Time series of bottom-water physico-chemical parameters at three benthic sites in Northern Brittany (France) : Aber Wrac’h estuary, Baie of Brest, Molène

Two discontinuous high-frequency time-series were conducted to characterize benthic seawater physico-chemical conditions in Northern Brittany (France), with sensors deployed at the bottom of the water column.
The first monitoring campaign was carried out at three rocky-bottom sites differing in wave exposure: (i) Roscanvel, located in the Bay of Brest and representing the most sheltered site (“ROSCANVEL–rocky station”; 48°20′01.41″N, 4°31′56.65″W); (ii) Aber Wrac’h, situated at the mouth of the Aber Wrac’h estuary and characterized by intermediate exposure to wave action (“ABER WRAC’H–rocky station”; 48°36′40.4″N, 4°35′29.4″W); and (iii) Molène, the most exposed site, located near Molène Island in the Iroise Sea (“MOLÈNE–rocky station”; 48°23′37.00″N, 4°52′31.44″W). These three stations were instrumented between April 14, 2022 and June 1, 2022 with RBRsolo T°C temperature loggers (RBR Ltd., Canada) and Rugged TROLL 100 water level loggers (In-Situ Inc., Fort Collins, CO, USA). Sensors were mounted on weighted frames and deployed directly on the rocky substrate at the bottom of the water column.
A second discontinuous time-series was conducted from March 15, 2023 to April 3, 2024 at two benthic stations located within the Aber Wrac’h site: (i) a kelp forest station, characterized by a rocky substrate with a macroalgal biomass of 5.0 ± 0.5 kg m⁻² (measured on February 15, 2023) and dominated by Laminaria digitata (“ABER WRAC’H–kelp forest station”; 48°36′45.7″N, 4°35′46.1″W); and (ii) a seasonal seagrass meadow station, consisting of a sandy bottom with seasonal seagrass cover, not quantitatively characterized (“ABER WRAC’H–seasonal seagrass meadow station”; 48°36′45.7″N, 4°35′46.1″W). Each station was equipped with custom-designed stainless-steel frames deployed on the seafloor to support autonomous loggers positioned 1 m above the substrate. The structures were secured using approximately 250 kg deadweights to ensure stability under hydrodynamic conditions. Both stations were instrumented with high-frequency autonomous sensors to measure temperature (°C) and total scale pH (pHT) using HOBO MX2501 loggers (Onset, USA); salinity (psu) and depth (m) using WiSens CTD and STPS sensors (NKE, France); and light intensity (lux) using HOBO UA-002-64 loggers (Onset, USA). In addition, vertical temperature and salinity profiles were collected at both stations using a CastAway CTD profiler (SonTek, USA).