The phototrophic sponge Phyllospongia lamellosa is found
to depths of 30 m on Davies Reef. Studies of the photophysiology show that
this corresponds to the depth at which the sponge–symbiont system can
meet 80% of its daily respiratory carbon needs photosynthetically. Net
24-h production was constant to a depth of 20 m (20 µmol
O2 g-1 fresh weight day
-1 ) and then decreased to compensatory levels at 25 m.
The maintenance of net 24-h production to a depth of 20 m was characterized by
reductions in the sub-saturating light intensity
(Ik ), indicating increased
efficiency of light usage at depth. At depths greater than 20 m the changes in
Ik could not compensate for the
reduced light intensity.
The respiration rate of Phyllospongia (3–5
µmol O2 g-1 fresh weight
h-1 ) was significantly greater than that of the
heterotrophic sponge Ianthella (2.0–3.6 µmol
O2 g-1 fresh weight
h-1 ) to an extent that depended on season and location.
Respiration rates for both species changed similarly between seasons, being
higher in summer. There was no evidence for increased respiration rates in
shallower water (<10 m), suggesting that this is not a cause for the
reduced occurrence of Phyllospongia in shallow waters.
The distribution and photophysiology of two forms of Cymbastela were investigated. One form, which fitted the description of C. notiana, was found in the gulf waters of South Australia. A second form was found on the protected sides of islands along the oceanic coast of Victor Harbor in South Australia. Both forms are rare but when present occur at depths of 5-15 m in association with foliaceous red and brown macroalgae.
A fully automated respirometer was used in situ to investigate the photokinetics of the oceanic form at West Island (SA) during winter (June 1993) and summer (January 1994). Owing to the rarity of this sponge only four samples, three in the winter and one in the summer, were investigated. This form of Cymbastela was capable of photosynthetically compensating on a net 24-h basis at 4.5 m depth in the winter, whereas it was a net producer at that depth during the summer. Photokinetic measurements were used to model the phototrophic production of this sponge. This model predicts that sponges would generally compensate at a depth of 11 m in winter. These results are tentative, however, because sample sizes are small owing to the rarity of this species.
A preliminary investigation of the production and photosynthetic efficiency of
a temperate, sub-tidal, turf algal community using
in situ measurements of photosynthesis and respiration
is reported. Results indicated that temperate turfs have high biomass specific
productivity, but are less productive on an areal basis than either the
surrounding macro-algal community or their tropical counterparts. Net 24 h
production ranges between 12 and 78 mmol O2
m-2 d-1 (corresponding to a carbon
fixation rate of 0.1–0.9 g C m-2
d-1). Inefficient use of the available substrata, due to
the early successional nature of these communities, is considered to be the
cause of this low productivity. A quantum efficiency of 0.034 µmol
O2 µmol photons-1 and a
sub-saturating light itensity of 134–210 µmol photons
m-2 s-1 indicate that
photosynthetic saturation was easily achieved and suggests that self-shading
in the turf community was not significant.
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