Field Trip: The New England Aquarium

After the nine thousandth call from the New England Aquarium informing me that my membership was about to / had expired, I figured I might as well march over there and renew it. They have a good sized coral tank, and I was looking for some photos I could use for raw material while working on the design of this blog.

It was interesting to observe the tank now, after five months of research into setting up my own tank. Previously it had been fairly inspirational, but now I was able to identify some short comings, or at least what would be viewed as such by the reef tank elite. Bubble and hair algae was rampant throughtout the tank, and the fish and invertebrate diversity was relatively low for what would be possible in a tank of that size. That said, it is still a beautiful aquarium and only one of the many tanks worth spending some time with at that facility.

Click any of these photos to head over to Flickr where you can get a larger view of them.

Reef Tank: Diatoms

Last night I noticed a golden-brown colored dust growing on the substrate and rocks. I spent some time searching for algae species identification charts, and eventually came across an About.com article regarding diatoms. A trip to Wikipedia and some other resources confirmed that was what I had most likely observed in my tank. Of particular interest to me was this section from About:

This type of algae outbreak typically occurs when a tank is just completing or has finished the nitrogen cycling process, new live rock is introduced, as the curing process can add nutrients when some organisms on the rock dies off, or tank maintenance has been neglected.

Obviously that would pertain to current events in my reef tank. I had assumed that ammonia levels, which had been as high as 8ppm three days earlier, would require at least another week to subside, and had resolved not to waste my time and test kits checking it every day. The growth of diatoms and subsequent information about them forced a change of mind, and I conducted my usual tests this evening with surprising results: ammonia had indeed dropped to somewhere between 0.25 and 0ppm, an impressive down swing from the levels recorded on Sunday. Nitrite and Nitrate were still high, but that would be expected as they are the products of processed ammonia.

Also of interest was this summary of diatoms and their use of silicates, found in the Wikipedia article:

Diatoms cells are contained within a unique silicate (silicic acid) cell wall comprised of two separate valves (or shells). The biogenic silica that the cell wall is composed of is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is then extruded to the cell exterior and added to the wall. Diatom cell walls are also called frustules or tests, and their two valves typically overlap one other like the two halves of a petri dish. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two valves and grows a smaller valve within it. As a result, after each division cycle the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide vegetatively, they reverse this decline by forming an auxospore. This expands in size to give rise to a much larger cell, which then returns to size-diminishing divisions. Auxospore production is almost always linked to meiosis and sexual reproduction.

Once again, an insightful article from Randy Holmes-Farley helps to clarify both the cause and effect. As mentioned above, diatoms construct their cell wall from silicate, hence their presence could be considered an indicator of silicates being present in the aquarium. His article discusses how silica occurs in the ocean and in the aquarium, as well as what organisms use it and how it can be controlled and dosed. Great stuff.

My assumption is that there would be a high level of silicates found in my tank due to a number of recent inputs:
• Unfiltered tap water for the initial tank fill
• Sand and sediment on the live rock
• Live sand substrate

So there should be plenty of raw material for diatoms, in addition to the high levels of light for photosynthesis (I've been running the tank lights 8 hours a day) and nitrate for fertilizer. Conventional wisdom seems to indicate that after the initial outbreak of diatoms in a new aquarium one can expect green algae to replace it. My initial hobbyist panic response to seeing my pristine new white sand bed polluted with some form of new algae has since been replaced with curiosity now that I've learned about the circumstances under which it appears. I intend to see if I can get a sample out of the tank and take a look under the microscope this evening, as the imagery on Wikipedia is quite stunning.

Todays Parameters:
Temperature: 81F
Specific Gravity: 1.026
pH: 7.9
Ammonia: .025ppm*
Nitrite: 5ppm
Nitrate: 10ppm

* The color of the ammonia test was actually somewhere between 0.25ppm and 0ppm, and closer to 0. In the interest of caution I am rounding up on the chart.

Links from this post:
Randy's article in Advanced Aquarist about silica and diatoms:
http://www.advancedaquarist.com/issues/jan2003/feature.htm

Wikipedia article on diatoms:
http://en.wikipedia.org/wiki/Diatoms

About.com article on diatoms:
http://saltaquarium.about.com/cs/algaecontrol/a/aa091100.htm