At the marine lab we have many seawater tanks and tables in various shapes sizes. For my purposes the most useful are the tables. The tables are shallow, about 20 cm deep, but what's nice about them is that water depth can be managed by varying the height of the stand pipe in the drain. I have some critters wandering free within tables and others confined to tanks, colanders, or small screened containers. One of my tables contains the paddle apparatus that stirs jars of babies when I'm raising larvae.
All of these tables are gravity fed from a supply of semi-filtered seawater supply in the ceiling of the building. The seawater flows through some sand filters before being pumped to the top of the building, but is by no means entirely clean. We get all kinds of things recruiting to the surfaces of tables, jars, or anything that sits in a seawater table for more than a few days. Some of the stuff that recruits is a nuisance, such as the spirorbid worms that build tiny calcareous spiral tubes on just about anything and scrape up the knuckles something awful. Other stuff is benign, and more or less ignored until it gets in someone's way. Or until I decide to take a close look at it.
Last year I finally decided to look at some of the red filamentous stuff growing on the bottom and sides of one of the tables. To the naked eye it doesn't look like much, which is why I love having access to a good compound scope. Here's my notebook page from that day:
Today I took some pictures of the same stuff. It's really pretty and delicate when you see it magnified!
I am always gratified when I look back at drawings I made in the past, and find that they still hold true and can be corroborated by photographs. The filamentous reds are so pretty! This is not the best time of year to find sexy algae, and I saw no reproductive structures on any of the filaments I examined. Maybe next spring.
In a different table (the table where the paddle apparatus is, actually) there is some brownish fluffy stuff growing on the bottom surface. I took a look at some of it and noticed right away that the threads didn't have their own inherent structure the way the Antithamnion defectum does. These threads seemed to be sticky, and when I picked up a little piece of the fluff it collapsed into a blob. I had to tease apart the threads in a drop of seawater to make sense of what was going on.
These diatoms are really cool! I have no idea which species they are, though. We do have local diatom genera (Thalasionema and Thalassiothrix) in which adjacent cells stick together at their ends to form this kind of wonky chain, but the cells themselves look different. So for now these are unidentified diatoms.
There's no doubt that they are diatoms, though. They have the typical diatom color, a golden-brown that I would name Diatom if I got to name colors, and I could see through the microscope that the cells are enclosed in a silica structure called a frustule.
This is the diatom color:
At higher magnification the sculpting on the frustule surfaces becomes visible. Unfortunately, at higher magnification you necessarily have less depth of field, so it's more difficult to take photos that show this kind of detail.
Some of these cells appear to be doubled. I think one of two things is going here: either the cells simply remain attached to each other by a thin layer of mucilage, or a cell has recently divided and the two cells that are stuck together are the resulting daughter cells. Throughout the growing season diatoms reproduce clonally (each cell divides to produce two genetically identical daughter cells), and their populations can expand very rapidly in response to either natural or artificial nutrient inputs. Because the cells are enclosed by a rigid frustule, however, this clonal replication cannot continue indefinitely. Perhaps diatom reproduction is fodder for another blog post, if people are interested.
But don't those cells look cool?