The Intertidal,Part 2 and Meiofauna

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The Intertidal,Part 2and Meiofauna

• Lecture 12
• Marine Biology

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Intertidal Sandy Shores
The most important factor is wave action Beaches
are defined by swash and backwash Swash - water
running up the beach (builds beaches) Backwash -
water running down the beaches (removes
beaches
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Swash and Backwash
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Beaches, cont.

• High wave action/strong waves leads to steep
  beaches with coarse particulate size.
• Low wave action leads to gentle sloping,
  fine-grained beaches
• Wave induced substrate movement - particles are
  picked up and redeposited. They are moved and
  sorted.
• Heavy wave action results in smaller particles
  which remain in suspension and are carried from
  the beach.
• Light wave action results in smaller depth of
  sediment being disturbed.

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Beach Types
Beach types Dissipative - strong wave action
and surf with fine sediments. Beach is flat and
maximally eroded. Swash is gentle. Wave energy
consumed by the surf. Reflective - wave action
is minimal. Sediment is coarse. No surf zone.
Large swash. Steep slope. Backwash and swash
collide to deposit sediments.
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Dissipative and Reflective Beaches
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Beaches, cont.
Abundance and diversity of macrofaunal organisms
are strongly correlated with particulate size and
slope. High abundance occurs in very exposed,
coarse-grained sediments with steep slopes versus
fine sand beaches, flatter slopes where wave
action is dissipated in surf rather than on the
beach. Thus, very exposed beaches can support
rich megafauna if it is a dissipative beach and
not reflective. Higher biomass of filter-feeders
correlated with dissipative conditions.
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Beaches, cont.
Seasonal changes are often dramatic. Few
organisms can permanently occupy surfaces on sand
or gravel beaches. This leads to a barren
appearance. Oxygen content can become limiting
in substrate. The finer the substrate, the higher
the potential for anoxic conditions to occur with
fewer organisms able to persist in these low
oxygen zones.
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Adaptations
Deep rapid burrowing (avoids dislodgement) Smooth
shells reduce surface resistance to facilitate
burrowing.Heavy shells anchor in the
substrate. No plants or sessile organisms in this
habitat.Annelids, crustaceans, and mollusks
dominate the infaunal diversity either as
suspension or filter feeders. Differences in
temperate and tropical communities exist with
respect to faunal composition
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Adaptations
Tube-building by worms and other invertebrates
combat sediment instability. Saturation of oxygen
in blood pigments occurs at very low oxygen
tensions (hemoglobin, hemerythrin occur as blood
pigments in many species) Glycogen stores -
function to provide energy under anaerobic
conditions (enable aerobic metabolism)
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Tide Pool Organisms
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Tidepool
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Fine and Coarse Grained Organisms
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Beach Types
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Intertidal Sand Organisms - Clams
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Organism Distribution in Sand
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New England Sand Community
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Sand Community Zonation
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Muddy Shores (mudflats)
Think of a muddy shore as a very protected
shore. - very fine sediments, rich in organics
(characteristic of
estuaries, salt marshes,
and mangroves) Habitat is completely
protected from wave action and found in proximity
to sources of very fine sediments such as
rivers.Anaerobic conditions prevail - The
transition between aerobic and anaerobic layers
referred to as redox potential discontinuity
layer (rpd).
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Muddy Shores, cont.
A rapid change in redox potential occurs within
the first few mms of the sediment surface, going
from ---gt - Below the rpd, a decomposition of
organic matter is by anerobic bacteria
(chemolithotrophic bacteria) This zone is
identified by transition from brown to grey to
black
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Muddy Shores, cont.
Why is this important? Reduced compounds
diffuse upwards where oxygen occurs and bacteria
oxidize compounds such as CO2, NO3, and SO4 -
these are important chemicals for starting the
base of the food chain. In the anaerobic zone,
bacteria reduce compounds and release phosphate.
This is crucial for new plant growth. In fact,
plant growth usually begins directly above the
hypoxic zone.
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New England Mudflat Community
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Intertidal Fish
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Intertidal Fish
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Intertidal Birds
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Intertidal Interactions
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Meiofauna
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Meiofauna, cont.
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Meiofauna, cont.
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Benthic Meiofaunal Food Web
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Meiofaunal Types
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Meiofauna Images
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Distribution of Meiofauna in Sediments