Guidelines for experimental set-ups in bioturbation studies under laboratory conditions

Bioturbation is a key process in aquatic environments with direct implications on ecosystem processes and functions. Because fieldwork on bioturbation is often challenging, ex situ laboratorial experiments have been developed to complement in situ monitoring. Nevertheless, due to different research questions, and to the technical difficulty to simulate natural dynamic environments, which elicits different experimental strategies, bioturbation studies on marine and estuarine sediments usually follow non-comparable protocols, ultimately impeding scientific progress in this field. Guidelines to standardize concepts and experimental set-ups are needed to allow comparisons across systems. A systematic literature review on Scopus and Web of Science databases yielded 518 publications, comprising a total of 624 experiments. These were analysed considering three key questions: [1] Why? i.e. the scientific question behind each publication; [2] How? i.e. the way each bioturbation experiment was run; and [3] What? i.e. what worked well and what needed improvement to overcome the gaps, namely in concepts, set-up and running of experiments. This analysis highlighted a mismatch concerning the type and size of experimental units, the lack of clear experimental descriptions, and potential experimental artifacts that are not considered. We recommend operational definitions for the concepts of microcosm (≤20 L) and mesocosm (>20 L), and practical guidelines to standardize procedures. These guidelines include the consistent reporting of experimental conditions, the use of adequate depths of incubated sediment, the use of water, lighting conditions, and animal densities that mimic the organisms' natural environment, as well as adequate timings for specimens handling and acclimation. The ability to avoid, minimize and acknowledge potential artifacts associated with the experimental set-up will work towards the standardization of bioturbation experiments. While there is no unique way to set-up a bioturbation experiment, it must be suitable to test the target research questions and associated hypotheses, with enough detail and scientific support to allow replicability and comparable results. Best practices for bioturbation studies under laboratory set-ups are proposed and discussed in this systematic review.