The nocturnal life of the great scallops (Pecten maximus, L.): First description of their natural daily valve opening cycle
Résumé
Valvometry techniques used to monitor bivalve gaping activity have elucidated numerous
relationships with environmental fluctuations, along with biological rhythms ranging from sub-
daily to seasonal. Thus, a precise understanding of the natural activity of bivalves (i.e., not
exposed to stressful environmental variations) is necessary as a baseline for detecting
abnormal behaviors (deviations). This knowledge is also needed to reliably interpret observa-
tions of bivalve gaping behavior and associated biological processes (e.g., respiration, nutri-
tion) acquired over time-limited periods. With this in mind, we investigated the natural daily
gaping activity of the great scallop (Pecten maximus) by continuously monitoring 35 individu-
als in several individual tanks and in situ (Bay of Saint-Brieuc, Brittany, France) using fully
autonomous Hall effect sensors. Our results revealed a circadian cycle (τ = 24.0h) in scallop
gaping activity. Despite significant inter-individual variability in mean opening and cycle
amplitude, almost all individuals (87.5%) exhibited nocturnal activity, with valves more open
at night than during the day. A shift in light regime in the tanks triggered an instantaneous
change in opening pattern, indicating that light levels strongly determine scallop activity.
Based on the opening status of scallops, we also identified several gaping behaviors deviat-
ing from the regular daily pattern (lack of rhythmicity, high daytime opening), potentially
reflecting physiological weakness. While further long-term studies are required to fully under-
stand the natural activity of scallops, these findings pave the way for studies focused on the
scallop response to external factors and introduce further research into the detection of
abnormal behaviors. Coupling observations of diel valve gaping cycles with other daily varia-
tions in organismal and environmental parameters could help explain mechanisms driving
the growth patterns of scallops observed in their shell striations. From a technical perspec-
tive, our field-based monitoring demonstrates the suitability of autonomous valvometry sen-
sors for studying mobile subtidal bivalve activity in remote offshore environments.
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