Lecture 8 - Rocky Shores Flashcards
Are rocky shores generally high or low energy?
High, depending on their exposure to waves.
In what way are rocky shores similar to reefs?
They are autochthonous - energy is derived from the same location that it is used.
What acts as food for detritivores in rocky shores?
Broken/rotting seaweed
Name four factors that favour life in a rocky shore environment.
- High primary productivity
- Low sediment supply
- Stable substrate that erodes slowly
- Diverse habitat types present (ledges, overhangs, crevices, pools etc.)
Give seven challenges faced by organisms in a rocky shore habitat.
- Desiccation
- Wave action
- Temperature fluctuation
- Salinity fluctuations
- Range of illumination
- Double predation
- Pollution
Give the three zonations in a rocky shore environment.
- Upper shore (furthest from ocean)
- Middle shore
- Lower shore (edge of ocean)
What is the main physical factor for marine organisms living in rocky shores?
Submergence
What organisms are often present in the upper shore, supra-littoral zone?
Lichens
Which zone of a rocky shore does tide never fully cover?
The ‘splash zone’, above the upper shore.
Name an organism found in high water.
Brown algae/seaweed.
Pelvetia canaliculata
Name the seaweed found at low water.
Fucus serratus
What is the fleshy algae normally found at the bottom of rocky shores?
Laminaria species.
Where on the rocky shore are limpets found?
At highest high tide.
What kind of organisms are normally found at lowest tide zone?
Soft-body organisms, such as sponges.
Name a species of lichen that is similar to a marine woodlouse.
Ligia italic
Name an organism found in the intertidal / Eulittoral zone within the:
a) Upper littoral
b) Mid-littoral
c) Lower littoral
a) Upper littoral = barnacles
b) Mid-littoral = limpets
c) Lower littoral = Actinia species (anemone)
Name some organisms that are found in the sublittoral.
- Kelps
- Soft sponges
- Urchins
Why do organisms at the bottom of the shore need to be more sticky?
Exposed to surging waves, which can remove things.
Name four biotic factors determining the distribution of organisms in a rocky shore habitat.
- Thermal tolerance
- Food availability
- Competition (for space and resources)
- Predation
Describe seaweed zonation in a rocky shore.
- Top of shore; Helvetia
- Upper shore; Fucus spiralis
- Mid shore; Fucus vesiculosus and Ascophyllum.
- Then Fucus serrates
- Then Laminaria
Describe Pelvetia.
Small, with waxy appearance.
Needs to be exposed.
Thick cuticle, preventing it from drying out.
Not good at photosynthesis as waxy cuticle prevents light from penetrating.
Describe Fucus spiralis.
Traps moisture inside the spiral form, keeping moisture inside the fronds.
Describe Fucus vesiculosus.
Has gas bubbles that enable it to float as tide comes in.
Describe Ascophyllum.
Flatter fronds.
Better at photosynthesis, but dries out quicker.
Describe Fucus serratus.
Very flat with serrated edge.
Describe Laminaria.
Requires immersion.
Long fronds that can reach the surface when tide is in.
What are upper limits of distribution determined by?
Desiccation tolerances
What are lower limits of distribution determined by?
- Competition for space
- Grazing invertebrates, e.g. limpets
What are epiphytes?
Plants that grow on top of other plants.
Why are seaweeds often referred to as microhabitats?
Remain moist when tide is out, and provide habitats for
- Epiphytes
- Small animals
Bryozoans form colonies on fucoid fronds.
Which grazers tend to be found in the middle shore?
Molluscs/gastropods.
Most commonly:
- Limpets
- Large periwinkle
What grazer is normally found in lower shores?
Urchins
Name the most common UK species of
a) Limpet
b) Sea urchins
a) Limpet = Patella vulgata
b) Sea urchin = Strongylocentrotus purpuratus
How are barnacles adapted for water loss?
Have thick calcium carbonate plates that water cannot evaporate through. When pull legs back in, they trap water inside the plates, to prevent them from drying out.
Describe an adaptation of Patella limpets for water loss.
Have secondary gills around the margin of the shell, and use water trapped on the rock surface around the edge of the gill.
Where do marine invertebrates found in rocky shores mostly lose their heat from?
Their foot
Describe the body structure of upper shore marine invertebrates to reduce heat exchange.
Small - tuck into nooks and crannies.
Dome structure, keeps their foot small relative to the size of their body.
Describe the body structure of lower shore marine invertebrates.
Flatter.
Have bigger feet.
Describe zonation in periwinkles.
- Top of shore; small periwinkle (Melarhaphe neritoides).
- Upper shore; Littorina saxitalis.
- Midshore; flat periwinkle Littorina obtusa.
- Bottom of shore; Littorina littorea (common periwinkle).
Describe some adaptations in periwinkles.
- Shells are light coloured, to reflect light and prevent heating
- Produce uric acid rather than ammonia to prevent water loss.
- High enzyme heat capacity.
- Can lower metabolic rate.
Describe some adaptations to wave action in
a) Molluscs
b) Mussels
c) Sea stars
d) Isopods
e) Kelps
a) Molluscs = low-profile, hydrodynamic shells.
b) Mussels = tethering byssal threads and glues.
c) Sea stars = thousands of suctioning tube feet.
d) Isopods = hook-like appendages.
e) Kelps = avoid breaking in high flow locations with their strength and flexibility.
What is stronger: the suctioning feet of sea stars, or beds threads of mussels?
Byssal threads of mussels
Why are mussel larvae more prone to desiccation stress?
Have larvae that float in the pelagic zone and do not have an adult shell.
What is the distribution of mussels driven by?
Where larvae can settle without driving out when tide goes out.
What enhances the settlement of mussel larvae?
The presence of barnacles, by providing rough-tetuned surfaces.
What is the lower boundary of mussel distribution set by?
Starfish predation
Describe Connell’s (1961) paper.
- Competition in species distribution.
- C stellatus and S balanoides species of barnacles.
- C stilettos better at surviving heat and desiccation upshore, but down shore there is competition between the two barnacles
- S balanoides can grow faster than C stellatus.
What are the key predators for barnacles?
Dog whelks
Describe a modification of dog whelks as predators.
Have a modified radula that drills into shells, injecting a paralytic enzyme. Can feed on things much bigger than themselves.
Describe the work of Paine (1969).
- First discovered role of starfish in maintaining diversity
- Pisaster ochracceuss; predates on mussels, controls their lower limit of the shore.
- Removing starfish left mussels to take over the shore, and greatly reduced community diversity.
