. • Middle Intertidal- Barnacles dominate in upper area. Lower areas compete with mussels and predators. • Mussels are the dominant space competitors. They are limited by air exposure and predation by sea stars. • Lower intertidal- red, green and brown seaweeds.

16. Vertical Zonation

17. Vertical Zonation

18. Soft bottom intertidal communities • Substrate is sediment- sand, clays, mud. • Fine sediments are often found in calm areas. • Coarse sediments on coasts that experience wave action. • Many animals burrow into the sediments, they are called infauna.

19. Sediment sizes

23. Life in the sediment • Less dessication- sediments hold water. • Many deposit feeders- most feed on detritus. Fine sediments have more detritus, sand has less. • Oxygen- decaying organic matter uses up oxygen- therefore interstitial water often is lacking in oxygen. • Anaerobic bacteria thrive here- produce H2S. • Other infauna must pump O2- rich water from above the sediment, or have extra hemoglobin and slow metabolism.

24. Life in the sediment- cont’d • Some worms help to oxygenate the sediment by mixing up the sediment. • Mobility- many soft bottom animals burrow in the sediment. • clams use their muscular foot. • Many tiny species live in between the sand grains, they are called meiofauna.

25. Clam Locomotion

26. Feeding strategies • Most soft bottom species feed on detritus. • Some plankton is also in their diet. • Deposit feeders- sea cucumbers and worms eat sediment, and digest the organic matter. • Sand dollars- use tube feet to pick up organic particles. • Clams use long siphons to reach nutrient rich surface sediment.

27. Predation • Moon snails burrow in the sediments looking for clams. • use their radula to drill through the clam shell and eat it. • During low tides, birds are important predators.

29. Zonation in Soft Bottom Intertidal Communities • Less obvious than on rocky shores. • Upper beach- Beach hoppers (sand fleas), ghost crabs and fiddler crabs. • Lower beach- Polychaete worms, clams, moon snails. • Just below tide line- sand dollars, blue crabs, sea cucumbers • On muddy shores- very little zonation.

31. Estuaries • Estuaries are semi-enclosed areas where fresh and sea water meet. • Low in biodiversity, but high in productivity. • Often among the most affected by human activity. • Large cities are often built in estuary areas or along the rivers that feed them. • Dredging or filling in of these areas, as well as pollution can be disastrous.

32. Types of Estuaries • Drowned river valleys- formed after the last Ice age - like the Chesapeake Bay • caused by sea level rise. • Bar Built estuaries-Sand bars and barrier islands are common. • Formed by deposition that isolates a body of water from the open ocean- like the Outer Banks.

33. Cape Hatteras is a bar-built estuary.

34. Types of Estuaries • Tectonic estuaries- formed when the land subsided (sank) due to plate movements. • Ex- San Francisco Bay • Glacial estuaries- also called fjords. • Formed by retreating glaciers carving out valleys along the coast. • Common in Alaska and Norway.

35. A fjord in New Zealand

36. Salinity and Estuaries • Dramatic fluctuations in salinity are common throughout the day. • Salinity drops as you travel upstream. • Salinity often increases with depth. • As salty tidal water come in, it forms a ‘salt wedge’- fresher, less dense water flows on the surface.

37. Salinity varies in an Estuary

38. During High tide

39. During Low Tide

40. Coping with Salinity changes • How far up and estuary an animal can live depends upon how well it can tolerate low salinities. • Animals that can tolerate a wide range are Euryhaline. • Stenohaline organisms can only survive a narrow range- they are less successful in estuaries.

41. Dealing with Osmosis • Estuarine species must be good osmoregulators or osmocomformers. • Many species do both, during extreme salinity fluctuations. • Many invertebrates osmoregulate at low salinities, and osmoconform in high salinities.

42. Other Factors in Estuaries • Substrate- like soft bottom intertidal communities. • Often less primary production by plankton due to poor water clarity. • Anoxic conditions are common. In these areas, anaerobic bacteria thrive.

43. Types of Estuarine Communities • Open water- Limited primary production. • -rich in shellfish- 90% of commercially important fish and shellfish in the Gulf of Mexico rely on estuaries. • Often called the oceans nurseries because many juvenile fishes seek shelter in estuaries. • Migration routes for catadromous and anadromous fishes.

44. Types of Estuarine Communities • Mudflats- found mostly where there are gentle slopes. • Mud exposed at low tide- community must deal with dessication as well as salinity changes. • Only a few producers like sea lettuce • Bacteria and burrowing infauna are common. • Worms, clams, snails, ghost shrimp, fiddler crabs are common • Important feeding grounds for shorebirds

45. Birds feeding on a mudflat at low tide

46. Mudflats on Prince Edward Island

48. Resource Partitioning- the different shapes and lengths of these birds beaks allow them to forage for different foods

49. Fiddler crabs hide in the sand and come out at low tide to feed. • Feed on detritus in the sand. • Male fiddlers have a one large claw to attract mates. • They attract mates by waving their claws at females, and by fighting each other. • Different species of fiddler crabs have different waving patterns to attract the ‘right’ mate

50. Sandpipers use their bills as probes in the sand