The 35th Polish Malacological Seminar

Abstract

S OF THE 35TH POLISH MALACOLOGICAL SEMINAR SPURTING – AN UNUSUAL BEHAVIOUR OF THE THICK-SHELLED MUSSEL (UNIO CRASSUS) DaViD c. alDriDGe1, adaM M. ĆMiel2, anna M. lipińska2, Manuel loPes-liMa3, ronalDo sousa4, aMilcar Teixeira5, kataRzyna zaJąc2, tadeusz zaJąc2 1Department of Zoology, University of Cambridge, Cambridge, UK 2Instytut Ochrony Przyrody Polskiej Akademii Nauk, Kraków, Poland 3Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Porto, Portugal 4Centre of Molecular and Environmental Biology (CMBA), University of Minho, Braga, Portugal 5CIMO – Mountain Research Centre, School of Agriculture, Polytechnic Institute of Braganca, Braganca, Portugal Spurting is an unusual behaviour of the thickshelled mussel (Unio crassus), first observed in the early 20th c. The females move to the river bank and spurt streams of glochidia-containing water toward the river bed. No similar behaviour has been observed in any freshwater bivalve species to date. Our aim was to verify the hypothesis that it might serve increasing of the glochidia dispersal and thus the probability of host fish infection. In May 2018 in the Biała Tarnowska River near Lubaszowa we measured the length of the mussels, frequency of spurting, spurting distance, volume of the spurted stream of water, number of glochidia per spurt; we recorded the number and behaviour of fishes near the spurting mussels. Statistical analysis showed a significant correlation between the mussel length, spurt volume and maximum spurting distance. There was no statistically significant dependence between the mussel length and number of glochidia per spurt, or mussel length and spurting frequency. The number of glochidia per spurt grew exponentially with the volume. Ca. 70% of fishes near the spurting mussels reacted to their behaviour. Spurting may increase the probability of infection of the host fish, albeit its range is limited. Bivalve reproductive behaviour is mostly unknown, but it may prove crucial to explaining the dramatic drop in abundance of endangered freshwater species. In the case of the thick-shelled mussel impossibility to come on shore to spurt may be the reason for its disappearance from regulated rivers. ALIEN VS. PREDATOR: DO DIFFERENCES IN ATTACHMENT STRENGTH AND SHELL RESISTANCE EXPLAIN PREDATOR SELECTIVITY BETWEEN DREISSENA POLYMORPHA AND DREISSENA ROSTRIFORMIS BUGENSIS? csilla BaloGh1, 2, zoltán seRfőző1, 2, JaRosłaW kobak3 1Centre for Ecological Research, Balaton Limnological Institute, Hungarian Academy of Sciences, Tihany, Hungary 2MTA Centre for Ecological Research, GINOP Sustainable Ecosystems Group, 8237 Tihany, Hungary 3Nicolaus Copernicus University, Faculty of Biology and Environmental Protection, Department of Invertebrate Zoology, Toruń, Poland The quagga mussel (D. rostriformis bugensis) has recently joined its long-established congener, the zebra mussel (D. polymorpha) in European waters. This is likely to result in forming new and modifying the existing inter-specific interactions, including direct relationships between the two species, as well as those between them and other organisms, such as inhabitants of mussel beds and molluscivorous predators. We checked how the appearance of the new invader might modify feeding conditions for molluscivorous fishes. We compared the attachment strength (after 2 days, 1 week and 1 month of exposure), shell crushing resistance and glycogen content of dreissenids across their entire size range; we tested whether and how these inter-specific differences translated into the fish predator (common carp, Cyprinus carpio) feeding preferences. The feeding experiment was conducted with unattached live mussels (of various sizes), attached (for 2 days) live mussels and soft mussel tissues freshly removed from the shell. Using this design, we intended to get insight into mussel traits responsible for the possible selectivity of the fish. Small zebra mussels had more resistant shells and stronger attachment than the quagga mussels. These differences were reduced (shell hardness) or reversed (long-term attachment) in larger individuals. Moreover, the zebra mussels had lower glycogen content than the quagga mussels. The fish clearly preferred the quagga over the zebra mussels, irrespective of their attachment status and size. The selectivity also persisted for soft mussel tissues removed from the shell. Thus, the preference of the fish for the quagga mussel depends on selection of higher quality food (higher glycogen content), rather than on the efficiency of the mus-