Particulate organic matter as a food source for a coral reef sponge.
2009
SUMMARY The ability of sponges to feed in diverse (including oligotrophic)
ecosystems significantly contributes to their ubiquitous aquatic distribution.
It was hypothesized that sponges that harbour small amounts of symbiotic
bacteria in their mass feed mainly on particulate organic matter (POM). We
examined the nearly symbiont-free (by microscopic observation) filter-feeding
Red Sea sponge Negombata magnifica in order to: (a) study removal
efficiency of naturally occurring organic particles, (b) measure the total
amount of absorbed particulate organic carbon (POC) and nitrogen (PON), and
(c) estimate organic carbon and nitrogen flux in this sponge. Total amount of
organic carbon and nitrogen in the Gulf of Aqaba was found to be
48.46±5.69 μg l –1 and 6.45±0.7 μg
l –1 , respectively. While detritus contributed 54% of POC,
most PON (84%) came from planktonic microorganisms, mainly prokaryotes.
Particle removal efficiency ranged from 99% (the cyanobacterium
Synechococcus sp.) to 37% (for eukaryotic cells >8 μm). On
average, N. magnifica ingested 480 μg C day –1
g –1 (wet mass, WM) sponge and 76.6 μg N
day –1 g –1 sponge. Ingested POC balanced 85%
of the sponge9s energetic demand but more is needed for biomass production
because it cannot digest all of the carbon. 54.4±16.1 μg N
day –1 g –1 (WM) nitrogen was excreted as
total ammonia nitrogen (TAN); however, nitrogen allowance should be higher
because more nitrogen is deposited for sponge biomass during growth. It is
hypothesized that the discrepancy in the nutritional requirements should be
covered by the sponge absorbing carbon and nitrogen from sources that are not
dealt with in the present research, such as dissolved organic carbon and
nitrogen. This study highlights the significance of detritus as a carbon
source, and prokaryotes as a PON source in sponge feeding.
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