Every country faces plagues. Rat plagues, mosquito plagues, cockroach plagues, mouse plagues… A plague occurs when the presence of a species becomes so numerous that it causes damage to the environment, agriculture, human health or infrastructure. In Spain, a specific pest is now being combated by eating the cause of it.
This is a pest in the Ebro Delta, one of the most important wetlands in the Mediterranean because of its biological richness. This wealth is now threatened by several environmental challenges. One of the most recent and notable of these is the invasion of the blue crab (Callinectes sapidus). This exotic species appeared in the natural park in 2012. Moreover, it quickly began to displace native species and destroy their habitats.
A tasty solution
Unlike other invasive species such as the zebra mussel and the apple snail, a unique solution has been found against the blue crab: it is eaten. Four years after its arrival, the blue crab was declared a commercial and edible product by the Catalan government. Since then, local restaurants have embraced crab and incorporated it into their menus.
Divided opinions
Although fishermen and restaurateurs are happy with the economic opportunities offered by the blue crab, biologists and conservationists are less enthusiastic. The crab is displacing native species such as the eel and the green crab, destroying their historic refuges. Nati Franch, a technical specialist of the natural park, emphasises in La Vanguardia that the goal is to stabilise the crab population and reduce it as much as possible.
Culinary challenges
Albert Guzmán, chef of a renowned restaurant in La Ràpita, only uses the blue crab as a base for broths and sauces because of its powerful flavour. Other local restaurants have incorporated the crab into their dishes and even organise cooking workshops around the blue crab. The public is enjoying the new culinary options, despite some misunderstandings about the colour of the crab after cooking. These are mainly based on the visual expectations of consumers and the lack of knowledge about the natural colour change of crustaceans during the cooking process. Cooking changes the colour of the blue crab to red or orange. That’s why some people confuse the blue crab with, for example, the king crab, which is naturally red.
Crab population management
The annual catch of the blue crab has now stabilised at approximately 350,000 kilos. According to Verónica López, biologist at the Institut d’Estudis Professionals Aqüícoles i Ambientals de Catalunya (IEPAAC), it is crucial to control the crab population to prevent environmental damage and maintain economic value.
Economic and environmental issues
Experts do not recommend processing and preserving the blue crab. This would lead to an increase in the crab population and that would actually be harmful to the biodiversity of the Ebro Delta. Moreover, the yield of the crab is low: only four kilos of meat are obtained from every 40 kilos of crab. That is why the crab is mainly sold fresh. Preference is given to crab caught in the sea because of its better taste.
Consequences of the plague for the Mediterranean Sea
In 2017, the blue crab was first sighted in the Guadalquivir estuary in Andalucia. Its arrival in the Gulf of Cádiz caused much controversy, especially among fishermen. Tiger prawm catches decreased significantly in 2021 and 2022. This led to the need to investigate the influence of the blue crab on the local economy and biodiversity.
A study by the project “The invasive blue crab in the Gulf of Cádiz” shows that the blue crab has a very varied diet. It mainly eats fish, molluscs and other crabs and therefore has a significant ecological impact on the existing ecosystem. In other parts of the Mediterranean, such as France, the blue crab is causing major problems for both conservationists and aquaculture companies. The crab eats everything, even oyster larvae, threatening entire industries.
Arrival of the blue crab
The blue crab is originally from the east coast of America. This crab is native to the Atlantic coast ranging from Nova Scotia in Canada to Uruguay in South America. The spread of the blue crab outside its native habitat is mainly due to human activity. For example, larvae were transported in the ballast water of ships.
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