Sarah Bedolfe
Sarah enjoys summer between two Dutch seas while researching invasive species.

In the 1960s, aquaculturists in Europe had seen the native European oysters (scientifically known as Ostrea edulis) decline and were looking for a new species to farm. The Pacific oyster seemed perfect: it succeeded in trials and it was unable to reproduce on its own in the chilly waters of the North Sea… Or so they thought. It turns out that the species thrives here, and so it began to spread.

Sarah on an oyster reef

Repping One World One Ocean during a warm day of field work. Although tourists often stop to ask our research team if we’re gathering dinner, these samples of mussels and oysters (and parasites!) are for experiments.

The Pacific oyster (Crassostrea gigas) in northern Europe is a classic example of an invasive species: it is found in a region that is far outside of its normal range, and it competes with native species that are accepted here, such as the blue mussel (Mytilus edulis). While the Pacific oyster was introduced to these waters intentionally, its expansion was unforeseen. As is so often the case with invasive species, by the time anyone noticed, it was too late to stop it.

Luckily, unlike some invasives, the oyster isn’t extremely destructive for the local ecosystem. In fact, in some ways it has been beneficial. As oysters grow, they create a reef structure that creates a habitat for many other species. And (so far) it has not posed a serious threat to the blue mussel.

Mixed bed of native blue mussels and invasive Pacific oysters

A mixed bed of native blue mussels and invasive Pacific oysters (also home to lots of snails and more) along the Wadden Sea shore of Texel.

However, a newer possible threat has emerged. It seems that when the Pacific oyster was introduced, it was infected with a parasite called Mytilicola orientalis. (These Latin names just roll off the tongue, don’t they?) I’ll call it Mytilicola for short.

The problem is that Mytilicola no longer infects only oysters; it now also infects the native blue mussels – and nobody knows what kind of effect it might have! My job now is to help figure out what that is. To answer this question, I recently moved to Texel, an island in North Holland that serves as home base for the NIOZ Royal Netherlands Institute for Sea Research. In total, I’ll spend six months doing research in the parasite lab and earning credit towards my Masters degree in Marine Biology at the University of Groningen.

Looking across the water to the mainland

Even on stormy days Texel is beautiful. The distance from the mainland to the island is just over 2.5 miles – but it’s a whole world away.

Exploring my new home in the sunny summer months has been a beautiful adventure. It’s always hard to compare beaches here to what I’m used to in Southern California but I can never complain about living on a coastline – much less a small island where I’m surrounded by water. A three-minute stroll from home takes me within view of the Wadden Sea. The beach on the island’s opposite shore faces the North Sea and is just a scenic twenty-minute bike ride away.

Swimming in the harbor

Summer, sunshine, swims – sometimes it almost felt like I was back home in California.


A sea nettle drifting in the harbor alongside a dock overgrown with algae.

I’ve also already spent some time in the field. Just like for my previous project involving diatoms, I have to go out onto the mudflats, but instead of staying on the soft sediment, this time I’m looking for the oyster and mussel beds. These solid reefs are where we collect the shellfish (and the parasites inside them) that I will use in my studies.

One highlight from my summer was trying a Dutch-ified version of a California hobby: stand-up paddle boarding! SUPping along our Laguna Beach coast was one of my favorite things to do with my One World One Ocean colleagues – I never thought I’d be doing it on a lazy river just a stone’s throw away from a field of cows!


SUPping: a visit to the rural back-country of the Netherlands gets a California twist.

Troost, Karin. 2010. Causes and effects of a highly successful marine invasion: Case-study of the introduced Pacific oyster Crassostrea gigas in continental NW European estuaries. Journal of Sea Research. Volume 64 pages 145-164. Link.


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