Shallow-water subtidal ecology

1. Pei-Yuan Qian Chapter 5: 179-235 Shallow-water subtidal ecology

2. Outline of Lecture • Definition • Environmental conditions • Sampling methods and problems • Community structure and distribution pattern • Introduction to some community

3. Definition • Subtidal---area of the oceans that lies between the area of lowest low water on the shore to the edge of the continental shelf at a depth of about 200 m. Overlying it are the waters of the neritic zone. • Most of this zone is composed of soft sediments, sand and mud, and a much lesser area of hard substrate.

4. Division of the oceans

5. Definition • Epifauna: Organisms living on the surfaces of substratum. • Infauna: Organisms living in the substratum • Macrofauna >0.5 mm in size • Meiofauna 0.062-0.5mm in size • Microfauna <0.062 mm

6. Environmental conditions • High turbulence--keeping inshore waters from becoming thermally stratified except for brief periods---nutrient abundance---high productivity---high population density of both zooplankton and benthic organisms. • Wave action---resuspension of fine particles of substratum • Variable salinity ( but does not change enough to be of ecological significance) • Variable temperature--definite seasonal change

7. Environmental conditions • Light penetration reduced by turbulence • Abundance of food • Low diversity of topographic features on soft bottoms--fewer infaunal species than epifauna species • Deposit feeders are dominant

8. Major types of subtidal habitats • Un-vegetated sedimentary environments • Hard substrates (dominated by low-encrusting plants and animals) • Kelp beds and forests • Seagrass

9. Parallel bottom communities: similar sediment types at similar depths around the world contain similar communities of organisms in which the dominant animals are similar ecologically.

10. SCUBA DIVER IN ACTION

11. Methods of sampling • Scuba diving • Close-range visual observations such as following larval dispersal of ascidians. • Precise sample location--easy to do transects • Experimental manipulations • Better quantitative works • Cheaper than other methods • Limits: only down to 40 meters

12. SUBMERSIBLE & MOTHER BOAT

13. Methods of sampling (con’t) • Submersible or submarine • Down to 6500 meters • Close-range visual observations (such as hot-vent observation in the deep sea) • Precise sample location • Close-range photo • Collect samples from deep sea with its mechanic arms or sucking guns • Experimental manipulation • Limits: too expensive to operate

14. GRABS AND DREDGES

15. Methods of sampling (con’t) • Dredge Components: • Heavy metal frames with cutting edges designed to move within the sediment • Attached burlap or chain bag collects the sediment behind   Problems: • Not precise (quantitative or location) • Not visible (what is in the bag is what you are getting) can be frustrating

16. Deep-sea bottom sampling gear (A) Epibenthic sled.

17. THREE TYPES OF GRABS

21. Methods of sampling (con’t) • Under water x-ray or camera system • Photo, monitoring, but can not collect specimen

22. Sedimentation Dahms 1997

23. General processes occurring within a sediment dominated by deposit feeders.

24. Biotic effects of burrowing organisms on substratum • Affect chemical properties--Chemical processes influenced by burrowing activity are • Rate of exchange of dissolved or absorbed ions, compounds, and gases across the sediment-water interface • For vertical gradients in Eh, pH, and pO2; depth of the RPD • Transfer of reduced compounds from below the RPD to the aerated surface sediment pore waters • Cycling of carbon, nitrogen, sulfur, and phosphorus.

25. Biotic effects of burrowing organisms on substratum • Increase the area of contact between the aerated and anoxic zones across the RPD (through the formation of tubes and the production of fecal pellets; macrofauna irrigating tubes and burrows pump oxygen-rich water into the sediment and produce oxidized burrows • Increase the heterogeneity of sediment through sediment feeding and the formation of fecal pellets.

26. Feeding biology and trophic structure • Benthic organisms classified by modes of obtaining food • Suspension feeders:collections of particle from water column • Deposit feeders: feeding on particles on or in the bottom by either pressing or aiming a feeding organ against or toward substratum. • Herbivore browsers: graze algae or marine grasses (not very common in soft bottom environment) • Carnivores:seize and capture animal prey, many are scavengers when live food is not abundant: most anemones, scleractinian corals trapping prey on tentacles armed with nematocysts specialized for puncturing, ensnaring or trapping with mucus; • Scavengers--feed actively on decaying tissues: crabs and urchins.

27. Carnivore feeders

28. Herbivore feeders

29. Deposit-feeders

30. Modes of deposit-feeding • Swallowers--ingested sediment many particles at a time with little particle size and qualitative selection.: Arenicola; sipunculis (peanut worm), urchin. • Tentacle feeders--use tentacular structure to gather detrital particles and transport them to the mouth, including sea cucumbers, nuculoid bivalves, tube-dwelling polychaetes • Surface siphon feeders--inhalent siphon ingests sediments like a vacuum cleaner, restricted to bivalves of superfamily Tellivacea • Setose deposit feeding--amphipod Corophium volutator scrapes surface detritus in its burrow with its gnathopods equipped with setae. • Other modes

31. Suspension-feeders

32. Modes of suspension feeding • Mucous-bag and mucous sheet– • Chaetopterusresides in a U-shaped tube & creates a current that is passed across a sheet of mucus stretched between a pair of specialized parapodia. The sheet fills up with particles & is rolled into a bag that is passed to the mouth • In ascidians, water enters an inhalent siphon, across a branchial basket studded with pores, mucous sheets across the basket's inner surface trap particles & cilia-aided tracts move mucous strings toward the esophagus.

33. Food of suspension-feeders • Phytoplankton, ranging from diatoms to flagellates • Bacteria suspended in sw, <5µ in diameter • Bacteria and other microorganisms living on inorganic particles and particulate organic detritus delivered by water current • Bacteria and other microorganisms living on particles resuspended from the bottom • Dissolved organic matter

34. Modes of suspension feeding • Ciliary-mucous mechanisms--mucus is also used to entrap suspended particles, cilia arranged in rows select particle and transport the particles; common in suspension-feeding polychaetes like Serpulids or Sabellids, bivalve, gastropods. • Setose suspension feeding--Current created by the movements of pairs of thoracic limbs are drawn through a series of filters formed by limbs equipped with setae (in arthropods) • Tentacle-tube feet suspension feeders--spionid polychaetes. • Passive suspension feeding

35. Benthic Association • Symbiosis-- refers to close relationships between unlike species, which seem to be either unharmful to either member or, more likely to be beneficial to one or both. (Does not include predator-prey relationship). • Commensalism--an association that is clearly to the advantage of one member (commensal) while not harming the other member (host). • Inquilinism--a special subdivision of commensalism, in which an animal (commensal) lives in the home of another (host), or in its digestive tract, without being parasitic.

36. Benthic Association • Mutualism--form of symbiosis in which two species associate to gether for their mutual benefit. In a mutualism relationship, the partners are often called symbionts • Parasitism--an association in which one species lives in or upon another and draws nourishment from that species at the expense of, or to the detriment of, the other (an association in which the advantage is solely to one member at the expense of the other.

38. Methods of sampling (con’t) • Shipboard-deployed gravity corer • Using weight to drive the corer into the bottom. • Take a sample of uniform depth and specified area • The box corer is a rectangular gravity corer that is guided into the bottom by a movable plunger mounted on a frame. A spade is released when the frame hits the bottom and digs into the sediment and closes the bottom of the corer as the frame is lifted by a wire.

39. Possible methods of food capture • Sieving--involves trapping particle with diameter greater than interfiber distances. • Direct interception--occurs when a particle following hydrodynamic streamlines comes within a distance of one particle radius. • Intertial impaction--occur when a particle deviates from the streamlines due to the particle's own inertia. • Motile particle deposition--occurs because small particles move randomly about relative to streamlines and may come within one particle radius of fiber

40. Deep-sea bottom sampling gear (B) Anchor dredge

42. Methods of sampling (con’t) • Grabs • Peterson grabs • With two or more sharp indigging sections. As grab hits the bottom & the supporting wire has some slack, the hook whose support depends on the wire's tension releases and allows a chain to pull the two sections closed • Problem: if the wire is suddenly slackened upon lowering, the device will fire prematurely. • Van-veen grab • Add a longer arms attached to the digging sections • Smith-McIntyre grab • Heavy spring-loaded device that digs efficiently in both sands and muds