Pei-Yuan QianChapter 5: 179-235

Shallow-water subtidal ecology

Outline of Lecture Definition Environmental conditions Sampling methods and problems Community structure and

distribution pattern Introduction to some community

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.

Division of the oceans

Division of the oceans

DefinitionEpifauna: Organisms living on the

surfaces of substratum. Infauna: Organisms living in the

substratum Macrofauna >0.5 mm in sizeMeiofauna 0.062-0.5mm in sizeMicrofauna <0.062 mm

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

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

Major types of subtidal habitats

Un-vegetated sedimentary environments

Hard substrates (dominated by low-encrusting plants and animals)

Kelp beds and forests Seagrass

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.

SCUBA DIVER IN ACTION

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

SUBMERSIBLE & MOTHER BOAT

Methods of sampling (con’t)

Submersible or submarineDown to 6500 metersClose-range visual observations (such as

hot-vent observation in the deep sea)Precise sample locationClose-range photoCollect samples from deep sea with its

mechanic arms or sucking gunsExperimental manipulation

Limits: too expensive to operate

GRABS AND DREDGES

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

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

THREE TYPES OF GRABS

Methods of sampling (con’t)

Under water x-ray or camera system

Photo, monitoring, but can not collect specimen

Sedimentation

Dahms 1997

General processes occurring within a sediment dominated by deposit

feeders.

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.

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.

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.

Carnivore feeders

Herbivore feeders

Deposit-feeders

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

Suspension-feeders

Modes of suspension feeding

Mucous-bag and mucous sheet– Chaetopterus resides 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.

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

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

  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. 

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.

Methods of sampling (con’t)

Shipboard-deployed gravity corerUsing 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.

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

Deep-sea bottom sampling gear (B) Anchor dredge

Methods of sampling (con’t)

GrabsPeterson 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 grabAdd a longer arms attached to the digging sections

Smith-McIntyre grabHeavy spring-loaded device that digs

efficiently in both sands and muds