Infectious Curiosity


The blue mussel (Mytilus edulis) filters the water around it in order to pick out tiny planktonic particles of food. Filter feeding is very common among ocean animals because there’s so much edible matter suspended in the water column. But it’s not only the way that mussels feed - it’s also how a mussel may inadvertently take in a parasite.

Armed with a microscope and pipette, I painstakingly moved parasite larvae
from their hatching dish to the tank of their host mussel. 

In the last two posts I described how an invasive species (Mytilicola orientalis) is parasitizing the native mussels of the Wadden Sea in the Netherlands though its effect is not yet known. I managed to extract the parasites and rear their eggs for research, but that’s not even the half of it. Next I had to collect uninfected mussels and get them to take up the newly hatched parasite larvae. Then I had to let them incubate for two months, all while running tests on the fitness of the mussels.

The larvae of the parasite Mytilicola orientalis go through several life stages. This one is not even a quarter of a millimeter long; the red spot is its single eye.

An aerated container with one of my experimentally infected mussels - or at least I hoped it was infected! I won’t be sure until the study is complete.

I expect that mussels that are infected will be stressed, and they will have less energy to spend on filtering.  Therefore my hypothesis is that infected mussels will feed slower and grow slower than mussels that are free of the parasite.

To measure how fast a mussel filters, I put a certain amount of food in the water (in this case microalgae) and measure how quickly the food disappears. With these measurements I can calculate the feeding rate. This became my weekly ritual: brewing algae concoctions, fiddling with the measuring devices - which have proven to be finicky instruments - and taking precisely timed samples from each of my mussels.

This is a carefully controlled scientific experiment, but it’s also an “experiment” in the sense that we had no idea if it would actually work! My main reference was done with a different species. The only way to confirm if the infection I am studying took hold is to dissect the mussel – so I have to wait months until the experiments finish before I can actually confirm that they succeeded. This gives me lots of time to be nervous about my results!!

The illusion of the Wadden Sea at low tide: the mudflat is still barely submerged, and the hikers on the horizon seem to be walking on water.

Considering that I never ran the risk of getting frostbite in lab, though, my working conditions have been downright luxurious compared to Melissa’s fishing in Canada. In fact, once the frustrating tech troubleshooting was past, the worst part was the monotony. In order to know that a certain result is a real effect and not just a coincidence, you need to run your experiment multiple times, so I had over 100 mussels that needed not only measuring but also regular feeding and cleaning.

Sometimes, I pulled my trusty waders back on and headed onto the mudflat to help with other projects and get some fresh air. This seemed like a great idea, at least until November when I realized it was past 8 AM, the sun still wasn’t up yet, and I had volunteered to brave the wind-swept expanse of mudflat at nearly freezing temperatures.

The island of Texel is reputed to be the Netherland’s sunniest but also windiest destination. A beautiful autumn afternoon was the perfect time to explore the northern point.  

I still have much left to explore on Texel so more relaxing excursions happened on weekends. On the island’s northern point, a friend and I climbed to the windy top of the lighthouse, looked across the channel to the next island in the archipelago, and sat in a beachside café while watching kite surfers zip across the waves. In stark contrast, the southern point is a broad, shifting sandbar best reached via a footpath through the dunes and then a long walk across the sandy flats.

The southern point of Texel is an undeveloped sandbar where the ceaseless wind carves seashell sculptures in the sand.

The whole time, of course, one question remained in the back of my mind: Did my experiment work? If my mussels failed to become infected by the Mytilicola orientalis larvae, then all my tedious work may have been for naught. Stay tuned because by my next post I’ll know…

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