Field and laboratory observation of Mediterranean mussel Mytilus galloprovincialis predation by flatworm Stylochus mediterraneus

Recently, large numbers of Polyclad flatworms (Stylochus mediterraneus) have been observed in Istrian County shellfish farms connected to intensive ascidian fouling. To assess a possible threat and determine whether the flatworm feeds only on weakened dead mussels or can also infest healthy mussels,...

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Bibliographic Details
Published in:	Aquaculture reports Vol. 36; p. 102164
Main Authors:	Privileggio, Luca, Balković, Ivan, Grozić, Kristina, Pavičić-Hamer, Dijana, Jaklin, Andrej, Suman, Daniele, Brumnić, Lea, Maurić Maljković, Maja, Labura, Hrvoje, Oštir, Srećko, Hamer, Matija, Tanković, Nikola, Hamer, Bojan
Format:	Journal Article
Language:	English
Published:	Elsevier B.V 01-06-2024 Elsevier
Subjects:	Behavioural response Mytilus galloprovincialis Predator-prey interaction Stylochus mediterraneus Valve Gaping Mussel Monitoring System Valve Gaping Mussel Monitoring System Mytilus galloprovincialis Stylochus mediterraneus Behavioural response Predator-prey interaction
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Summary:	Recently, large numbers of Polyclad flatworms (Stylochus mediterraneus) have been observed in Istrian County shellfish farms connected to intensive ascidian fouling. To assess a possible threat and determine whether the flatworm feeds only on weakened dead mussels or can also infest healthy mussels, we have conducted a field research and laboratory mussel predation experiments. Performed field observations (August 2022–May 2023) indicated increased mussel mortality and, at the same time, increased abundance of flatworms from < 2 to 6/40 kg mussel ropes. Under laboratory conditions, flatworm feeding experiments with mussels (Mytilus galloprovincialis) and invasive tunicate species (Clavelina oblonga), showed a clear preference of flatworms for mussels. Using a newly developed valve gaping monitoring system (VGMM), based on an Arduino microcontroller platform and Hall sensors, we monitored valve gaping (VG) of mussels during acclimatisation (one day) and after exposing them to flatworms until the death of the first mussel (two days). Before and during exposure of mussels to flatworms, we were able to observe the normal daily rhythm of mussels VG (> 70 % time filtrating with the valve open > 50 %, with 1–5 resting periods), the behavioural changes of exposed mussels compared to control mussels, the timing of flatworm attack, the response of mussels during predation, and the timing of mussel death. We conclude that the flatworm S. mediterraneus is most likely a very opportunistic species that prefers weaker mussels but can also feed on healthy mussels. This investigation brings new knowledge and assumptions on the behavioural patterns of investigated flatworms. Further studies should consider that "experienced" flatworms attack and kill the mussels, while the rest simply eat a free meal using the strategy of the predator pack. [Display omitted] •Stylochus mediterraneus is an opportunistic species that prefers weaker mussels but can also feed on healthy mussels.•Mussels undergo rapid death approximately one day after infestation by the Polyclad flatworm.•Feeding experiments mussels vs. ascidians, showed a clear feeding preference of the flatworm for mussels.•Mussels generally filter more than 70 % of the time with the valve open more than 50 %.•Mussels show 1–5 resting periods daily without filtering with the valve open less than 30 %.
ISSN:	2352-5134 2352-5134
DOI:	10.1016/j.aqrep.2024.102164