1. Although parasites represent a substantial part of marine communities’ biomass and diversity, their influence on ecosystem functioning, especially via the modification of host behaviour, remains largely unknown. Here, we explored the effects of the bopyrid ectoparasite Gyge branchialis on the engineering activities of the thalassinid crustacean Upogebia pusilla and the cascading effects on intertidal ecosystem processes (e.g. sediment bioturbation) and functions (e.g. nutrient regeneration).

2. Laboratory experiments revealed that the overall activity level of parasitized mud shrimp is reduced by a factor 3.3 due to a decrease in time allocated to burrowing and ventilating activities (by a factor 1.9 and 2.9 respectively).

3. Decrease in activity level led to strong reductions of bioturbation rates and biogeochemical fluxes at the sediment-water interface.

4. Given the worldwide distribution of mud shrimp and their key role in biogeochemical processes, parasite-mediated alteration of their engineering behaviour has undoubtedly broad ecological impacts on marine coastal systems functioning.

5. Our results illustrate further the need to consider host-parasite interactions (including trait-mediated indirect effects) when assessing the contribution of species to ecosystem properties, functions and services.

For more details, please see section 2. Materials and methods in the paper.

Data are organized in five tabular data files (.txt files; separator = tab; decimal = .)

Information on the experimental design (seasons and treatments) can be found in the section 2.1. Field sampling and experimental design in the paper.

Data on the proportion of time allocated to identified behaviours (activity.txt)

The data file contains the proportion of time (in %) allocated to the four identified behaviours (i.e. "Walking", "Burrowing", "Ventilating" and "Resting") of parasitized (i.e. infested by the ectoparasite Gyge branchialis) and non-parasitized (i.e. not infested by Gyge branchialis) mud shrimp (Upogebia pusilla). Since mud shrimp were not visible enough during wintertime, this file includes only data from summertime (see section 3.1. Behaviour in the paper for more details). Please note that the recording duration of mud shrimp behaviour was 72 hours for each replicate. Therefore, the data (in %) can be easily translate in time data.

Data on burrow characteristics (burrow_characteristics.txt)

The data file contains the number of burrow openings at the sediment surface ("opening" in the file), the number of turning chamber ("chamber" in the file), the vertical extension of the burrow  (in cm; "depth" in the file), the total lenght of the burrow (in cm; "length" in the file), the thickness of the reworked sediment layer surrounding the burrow wall (in cm; "trs" in the file), the volume of reworked sediment surrounding the burrow (in cm³; "brs" in the file) and the volume of sediment expelled onto the sediment surface (in cm³; "ves" in the file). These variables have been counted and measured at the begining of experiments (t0) and after four (t4) and thrity (t30) days in winter and summer for control (without mud shrimp), parasitized and non-parasitized mud shrimp. Explanations can be found in the section 2.3.1. Sediment reworking in the paper.

Data on sediment reworking rates (sediment_reworking.txt)

The data file contains the output of the biodiffusion-bioadvection transport model (see section 2.3.1. Sediment reworking in the paper for more details) for control (without mud shrimp), parasitized and non-parasitized mud shrimp in winter and summer. It includes biodiffusion (D_b in cm² y^-1; "db" in the file) and bioadvection (Vb in cm y^-1; "vb" in the file) coefficients.

Data on bioirrigation rates (bioirrigation.txt)

The data file contains the output of the bioirrigation model (see section 2.3.2. Bioirrigation in the paper for more details) for control (treatment "seagrass" in the file), parasitized and non-parasitized mud shrimp in winter and summer. It includes bioirrigation rate (Q in mL h^-1; "q" in the file). Explanations can be found in the section 2.3.2. Bioirrigation in the paper.

Data on benthic fluxes (benthic_fluxes.txt)

The data file contains the flux (in mmol m^-2 d^-1) of oxygen ("o2" in the file), ammonium ("nh4" in the file), nitrate ("no3" in the file) and dissolved silicate ("dsi" in the file) at the sediment water interface for control (treatment "seagrass" in the file), parasitized and non-parasitized mud shrimp in winter and summer. It also includes the respiration rate (in mmol m^-2 d^-1) of parasitized ("respp" in the file) and non-parasitized ("respnp" in the file) mud shrimp in winter and summer, as well as excretion rate (in mmol m^-2 d^-1) of parasitized (treatment "excp" in the file) and non-parasitized (treatment "excnp" in the file) mud shrimp in winter and summer.