Candyman, this "brown dust" is likely a particulate buildup of organic and inorganic matter that failed to complete the pathway through the decomposition channel to re-utilization. Commonly termed by aquarists as "detritus", these "dusts" can be generically lumped into the foramol sediment category (see the recently archived "I can't see a thing" thread) as far as sedimentology goes.
It is a safe assumption, based on the demographics of most hobbyists' systems to qualify "detritus" as a composition of fecal matter from fish, invertebrates, etc, as well as but not limited to coral mucus, chitinous invertebrate molts, algae particles, as well as many other constituents ranging from uneaten manners of food to the byproducts of general aquarium infauna (worms, grazers, etc) to planktonic community denizens. It also houses living organism, and can be tentatively referred to as an ecological patch all its own. In the wild, constitution largely depends on the locale of generation, and its ecological and biological components.
Depending on how the currents and energies prevail, in the wild, when cryptic or heterotrophically specific fauna and their dependents (everything from coral to grazing fish may consume particles similar to this while still topographically on the reef structure. Holothurians and small shrimp are generally the first to consume structure trapped detritus) get their trophic saturation, or even just get to consume whatever happens to pass their way, the rest is removed. Many many species of animals consume this in a
high energy reef environment, this cannot be stressed enough.
Relying on tides and currents in a suspended state, it can be sent inshore where it is processed by a number of adapted ecological patches (seagrass beds, mangrove hammocks), or even beaches (prominent function on oceanic, high current-traffic beaches). It can also be sent offshore, where the massive foraminiferal population can convert it indirectly over periods to the foraminiferal sludge that covers most of the oceanic abyssal plains of the world.
In our aquaria, most infauna can consume detritus, but almost always there is some left over from trophic saturation, or due to some other means, like a paucity of resuspension (via lack of current in the system to suspend the sediments from their point of manufacture), that inherently must be dealt with. Often, refugia or deeps
sand beds can contribute to the removal of these "leftovers", but even in lagoonal systems (that, like all other aquaria, cannot physically be set up to be as demographically functional as their wild counterparts).
Cheers,
Chris
[ 07-08-2001: Message edited by: galleon ]
