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The Rocky Shore
Rocky shores are diverse and dynamic ecosystems
where the inhabiting communities survive between
two worlds – the sea and the land
The familiar shoreline or littoral region is that area of shore
which lies between the high-water mark and the low-water
mark of spring tides
These littoral zones may differ greatly from one another as
local geology, wave action and aspect, influence the
structure of the shoreline
Living organisms in these intertidal regions face continual
fluctuating environmental conditions as they are subjected
to cyclic exposure and submergence from tidal activity
The distribution of life on the littoral shore reflects the
development of specialised structures and tissues that adapt
the different species to the prevailing conditions
Differences in exposure to the force of the waves have
a modifying effect on the communities inhabiting
sheltered and exposed shores
Diversity on The Rocky Shore
The sheltered rocky shore provides a variety of
habitable environments where the diversity and the
composition of species can be related to their
positions on the shore
The exposed rock faces, cervices and intertidal pools provide
habitats for a range of species that display adaptations to the
local prevailing conditions
The sheltered rocky shore described here is located on the east
coast of North Yorkshire where encrusting barnacles and
mussels and seaweeds dominate the shore
The following discussion describes the findings of a group of
students who surveyed the shore and who carried out a
number of investigations based upon their observations
The Lower Shore
Environmental conditions on the lower shore are
less harsh and relatively stable as surface populations are
never uncovered by the tide for more than a few hours at a time
Species diversity is high on the lower shore and competition
for food and space is fierce
Fucus serratus (toothed-wrack) is the dominant brown
alga of the lower shore and is intolerant of desiccation
(cell wall thickness 0.45 mm)
Red algae are intolerant of desiccation and form dense turfs
beneath the carpet of Fucus serratus; these algae are tolerant
of shade and possess the additional pigment (phycoerythrin)
for efficient photosynthesis at low light levels
Sponges, anemones, sea slugs, blenny fish and shrimps occupy
this zone alongside many other species of animals and algae
The Laminaria Zone
The Laminaria Zone is occupied by species that are
rarely uncovered by the tide but are subjected
to intense wave action
Environmental conditions in this zone are relatively constant
and productivity is high; this is the least harsh area of the
rocky shore providing niches for the establishment of a
large diversity of organisms where competition is fierce
The kelps (Laminaria species) are the dominant brown algae
of this zone where they form underwater ‘forests’
displaying prolific growth
These giant algae are intolerant of desiccation and possess
flexible stipes that attach firmly to the ocean bottom
with their powerful holdfasts
Numerous, shade-tolerant species of red algae are found
growing among the kelps
Starfish, brittle stars, marine worms and sea urchins are
found feeding in this zone
Zonation and Diversity
The zonation of both plants and animals observed on this
sheltered shore reflected adaptations to different
environmental conditions, with diversity increasing from
the harsh upper shore to the less harsh lower shore
The brown algae displayed a distinctive zonation pattern
that related largely to their ability to resist desiccation
and to photosynthesise effectively
Brown algae have developed specialised structures and
tissues for reducing desiccation, anchoring themselves to the
rocks and ocean bottom, and photosynthesising effectively
Brown algae are distinguished by the presence of the
accessory pigment, fucoxanthin; this brown pigment enables
the algae to absorb blue-green light
(the wavelengths that penetrate deep into the water)
The holdfast at the base of the stipes of these brown algae anchors
them to the rocks
Organisms inhabiting
the upper shore are
subjected to fluctuating
environmental conditions
and the drying effects
of the air during the
tidal cycle
Zonation pattern
of brown seaweeds
on the sheltered
rocky shore
A group of students investigated the
distribution of brown algae along a
sloping sheltered rocky shore
A transect was laid down along the
shore by laying a tape, at right
angles to the sea, from the splash
zone to the low water mark (LWM)
A one metre, square quadrat frame
was used to determine the
percentage cover of algae at twometre intervals along the tape
A five-point abundance scale was
used to record the percentage cover
of algae within each frame
Abundance scale
% Cover
1
< 5%
2
5 – 25%
3
>25 – 50%
4
>50 – 75%
5
75%
Transect Results
Species of Brown Algae
Splash
zone
Upper
Shore
Middle
shore
Lower
shore
Pelvetia
canaliculata
Fucus
spiralis
Fucus
vesiculosus
Fucus
serratus
Laminaria
sp.
2
5
1
2
2
2
3
5
3
2
1
4
1
2
1
2
4
2
1
4
3
0
1
3
5
18
HWM 16
14
Distance
from
low
water
mark (m)
LWM
12
10
8
6
4
4
• Draw kite diagrams to illustrate the distribution of algae along the
shore
• Discuss the pattern of distribution displayed by the different species
of algae
• Suggest reasons for the pattern of distribution observed
Kite Diagram
for rocky shore
transect
Pelvetia
canaliculata
16
Upper shore
14
12
10
Middle shore
8
6
4
Lower shore 2
0
Fucus
Fucus
spiralis vesiculosus
Fucus
serratus
Laminaria
sp.
Brown Algae and Desiccation
Students collected samples of three different
species of brown algae in containers of seawater
and returned them to the laboratory for
further investigation
Each group of students collected three samples of Fucus serratus,
Fucus spiralis and Fucus vesiculosus
After blotting off the excess seawater, all the samples were weighed
and their initial masses recorded
Clamp stands and string were used to construct ‘washing lines’ to
which the algae were then attached
The algae were weighed every thirty minutes for the first two hours
and then hourly for a further three hours
The percentage fresh mass at each time interval was calculated for
each species and the group results were pooled
The mean percentage fresh mass was determined and the results
presented graphically
Pooled Results
Time (mins)
Mean Percentage Fresh Mass
Fucus spiralis
Fucus vesiculosus
Fucus serratus
0
100
100
100
30
93.14
87.33
81.32
60
84.79
78.08
73.62
90
77.77
73.13
66.61
120
72.69
61.73
54.97
180
62.47
54.36
47.36
240
56.32
48.75
42.36
300
51.44
44.22
38.57
Construct a graph of the data obtained
Mean % Change in Mass against Time
for different species of brown algae
Relate these results to the zonation pattern of the algae