Distribution and abundance of Turbinaria ornata on the north side of
Moorea, French Polynesia
Chad Hanson, Kendra Karr, & Alison Kendall
University of California, Santa Cruz 95064
Abstract. Natural disturbance coupled with a recent rise in anthropogenic
perturbation have catalyzed the widespread expansion of algal populations in the coral
reef ecosystems of Moorea, French Polynesia. This study sought to determine whether
densities of the invasive Fucalean alage, Turbinaria ornata, varied along exposure
gradients. No significant difference was found in T. ornata abundance among the various
sites; Turbinaria cover averaged 5% throghout all three transects. Substantial differences
were apparent between West Opunohu and the Tiahura and East Opunohu transects. West
Opunohu was an outlier in terms of percentage of sand, rubble, pavement, dead coral, live
coral, Sargassum, and Halimeda; only Turbinaria and Padina were consistent (no
significant relationship) among all transects. Finally, this study surveyed associated
species assemblages (fish, epifauna, and epiphytes) in an attempt to decipher variation
within and among sites.
Introduction
Within the last two decades, a rise in the population and distribution of a Fucalean
algae, Turbinaria ornata, has occurred within the reef systems of French Polynesia.
Setchell (1926) described this species in an early record of French Polynesian marine life.
Subsequent studies carried out at the Tiahura transect, Moorea, French Polynesia showed
that there had been a dramatic increase in the distribution and abundance of Turbinaria
ornata between 1978 and 1982 (Payri, 1982). This increase in the Turbinaria population
followed an expansion of agriculture and construction, and a subsequent rise in nutrient
runoff (personal comunication, Payri). T. ornata remains reproductive throughout the
year and exhibits intrinsic rates of growth under ideal conditions. This life history is
consistent with a ‘r-strategy’ mode of growth, which enables the algae to successfully
colonize and invade new areas (Stiger, Payri, 1999).
The present study aimed to addressed three hypotheses: 1) The abundance of
Turbinaria will be high in areas of high disturbance; 2) The abundance of Turbinaria has
increased over time; (3) Associated fish, epiphyte, and epifaunal communities will differ
along exposure gradients.
Materials & Methods
Study site description
Sampling was conducted over a period of three weeks from November to
December 2000. To detect variation among different areas of the lagoon three study sites
were chosen. The sites differed significantly in the degree of exposure they receive. The
West Opunohu (WO) transect lies very close to the large Tareu pass and includes regions
with direct exposure to swell and large wave events, making it the most exposed site in
the study. Both the Tiahura (T) and East Opunohu (EO) transects are further from passes
and are thus more protected.
All sites spanned the lagoon along the North side of Moorea, French Polynesia
(Fig. 1). The T transect is composed of a fringing reef, a boat channel prone to high
current flow, and a barrier reef (BR) which extends to the reef crest (C). The WO transect
includes a narrow fringing reef (FR) followed by a deep channel, a shallow bank followed
by another channel, and a barrier reef extending to the crest. The EO transect consists of a
fringing reef, an extensive sand flat, and barrier reef which is divided by a boat channel
near the crest.
To determine the current distribution and abundance of Turbinaria ornata we
divided each transect into zones based upon distinct geomorphological features. We
measured the length of each zone and sampled percent coverage of T. ornata, S.
mangarevense, Halimeda, Padina, dead and live coral, and substrate using 12 2.5X2 m
quadrats per zone. Counts were made of juvenile and adult Turbinaria as well as urchins.
Epifauna and Epiphytes
To examine community structure we assessed epifauna and epiphytes for each
transect. Samples were collected from both fringing reef and crest zones at all three sites.
Eight mature thalli were randomly chosen within each zone and taken to the lab for
classification. Each (plant) was shaken for 15 seconds in a jar of seawater, followed by 15
seconds in 50% mixture of freshwater/seawater. Epifauna were collected from the rinse
water and examined under a dissecting microscope. Epiphytes were either examined on
the thallus or removed by hand. Organisms were grouped to Class level.
Fish Assemblages
To determine fish community structure we carried out observations of fish
assemblages within the barrier reef zones of each study site using fish transect sampling.
Fish were counted along 30x3 meter transects 1 meter above the bottom. Two transects
were done per barrier reef zone, for a total of 10 transects for T, 8 for WO and 6 for EO.
Numbers of any of the 161 species encountered on the data sheet were recorded.
Data Analysis
The data collected were categorized by transect according to zone. The length of
each zone was measured, but was not taken into account during statistical analysis. Using
the software SYSTAT, one-way ANOVA tests were completed for the species surveyed
using the factor, ‘transect’. Two-way ANOVA tests were conducted using ‘transect’ and
‘zone’ for selected substratum and algal species. Quadratic discriminate analyses were
performed using Wilk’s Lambda and Pillai Trace to detect differences between specific
variables. Past data were referenced to establish whether significant change has taken
place in T. ornata abundance and the composition of its associated reef communities over
time. We defined the communities by their respective fish assemblages, and
epiphyte/epifaunal associations.
RESULTS
Spatial Variation
Among site variation
The results of the Univariate F-test (Table 1) show that there are significant
differences between the transects in terms of algae and substrate percent cover with the
exception of Padina (p= 0.83), and T. ornata (p=0.55). Further analysis revealed that
substantial differences in percent cover exist between the WO transect and the other two
sites. WO was an outlier in terms of percentage of sand, rubble, pavement, dead coral,
live coral, Sargassum, and Halimeda; only Turbinaria and Padina were consistent (no
significant relationship) among all transects (Figure 1)
Table 1. Among transect comparison
Univariate F-test
Effect
Sand
Rubble
Pavement
Dead Coral
Live Coral
Turbinaria
Sargassum
Padina
Halimeda
p-value
0.000000
0.000000
0.000000
0.000002
0.000001
0.552447
0.000000
0.826531
0.001076
Significant
Y
Y
Y
Y
Y
NS
Y
NS
Y
Further analysis revealed that substantial differences in percent cover exist
between the WO transect and the other two sites. WO was an outlier in terms of
percentage of sand, rubble, pavement, dead coral, live coral, Sargassum, and Halimeda;
only Turbinaria and Padina were consistent (no significant relationship) among all
transects (Figure 1). Linear regression indicates a positive relationship between adult
number of Turbinaria and percent cover of Sargassum at T and EO. Again, no correlation
was observed at WO (Graph 2). Adult numbers of T. ornata are correlated with S.
mangarevense percent cover. No relationship was found between percentage of T. ornata
and live coral (Graph 3), nor was there any apparent connection between T. ornata and
dead coral (Graph 4). A negative relationship was determined for percent cover of S.
mangarevense and live coral at T and EO, but no correlation was established for WO
(Graph 5). The difference in exposure between transects is apparent in the data, with
Tiahura and East Opunohu grouped separately from West Opunohu for many of the
categories surveyed.
Within transect variation
The substrate at West Opunohu is consistent with a high exposure area. In contrast
to the other two low exposure sites, the WO transect has significantly lower percentages
of sand and coral cover (both live and dead), in addition to higher coverage of pavement
and rubble (Figure 1). In terms of biological variables, T. ornata is relatively constant
among zones and transects while S. mangarevense tends to dominate in the crest zones
and at West Opunohu in particular. Positive correlations between cover of T. ornata and
S. mangarevense were found for the T and EO transects while there was no significant
correlation for WO (Graph 6).
Temporal Variation
In comparing current data with that of Payri (1987), there has been an observable
increase in the density of Turbinaria ornata in the last two decades. In the 1987 survey,
T. ornata coverage was 5% or less moving from the boat channel towards the crest.
Present data indicates that percent cover fluctuates within 5 and 10% along the barrier
reef. As for the fringing reef, there was a rise in the density of Turbinaria coverage from
2% or less in 1987, up to 8% or less (Figure 6 ; Graph 1).
Fish Assemblages
Number of transects sampled varied between sites, therefore, data were weighted
accordingly (Table 3). Turbinaria was consistent across the board yet the associated
species assemblages appear to vary. Certain species (i.e. Centropyge flavissimus,
Thalassoma hardwicke) followed the patterrn in which WO was an outlier, however, this
did not hold true for all species. Higher densities of both Scarids (Scarus sordidus,
Scarus psittacus) were recorded at EO compared to the other two sites. No significant
difference was observed for the data collected.
Epifaunal/epiphyte assemblages
No apparent relationship can be concluded between the crest and fringing reef
with respect to epifanual and ephiphyte ditribution among the transects (Table 2).
DISCUSSION
Spatial comparisons
After assessing the distribution and abundance of T. ornata on large and small
spatial scales several patterns became apparent. Statistical results did not support the
original hypotheses that the large scale distribution and abundance of Turbinaria would
differ along exposure gradients. Despite the fact that the West Opunohu transect is
subject to extreme levels of disturbance, the percent cover of Turbinaria remained
consistent with the other two transects. Within transect data revealed slightly more
variance in Turbinaria densities, although it was not statistically significant.
By looking at the abundance of T. ornata relative to S. mangarevense between
transects and between zones it can be seen that the two species are present in roughly
equal amounts with the exception of West Opunohu and the crest zone at Tiahura (Graph
6).
This indicates that S. mangarevense is out-competing T. ornata under high
disturbance. The dominance of S. mangarevense over T. ornata at West Opunohu - our
high exposure transect - may be explained by differences in thallus morphologies. T.
ornata has a rigid, bulky structure, whereas S. mangarevense is comprised of many
flexible, streamlined blades, making it less susceptible to hydrodynamic drag. Thus S.
mangarevense can persist under levels of disturbance that would otherwise remove T.
ornata. The tendency of T. ornata to become detached from the substrate during large
wave events, however, may be at least partially beneficial.
The rafts of floating
Turbinaria may function in dispersal, transporting sufficiently large quantities of
reproductive individuals to colonize new habitats (Stiger, Payri). Additionally, the rafts
may serve as refuge for juvenile fish and invertebrate recruits, which would in turn make
Turbinaria more valuable to the reef community.
Temporal comparisons:
An observable increase in the density of Turbinaria ornata in the last two decades
is correlated to the increase of anthropogenic disturbances of hotel development and
boating activities. Areas along the study site that were not previously composed of algal
species have been colonized by T. ornata and S. mangarevense, with T. ornata displaying
the sharpest increase in cover. The validity of this comparison is questionable due to the
differences in sampling methods. Our studies were constrained by time.
Associated species assemblages
The data implicated slight patterns in the distribution of certain fish families, and
classes of epifauna within and among sites (Table 2). Samples were gathered over the
course of a week from all six sites which may have introduced experimental due to
temporal variability. For instance, Anthozoans were found at Tiahura FR and crest, and
EO crest but were absent from the other sites. These zones were collected on the same
day which may indicate a recruitment pulse which the other sites, collected on different
days, did not account for. Therefore, the data obtained for this brief survey may not
represent complete sampling of fringing reef and crest areas. Further studies can be
carried out to determine whether there is refuge selection along exposure gradients.
Our fish assemblage survey sought to determine whether there was
variation in the associations of fish, with respect to exposure, between Turbinaria areas
and non-Turbinaria areas. Minute trends were observed in fish communities where, for
example, higher densities of Scarids were present at EO compared to the other two sites.
Surveys were limited to barrier reef zones, therefore, there could be no comparison along
exposure gradients within sites. Furthermore, we expected to see differences between
assemblages at WO in comparison to EO and T, since WO was an outlier in terms of
community organization, yet no significant differences were observed. More sampling is
necessary in order to elucidate any true variation.
Figure 1. Among Transect Comparisons
120
100
100
% SAND
80
60
40
20
0
90
80
90 % PAVEMENT
80
70
70
60
60
50
50
40
40
30
30
20
20
10
EO
T
WO
TRANSECT
0
90
90
80
80
70
% DEADCORAL
70
60
60
50
50
40
30
40
T
WO
TRANSECT
% LIVE CORAL
T
WO
TRANSECT
0
% SARGASSUM
70
30
50
% TURBINARIA
20
10
EO
T
WO
TRANSECT
0
EO
T
WO
TRANSECT
25
% PADINA
% HALIMEDA
20
25
60
50
20
15
40
15
10
30
10
20
5
5
10
0
T
WO
TRANSECT
30
35
90
EO
40
10
EO
0
60
20
10
80
10
EO
30
20
0
100
% RUBBLE
EO
T
WO
TRANSECT
0
EO
T
WO
TRANSECT
0
EO
T
WO
TRANSECT
Graph 1. Percent cover of T. ornata within zones
TRANSECT
EO
T
WO
60
TURBINARIA
50
40
30
20
10
0
0
2
4
6 8 10 12 0
ZONE
2
4
6 8 10 12 0
ZONE
2
4
6 8 10 12
ZONE
Graph 2. Correlation between Adult Number and Cover of
S.mangarevense
TRANSECT
EO
T
WO
Turbinaria
(density)
50
0
40
0
30
0
20
0
10
0
0
0 10 20 30 40 50 60 70 80 90
0 10 20 30 40 50 60 70 80 90
0 10 20 30 40 50 60 70 80 90
SARGASSUM
SARGASSUM
SARGASSUM
Graph 3. Correlation between Cover of Live Coral and
T. ornata
TRANSECT
EO
T
W
O
0 10 20 30 40 50 60 0 10 20 30 40 50 60 0 10 20 30 40 50 60
TURBINARIA
TURBINARIA
TURBINARIA
Graph 4. Correlation between Cover of Dead Coral and
T. ornata
TRANSECT
EO
T
WO
DEADCORA
L
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 0 10 20 30 40 50 60 0 10 20 30 40 50 60
TURBINARIA
TURBINARIA
TURBINARIA
LIVECORAL
90
80
70
60
50
40
30
20
10
0
Graph 5. Correlation between Cover of Live Coral and
S. mangarevense
TRANSECT
EO
T
WO
0 10 20 30 40 50 60 70 80 90
0 10 20 30 40 50 60 70 80 90
SARGASSUM
0 10 20 30 40 50 60 70 80 90
SARGASSUM
SARGASSUM
Graph 6. Correlation between Percent Cover ofT. ornata and S. mangarevense within
Transects
TIAHURA
60
WEST OPUNOHU
90
Per 50
cen
t
40
Co
ver
30
Per
cen 70
t 60
Co
ver 50
40
40
Val
ue
30
20
30
20
50
20
10
0
0
EAST OPUNOHU
60
80
10
10
2
4
6
8
ZONE
10
12
0
0
1
2
3
4
ZONE
5
T. ornata
S. mangarevense
6
7
0
0
1
2
3
4 5
ZONE
6
7
8
LIVECORAL
90
80
70
60
50
40
30
20
10
0
Table 2. Epifauna & epiphytes found on Turbinaria ornata
Tiahura fringing reef
Tiahura crest
Epifauna
1 Decapoda
3 Tangle worm
2 Gastropods
2 Opisthobranchs
Epiphytes
Dictyota
Jania
Boodlea
Padina
4 Polychaetes
5 Crustaceans
5 Flat worms
8 Anthozoans
Bryozoans abundant on
holdfasts
filamentous red
West Opunohu fringing
Epifauna
5 Echinoderms (Ophioroidea)
3 Terebellid Polychaetes
3 Opisthobranchs
West Opunohu Crest
Epiphytes
Epifauna
Jania
3 Opisthobranchs
filamentous green 5 Polychaetes
filamentous
10 larval Crustaceans
brown
1 Flat worm
1 Decapod
Encrusting Bryzoan on
haptera
2 Flat worms
1 Gastropod
21 larval crustaceans
East Opunohu fringing
Epifauna
4 Opisthobranchs
5 Anthozoans
5 Polychaetes
1 Gastropod
15 larval Crustaceans
Epifauna
2 Opisthobranch
7 Anthozoans
1 Decapod
1 Echinoderm
(Ophioroidae)
7 larval Crustaceans
5 Polychaetes
1 Flat worm
1 Sponge
Epiphytes
Jania
filamentous red
filamentous green
Halimeda
Epiphytes
Dictyota
Jania
filamentous brown
West Opunohu Crest
Epiphytes
Dictyota
Jania
Culpemenia
filamentous green
Epifauna
2 Pycnogonids
4 Opisthobranchs
>25 larval crustaceans
Epiphytes
Jania
Sargassum
Dictyota
filamentous red
crustose red (haptera)
Table 3a. Unweighted average of common fish species among transects
Family
Genus and Species
Acanthuridae Acanthurus nigrofuscus
Scaridae
Scarus sordidus
Scarus psittacus
Labridae
Thalassoma hardwicke
Pomacentrid Stegastes nigricans
ae
Chrysoptera
leucopoma
Pomacanthid Centropyge flavissimus
ae
Tiahura
East Crest
97
2
6
17
39
West
Opunohu
47.0
3.0
3.0
4.0
11.0
2
15.0
17
12
4.0
9
52
25
19
13
16
Table 3b. Weighted averages of common fish species among transects
Family
Genus and Species
Acanthuridae Acanthurus nigrofuscus
Scaridae
Scarus sordidus
Scarus psittacus
Labridae
Thalassoma hardwicke
Pomacentrid Stegastes nigricans
ae
Chrysoptera
leucopoma
Pomacanthid Centropyge flavissimus
ae
Tiahura
East Crest
9.7
0.2
0.6
1.7
3.9
West
Opunohu
5.9
0.4
0.4
0.5
1.4
0.2
1.9
2.8
1.2
0.5
1.5
8.7
4.2
3.2
2.2
2.7
References
Payri, Claude E.; N’Yeurt, Antoine D.R. 1997. A revised checklist of Polynesian
benthic marine algae. Australian Systematic Botany. 10(6): 867-910.
Payri, C.E. 1982. Les macrophytes du lagon de Tiahura (ile de Moorea, Polynesie
francaise). Inventaire floristique – Repartition – Biomasse – Variations
saisonnieres – Dynamique des populations de Turbinaria ornata (Pheophycees,
Fucales). These d’Etat, Universite des Sciences et Techniques du LanguedocRoussillon, Montpellier. 260 pp.
Payri
Setchell, W.A. 1926. Tahitian Algae. – Publications in Botany, University of
California, 12 (5) : 61-142, pl. : 7-22
Stiger, V.; Payri, C.E. 1999. Spatial and seasonal variations in the biological
characteristics of two invasive brown algae, Turbinaria ornata (Turner) J. Agardh
and Sargassum mangarevense (Grunow) Setchell (Sargassaceae, Fucales)
spreading on the reefs of Tahiti (French Polynesia). Botanica Marina. 42: 295306.
Stiger, V.; Payri, C.E. 1999. Spatial and temporal patterns of settlement of the brown
macroalgae Turbinaria ornata and Sargassum mangarevense in a coral reef on
Tahiti. Marine Ecology Progress Series. 191: 91-100.