The Attack of the Killer Rhododendrons (5 page)

P
ARTY TIME WAS OVER.
It was time to seek oysters in the Wadden Sea. Stavoren, also known as Starum, is in the
súd westhoeke
region of Friesland, also known as Fryslân. To the residents of Holland, also known as the Netherlands, everything is known as something else. Getting to Stavoren isn’t difficult. Getting away from Stavoren is a lot more challenging. Our target was the island of Texel in the Wadden Sea, where Lisa and I were to find Pacific oysters, also known as Japanese cupped oysters. Without a car, we were forced to take what was disparagingly referred to as the “tourist route.” This meant a ferry from Stavoren to Enkhuizen, a train to Hoorn, another train to Heerhugowaard, another train to Den Helder, and then a ferry to Texel.

The Netherlands is not a really big place. Even so, we got to see an awful lot of water and this was contaminated by an incredible assortment of introduced aquatic species. These include clawed frogs from Africa, water ferns from Brazil, Pacific crabs from Japan, round gobies from Russia, tubenose gobies from Germany, slipper limpets from the U.S., pond turtles from Italy, Wels catfish from Hungary, and soft-shelled clams from Canada.

The Wadden Sea is 500 kilometres of coastal waters stretching northeast from Den Helder in the Netherlands, past Germany, and on to Denmark. It is a region of low-lying islands, sandbanks, and mud flats, and long recognized as home to incredible biological diversity, making it a sought-after refuge for citizens looking for an unspoiled corner of Europe. Those with a commercial mind think of it as an important nursery for edible North Sea marine life.

In the 1800s, the Wadden Sea had a thriving oyster fishery based on the native European oyster. But, as so often happens, the harvest was a bit too zealous, and the fishery collapsed. Over the years
attempts were made to find ecological replacements for the native oyster, including the American oyster and the Portuguese oyster, but these efforts met with failure. Then came the new kid on the block.

In biology circles, the Pacific oyster has a rather nasty reputation for being where it shouldn’t be, including the Wadden Sea. Around sixty countries have reported it in their coastal waters, and it has become well established in at least twenty-four. In countries including Australia, Canada, Chile, and the Netherlands, the Pacific oyster is considered to be invasive, having a negative impact on the ecosystem and/or the economy.

The Netherlands has long been a seafaring nation, and Pacific oysters have probably been arriving in the Wadden Sea for centuries, attached to the hulls of ships. For reasons not fully explored, these oysters didn’t establish themselves. Then they were introduced intentionally in the hopes of re-establishing the oyster fisheries where their American and Portuguese counterparts could not. The Pacific oyster followed a pattern typical of the establishment of introduced species; their numbers remained low for a protracted period before rapidly growing in quantity and distribution. Today there are more than 60,000 tonnes of Pacific oysters living on the Wadden Sea’s tidal flats. Thirty years after first being reported as a self-sustaining species, their numbers in the Netherlands show no evidence of levelling off.

Pacific oysters are filter feeders, extracting plankton and organic material from the water with great efficiency. We are most familiar with them in their adult form, with two hard shells hinged along one side. But like others of their kind, very young Pacific oysters first spend three or four weeks as tiny free-swimming larvae before settling down to mature. When first establishing themselves in an area, Pacific oysters settle on a hard substrate, such as blue mussel shells. Once the oyster population is established, young oysters are perfectly capable of settling on the shells of older oysters. They require about two years to reach a size worth eating. They don’t stop there, living as long as thirty years, during which time they
grow to forty centimetres in length and more than a kilogram in mass. In places, they can grow to a density of between 500 and 1,500 individuals per square metre.

How bad are Pacific oysters in the Wadden Sea? There may not be much of an oyster fishery left in the region, but native blue mussels are still harvested. In places, oysters have overgrown blue mussel beds, creating difficulties for that fishery. Oyster numbers are up and mussel numbers are down, but it has proved difficult to draw a direct line from cause to effect and rule out coincidence. Blue mussel beds are fundamental for biodiversity in the region, providing a home for myriad marine life. It is not yet clear if oyster beds will provide the same foundation. The Pacific oyster is now a dominating species on Wadden Sea tidal mud flats and may, in the future, profoundly alter the ecology of the region.

France harvests about 150,000 tonnes of Pacific oysters annually. However, this is a fishery based on cultured oysters that are harvested when they are small. Wild Pacific oysters are not attractive to the consumer. They develop in huge clumps, grow so large as to be unpalatable, and come to the table covered with barnacles and other encrusted sea life.

A
MONG THE COUNTLESS PROBLEMS
associated with cellular telephones is the fact that I don’t have one. Moreover, when you try to call a cellphone from a payphone, you need to shovel in coins at a furious rate. So when Lisa and I discovered that some feebleminded city planner had put the end of the rail line in Den Helder on the opposite side of town from the ferry that would take us to Texel, we had to call my contact, Norbert Dankers, on his cellphone to tell him about the delay.

Almost as soon as the call was connected, the payphone started to beep to tell me that my 50 cents had been used up. As Norbert began to give me instructions to the ferry terminal, I dug out a €1 coin, and stuffed it into the hungry slot. “Look for a big town square then BEEP BEEP BEEP.” Another euro. “… Go straight ahead until you see BEEP BEEP BEEP.” By this point, I was out of
€1 coins, and the box then proceeded to ignore the parade of other coins I stuck into it, choosing instead to beep at me until I hung up.

The ferry to Texel was big and zoomy, and decorated in all the latest designer colours. After a twenty-minute ride, we found Norbert waiting for us with a van from the Royal Netherlands Institute for Sea Research. Norbert explained that the ferry was a little more crowded than normal because the region had been visited by its first humpback whale in 300 years, and folks were flocking to the region to see it.

With a grey beard and wire-rimmed glasses, Norbert is a classic example of a field biologist. Three years from retirement, he had a face that showed the effects of many mornings spent in a bracing wind. However, as a resident of the Land of the Super-fit Citizen, he cycles ten kilometres to and from work every day. Not satisfied with this, he trains once a week with a cycling group to improve his speed. That is before his training to run half-marathons.

In Norbert’s office at the Institute, we were joined by Rob Dekker and Gerhard Cadée, both with an interest in introduced species and the way that these creatures fit themselves into the local food web. They began filling us in.

When considering the potential impact of introduced species, they explained, it is important to assess whether or not local species are suffering from the intrusion. The intruder might be finding its own little niche and simply fitting in. Are Pacific oysters messing things up for the local fauna? Mussels are generally between 30 and 40 percent meat, and the rest is shell. In some regions where Pacific oysters have become very abundant, the meat of mussels has fallen to 18 percent.

Not all the mussel beds in the Wadden Sea have been taken over by oysters. However, as with all such things, it is hard to predict what the eventual outcome might be. In other regions, attempts to remove them have cost €30,000 per hectare. If an effort were made to try to control oysters in the Wadden Sea, we were told, it would probably require ten full-time ships.

Lisa and I heard that once Pacific oysters have grown to full
size, and after they have reached reproductive age, they are very stress-tolerant. They can deal with low salinity, and it takes exposure at low tide at –10°C to kill them. Lisa admired the shell of a particularly crenulated oyster that Norbert said was the result of the chemical tributyltin (TBT), an anti-fouling agent painted on ships’ hulls to discourage barnacles and other nasty hitchhikers. TBT didn’t kill Pacific oysters; it just made their shells more ornate.

Much of the Netherlands is either created or transformed landscape. Islands like Texel are just about the last bit of unaltered area of their type—naturally created and constantly moving sandbanks. We heard that the North Sea is overfished, but as it’s a marine environment, people cannot directly see the damage and so have trouble imagining the scale of the destruction. In contrast, the coastal portions of the Wadden Sea are exposed at low tide; you can see the area, and so people become involved in its preservation. There is interest in having the Wadden Sea established as a World Heritage Site. The region is generally thought to play an important ecological and economic role and is recognized as an important nursery for North Sea fishes.

T
HE FELLOW WHO CHECKED US
in to our hotel in Den Burg was the very model of a company man. As he waved his shaven head at us hypnotically, he explained that the hotel restaurant was a fine place to dine. “It can be put on your bill!” We said that we would probably find something to eat in town. He went on to extol the virtues of the hotel’s bar, explaining that the tab could be put on the bill. “Well, that sounds nice,” we said, even though it didn’t. We asked about our options for renting bicycles. “I can make a reservation for you and put it on your bill.” Lisa asked for alternatives. He responded: “Rent a bicycle or rent a car.” We allowed him to make the bicycle reservation and put it on our bill.

“I am sure that you will want this guidebook. It has everything you will want to know about Texel. It has maps.”

“I have good maps.”

“It has a tide table for Texel.”

“I downloaded a tide table for Texel.”

“It has everything,” he claimed. Lisa asked if he had an English version.

“No, just Dutch and German.”

“But we don’t read Dutch or German.”

“I can put it on your bill.” After that much sales effort, I let him put it on our bill. If Lisa hadn’t been with me, I suspect he would have offered to find me a prostitute and put her on my bill.

In the town’s main square, we found a nice little restaurant that served pancakes and the products of the Texel
bierbrouwerij.
On offer was Texels Amber and Texels Goud, but I settled on a Texels Witbier. It was close enough to vile as to be quite refreshing. Lisa pointed out that the restaurant’s music system played nothing but mid-’70s one-hit wonders. We watched the parade of cyclists, from pre-schoolers through advanced seniors, with not a helmet in sight. As a young boy, I probably would have donned a wig and called myself “Brenda” before I would have put my leg over a girls’ bike, the type with no cross-bar. On Texel, there was no obvious “thing” about a man riding a girls’ bike.

T
HE DAWN PROVIDED BEAUTIFUL SUNNY SKIES
and no wind. Slathered in SPF 20 sunblock, Lisa and I set off for the bicycle rental shop. This was pretty brave of me. The last time Lisa had got on a bicycle, about fifteen years earlier, she had swerved out of control and run me down. Growing up in rural Alberta, surrounded by gravel roads, Lisa had never come to terms with pedal power. But, she explained, she would have felt foolish trying to get around Texel any other way. It was going to be transportation the way the locals did it or nothing at all. She had been worried about having no control and swerving into the path of oncoming Dutch seniors. But once she got over trying to grip the handlebars too hard, she developed a mastery of her two-wheeled beast and was left with a sense of personal accomplishment. “I even managed to signal twice without going out of control.” She used the expression “KaPEEba” to indicate what the crash would have sounded like, and I resisted
the temptation to ask what part of the collision would have made that sound.

We set out from Den Burg along scenic and perfectly flat bicycle paths, past Oosterend, along a nasty detour for road construction near Oost, and on to the Lancasterdijk that separates the low-lying parts of the island from the Wadden Sea. The dyke was given its name in commemoration of the crew of an Allied Lancaster bomber that crashed there in WWII.

We reached the sea about an hour before low tide would expose the oysters, and so watched shorebirds foraging on sea life left behind by the receding waters. Adjacent fields were filled with lapwings, spoonbills, and avocets. We also watched a rich cross-section of the island’s residents and visitors cycle by. Many of these cyclists were considerably older than us, and were probably pedalling further. If I were to move to Texel, I suppose I would have to begin a diet of muesli and mega-vitamins just to keep up.

Lisa and I leaned back on the Lancaster dyke, soaking up the sun, eating almond pastries and waiting for the sea to recede. We didn’t really know what a Pacific oyster bed might look like from the shore, but big black smudges were being revealed at the water’s edge some hundreds of metres away. We walked across the tidal flat, trying to choose a route to the biggest smudge that would be least disturbing to the birds foraging on what the outgoing tide had left behind.

As we proceeded, the smudges revealed themselves as patches of oysters. Shoal beds, they stretched a couple of hundred metres. Ugly little devils. Rob had told us that they are unappealing to eat because they are too big to swallow in one gulp. They were grey, corrugated, rock hard, and cemented to everything else in sight. In turn, everything else was cemented to them, including barnacles, snails, and red and brown algae.

You have to give Pacific oysters in the Wadden Sea a high score on the yuck scale even before getting to the squishy bit on the inside. They would probably be best described as beautiful when covered at high tide. Lisa claimed to be surprised that there weren’t
more of them, given the big hype. Nasty-Pacific-oysters-as-far-as-the-eye-can-see sort of thing. But it was clear that if they continued to spread, occupying more and more of the intertidal zone, Pacific oysters would become an ecological force to be reckoned with.