The Ecology and Biodiversity of HK Sandy Shores

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The Ecology and Biodiversity of HK Sandy Shores

• YSCN0024
• 6th April 2007

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Sandy versus Rocky Shores

• Why are some shores muddy, or sandy, or rocky?

• Main factors are
• topography (surface structure)
• Wave/current energy

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Energy of Coastal Environments
Energy is related to water current speeds and
degree of wave action Low current speeds ?
deposition of particles High current speeds ?
erosion of particles
Muddy shore Sandy shore
DEPOSITIONAL shore
EROSIONAL shore
Boulder shore Rocky shore
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What Are Sandy Shores?

• Sandy shores are
• gently sloping coastal soft shores
• depositional beaches consisting of accumulations
  of sand particles of varying size.

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• Sandy shores can be broadly classified into 2
  major types according to wave action

Open sandy shores face open sea, most exposed
and stronger wave action
Tai Long Wan
Protected sandy shores sheltered by land
features (e.g. headlands), with reduced wave
action.
In fact, there is a gradient between these two
types.
Hoi Ha Wan
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Coarse sand particles
Fine sand particles

• Wave action determines the particle size on the
  shore.

• Particle size determines amount of space between
  the sand grains, hence
• amount of water held
• rate at which the sand dries out

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• In general,
• Shores with larger sized particles dry out faster
  and support fewer species
• Shores with finer particles dry out slower and
  support more species

• Wave action can disturb the sand and produce an
  unstable substrate
• coarser sand is less stable
• finer sand is more stable

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Sandy Shores

• OPEN SANDY SHORE
• - Greater wave action
• - More unstable substrate
• - More varied particle sizes
• - Lower species diversity

• PROTECTED SANDY SHORE
• - Weaker wave action
• - More stable substrate
• - Finer particle sizes
• - Higher species diversity

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Our Study Site Starfish Bay
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Our Study Site Starfish Bay
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Intertidal zone extent of the shore between
High Water Mark (HWM) and Low Water Mark (LWM) of
the tidal range
SEA
LAND
High shore
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Starfish Bay Zonation Patterns
Flat, with a wide intertidal zone
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Ecological Gradients on a Sandy Shore

• 1. Vertical gradient (tides)
• 2. Horizontal gradient (local topography, e.g.
  streams)
• 3. Depth gradient (depends on oxygen
  availability)

Sandy shores are 3-dimensional habitats so, we
need to DIG!
Clam Collector
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Position of last high tides are evident from
strandlines
Coastal vegetation
Vertical transect
MID SHORE
HIGH SHORE
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Coastal Vegetation

• Above the strandline are coastal (terrestrial)
  vegetation, including associated mangrove
  species. But NO true mangroves here why?

Clerodendrum
Hibiscus
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Faunal Groups

• Marine fauna can be classified into
• Surface dwellers, collectively called epifauna
  some are highly mobile crustaceans.
• Burrowers, collectively known as infauna
  includes shallow burrowers and deep burrowers.
• Temporary burrowers may be surface dwellers or
  burrowers depending on the phase of the tidal
  cycle.

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Surface Dwellers or Epifauna
Clithon oulaniensis
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Highly Mobile Epifauna

• You have to be fast (or very quiet) to see these

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Infauna

• On the surface, burrow holes may be seen

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Starfish Bay is so-called because?

• The deposit-feeding starfish, Archaster, is an
  epifaunal species of sandy shores low shore.

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Temporary Burrower
Carleton College
Soldier crabs (Mictyris longicarpus)

• Live in burrows at high tide
• Feed by moving over the sand at low tide in large
  numbers
• Feed on surface detritus and algae

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• But what you will usually see is.

Sand worked over by crabs during feeding just as
tide goes out
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Procedure
Investigate diversity of epifauna and infauna
from the high shore to the low shore
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Note the Adaptations of Sandy Shore Animals

• Surface dwellers
• Infauna

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• But look carefully, first appearances can
  some-times be deceptive!