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Avicennia canopy effects on mangrove algal communities in Spencer Gulf, South Australia
Aquatic Botany, 17 (1983) 309--313
309
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
Short Communication
A VICENNIA CANOPY E F F E C T S ON M A N G R O V E A L G A L COMMUNITIES IN SPENCER GULF, SOUTH A U S T R A L I A
WARWICK R. BEANLAND and Wm. J. WOELKERLING
Department o f Botany, La Trobe University, Bundoora, Victoria 3083 (Australia) (Accepted for publication 5 October 1983)
ABSTRACT Beanland, W.R. and Woelkerling, Wm.J., 1983. Avicennia canopy effects on mangrove algal communities in Spencer Gulf, South Australia. Aquat. Bot., 17: 309--313. Studies of mangrove algal communities at eight localities in Spencer Gulf, South Australia, provide evidence that the presence or absence of an Avicennia tree canopy m a y influence the frequency distribution of algal species on pneumatophores. Certain algae occurred with significantly higher frequencies on pneumatophores beneath the canopy, while other species were significantly more frequent on pneumatophores beyond the canopy. The distribution of total algal cover, total algal biomass, and total species diversity, however, does not appear to be correlated with the presence or absence of a tree canopy.
INTRODUCTION
Based on studies of Rhizophora mangle L. dominated mangrove algal communities in Puerto Rico, Almodovar and Pagan (1971) concluded that algal diversity was greatest in shaded regions and that species of the red algal genera Bostrychia, Caloglossa, and Catenella were absent from sunexposed regions of the community. The possibility that similar sun--shade effects occurred in Avicennia marina (Forsk.) Vierhapper dominated mangrove algal communities in Spencer Gulf, South Australia, became evident during the course o f floristic studies in this region (Beanland and Woelkerling, 1982), and the hypothesis that the presence or absence o f a tree canopy over the Avicennia pneumatophores influences the nature of the algal communities seemed w o r t h y o f further investigation. Thus, while collecting floristic information on Spencer Gulf mangrove algae, some additional data were obtained from eight localities (Fig. 1) to determine whether marked differences occurred in the species frequency, cover, biomass and/or total diversity in algal communities on pneumatophores situated underneath the Avicennia canopy as opposed to pneumatophores situated b e y o n d the canopy along the seaward margin of each mangrove community.
0304-3770/83/$03.00
© 1983 Elsevier Science Publishers B.V.
310
DPOPt ~Augusta Blanche
Cowled$
Franklin
Landing
HsPiDOUP
Q
tPled Chff
Davis
I
Harbl
Wall@too
SPENCER Turnby
Bay •
GULF
GULF ST. VINCENT 0
10
20
30
km
Fig. 1. Map showing localities sampled in Spencer Gulf, South Australia. METHODS
Using random, paired c o o r d i n a t e s , 25 pairs of pneumatophores were collected from each of three 10 m wide, 50 m long c o n t o u r e d belt transects located along the seaward margin o f the mangrove canopy; one o f each pair of p n e u m a t o p h o r e s came from beneath the tree canopy while the other came from the more sun-exposed region b e y o n d the canopy. A total o f 600 pairs of pneumatophores (75 pairs for each o f the S localities) were sampled. Species frequency, cover, biomass and total algal diversity data were determined for the canopy-covered and the exposed pneumatophores in each transect. Cover data represent the length of pneumatophores occupied by algae as a percentage of the total p n e u m a t o p h o r e length sampled at each locality. Dry weight biomass was obtained by carefully scraping the algae into aluminium 'boats', removing any flecks of bark, and drying to constant weight at 70 ° C; biomass data have been expressed as algal mass per total length o f p n e u m a t o p h o r e in mg cm -1.
311
RESULTS AND DISCUSSION
Data on species frequency for the 15 most commonly occurring algae are summarized in Table I. Based on T-distribution analyses (P = 0.01) of mean frequency values for canopy-covered versus exposed pneumatophores from all localities, six species [Bostrychia moritziana (Sonder in Kiitzing) J. Agardh, B. radicans (Montagne) Montagne, Caloglossa lepreurii (Montagne) J. Agardh, Gelidiella nigrescens (Feldmann) Feldmann and Hamel, G. tenuissima Feldmann and Hamel, and Wittrockiella salina Chapman] occurred with significantly greater frequencies on pneumatophores TABLE
I
Summary of frequency pneumatophores
data
o
CHLOROPHYTA C l a d o p h o r a sp.
for the
15 most common
0.33 0.20 0.39 0.13 0.39 0.19 0.04 0.05
-0.11
0.01 0.03
0.59 0.88
0.35 0.05 0.39 0.05 0.03 0.01 0.45 0.43 0.35 0.12 0.12 0.21
A B A B
0.12 0.05 0.13 0.08
0.79 0.29 0.49 0.05
0.47 0.21 0.04 --
Caloglossa leprieurii Centroceras clavulatum Gelidiella n igrescens G. t e n u i s s i m a
A B A B A B A B A B A
-0.21 -0.03 0.07 0.41
0.01 0.31 0.01 0.52 0.23 0.68
0.12 0.39 -0.21 0.68 0.44 0.07 --
Spyridia filarnentosa
B A B
Percursaria percursa Rhizoclonium riparum Ulva lactuca Wittrockiella salina C YANOPHYTA Rivularia atra R. polyotis RHODOPHYTA Bostrychia moritziana B. radicans
0.03 0.01 0.01 0.03
0.01 0.01 0.03
and canopy-covered
"o
A B A B A B A B A B A B
E n t e r o m o r p h a sp.
algae o n s u n - e x p o s e d
0.12 0.01 --
*Significance (P = 0.01) for comparisons
0.36 0.05 0.71 0.43
0.48 0.26 0.03 0.01 0.11 0.01
0.05 --
0.01 -0.11 0.01
of sun-exposed
0.01 0.01
0.03 0.32
0.19 0.47 0.13 0.12 0.03 0.25 0.24 0.71
0.32 0.07 0.44
0.05 0.05
0.60 0.39
0.90 0.20
0.98 0.70 0.04 --
0.63 0.35
0.55 0.65
0.20 0.08 0.25 0.26
0.04 0.04 0.27 0.32 0.08 0.21 0.03 0.04
0.12 0.80 0.10 0.89 0.54 1.00
0.03 0.36 -0.61 0.21 0.94 0.12 --
0.24 0.28
*Sun
*Shade
*Sun *Sun
--
-0.17 0.05 0.67 0.05 0.11 -0.12 0.08 O. 6 4 0.29
0.05 0.30 0.04
0.72 0.21 0.27
(A) and canopy
*Sun
-0.85
0.31 0.12
0.33 0.12
covered frequencies
*Shade *Shade *Shade *Sun *Shade * Shade *Sun
(B)
312
situated underneath the canopy. Six other taxa [Centroceras clavulatum (C. Agardh) Montagne, Cladophora sp., Enteromorpha sp., Rivularia atra Roth, R. polyotis (J. Agardh) Bornet & Flahault, and Spyridia filamentosa (Wulfen) Harvey] occurred with significantly greater frequencies on pneumatophores situated in the more sun-exposed region beyond the canopy. Significant differences did not occur for Percursaria percursa (C. Agardh) Rosenvinge, Rhizocloniurn ripariurn (Roth) Harvey or Ulva lactuca L. Data on algal cover and biomass and on species diversity are summarized in Table II. Based on comparisons of canopy-covered and exposed pneumatophores using Mann-Whitney U tests (P = 0.05), both cover and biomass were significantly higher on canopy-covered pneumatophores at four localities (Blanch Harbour; Red Cliff; Tumby Bay, Wallaroo). At Port Davis, however, both cover and biomass were significantly higher on sun-exposed pneumatophores. At Cowleds Landing, moreover, cover, but not biomass, was significantly higher under the canopy, while at Port Augusta biomass but not cover was significantly higher beyond the canopy. The levels of mean cover and biomass present at the eight localities (Table II) varied greatly and this, in part, was due to the types of algae present. At Wallaroo, for example, the comparatively high levels of biomass present reflect the occurrence of the fucoid brown alga Hormosira banksii (Turner) Decaisne TABLE II Summary of data on algal cover, biomass and species diversity. Values for cover and biomass represent means o f 75 measurements (S.D. given in parentheses) Algal cover (%)
Algal biomass (rag algae cm -I pneumatophore)
Total species diversity
Habitat
A
B
A
B
A
B
Blanche Harbour
13.8 (20.4) 53.8 (33.3) 50.4 (32.8) 53.0 (38.1) 94.1 (8.7) 35.5 (30.1) 11.3 (18.7) 26.8 (23.5)
28.5* (33.2) 77.5* (27.4) 48.6 (36.4) 50.8 (36.9) 83.9* (18.1) 80.3* (26.0) 61.8" (36.9) 67.1" (30.5)
0.63 (0.42) 3.13 (3.04) 2.40 (1.36) 1.56 (0.41) 6.29 (1.47) 1.37 (1.09) 0.30 (0.16) 6.70 (11.89)
1.29" (0.70) 3.55 (0.72) 2.55 (0.77) 0.90 (0.47) 4.35* (0.66) 5.09* (1.67) 4.07* (0.98) 20.37* (11.70)
10
13
16
17
19
14
13
8
7
5
14
11
14
14
21
23
Cowleds Landing Franklin Harbour Port Augusta Port Davis Red Cliff T u m b y Bay Wallaroo
A = sun exposed;
B ffic a n o p y - c o v e r e d ;
* = significance ( P = 0.05).
313
on some pneumatophores. Attached plants of this species did not occur in samples from other localities. At most localities, total algal diversity (Table II) was similar on canopy covered and on more sun-exposed pneumatophores, although at most localities, some o f the rare species (frequencies of 0.05 or less) were recorded only from one of the t w o habitats. Only at Port Augusta did a marked difference in total diversity occur between canopy-covered and more sun-exposed pneumatophores, but since seven o f the thirteen species at Port Augusta occurred with overall frequencies of 0.05 or less (see Beanland and Woelkerling, 1982: Table 4), this difference may be of little consequence. Several conclusions emerge from results obtained during this study. Firstly, the data provide evidence that the presence or absence of a tree canopy may influence the frequency distribution of algal species on pneumatophores along the seaward margin of a mangrove community. Some species occurred far more frequently beneath the canopy while others occurred far more frequently b e y o n d the canopy. Although species of Bostrychia and Caloglossa had significantly higher frequencies beneath the canopy, they were not totally absent in more sun-exposed regions as was the case in Puerto Rico (Almodovar and Pagan, 1971). Secondly, the presence or absence of a tree canopy does not appear to be correlated with the distribution of algal cover or biomass. Thirdly, total algal diversity was not markedly different beneath and b e y o n d the canopy, in contrast to the situation reported by Almodovar and Pagan (1971). To date few ecological data are available for macroscopic algal communities of mangroves in Australia (Davey and Woelkerling, 1980; King, 1981a, b) or elsewhere (Chapman, 1976, 1977). Results from the present investigation, however, suggest that more detailed ecological studies of mangrove algal communities are warranted, especially if extended to include the entire mangrove fringe. REFERENCES Almodovar, L.R. and Pagan, F.A., 1971. Notes on a mangrove lagoon and mangrove channels at La Parguera, Puerto Rico. Nova Hedwigia Z. Kryptogamenkd., 21: 241-253. Beanland, W.R. and Woelkerling, W.J., 1982. Studies on Australian mangrove algae. If. Composition and geographic distribution of communities in Spencer Gulf, South Australia. Proc. R. Soc. Victoria, 94: 89--106. Chapman, V.J., 1976. Mangrove Vegetation. J. Cramer, Vaduz, VIII + 447 pp. Chapman, V.J. (Editor), 1977. Ecosystems of the World. I. Wet Coastal Ecosystems. Elsevier, Amsterdam, XI + 428 pp. Davey, A. and Woelkerling, Wm.J., 1980. Studies on Australian mangrove algae. I. Victorian communities: Composition and geographic distribution. Proc. R. Soc. Victoria, 91: 53--66. King, R.J., 1981a. Mangrove and saltmarsh plants. In: M.N. Clayton and R.J. King (Editors), Marine Botany: A n Australasian Perspective. L o n g m a n Cheshire, Melbourne, pp. 309--328. King, R.J., 1981b. The free living Hormosira banksii (Turner) Decaisne associated with mangroves in temperate eastern Australia. Bot. Mar., 24: 569--576.
309
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
Short Communication
A VICENNIA CANOPY E F F E C T S ON M A N G R O V E A L G A L COMMUNITIES IN SPENCER GULF, SOUTH A U S T R A L I A
WARWICK R. BEANLAND and Wm. J. WOELKERLING
Department o f Botany, La Trobe University, Bundoora, Victoria 3083 (Australia) (Accepted for publication 5 October 1983)
ABSTRACT Beanland, W.R. and Woelkerling, Wm.J., 1983. Avicennia canopy effects on mangrove algal communities in Spencer Gulf, South Australia. Aquat. Bot., 17: 309--313. Studies of mangrove algal communities at eight localities in Spencer Gulf, South Australia, provide evidence that the presence or absence of an Avicennia tree canopy m a y influence the frequency distribution of algal species on pneumatophores. Certain algae occurred with significantly higher frequencies on pneumatophores beneath the canopy, while other species were significantly more frequent on pneumatophores beyond the canopy. The distribution of total algal cover, total algal biomass, and total species diversity, however, does not appear to be correlated with the presence or absence of a tree canopy.
INTRODUCTION
Based on studies of Rhizophora mangle L. dominated mangrove algal communities in Puerto Rico, Almodovar and Pagan (1971) concluded that algal diversity was greatest in shaded regions and that species of the red algal genera Bostrychia, Caloglossa, and Catenella were absent from sunexposed regions of the community. The possibility that similar sun--shade effects occurred in Avicennia marina (Forsk.) Vierhapper dominated mangrove algal communities in Spencer Gulf, South Australia, became evident during the course o f floristic studies in this region (Beanland and Woelkerling, 1982), and the hypothesis that the presence or absence o f a tree canopy over the Avicennia pneumatophores influences the nature of the algal communities seemed w o r t h y o f further investigation. Thus, while collecting floristic information on Spencer Gulf mangrove algae, some additional data were obtained from eight localities (Fig. 1) to determine whether marked differences occurred in the species frequency, cover, biomass and/or total diversity in algal communities on pneumatophores situated underneath the Avicennia canopy as opposed to pneumatophores situated b e y o n d the canopy along the seaward margin of each mangrove community.
0304-3770/83/$03.00
© 1983 Elsevier Science Publishers B.V.
310
DPOPt ~Augusta Blanche
Cowled$
Franklin
Landing
HsPiDOUP
Q
tPled Chff
Davis
I
Harbl
Wall@too
SPENCER Turnby
Bay •
GULF
GULF ST. VINCENT 0
10
20
30
km
Fig. 1. Map showing localities sampled in Spencer Gulf, South Australia. METHODS
Using random, paired c o o r d i n a t e s , 25 pairs of pneumatophores were collected from each of three 10 m wide, 50 m long c o n t o u r e d belt transects located along the seaward margin o f the mangrove canopy; one o f each pair of p n e u m a t o p h o r e s came from beneath the tree canopy while the other came from the more sun-exposed region b e y o n d the canopy. A total o f 600 pairs of pneumatophores (75 pairs for each o f the S localities) were sampled. Species frequency, cover, biomass and total algal diversity data were determined for the canopy-covered and the exposed pneumatophores in each transect. Cover data represent the length of pneumatophores occupied by algae as a percentage of the total p n e u m a t o p h o r e length sampled at each locality. Dry weight biomass was obtained by carefully scraping the algae into aluminium 'boats', removing any flecks of bark, and drying to constant weight at 70 ° C; biomass data have been expressed as algal mass per total length o f p n e u m a t o p h o r e in mg cm -1.
311
RESULTS AND DISCUSSION
Data on species frequency for the 15 most commonly occurring algae are summarized in Table I. Based on T-distribution analyses (P = 0.01) of mean frequency values for canopy-covered versus exposed pneumatophores from all localities, six species [Bostrychia moritziana (Sonder in Kiitzing) J. Agardh, B. radicans (Montagne) Montagne, Caloglossa lepreurii (Montagne) J. Agardh, Gelidiella nigrescens (Feldmann) Feldmann and Hamel, G. tenuissima Feldmann and Hamel, and Wittrockiella salina Chapman] occurred with significantly greater frequencies on pneumatophores TABLE
I
Summary of frequency pneumatophores
data
o
CHLOROPHYTA C l a d o p h o r a sp.
for the
15 most common
0.33 0.20 0.39 0.13 0.39 0.19 0.04 0.05
-0.11
0.01 0.03
0.59 0.88
0.35 0.05 0.39 0.05 0.03 0.01 0.45 0.43 0.35 0.12 0.12 0.21
A B A B
0.12 0.05 0.13 0.08
0.79 0.29 0.49 0.05
0.47 0.21 0.04 --
Caloglossa leprieurii Centroceras clavulatum Gelidiella n igrescens G. t e n u i s s i m a
A B A B A B A B A B A
-0.21 -0.03 0.07 0.41
0.01 0.31 0.01 0.52 0.23 0.68
0.12 0.39 -0.21 0.68 0.44 0.07 --
Spyridia filarnentosa
B A B
Percursaria percursa Rhizoclonium riparum Ulva lactuca Wittrockiella salina C YANOPHYTA Rivularia atra R. polyotis RHODOPHYTA Bostrychia moritziana B. radicans
0.03 0.01 0.01 0.03
0.01 0.01 0.03
and canopy-covered
"o
A B A B A B A B A B A B
E n t e r o m o r p h a sp.
algae o n s u n - e x p o s e d
0.12 0.01 --
*Significance (P = 0.01) for comparisons
0.36 0.05 0.71 0.43
0.48 0.26 0.03 0.01 0.11 0.01
0.05 --
0.01 -0.11 0.01
of sun-exposed
0.01 0.01
0.03 0.32
0.19 0.47 0.13 0.12 0.03 0.25 0.24 0.71
0.32 0.07 0.44
0.05 0.05
0.60 0.39
0.90 0.20
0.98 0.70 0.04 --
0.63 0.35
0.55 0.65
0.20 0.08 0.25 0.26
0.04 0.04 0.27 0.32 0.08 0.21 0.03 0.04
0.12 0.80 0.10 0.89 0.54 1.00
0.03 0.36 -0.61 0.21 0.94 0.12 --
0.24 0.28
*Sun
*Shade
*Sun *Sun
--
-0.17 0.05 0.67 0.05 0.11 -0.12 0.08 O. 6 4 0.29
0.05 0.30 0.04
0.72 0.21 0.27
(A) and canopy
*Sun
-0.85
0.31 0.12
0.33 0.12
covered frequencies
*Shade *Shade *Shade *Sun *Shade * Shade *Sun
(B)
312
situated underneath the canopy. Six other taxa [Centroceras clavulatum (C. Agardh) Montagne, Cladophora sp., Enteromorpha sp., Rivularia atra Roth, R. polyotis (J. Agardh) Bornet & Flahault, and Spyridia filamentosa (Wulfen) Harvey] occurred with significantly greater frequencies on pneumatophores situated in the more sun-exposed region beyond the canopy. Significant differences did not occur for Percursaria percursa (C. Agardh) Rosenvinge, Rhizocloniurn ripariurn (Roth) Harvey or Ulva lactuca L. Data on algal cover and biomass and on species diversity are summarized in Table II. Based on comparisons of canopy-covered and exposed pneumatophores using Mann-Whitney U tests (P = 0.05), both cover and biomass were significantly higher on canopy-covered pneumatophores at four localities (Blanch Harbour; Red Cliff; Tumby Bay, Wallaroo). At Port Davis, however, both cover and biomass were significantly higher on sun-exposed pneumatophores. At Cowleds Landing, moreover, cover, but not biomass, was significantly higher under the canopy, while at Port Augusta biomass but not cover was significantly higher beyond the canopy. The levels of mean cover and biomass present at the eight localities (Table II) varied greatly and this, in part, was due to the types of algae present. At Wallaroo, for example, the comparatively high levels of biomass present reflect the occurrence of the fucoid brown alga Hormosira banksii (Turner) Decaisne TABLE II Summary of data on algal cover, biomass and species diversity. Values for cover and biomass represent means o f 75 measurements (S.D. given in parentheses) Algal cover (%)
Algal biomass (rag algae cm -I pneumatophore)
Total species diversity
Habitat
A
B
A
B
A
B
Blanche Harbour
13.8 (20.4) 53.8 (33.3) 50.4 (32.8) 53.0 (38.1) 94.1 (8.7) 35.5 (30.1) 11.3 (18.7) 26.8 (23.5)
28.5* (33.2) 77.5* (27.4) 48.6 (36.4) 50.8 (36.9) 83.9* (18.1) 80.3* (26.0) 61.8" (36.9) 67.1" (30.5)
0.63 (0.42) 3.13 (3.04) 2.40 (1.36) 1.56 (0.41) 6.29 (1.47) 1.37 (1.09) 0.30 (0.16) 6.70 (11.89)
1.29" (0.70) 3.55 (0.72) 2.55 (0.77) 0.90 (0.47) 4.35* (0.66) 5.09* (1.67) 4.07* (0.98) 20.37* (11.70)
10
13
16
17
19
14
13
8
7
5
14
11
14
14
21
23
Cowleds Landing Franklin Harbour Port Augusta Port Davis Red Cliff T u m b y Bay Wallaroo
A = sun exposed;
B ffic a n o p y - c o v e r e d ;
* = significance ( P = 0.05).
313
on some pneumatophores. Attached plants of this species did not occur in samples from other localities. At most localities, total algal diversity (Table II) was similar on canopy covered and on more sun-exposed pneumatophores, although at most localities, some o f the rare species (frequencies of 0.05 or less) were recorded only from one of the t w o habitats. Only at Port Augusta did a marked difference in total diversity occur between canopy-covered and more sun-exposed pneumatophores, but since seven o f the thirteen species at Port Augusta occurred with overall frequencies of 0.05 or less (see Beanland and Woelkerling, 1982: Table 4), this difference may be of little consequence. Several conclusions emerge from results obtained during this study. Firstly, the data provide evidence that the presence or absence of a tree canopy may influence the frequency distribution of algal species on pneumatophores along the seaward margin of a mangrove community. Some species occurred far more frequently beneath the canopy while others occurred far more frequently b e y o n d the canopy. Although species of Bostrychia and Caloglossa had significantly higher frequencies beneath the canopy, they were not totally absent in more sun-exposed regions as was the case in Puerto Rico (Almodovar and Pagan, 1971). Secondly, the presence or absence of a tree canopy does not appear to be correlated with the distribution of algal cover or biomass. Thirdly, total algal diversity was not markedly different beneath and b e y o n d the canopy, in contrast to the situation reported by Almodovar and Pagan (1971). To date few ecological data are available for macroscopic algal communities of mangroves in Australia (Davey and Woelkerling, 1980; King, 1981a, b) or elsewhere (Chapman, 1976, 1977). Results from the present investigation, however, suggest that more detailed ecological studies of mangrove algal communities are warranted, especially if extended to include the entire mangrove fringe. REFERENCES Almodovar, L.R. and Pagan, F.A., 1971. Notes on a mangrove lagoon and mangrove channels at La Parguera, Puerto Rico. Nova Hedwigia Z. Kryptogamenkd., 21: 241-253. Beanland, W.R. and Woelkerling, W.J., 1982. Studies on Australian mangrove algae. If. Composition and geographic distribution of communities in Spencer Gulf, South Australia. Proc. R. Soc. Victoria, 94: 89--106. Chapman, V.J., 1976. Mangrove Vegetation. J. Cramer, Vaduz, VIII + 447 pp. Chapman, V.J. (Editor), 1977. Ecosystems of the World. I. Wet Coastal Ecosystems. Elsevier, Amsterdam, XI + 428 pp. Davey, A. and Woelkerling, Wm.J., 1980. Studies on Australian mangrove algae. I. Victorian communities: Composition and geographic distribution. Proc. R. Soc. Victoria, 91: 53--66. King, R.J., 1981a. Mangrove and saltmarsh plants. In: M.N. Clayton and R.J. King (Editors), Marine Botany: A n Australasian Perspective. L o n g m a n Cheshire, Melbourne, pp. 309--328. King, R.J., 1981b. The free living Hormosira banksii (Turner) Decaisne associated with mangroves in temperate eastern Australia. Bot. Mar., 24: 569--576.