Download Does the size of a rock affect the diversity of the epilithic fauna?

A presentation by:
Christine Adams, Louise Tunnah, Jen Dwyer, Steven Sutcliffe,
Jenn O’Blenes, and Jill Briand

The intertidal is broken up into three different
zones:
 supralittoral zone
 midlittoral zone
 infralittoral zone

Factors affecting zonation

Species commonly found
Ascophyllum nodosum
Mytilus edulis
Fucus vesiculosus Semibalanus balanoides

Wave Stress creates
disturbance events

Organisms adaptation

Wave stress interacts with substrate



Not all substrate equal for organisms
Larger rocks such as boulders preferred
Medium rocks balance between disturbance
and competition/predation (high diversity)



100 Meter transect at each point
50 meter transect on the other side of Greens
Point
Samples taken every 10 meters using a meter
by meter quadrat

The meter by meter quadrat was divided into four
sections, for time purposes, only one quarter of the
quadrat was sampled

Rocks within the quarter quadrat were measured
and recorded as specific rock type based on the
Wentworth Scale

Rocks were classified as:
 Sand – Less than 4mm
 Pebble - 4mm and 64mm
 Cobble - 64mm to 256mm
 Boulder - greater than 256mm
 Bedrock

Invertebrates were then identified and
counted on each rock measured

For identification purposes, some species
were bagged and brought back to the lab

Simpsons Diversity Index was calculated for
each individual quadrat as well as each entire
sampling site

One way ANOVAs were then performed to
determine the percent cover at each site and
the difference between the sampling sites

A regression analysis was then done to compare
rock type and species diversity at each sampling
site

To determine the percent coverage of rock in each quadrat:
 pictures were taken of each quadrat
 analyzed on the computer program ImageJ.

For each image, a scale meter was set using the markings on
the quadrat

Different sized substrate were measured to determine the
Wentworth classification of each

Each different substrate was traced and the area was
measured.

These measurement were used to find the percent cover of
each substrate type for each quadrat.
10000
Log # Found
2157
932
1000
439
138
100
71
27
10
8
4
4
3
1

Patellogastropoda
Nudibranchia
Nuculoida
Neogastropoda
Mytiloida
Neotaenioglossa
Mollusca
Polycladida
Echino
heteronemertea
Arthro
Forcipulatida
Decapoda
Sessila
1
Nemert
Platy
Figure 1: Taxonomic distribution of all organisms sampled at Indian
Point, Green’s Point 1, Green’s Point 2 and Barr Road. (n=3784).
100
90
Mean %Rock Cover
80
% sand
70
% barnacle
60
% bedrock
50
% boulder
40
% cobble
30
% pebble
20
10
0
Indian Point

Greens Point 1
Greens Point 2
Barr Road
Figure 2: Mean Rock Composition and relative cover at all four
sample sites.
Simpson's Diversity Index
1
0.95
0.9
0.85
0.8
0.75
Indian Point

Green's Point 1
Green's Point 2
Barr Road
Figure 3: Simpson’s Diversity Indices for each of the four sample
sites with a non-significant p-value of 0.1389.
70
%pebble/quadrat
60
50
y = 49.019x + 2.25
R² = 0.3972
40
30
20
10
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Simpson's Diversity Index

Figure 4: Regression Correlation between diversity and rock type at Green’s
Point Sites 1 and 2.

a) %Pebble at Greens Point 1 compared to diversity had a significance value of p=0.0402.
120
%bedrock/quadrat
100
80
60
y = -116.04x + 84.013
R² = 0.5841
40
20
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Simpson's Diversity Index

Figure 4: Regression Correlation between diversity and rock type at Green’s
Point Sites 1 and 2.

b) %Bedrock at Green’s Point 1 compared to diversity had a significance value of p=0.0063.
50
45
%boulder/quadrat
40
35
30
25
y = -63.104x + 38.913
R² = 0.825
20
15
10
5
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Simpson's Diversity Index

Figure 4: Regression Correlation between diversity and rock type at Green’s Point Sites 1
and 2.

c) % Boulder at Green’s Point 2 compared to diversity had a significance value of p=0.0301.

Wide variation in substrate type however no
significant difference in diversity

Does this relate to exposure?

Potential impact on species found?
Reasons for relatively low species diversity:
 Temperature
 Dissolved oxygen content
 Exposure
 Salinity
 Food supply
10000
2157
Log # Found
932
439
1000
138
100
10
71
27
8
4
4
3
1
Arthro
Echino
Mollusca
Polycladida
heteronemertea
Patellogastropoda
Nudibranchia
Nuculoida
Neotaenioglossa
Neogastropoda
Mytiloida
Forcipulatida
 Stability
Sessila
1
Decapoda

Nemert Platy
Diversity vs. Substrate

Green’s Point 1
 Bedrock low diversity
▪ high exposure
 Pebble high diversity
▪ protection
Green’s Point 2
Boulder low diversity
 stability and
competition
Why there was no significant difference
found in diversity between all the sites?
 All within the mid-intertidal zone
 Low and high wave exposure sites
 Slope and substrate size
1
Simpson's Diversity Index

0.95
0.9
0.85
0.8
0.75
Indian Point
Green's Point 1 Green's Point 2
Barr Road
QUESTIONS?