Two colleagues from the ELKH Balaton Limnological Research Institute (BLKI), Csilla Balogh and Zoltán Serfőző, in collaboration with Jaroslaw Kobak from Nicolaus Copernicus University in Poland, have been studying the competition of invasive mussels and the related food preferences of carp in Lake Balaton. Researchers have shown that carp prefer quagga mussel due to its nutritional value. This means the successful spread of mussels is not due to protection against predation, but to a different strategy. The paper presenting the results have been published in the prestigious journal Freshwater Biology.
Currently, two invasive mussel species are competing to take over Lake Balaton: the zebra (Dreissena polymorpha) and the quagga mussel (Dreissena rostriformis bugensis). The two similar species have different survival strategies, with the quagga mussel proving more efficient.
Invasive zebra and quagga mussels from the Ponto-Caspian region have become dominant members of benthic communities after their appearance in European and North American waters. There is fierce competition between the two species, with the quagga mussel emerging victorious in most cases.
"We looked at the characteristics of the two mussel species that are important for fish food, such as shell and attachment strength, and nutritional value. In a behavioural ecology experiment, we monitored whether common carp (Cyprinus carpio) selects between the two Dreissena species and, if so, which mussel traits are responsible for the discrimination. The results showed that the fish's decision is influenced by the mussel's intrinsic value, such as caloric and glycogen content – which is higher in quagga mussels – and by the chemical properties that are thought to accompany it, such as odour and taste. The carp consistently chose the quagga mussel, regardless of its size, the hardness of the shell and the strength of attachment to a solid surface. This confirms our observation that it is not predatory pressure that plays an important role in the displacement of zebra mussels, but the preferential traits of the quagga mussel," explains Csilla Balogh, BLKI research fellow and primary author of the paper.
BLKI staff also sought to find out what might be behind the success of the quagga mussel. Previous results have shown that the quagga mussel grows faster and is more active in nutrient storage than the zebra mussel. The zebra mussel spends a lot of energy on defence, thanks to its harder shell and stronger attachment, while the quagga mussel focuses on growth and reproduction. This is an advantageous strategy in Lake Balaton, where the quantity of mussels is significant and predatory pressure is comparatively low.
The research was supported by Balaton Halgazdálkodási Nonprofit Zrt., under project No. MAHOP-2.1.1.-2016-2017-00005; NKFIH-872.