Daniel Prinz: Zonation on an exposed rocky shore. Abundance of flora
and fauna in the different tidal zones of St. Donat's Beach
Introduction
Aim
The aim of the practical work is to investigate the abundance of plants and animals in the different
tidal zones on St. Donats Beach. (In the practical work abundance will mean either the number of
individuals or percentage cover.)
Location and ecosystem
St. Donats Beach is a rocky shore on the Bristol Channel situated
51°N 3°W next to the campus of the United World College of the
Atlantic. The wind comes from south-west, the tidal range is the 2nd
highest in the world. At the time of the practical work the shore was
not covered with water, but small pools of water were noticed in
every tidal zones.
Hypothesis
Our prediction was that the abundance is increasing in the direction
of the sea. The plants and animals depend on water as water itself
and the nutrition carried by the water are of vital importance,
consequently the more water they get (in this case the more time
they spend under water) the bigger is their abundance. Because of
the tidal changes the areas next to the sea get more water than the
areas far from the sea.
Image 1: Photo of the area (maps.google.com)
Variables
In the practical work the distance from the shoreline is the independent, the abundance is the
dependent variable. The distances between the points of measurement, the use of the quadrat, the
people doing the whole measurement, the weather are assumed to be controlled variables.
Apparatus
The apparatus of the practical work consisted of a metre rule, a quadrat, species keys and a table for
the notation of species and distances.
Method
The quadrat was laid down to the ground at every 2
meters from the cliffs until 40 meters and at every 5
meters onwards. The abundance was measured
within the quadrat as an estimation of percentage
cover using eyesight or in the case of some species
the number of individuals was counted. The species
were identified with species keys, the data was
written to the notation tables.
Image 2: A simple image of the method
Results
Irish moss
Barnacles
Gut weed
Coral weed
Black tar lichen
Brown lichen
Fucus spiralis
Fucus vesicolosus
Periwinkle
Fucus serratus
Gelidium spinosum
Lithothamnion
Cladophora
Dulse
15 20
25
10
80
25 10
5
10
90
50
5
90
10
5
5
5
10
5
5
5
5
10
5
5
5
5
Top shell (pcs)
Anemonie (pcs)
Mussel (pcs)
Whelks (pcs)
Limpet (pcs)
2
2
2
5
5
5
15
10
15
5
1
4
3
4
2 10
5 10
5
6
1
9
1
1
2
4
4
6
6 13 10 10 15
5
1
4
1 10
2
2 15
9
*clear water!
Table 1: The abundance of flora and fauna on St. Donats Beach
Uncertainties in the data
The main uncertainties of the data are caused by the percentage cover measured with eyesight and
the inaccuracies of the distance caused by the lack of flatness on the seashore. Especially the
percentage covers are just harsh measurements.
The sum of the measurements of the different species have been taken and two graphs occurred: one
presenting the group of species which have an abundance measured with the estimation of
percentage cover (Graph 1) and one presenting the group of species which have an abundance
measured with counting individuals (Graph 2).
3
110
100
90
Abundance (%)
80
70
60
50
40
30
20
10
0
0*
4
2
8
6
12
10
16
14
20
18
24
22
28
26
32
30
36
34
40
38
50
45
60
55
70
65
80
75
90
85
100
95
110
105
Distance from the cliffs (m)
Abundance (pcs)
Graph 1: Sum of the abundance of the species with an abundance measured with the estimation of
percentage cover
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0*
4
2
8
6
12
10
16
14
20
18
24
22
28
26
32
30
36
34
40
38
50
45
60
55
70
65
80
75
90
85
100
95
110
105
Distance from the cliff (m)
Graph 2: Sum of the abundance of the species with an abundance measured with counting
individuals
Analysis
The data shows an increasing abundance from the cliffs to the shore. An outstanding exception is
the large abundance of lichens and gut weed just at the cliff. It is caused by the presence of clear
water coming from the top of the cliff. It is also noticeable that despite of the general increase of
the abundance in the direction of the sea, there are points where it immediately falls. A possible
cause of the phenomenon is the presence of the small pools of water mentioned when the ecosystem
was described. So the abundance may be influenced by two factors: the distance from the sea and
the presence of the small pools. The distance factor causes the general increase of the abundance,
the pools cause the local declines and increases.
We can see a clear specific example below on Graph 3:
Number of limpets
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
26
28
30
32
34
36
38
40
45
50
Distance from the cliffs (m)
Graph 3: Number of limpets from 26 m to 50 m
It is also visible that there are different species in the different zones. It may suggest the idea of an
alternative zonation based on the typical species rather than the total abundance.
Three possible zones according to their typical species (from the cliff to the sea):
Table 2: Typical species in the different zones
0-26 m from the cliff
26-50 m from the cliffs
Gut weed
Irish moss
Black tar lichen
Barnacles
Brown lichen
Coral weed
Fucus spiralis
Lithothamnion
Fucus vesicolosus
Anemonie (pcs)
Periwinkle
50+ from the cliff
Irish moss
Barnacles
Cladophora
Top shell (pcs)
Whelks (pcs)
Images
3-5: Gut weed (teara.govt.nz), limpet (dpo.uab.edu) and whelks
(imagecache2.allposters.com)
Conclusion
The division of St. Donats Beach into zones is possible. There are two concepts which can be
investigated: the total abundance and the actual species. The total abundance shows a general
increase with local declines, possibly caused by the small water pools. The species are different in
the different zones depending on the circumstances which make various plants and animals to
adapt.
Our hypothesis has been proven to be fairly right, however other factors have to be taken into
consideration in addition to the distance from the cliffs.
Evaluation
The estimation process contains a number of factors which make it to be uncertain. First of all as it
was mentioned earlier the seashore is not flat, making the measurement of the distance slightly
uncertain. This uncertainty grows with the change of the distances between the measurement points:
caused by a lack of time this distance was changed from 2 meters to 5 meters. The smaller is the
distance the more precise is the experiment. These problems could be solved with a better use of
time and calculations before the practical work of the time needed and what it lets us to do
(meaning if we just have time to do measurement at every 5 meters, than it is better than changing
the distance during the experiment). The problem of the lack of flatness could be solved by
measuring the abundance at various transects and taking an average.
The permanent level of the sea during the practical work was assumed but in fact the level of the
sea and the changes in the level always influence the abundance. The higher is the tide and the
nearer we are to the high tide in time, the bigger abundance will occur.