HIPPO environmental monitoring: Impact of phytoplankton dynamics on water column chemistry and the sclerochronology of the king scallop (Pecten maximus) as a biogenic archive for past primary production reconstructions

Given the importance of phytoplankton for marine ecosystems (oxygen production, carbon sequestration, base of food webs, etc.), many studies focus on the reconstruction of its past temporal dynamics. Over the last decades, important changes of these dynamics have been observed, both in the phenology of the blooms and in the composition of microalgal communities. However, currently available data do not allow to go back far enough in time to quantify the actual impact of anthropogenic activities on these changes. However, the structural and/or chemical studies of the shell of the king scallop, Pecten maximus, hold the potential to cover this lack of data and provide informations about the environment they experienced. In order to better understand the processes which drive the incorporation of chemical elements into scallop shells and their links with phytoplankton dynamics, an environmental monitoring was conducted at Lanvéoc (Bay of Brest; France; 48°17'39"N - 04°27'12"W) between March and October 2021. During this survey, water samples from surface and bottom layers were collected in a bi-weekly or a weekly basis in order to analyse various environmental parameters (nutrients, phytoplankton dynamics, trace element concentration in the particulate and dissolved fraction, particulate organic carbone and nitrogen, chlorophyll, pheophytin, biogenic silicon, etc.). A sediment trap has also been used to better understand the chemical dynamics of the sedimenting matter. Simultaneously, several instruments, such as an Underwater Vision Profiler (UVP6) and sambat probes, were deployed at Lanvéoc throughout the year and continuously recorded additional parameters (particle concentration, temperature, salinity, pH, dissolved oxygen, etc.). Furthermore, scallops which experienced one winter season (age-class I) were deposited at the beginning of the survey both in direct contact with the substract and in a cage, located 1 m above it. At the end of the monitoring, these scallops were recovered and their growth rates as well as the chemical composition of their calcitic stuctures were measured in a daily basis. In addition to the objectives of the HIPPO project, the dataset that is available here can potentially be very useful for other scientists performing sclerochronological investigations, studying biogeochemical cycles or conducting various ecological research projects.