Spoiler alert, the Hokey Pokey is not what this cruise is all about. I am here with NOAA’s Antarctic Ecosystem Research Division. Their mission, the reason for their whole existence is to study Antarctic marine ecosystems to support fisheries management and conservation. It’s a dual mandate that can be a bit conflicting at times. If you increase fishing you could compromise ecosystem functioning. If you have too many conservation measures, you could unnecessarily harm economically important fisheries. The trick is to find the sweet spot that preserves biodiversity and ecosystem function while allowing for healthy sustainable fisheries. The key to achieving this goal is through careful study and monitoring of fished species and all key dependent and associate species. The largest fishery in the Antarctic is the krill fishery. Mission one of this cruise is to understand how krill and associated zooplankton are distributed in in the region.
If you want to understand zooplankton, you must become zooplankton. Or, you know, just use a fine mesh net to fish some out of the water so you can study them.
Our net weighs about 150 lbs. Most of that weight is in the steel frame that holds the net open. The net itself is about 25 feet long (I think but I haven’t actually measured it). The net width, mesh size, and length are all fine tuned to ensure that the zooplankton experience the correct water velocity and don’t get destroyed in the net.
All that net leads into the “cod end”. You can see from the photo that the cod end is slightly smaller than a five gallon bucket. It is essentially a PVC pipe that has been capped off. A few holes have been drilled into it and covered with very fine mesh to allow water out, but keep microscopic critters in.
If there is a lot of slush in the water, the cod end turns into a giant snow cone. We then have to melt the ice before we can start looking at critters.
Once everything is melted we pour the catch into plastic trays and start the “picking and clicking”. We pull everything large out of the trays, identify and count them all. We use handheld clickers, the same kind they use at events to keep track of attendance, to keep count for each species
We are most interested in krill. When we get a full haul of krill it is ‘’game on”.
Krill can form huge swarms of millions of animals. When we find large swarms we just get over whelmed. We cannot count and take data on tens of thousands of krill between tows. At most we can count around 1,000 krill, and sub sample about 200 of them for length, sex, and maturity. One tow we got an estimated 35,000 krill. That was time to subsample! Don’t think we are just lazy, once krill die, they start decaying almost immediately. Within minutes of death they turn to opaque mush. It is nearly impossible to see their secondary sexual characteristics or even measure them.
Ok the decay thing usually happens, but Franken krill did not get the memo. “What is a Franken Krill?” you may well ask. Well one day in a really big krill tow, we found the back half of a krill. It was completely headless and then some. Its little swimming legs were still beating, its body was opaque but not mushy. We were fascinated, so we put it in seawater on ice just to see how long it would last. It made it 24 hours, but then we forgot to change the ice. Franken Krill got warm, the dish filled with fresh water, and then Franken krill was no more. Who knows how long it could have lasted if we had been better care takers.
There are some big things that we can easily identify in the trays like krill. But a lot of the time we must ‘scope it out to determine what species it is exactly.
Ok, ok actually we know what these are without scoping. There are three purple amphipods (Themisto gaudichaudi), and two pteropods (the orange at the bottom is Clione limacina). The orange at the top is a sipunculid, also known as a peanut worm, There is an assortment of clear jelly organisms. The ones with orange inside are siphonophores (Diphyes antarctica); the ones with yellow and brown inside are salps (Salpa thomsoni)
How do we ID the amphipod above? We use the micropes to look at eye shape, size, and color. As well as head shape, and the shape and length of legs.
The little amphipod is psuedorchomene plebs. We also spend a lot of time ‘scoping out larval fish.
Without a scope, I can not tell you what these little guys are. Most of the fish we get look like this. Super tiny, sort of white, with big eyes. We manly use eye shape and positioning of colored dots (melanophores) to determine the species.
We do between 2 and 4 tows during a 12 hour ship. We just crank though all the picking, clicking, and scope work. It can be exhausting.
So that is life in the zoooplankton lab. We pick and click 24 hours a day, seven days a week. Thank goodness we work shifts!
PS while all this is going on , another team is busy studying water column properties. They look for phytoplankton (chlorophyll and other chemicals in the water). They get all of their sample from a CTD rosette that is lowered through the water column immediately before the net. CTD is an acronym for connectivity, temperature, and depth.