ECOLOGICAL STUDIES AT LOUQH INE
251
Rapids, and on the Sill both are mainly confined to the frills and holdfasts. At the seaward stations both show a progressive and drastic de
crease towards the open coast, and both show a similar restriction towards the frills and holdfasts as they die out. Possibly water movements either prevent the settling of larvae or dislodge the settled
organisms.
Three species, namely Tubularia bellis (Fig. 5 l), Membranipora membranacea (Fig. 52), and Jassa falcata, had a marked preference for the
Rapids area but were absent from, or sparse at, all the seaward stations.
As these are all species which have been shown to favour moderate or
strong currents within the Rapids area, it seems either that the favourable effects of current are not produced by wave-action or that there is
another over-riding factor which causes these species to prefer the
Rapids area. For instance, it is possible that the continuous current of
the Rapids area provides unusually favourable feeding conditions or
that physical or chemical conditions resulting from the outflow of lough
water are more advantageous.
One species, Patina pellucida, has been treated more fully (Fig. 53
and Table 111). Account has been taken of variations in algal frond
weight, which has an approximately rectilinear relation to frond area.
TABLE I11
Distribution of Patina pellucida on Saccorhiza polyschides,
Laminaria digitata and L. hyperborea in July 1951
Number of
plants
~
Saccorh iza
polyschides
North Rapids
25
Sill
26
South Rapids
28
Barloge Point
28
Cave Island
37
South Bullock 21
Laminaria digitata
Sill
28
South Bullock 21
L. hyperborea
Barloge Point
21
South Bullock 12
Frond weight
Number of
Stan(€9
Patina per plant sion
dard
- - coeffi- error
Range Mean Range Mean
cient
60-2040
735
1- 39
14.5
0.0106
0.0034
78-1 870
584
0- 10
2.7
0.0024
0.0026
280-3400 1193
0-264
118.7
0'0667
0.0170
150-1800
632
8-180
60.6
0.0767
0.0136
10- 740
134
0-829
264.3
1.0229
0.1541
70- 900
423
6-621
212.1
0.3145
0.1430
50- 740
357
0- 2
0.2
-
-
15- 400
161
0- 33
10.3
0.0141
0.0205
220-1000
585
8- 82
37.7
0.0646
0.0185
35- 480
269
4- 75
30.4
0.0202
0.0419
251
Rapids, and on the Sill both are mainly confined to the frills and holdfasts. At the seaward stations both show a progressive and drastic de
crease towards the open coast, and both show a similar restriction towards the frills and holdfasts as they die out. Possibly water movements either prevent the settling of larvae or dislodge the settled
organisms.
Three species, namely Tubularia bellis (Fig. 5 l), Membranipora membranacea (Fig. 52), and Jassa falcata, had a marked preference for the
Rapids area but were absent from, or sparse at, all the seaward stations.
As these are all species which have been shown to favour moderate or
strong currents within the Rapids area, it seems either that the favourable effects of current are not produced by wave-action or that there is
another over-riding factor which causes these species to prefer the
Rapids area. For instance, it is possible that the continuous current of
the Rapids area provides unusually favourable feeding conditions or
that physical or chemical conditions resulting from the outflow of lough
water are more advantageous.
One species, Patina pellucida, has been treated more fully (Fig. 53
and Table 111). Account has been taken of variations in algal frond
weight, which has an approximately rectilinear relation to frond area.
TABLE I11
Distribution of Patina pellucida on Saccorhiza polyschides,
Laminaria digitata and L. hyperborea in July 1951
Number of
plants
~
Saccorh iza
polyschides
North Rapids
25
Sill
26
South Rapids
28
Barloge Point
28
Cave Island
37
South Bullock 21
Laminaria digitata
Sill
28
South Bullock 21
L. hyperborea
Barloge Point
21
South Bullock 12
Frond weight
Number of
Stan(€9
Patina per plant sion
dard
- - coeffi- error
Range Mean Range Mean
cient
60-2040
735
1- 39
14.5
0.0106
0.0034
78-1 870
584
0- 10
2.7
0.0024
0.0026
280-3400 1193
0-264
118.7
0'0667
0.0170
150-1800
632
8-180
60.6
0.0767
0.0136
10- 740
134
0-829
264.3
1.0229
0.1541
70- 900
423
6-621
212.1
0.3145
0.1430
50- 740
357
0- 2
0.2
-
-
15- 400
161
0- 33
10.3
0.0141
0.0205
220-1000
585
8- 82
37.7
0.0646
0.0185
35- 480
269
4- 75
30.4
0.0202
0.0419