Methodological approaches to using bivalve gaping behavior as bioindicator

Bivalve mollusks are ecologically and economically important filter feeders which are considered useful bioindicators of environmental change. Their sedentary lifestyle integrates local conditions over time, while their continuous filtering activity makes them sensitive to changes in water quality. Their filtration and physiological status are potentially reflected in their shell opening behavior. This behavior can be measured by so-called valvometry, which has been applied across diverse research fields. Here, we summarize existing research on valve gaping to provide an overview over valve gaping behavior as ecological indicator across different species, habitats and applications. A systematic literature search was conducted, resulting in 196 studies on bivalve gaping behavior. For each study, we examined four categories of methodological decisions: species used, measurement approaches applied, employed methods for analyzing data, and study targets pursued. The screened studies covered 64 species from 9 taxonomic orders, with a strong bias towards marine species. Sensors directly attached to individuals without additional measurement units were the most commonly used measurement approach (72.4%). Study targets were highly diverse, resulting in a classification with two major groups (technology vs. biology) and several subgroups. For data analysis, seven biological endpoints were identified as the most commonly used bases, alongside various additional analytical approaches. We identified a lack of standardization in use of biological endpoints as a key challenge, and we propose the introduction of a minimum reporting standard for future studies. Additionally, we highlight interdependencies between methodological choices and discuss gaps and biases in the current literature, with the aim of connecting diverse research fields and supporting more cumulative scientific progress.