Short-term response of benthic foraminifera to fine sediment depositional events simulated in microcosm

• Main Authors: Guilhermic, Corentin, Nardelli, Maria Pia, Mouret, Aurélia, Moigne, Damien, Howa, Hélène
• Format: Text
• Language: English
• Published: 2023
• Subjects: Tidewater
• Online Access: https://doi.org/10.5194/bg-2023-31; https://bg.copernicus.org/preprints/bg-2023-31/

A microcosm experiment was designed to describe how benthic foraminifera react to fine sediment deposits varying in frequency and intensity, as it may occur regularly or occasionally in coastal benthic environments, caused by discharges from (e.g.) river flooding, tidewater glacier melting in polar regions or diverse anthropic activities linked to harbour or watershed management. The influence of seabed burial resulting from these events on the ecology of benthic ecosystems is often overlooked, and the resilience of benthic communities is poorly known. During a 51-day long experiment, a typical northeastern Atlantic intertidal foraminiferal community, mainly represented by Ammonia confertitesta and Haynesina germanica species, was subjected to two kinds of sedimentary disturbance: 1) one-time high volume (OHV) deposit, i.e. about 3 cm thick sediment added in one time at the beginning of the experiment; and 2) frequent low volume (FLV) deposits, i.e. about 0.5 cm added each week for 4 weeks. The geochemical environment (e.g. dissolved oxygen penetration in the sediment, salinity, temperature and nutrient content in the supernatant water) was monitored to follow the microcosm steady state before and during the experiment. In both disturbed microcosms, H. germanica showed a significant linear decrease in abundance during the experiment while the total abundance of foraminifera was significantly affected only by the OHV treatment, suggesting a stronger effect of a single thick deposit on standing stocks and biodiversity compared to frequent low sediment supplies. Concerning the vertical migration of foraminifera after sedimentary disturbances, the two dominant species moved upwards to the water- sediment interface with migration speeds estimated at 0.41 and 0.47 mm/h respectively for A. confertitesta and H. germanica . In the FLV treatment, the resilient state was already reached within the day following a low thickness burial while in the OHV it was achieved between 1 and 7 days after the 3 cm thick deposit. These ...