Transcript Subtidal ecology

Shallow-water
subtidal ecology
Pei-Yuan Qian
Chapter 5: 179-235
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
Definition
Epifauna: Organisms living on the
surfaces of substratum.
Infauna: Organisms living in the
substratum
Macrofauna
Meiofauna
Microfauna
>0.5 mm in size
0.062-0.5mm in size
<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 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
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 oxygenrich 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, tubedwelling 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 suspensionfeeders
 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 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.
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)
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