1. Biological Pressures 1. Predation I - Thick strong shell
- Stinging tentacles
- Mucus coated body
- Chalky granules
The following slides put practical examples from the rocky shore that put the theory of the previous slide into practice.
From left to right:
1 – Periwinkle – a thick, hard shell to avoid being eaten
2 – Beadlet anemone - Stinging tentacles and a secretion of mucus makes the beadlet anemone unpalatable to most organisms.
3 – Coralline algae - by having chalky granules, other organisms live in coralline algae to avoid predation because chalky granules are unpalatable to most organisms – Good example hermit crabs.

2. Biological Pressures 1. Predation II - Empty shells
- Anemone camouflage
- Both benefit
- Settling in large populations
From left to right:
1 – Hermit crabs – Use the empty shells of marine snails to avoid being eaten. Hermit crabs also sometimes place anemones on their shells. This provides a nasty sting for any organism trying to eat the hermit crab. The anemone also benefits as it takes food scraps which wash over the hermit crab. This is termed a mutually beneficial relationship as both organisms benefit.
2 – Barnacles – live In large colonies – safety in numbers.

3. Biological Pressures 2. Competition Light – For seaweeds
Mates –
For reproduction
Empty shells –
Hermit crabs
Light – For seaweeds
and other marine plants
Food
Space – Most important
factor
Competition is the single biggest influence on life on the rocky shore
Before the information on the slide comes up, ask pupils to think about what organisms might compete for on the rocky shore.
This produces obvious patterns of where plants and animals choose to live, which often influences the adaptations they posses which we will go onto shortly.
Competition can be between members of the same population e.g. for mates, empty shells or between members of the same community e.g. for food, light, shelter or most importantly space
Many ways organisms act to prevent this being a problem
E.g. barnacles and limpets are well adapted to live high on the rocky shore to occupy a space not many others can due to risk of drying out
Some organisms such as seaweeds overgrow each other on the lower shore and shade each other out to reduce light exposure
Brushing action of seaweeds on the lower shore clears any animals trying to settle there.
We will often find organisms living within and on seaweeds to stay moist or to avoid being eaten. Already seen this example in the case of coral weed with organisms retreating here such as hermit crabs to avoid predation.

4. Environmental Factors
3. Adaptation
a) Drying out (desiccation) I
From left to right:
1 – Sea lettuce – During low tide, fronds collapse to reduce surface area for water loss. During high tide the expand broadly to maximise surface area for photosynthesis.
2 – Limpets – on the upper shore limpets have large and tall shells, to store as much water as possible to avoid drying out during low tide. On the lower shore however, limpets are flat and streamlined in shape to lower water resistance during wave crash on the lower shore and therefore avoid being washed off the rocks.
3 – Periwinkle – can close off its shell completley using a trap door or ‘operculum’. It also retreats under seaweeds to stay moist during low tide.
- Fronds collapse when out of water to reduce surface area for water loss
- High shore limpets – large and tall shells
- Wears a homescar (groove) into the rock
Has an operculum
- Hide under seaweeds

5. Environmental Factors
a) Drying out (desiccation) II
- Hard carapace, but limbs vulnerable to water loss
- Remains motionless during low tide in cracks and crevices
- Thick mucus covered fronds
- Green seaweeds can dry out at low tide and stay alive
- Draws in tentacles and produces a mucus
- Generally lives in cracks and crevices
From left to right
1 – Edible crab
2 – Bladder wrack
3 – Beadlet anemone

6. Environmental Factors
b) Wave crash
- Low shore limpets - streamline shaped shell: lower resistance to wave action
- Strong muscular foot to hold on tight
- Strong ‘holdfast’ stay attached to the rock
- Leathery fronds and stipes that bend easily
- Exposed shores – thinner shell, better developed foot
- Sheltered shores – thicker shell, less well developed foot
From left to right:
1 – Limpets – As explained in the previous slide referring to high shore limpets.
2 – Kelp – By having leathery fronds and flexible stipes, water resistance is lowered reducing the risk of fronds being ripped off by wave crash or the receding tide.
3 – Dog whelk – Exposed shore dog whelks invest more effort into foot development to hold on tight on exposed shores which have greater levels of wave crash. Sheltered shore dog whelks invest more effort into shell thickness because predation is a strong factor affecting life on sheltered shores.

7. Environmental Factors
c) Light
From left to right
1 – Sea lettuce
2 – Bladder wrack
3 – Irish moss – This point has physics links in that it discusses light absorption and reflection in relation to the colour spectrum.
- Fronds open broadly, during high tide, to maximise surface area to sunlight for photosynthesis
- Has air ‘bladders’ to help it float nearer to the surface to get light for photosynthesis
- Has red pigment which means it can absorb light for photosynthesis deeper than other seaweeds

8. Environmental Factors
d) Temperature extremes
- Settle together to form ‘microclimates’
Operculum closes: retain heat
- Operculum opens: to ‘sweat’
- Has an operculum which it closes to retain water
- Take refuge in microhabitats (cracks and crevices) to shade from the sun
From left to right:
1 – Barnacles – settle together in colonies which actually forms a micro-climate around the population. This is a similar effect to penguins. During cold days on the rocky shore, all barnacles close their opercula (trap doors to their shells) which retains heat. This keeps the population several degrees warmer than the surrounding rock. During warm days, all opercula in the population opens, and the barnacles produce small water bubbles which has similar effect to humans sweating. This keeps the population several degrees cooler than the surrounding rock.
2 – Periwinkle – Also have opercula which enable them to keep warm.
3 – Edible crab – Shading in cracks and crevices during low tide helps crabs avoid drying out and being predated by seabirds.

9. Environmental Factors
e) Salinity changes
This slide relates somewhat to the early ideas of osmosis and is therefore more advanced than expected at Key Stage 3. However, salinity changes are an important environmental factor affecting life on the rocky shore.
From left to right
1 – Blue velvet swimming crab – Because it can regulate ion concentrations in its body, the crab can live pretty much anywhere it wants to on the rocky shore, including in fresh water outputs, rock pools – which range greatly in salinity from full strength such as on hot, sunny days when there are high levels of evaporation in rock pools, to weak strength salinity where there is much rainfall/freshwater inputs.
2 – Starfish – In contrast to crabs, starfish are very poor at regulating the ion concentrations in their bodies. They therefore are restricted to live right down on the lower rocky shore where there is much competition for space and wave crash to deal with. The starfish is therefore very good at clinging on tight to the rocks to avoid being washed away.
- Can get rid of excess salt in its body
- Very poorly adapted to life in anything less than full-strength sea water

10. Who lives in a habitat like this?
Break Time game…
Who lives in a habitat like this?
This game is designed to consolidate pupils knowledge based on what they have learned about the adaptations of rocky shore organisms to habitats on the rocky shore. Each of the following slides present a separate habitat on the rocky shore – Cracks and crevices, Open bedrock, Rock pools and the low water mark. Bring up each slide in turn and ask pupils what the principle environmental conditions might be in each habitat. Then ask pupils from what they remembered from the examples given which organisms might be adapted to living in those environmental conditions.
Based on this exercise, the plenary activity to this session is for pupils to design their own rocky shore collage using the rocky shore organism drawings provided or asking pupils to draw their own. This is described in the accompanying teachers notes to adapting to the extreme.

11. Cracks and Crevices Environmental conditions: - Damp
Low levels of light, depending on aspect
Low levels of wave crash -

12. Open Bedrock Environmental conditions: Dry High levels of light
Temperature extremes

13. Rock Pools Environmental conditions: Damp
Limited levels of light in deeper rock pools
Prone to salinity changes
Prone to temperature extremes

14. Low Water Mark Environmental conditions: High levels of wave crash
Unlikely to be exposed to temperature extremes or salinity changes
May be effected by limited levels of light

15. Take home messages
That organisms on the rocky shore show adaptations to living in quite an extreme environment
That population sizes are determined by biological (e.g. predation and competition) and environmental (e.g. temperature, light intensity) factors