Henriette Gesine Horn

• Horn, Henriette G.; van Rijswijk, Pieter; Soetaert, Karline & van Oevelen, Dick (2023). Drivers of spatial and temporal micro- and mesozooplankton dynamics in an estuary under strong anthropogenic influences (The Eastern Scheldt, Netherlands). Journal of Sea Research. ISSN 1385-1101. 192. doi: 10.1016/j.seares.2023.102357. Full text in Research Archive Show summary

  The Eastern Scheldt estuary in the Netherlands has been anthropogenically changed by the construction of a storm surge barrier about 30 years ago, affecting abiotic conditions as well as phytoplankton and zooplankton (ZP). As ZP communities have not been sampled in the last decades, it is unclear to what extent they have changed during the last 30 years. We analyzed the micro- and mesoZP composition and background parameters at eight stations in the Eastern Scheldt in spring, summer, and autumn 2018. Additionally, we conducted dilution experiments to estimate phytoplankton growth and microZP grazing rates. Seasonal variability of ZP was higher than spatial variability, but there were differences between stations. In agreement with data from the 1980s, we identified salinity and chlorophyll a as the most important factors in explaining the ZP community. Suspended particulate matter and water retention time were additionally identified for mesoZP, as well as dissolved inorganic nitrogen and phosphate concentration for microZP. We observed some changes in ZP composition with respect to the 1980s, most of which could be explained by the changes induced by the barrier construction. However, increased abundances of the cyclopoid copepod Oithona sp. were likely related to changes in phytoplankton composition due to large-scale bivalve cultivation in the estuary. Phytoplankton growth and microZP grazing rates were variable between seasons, which could be explained by changes in the phytoplankton community during the annual plankton succession. Overall, the observed alterations in the ZP community due to changed background parameters and intense bivalve filtration could affect the microbial loop as well as consumers of mesoZP and thus the functioning of the pelagic food web.

• de Froe, Evert; Maier, Sandra R.; Horn, Henriette G.; Wolff, George A.; Blackbird, Sabena & Mohn, Christian [Show all 16 contributors for this article] (2022). Hydrography and food distribution during a tidal cycle above a cold-water coral mound. Deep Sea Research Part I: Oceanographic Research Papers. ISSN 0967-0637. 189. doi: 10.1016/j.dsr.2022.103854. Full text in Research Archive Show summary

  Cold-water corals (CWCs) are important ecosystem engineers in the deep sea that provide habitat for numerous species and can form large coral mounds. These mounds influence surrounding currents and induce distinct hy- drodynamic features, such as internal waves and episodic downwelling events that accelerate transport of organic matter towards the mounds, supplying the corals with food. To date, research on organic matter distribution at coral mounds has focussed either on seasonal timescales or has provided single point snapshots. Data on food distribution at the timescale of a diurnal tidal cycle is currently limited. Here, we integrate physical, biogeochemical, and biological data throughout the water column and along a transect on the south-eastern slope of Rockall Bank, Northeast Atlantic Ocean. This transect consisted of 24-h sampling stations at four locations: Bank, Upper slope, Lower slope, and the Oreo coral mound. We investigated how the organic matter distribution in the water column along the transect is affected by tidal activity. Repeated CTD casts indicated that the water column above Oreo mound was more dynamic than above other stations in multiple ways. First, the bottom water showed high vari- ability in physical parameters and nutrient concentrations, possibly due to the interaction of the tide with the mound topography. Second, in the surface water a diurnal tidal wave replenished nutrients in the photic zone, supporting new primary production. Third, above the coral mound an internal wave (200 m amplitude) was recorded at 400 m depth after the turning of the barotropic tide. After this wave passed, high quality organic matter was recorded in bottom waters on the mound coinciding with shallow water physical characteristics such as high oxygen concentration and high temperature. Trophic markers in the benthic community suggest feeding on a va- riety of food sources, including phytodetritus and zooplankton. We suggest that there are three transport mecha- nisms that supply food to the CWC ecosystem. First, small phytodetritus particles are transported downwards to the seafloor by advection from internal waves, supplying high quality organic matter to the CWC reef community. Second, the shoaling of deeper nutrient-rich water into the surface water layer above the coral mound could stimulate diatom growth, which form fast-sinking aggregates. Third, evidence from lipid analysis indicates that zooplankton faecal pellets also enhance supply of organic matter to the reef communities. This study is the first to report organic matter quality and composition over a tidal cycle at a coral mound and provides evidence that fresh high-quality organic matter is transported towards a coral reef during a tidal cycle.

• Osma, Natalia; Vargas, Cristian A.; Algueró-Muñiz, Maria; Bach, Lennart T.; Gomez, May & Horn, Henriette G. [Show all 12 contributors for this article] (2021). Ocean acidification induces distinct metabolic responses in subtropical zooplankton under oligotrophic conditions and after simulated upwelling. Science of the Total Environment. ISSN 0048-9697. 810. doi: 10.1016/j.scitotenv.2021.152252.

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