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and untagged which had appeared in the cleared quadrats were counted. The data were analysed using regression analyses Zar, 1984.
A second study investigated the direction of dispersal and the distance moved by tagged clumps at the RB 1 site during an 11-day period of calm weather, and again after
an additional 21 days of rough weather caused by a tropical cyclone. Three replicate groups of 10 clumps, each with multiple branches and an attachment to one or more
small pieces of coral rubble rubble weight .1 g, were collected from the site. The clumps were marked by threading coloured, plastic flagging tape through a branch of the
association, using a large sewing needle. About 5 cm of tape was left protruding from each side of the branch. This tape was very light and flexible, so it did not become
caught in the rubble and was not likely to alter the rate of current-induced movement by the clump. Each replicate group was marked using different coloured tape and the
clumps, still attached to the rubble pieces, were placed at a point of origin marked by a tent peg flagged with the same coloured tape. The groups were placed along the same
depth contour, separated by |15 m. After 11 days, the distance from the point of origin and the net direction of movement were measured for each clump.
2.6. Growth Estimates of growth rates were obtained from photographic records, taken during
January and July 1994, of five small clumps of the association from the centre of the lagoon. From the January photographs, the combined length of all the branches in
individual clumps was determined, and the total was multiplied by the known, mean weight of a piece of the association 1 cm in length determined from 120 measurements.
During the following field trip 7 months later the clumps were photographed again and a second weight was calculated for each clump. The difference between the two weights
was divided by the number of days in the growth period, to give the average growth rate
21
in g wet weight day .
Several other methods for estimating the growth rate of the association were tested, including tagging branches and measuring increases in length from the tag to the tip, and
buoyant weighing; however, these methods often damaged or killed the clumps. Measuring the maximum height and width of individual clumps at the rubble banks, and
taking photographs of clumps along permanent transects to measure growth at the rubble bank sites were also unsuccessful, as strong currents often fragmented the clumps or
moved them out of the study area.
3. Results
3.1. Biomass Results of biomass harvesting at RB 1 supported the hypothesis that the standing
stock of the Haliclona Ceratodictyon association increased over time between De- cember 1989 and January 1994. This increase occurred despite the fact that at least one
severe storm October 1990 and two tropical cyclones March 1992 and January 1994
D .A. Trautman et al. J. Exp. Mar. Biol. Ecol. 244 2000 87 –105
95
passed almost directly over One Tree Lagoon during this period. The mean biomass of
22
the association increased t-test, P 50.001, from 6.2 g dry weight m 37.2 g wet
22 22
22
weight m to 25 g dry weight m
150 g wet weight m over the 50-month study
period Fig. 3a. In contrast, at RB 2, where the band of coral rubble between the reef crest and the
lagoon floor was only about 5 m wide, the hypothesis was not supported. There were at least two marked declines in the biomass of the association. These declines in biomass
were recorded soon after the passing of the October 1990 storm and the March 1992 cyclone. After these events, the recovery of the sponge population at this site was quite
rapid, but the biomass tended to remain at the same mean level, around 18 g dry weight
22
m , during the periods between the storms Fig. 3b.
22 2
Fig. 3. The biomass g dry weight m of Haliclona Ceratodictyon collected from an area of 16 m at a RB
1 and b RB 2. Collections were made from December 1989 to January 1994 mean6S.D.; n 58.
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The wet weight of Haliclona Ceratodictyon was 5.961.1 times the dry weight mean6S.D., n 5105. The dry weight to ash-free dry weight ratio was 1.560.2:1
following incineration at 5508C, and the intact association had an ash content of 32.865.1. No statistically significant differences were found between any of the
weight ratios of the clumps collected from the two sites. The wet weight to dry weight ratio of cultured C
. spongiosum was 7.8662.49:1 and the dry weight to ash-free dry weight ratio was 1.660.3:1 mean6S.D., n 55. The cultured alga had an ash content of
35.2610.9. There was significantly more algal tissue than sponge tissue in the association t-test,
P ,0.0001. A mean of 41.665.6 mean6S.D.; n 514 of the cross sectional area was occupied by the alga, compared with only 12.961.6 occupied by the sponge. Some of
the remaining ‘empty’ area may have resulted from damage to the association during fixation and sectioning, but it is likely that the most of this area was occupied by the
sponge aquiferous system. A small proportion of this area was also occupied by polychaete worms; the area taken up by these worms was not measured. The ratio of
algal to sponge tissue, 3.2:1, did not vary with season.
3.2. Size-frequency distribution At all four sites, the longest branches of 99 of the measured clumps were in the
range of 10 to 120 mm. At each of the three rubble bank sites the size-frequency distributions of the sponges were strongly skewed to the left Fig. 4a–c, indicating that,
at these sites, individual clumps of the association tend to be small, with the longest branch less than 80 mm long Kolmogorov–Smirnov test, P ,0.0126. At the site in the
centre of the lagoon, where there was less mass water movement, the size-frequency distribution of the sponges was normal Kolmogorov–Smirnov test, P 50.206 Fig. 4d.
These results supported the hypothesis that the maximum size of the clumps of the association is influenced by the degree of turbulence to which the clumps are exposed.
A one-factor analysis of variance showed that there were no significant differences in mean branch length between the four sites. The mean lengths of the longest branch
ranged from 50 to 57.3 mm at all sites. 3.3. Reproduction
Sperm cysts were found in about 5 of the clumps, between December and March, but no oocytes or larvae were observed in any of the histological sections of the
Haliclona Ceratodictyon association, whether collected from the centre of the lagoon or the rubble bank sites, at any time of year. Although both mature eggs and larvae are
large enough to be visible under a dissecting microscope Fromont, 1994, examination of longitudinally cut branches of the association collected from all sites during the
summer of 1993 94 did not reveal any sponge reproductive products. Periodic sampling since then has never shown any sponge eggs or larvae either.
Algal reproductive structures are, however, common during the summer. Up to 84 of the clumps of Haliclona Ceratodictyon at the rubble bank sites had sporangial
nemathecia with either carposporangia or tetrasporangia during December and January in each year.
D .A. Trautman et al. J. Exp. Mar. Biol. Ecol. 244 2000 87 –105
97
2
Fig. 4. Size-frequency distribution of the Haliclona Ceratodictyon association within an area of 60 m , at the sites of each of the four major populations in One Tree Lagoon; a RB 1, b RB 2, c RB 3, and d RR 1.
The data shown are the lengths of the longest branch in each clump.
3.4. Dispersal Over a period of 15 days, between 12 and 40 of the tagged clumps were lost from
each of the quadrats at RB 3. The mean rate of loss from this site was equivalent to
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0.04460.013 clumps m day
1.561 of the population per day; mean6S.D., n 53
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in summer, while in winter the mean rate of loss from the quadrats was equivalent to
22 21
0.08760.021 clumps m day
1.460.2 of the population per day. At RB 1, between 4 and 22 of the tagged sponges were lost from the quadrats over the 15-day
22 21
study period, at a mean rate of loss of 0.03660.026 clumps m day
0.860.6 of
22 21
the population per day during summer, and 0.0660.025 clumps m day
1.260.2 of the population during winter Fig. 5a and b.
The number of clumps which were moved back into the cleared quadrats after 15 days
22
ranged from 1 to 11 at RB 3, equivalent to a mean rate of 0.0360.03 clumps gained m
21
day during summer. During winter, between 0 and 8 clumps were moved into the
22 21
cleared quadrats at a mean rate of 0.0460.02 clumps gained m day
. At RB 1, between 6 and 14 clumps were counted in the cleared quadrats after 15 days, at a mean
Fig. 5. The percentage of tagged clumps of Haliclona Ceratodictyon which remained in the marked quadrats over 15 days during a July 1993 winter and b December 1993 summer, and the number of clumps which
were carried into cleared quadrats by the action of currents over 15 days during c July 1993 and d December 1993 at RB 1 d and RB 3 j means6S.E.; n 53.
D .A. Trautman et al. J. Exp. Mar. Biol. Ecol. 244 2000 87 –105
99
22 21
rate of 0.0560.02 clumps gained m day
during summer; while during winter, between 10 and 22 clumps were moved into the cleared quadrats at the mean rate of
22 21
0.0960.03 clumps gained m day
Fig. 5c and d. These results support the hypothesis that there is substantial movement of the clumps around the rubble bank sites.
Intact clumps of the Haliclona Ceratodictyon association were moved up to 3.76 m in 11 days in calm conditions Fig. 6. During this time, five of the clumps used in this
experiment had formed secure attachments to large pieces of coral and were considered to have become immobile under calm weather conditions. After an additional 21 days of
rough weather caused by a tropical cyclone, clumps were found up to 24 m from the initial point of origin. As only 18 of the 30 tagged clumps were recovered after this
period, it is likely that some were transported even further, outside the area searched.
The hypothesis that clumps of the association are moved randomly around the site was not supported. The direction of dispersal of the clumps was generally southerly,
corresponding to the direction of the prevailing current flow across the reef Frith, 1981. Only one clump was found a short distance north of the point of origin.
3.5. Growth All five clumps used to measure the growth rates of the association were estimated to
weigh between 10 and 12 g at the start of the experiment, when they had either three or four branches. Photographic records of these clumps showed a mean increase in branch
21 21
length of 0.38 mm day , which is equivalent to |91 mg wet weight day
for each
21 21
21
clump, or 0.0083 g g wet weight day
, or 3.5 cm year linear growth, totalled
over all the branches; or a doubling time of about 120 days, over a period of 192 days from January to July 1994. This increase in weight corresponded to at least a 250
increase in the mass of the association over this period.
Fig. 6. The distances and directions that members of three replicate groups of 10 tagged clumps were moved by the action of currents at RB 1, over a period of 11 days. The point of origin for each group is the point from
which all the lines in each group diverge scale bar5100 cm.
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4. Discussion
