The shore environment
Number of marine species
• More land species than marine species
• Ocean relatively uniform conditions
• Less adaptation required, less speciation
• Marine species overwhelmingly benthic
rather than pelagic
The shore environment
The major gradients
• 1. The vertical gradient; from sea to land
• 2. The horizontal gradient of exposure to wave
action
• 3. The particle size gradient
• 4. Marine-freshwater gradient of salinity
1. The vertical gradient; from sea to land
Many intertidal animals are very patchy from place to place on a shore.
Most intertidal animals respond mainly to the threat of desiccation, but
their behaviour is actually more complex. It involves many other
environmental factors in the shore.
Unidirectional stress
Intertidal zone organisms
• Spray zone: Usually dry
– Crabs
– Hermit crabs
• High tide zone: Wet during high tide
–
–
–
–
–
–
Isopods
Periwincle snails
Barnacles
Limpets
Crabs
Hermit crabs
Intertidal zone organisms
• Middle zone: Wet and dry
–
–
–
–
Barnacles
Mussels
Isopods
Sea urchin
• Low tide zone: Usually wet
–
–
–
–
–
–
–
Chitons
Sea anemone
Limptes
Mussels
Isopods
Sea star
Sea urchin
2. The horizontal gradient of exposure to
wave action
How much wave action a shore experiences
• Exposed conditions
– Mussels
– Goose barnacles
– Sea anemones
Sea anemones
Mussels
• Sheltered conditions
– Crabs
– Limpets
Horizontal wave action gradient
• Benefits:
–
–
–
–
More highshore wetting
More food for suspension feeders
Greater larval supply
Greater oxygen and nutrients
• Stresses
–
–
–
–
More problems with settlement
Greater risk of dislogement
Foraging impaired; mobile animals
Interference with respiration; silting
3. The particle size gradient
• Particle size may be,
– Few micrometers – Mud flat
– Several hundred micrometers – Sandy beach
– A few centimeters – Gravel/ shingle habitats
– Tens of cm – Boulder shores
– Tens of meters – Marine boulders/ cliffs
Sandy beach
Boulder shores
Micro habitats in Rocky shores
Exposed rocks
Gullies
Crevices
Rock pools
Turf algae
Hard rocks: More secure anchorage
Soft rocks: Organisms will burrow
• Rock pools
– sea slugs
– camouflage crabs
– small fishes
• Crevices
– Centipeds
– Millipeds
– Terebellid worms
• Littoral zone
– Porphyra
– Black lichens
– Blue green algae
– Littorines, Barnacles
• Sub littoral zone
– Brown algae
– Barnacles
– Mussels
– Sea urchins
Rocky shore organisms
• They fixed in one place as adults
– Species with restricted dispersal
• Sea palm, Spirobid polychaets, Bryozoans
– Widely dispersed species
• Barnacles, Mussels
Rocky shore organisms
• Problems encountered
–
–
–
–
Desiccation
Heat
Shelter & exposure; Osmotic problems
Respiration
• Adaptations
–
–
–
–
–
–
–
Withdraw inside a shell: Gastropods, bivalves
Mucus secretion – to attach and avoid heat
Ridged or pimples shells - deflect light
Respiratory mechanisms eg. Anaerobiosis etc.
Adaptations to freezing
Use various cements to attachment; byssal threads; mucus, tube feets
Flat shells
• Fine particle shores/ sandy beaches/
muddy shores/ mud flats
– Zone 1 – Top of the beach (dry sand)
» Zone of drying
– Zone 2 – Water retention (damp not wet at low tide)
» Zone of retention
– Zone 3 – Area of resurgence (Interstitial water flows in & out
of the sediment with tide)
» Zone of resurgence
– Zone 4 – Permanently saturated (Little exchange of water
over the tidal cycle)
» Zone of saturation
Zonation of wetness in a sandy shore
Zone 4
Saturation
Zone 3
Resurgence
Zone 2
Retention
Zone 1
Drying
It is possible to
recognize the
major zones from the
physical appearance
and wetness of
the sediment.
Fauna in a sandy shore
• Areas of moderate disturbance
– Nereis
– Haustorial amphipods
– Ophelia
Fauna in a sandy shore…
• Seltered beaches & mud flats
– Burrowing bivalve molluscs
• Tellinids
• Large clams
• More exposed shores
– Bivalve (Donax)
– Gastropods (Bullia)
Fauna in a sandy shore……
• Fine particle shores
– Deposit & filter feeders
•
•
•
•
Nematodes
Herpacticoid copepods
Oligochaetes
Tardigrades
Tardigrades are small aquatic
animals that need water to live and
are found in marine, freshwater, and
semi-aquatic terrestrial habitats.
Coping with the life in sandy shores
• Burrowing
– Polychaete worms, Anemones, Bivalves
• Respiration at low tides
– Haemoglobin of polychaetes, decapod
crustaceans
Behavioural adaptations of shore dwelling
organisms
• Returning to a refuge
• Retreating inside a shell
• Rhythmic behaviour
• Secrete mucus to deter predators
• Kill predators eg. Mussels