The culture lab is where Two Oceans Aquarium Aquarist Michelle Kirshenbaum grows billions of microscopic organisms, forming the base of the Aquarium's food web. For many species, from jellyfish to seahorses, their daily meals are raised right here in this small laboratory.
We chatted with Michelle about her cultures
Nannochloropsis aka "green water"
This is a genus of marine algae with very simple structures. They are unique among single-celled algae genera for their use of a chemical called chlorophyll A for photosynthesis, which gives Michelle's "green water" its characteristic green-yellow colour (rather than the more common blue-green). Nannochloropsis is tiny - each organism is only about 2 micrometres, so small that you could fit 125 of them into a drifting particle of morning mist.
Michelle says: "To feed the rotifers I make 'green water' , which is a colony of Nannochloropsis, which I source from overseas to make sure it is a pure, uncontaminated culture. It looks like a paste, but this is actually a live plant that can grow. We grow these in glass jars in the 'green lab', a temperature- and light-controlled environment."
"For an idea of how fast they grow: from a 25 litre batch, I remove 10 litres every day to feed to the rotifers and within the next 24 hours all that Nannochloropsis grows back. Just like plants in your garden, they use the water, they need air and light to grow back. Every week or so, the buildup of algae on the side of the jar facing the lights becomes too thick, so I need to strain it all, clean my equipment and start a new culture."
Rotifers aka "wheel animals"
Rotifers are a phylum of more than 2200 micro-organisms, usually inhabiting freshwater, but a few rare species (like those at the Aquarium) are marine and form part of the ocean's zooplankton. They reproduce a lot - females can easily clone themselves, making them the ideal prey for a huge number of ocean creatures, from tardigrades to comb jellies.
"Our starter cultures of rotifers came from the Seapoint Marine Research Aquarium, which we have a great relationship with," says Michelle. "Because rotifers are always reproducing, I am just moving the culture into larger containers and adding more water."
"Most fish farms use rotifers, because they are so small. As one of the smallest organisms, it is one of the few foods that tiny fish fry are able to eat. Ideally, you want a dense colony of rotifers so that the fish don't need to burn much energy trying to find food. As the fish grow they will move on to Artemia. Rotifers are also fed to the jellyfish and sometimes sea fans."
Artemia aka "sea monkeys"
You've probably heard of Artemia by their colloquial name, "sea monkeys." Despite this name, they do not live in the sea, and are not primates - they are tiny brine shrimp that live in salty lakes.
"We import dehydrated Artemia eggs from America, which are actually harvested in Great Salt Lake, Utah", says Michelle. "Locals actually get fishing rights and stake out a claim in the lake which they will harvest when water levels drop. The three major supplies are Argentina, Siberia and Salt Lake. We prefer the Salt Lake Artemia as it is a higher grade - meaning we can expect more of the eggs to hatch."
Michelle continues: "In order to get the Artemia to hatch, I rehydrate the eggs for about two hours with fresh water. Then I add household bleach which breaks down the eggs' shells, and then I neutralise the bleach by adding vinegar. White vinegar, not balsamic because the fish don't like their food flavoured."
"The Artemia eggs are then left to grow overnight. We would normally let them hatch in fresh water, but because of Cape Town's drought, we do it in full-salinity seawater now, with a warm temperature and a constant air supply. We make sure that the air is bubbled through the eggs to make sure that they are all exposed to light and water and don't just sit at the bottom."
"Within eight hours we can expect the Artemia to hatch, and they will be able to feed on their yolk for the next three to six hours," continues Michelle. "Thereafter, they are fed Nannochloropsis, so that by the time the Artemia are fed to other Aquarium animals they are about three days old and have been sufficiently nutritionally enriched."
"The Artemia is what we feed to most of the invertebrates, from feather anemones to jellyfish, and even to juvenile fish larvae and seahorses. In nature, these animals would be feeding on mysid shrimps, but because we cannot easily culture mysids without a very large area, we substitute Artemia. Artemia's uniquely hardy eggs also allow us to make an exact amount of food as needed," concludes Michelle.
I worked in publishing and now I look at microscopic animals under the microscope, as well as grow them. Which is a major satisfaction point. If I had known, when I was at school a 100 years ago, that this is what makes me happy, my whole life would be different.” – Michelle Kirshenbaum, Aquarist
This is just a tiny look behind the scenes at the incredible intricacy that keeps the Two Oceans Aquarium afloat. From the hundreds of passionate employees, like Michelle, who arrive before our doors open to the logistical challenges of internationally shipping giant spider crabs - there's a whole lot more to discover about the Aquarium. Tune into the M-Net 101 for the next episode of The Wild Ones: Aquarium: An Aquatic Life to delve deeper.
Want to know more? #AskAnAquarist!