Illustration Roland Blokhuizen
It could be the scenario of an 80s B-horror movie: the world is threatened by an unstoppable march of mutated ‘homarids’ who can clone themselves. But they really do exist, these female crustaceans, which reproduce asexually in our ditches, lakes and canals. The marbled crayfish is a mutation of the American Florida crayfish that entered the ecosystem through the aquarium trade. Sounds terrifying. But to be very honest, this marble crab the least of our problems.
The Dutch ditches are overrun by as many as six different species of American crayfish, including the knobby, the spotted, the Californian, the striped and the red. That freaky cloning marbled crayfish is the smallest of the invasive bunch and actually only thrives in places where no other crayfish species occur.
What we should be concerned about are the last two in particular. The striped and red are the perfect invasive exotics: they are almost indestructible, eat everything, spread at breakneck speed and are resistant to diseases that eliminate their native competition. The males of the red American go one step further: they even come out of the ditch at the end of the summer. Those are the cheeky ones that you can find on the bike path or in the playground in August, menacing with the scissors in the air.
The first American crustaceans probably arrived in Europe more than a century ago. In the Netherlands there is no patient zero to designate. The spotted bird entered via the Meuse on its own, after it was imported elsewhere in Europe as fishing bait. “We strongly suspect that the other species were imported for culinary reasons,” says Ivo Roessink, researcher at Wageningen Environmental Research. “There is a story that somewhere in the eighties in the region of The Hague there was a restorer who dumped his surplus of red American crayfish into the canal. But that is of course impossible to control.”
Roessink conducts research into environmental stress. This also includes the impact of invasive exotics on the ecosystem. He has been involved with crayfish since 2009. The biggest ecological problem is that they are all carriers of the lobster plague. A water fungus to which the Americans are resistant, but to which the native European crayfish die within a few days. As a result, the European crayfish has been decimated in the Netherlands. There is only one population left, somewhere near Arnhem. “Our own crayfish already had a hard time due to the canalization of the waterways and increasing water pollution. Then there was the lobster plague. And a high competitive pressure: these European crustaceans are adapted to the cold Northern European climate: they grow more slowly and reproduce more slowly. Those invasive species are smaller, faster and produce many more offspring.”
This endangers the entire ecosystem, because they eat everything: aquatic plants, fish eggs, rare amphibians. And they dig a lot more than the European lobsters.
Then such an ecosystem ends up in a vicious circle: “Fewer aquatic plants means more turbid water. In addition, digging increases the amount of sediment in the water column. As a result, less light comes through the water and the few aquatic plants that are left will do even less well. The number of small water creatures is decreasing, fish are less able to lay their eggs. The risk is that you end up with a bare tank of green algae soup and a few robust animals like bream and carp and some mosquito larvae.” And more and more of those invasive lobsters, because they themselves are not bothered by it. “They’re like tanks. When the aquatic plants are finished, they start to use the organic material on the bottom. When that’s gone, they eat each other. They are really the last ones to get out.”
Digging those holes not only causes damage to the ecosystem, in the worst case it leads to bank subsidence. The indirect economic damage caused by the disappearance of aquatic plant structures is less visible. “But it is becoming increasingly evident now that various water boards are claiming that the suffocation of the water also leads to more blue-green algae, so that cows can no longer drink from the ditches and recreational areas have to be closed,” says Roessink, who researches Crayfish within the Knowledge Platform. how scientists, water managers and inland fishermen can tackle this problem together. “A quick solution is no longer possible, because these critters have been able to go about their business undisturbed for thirty years.”
There are some native predators, such as grebes, herons, gulls, pike and bass, who are told that these invasive crustaceans are high in protein and well stocked. But that won’t turn the tide. Roessink: “It is rare in nature that a predator causes a prey to become extinct. It almost always works the other way around.” There is only one top predator for whom this applies: humans. Then active fishing and eating is the most obvious solution to the crayfish problem. But then we have to fish all the crayfish, not just the large ones.
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Regardless of whether fishing is theoretically the most effective method of combating the crayfish plague, it is a totally absurd situation that the supermarket here is full of exactly the same American red crayfish tails, but grown and completely imported from China, while here they are literally the walk out of the ditch. Then it makes no sense not to eat them. The condition is therefore that we make it profitable for inland fishermen to fish and land all crayfish, including and especially the small ones. Fortunately, there is also a perfect, super tasty application for the very little ones.
Crayfish are small critters, so we mainly eat them for the tail meat – the claws are rarely worth cracking. Crayfish, like their saltwater cousins, are pleasantly sweet and the structure of the flesh – if not cooked for too long – is nice and springy when chewed. This is because the protein composition and structure of all lobsters is broadly the same, says Gert Flik, former professor of animal physiology at Radboud University.
However, most of the flavor is in the parts we usually throw away. The abdomen (the part chefs call the tail) is actually a large mass of swimming muscles that move the fin-like plates on the underside – allowing the lobster to swim back relatively quickly if danger threatens. What we refer to as the ‘head’ in shrimps and lobsters is actually the cephalotorax (a kind of head and body in one). There are the digestive, respiratory and circulatory, nervous and reproductive systems. The most important culinary organ is the hepatopancreas, the midgut gland. It is often referred to in the kitchen as the liver, but in fact it is an organ that functions as the liver and the pancreas at the same time. This is where the digestive enzymes are produced and it serves as a storage place for energy-rich fats. This makes it one of the fattest and therefore tastiest parts of most crustaceans. That is why real gourmands always suck out the ‘cups’ of the prawns.
The armor itself, which consists of proteins and minerals, also contains taste. Particularly in the epithelium, the ‘skin layer’ just below the hard exoskeleton – which contains the tissue responsible for the calcification of the armor – potentially contains a lot of flavourings, says Flik. He conducted research into the absorption of calcium in European lobster. The biggest difference in taste between a freshwater and a saltwater crayfish lies precisely in this: calcium. River water contains ten times less calcium than sea water. Logically, the exoskeleton of a crayfish contains less calcium, explains Flik. Calcium is so scarce and valuable to crayfish that they remove it from their shell before molting and store it temporarily in stomach stones (gastroliths). They then use that in the formation of the new, larger armor, according to Flik.
The trick is – that goes for all shellfish – to use a lot of fat when frying the armor before adding water.
They therefore lack that salty and ‘chalk’ taste. But you can just as easily make a delicious bisque from crayfish. And that is exactly what you can use the very small ones for. The trick is – that goes for all shellfish – to use a lot of fat when frying the shells before adding water. During heating, tissues disintegrate and proteins denature. This releases aromas and pigments – which is why a lobster turns red when cooked. Both the pigments and the aromas like to dissolve in oil. So a lot of fat in the beginning ensures better flavor extraction. You eventually want to see those little red ‘fat eyes’ floating when the broth is reduced, which contains the pigments and the aromas – so you can use the color as a signal substance for the taste. The water phase of the soup also contains taste, of course, other aromas dissolve in water. But without those fat-loving aromas, the taste of the soup is simply flatter and duller.
For an optimal taste experience, we also have to make sure that we find all the aromas in every bite – and not just in those first few spoons. We do this by putting the immersion blender with a few knobs of cold butter in the soup or sauce just before serving. In the kitchen this is called ‘assembly’. You use this to emulsify the sauce or soup: the immersion blender breaks the fat globules and distributes them evenly in very small fragments over the water phase, so that it looks like a homogeneous mass. Now you can enjoy the full potential of both fat and water dissolved aromas with every bite.