Mystery fuzz floating at the surface of the pond. The small gas bubbles may be produced by photosynthesis.Over the surface of the sediment in the pond, there is a fuzzy layer of what appears to be brown algae. It gathers around patches of macroalgae, is soft to the touch, and sometimes floats to the surface in patches (see the above picture), especially at night. According to some of the graduate students in Oceanography, who have been working in the pond for years already, this fuzz showed up about a year and a half ago. We have speculated for a while as to what it might be (filamentous brown alga? Cyanobacteria? Other bacteria?) and finally looked at it under a scope today. It is a thick sludge of diatoms, held together in places by soft lumps of marine snow. The diatoms are pink in this picture because I took the picture under a fluorescent light (normally they're green or brown). The marine snow is that hazy, greenish stuff (it's grey under normal light).
A quick note about diatoms: they're algae, members of the division Ochrophyta, and are usually unicellular. The cells have a silica casing, known as a valve or frustule. Pennate diatoms like the ones we found here are long and slender as opposed to centric or "hat-box" shaped, and have a central groove called a raphe. Identification of diatoms almost always requires examination of the frustule, cleaned of organic matter, under Transmission Electron Microscopy (TEM). Since I haven't done this yet, I haven't identified these diatoms, but pennate diatoms are often found in areas with some freshwater input, which may explain their presence in the fishpond.
Microalgae at the sediment-water interface are important because many of the fish raised for food (awa, aholehole, moi) eat them. In most papers this combination of diatoms, cyanobacteria, and filamentous algae is just called microphytobenthos, or MPB.
