An indoor pelagic mesocosm facility to simulate multiple water-column characteristics

Abstract

Mesocosms are important research tools in aquatic ecology because they close the gap between laboratory studies at the individual or lower organization level and field studies at the population and ecosystem level. However, most mesocosm studies regarding the pelagic environment do not consider the effects of physical factors like water-column stratification, turbulence and mixing. Neglecting such factors might bias the results compared to the natural system. Using a unique indoor mesocosm facility, we present results on how different water-column stratifications can be made and how they act as barriers for exchange between water layers. Turbulent mixing, simulated by vertically rotating incubation vessels, is shown to be of high importance for primary production, generating up to nine times higher production in humus-rich water than incubation vessels at fixed depths. Convective stirring is shown to be an attractive method for generating different turbulence conditions, and different temperature settings can be used to get turnover times from 84 h or more down to 17 min for a 5-m water parcel. We also demonstrate how an anoxic bottom layer can be achieved by stimulating heterotrophic bacteria through addition of bioavailable organic carbon.

Artificially generated turbulence: a review of phycological nanocosm, microcosm, and mesocosm experiments

“…Furthermore, as the gas has typically undergone pressurisation prior to release, there may also be associated adiabatic thermal effects. Båmstedt and Larsson (2018) noticed an aggregation of bacteria, algae and detritus at the water surface of their unmixed cosms during experiments. This was thought to be the result of surface heating from the overhead irradiance lamps causing a thermal lid effect in the upper 60 cm.…”

“…However, larger mesocosms and limnocorrals are typically used to look at natural planktonic communities that may be comprised of multiple trophic levels and organisms of different sizes. Land-based facilities are typically filled via pumping offshore waters from a particular depth into the enclosures (Båmstedt and Larsson, 2018). Ideally, sets of cosms will be filled simultaneously or as close timed as possible to insure homogeneity across all replicate cosms.…”

“…It is important that the pump filling system does not inadvertently preclude any larger species nor damage them in their transport through the pump system (Striebel et al, 2013). Some facilities are able to filter certain size fractions from the inflow water (Båmstedt and Larsson, 2018), thereby allowing, e.g. microzooplankton through but omitting mesozooplankton that might graze upon certain size fractions or cause morphological changes via infochemicals (Long et al, 2007;Fig.…”

“…With regards to the light spectrum that organisms are exposed to, it is best to use direct sunlight to capture all spectrographic components of the sun at surface level. While this will be the natural default in outdoor facilities and limnocorrals, indoor facilities traditionally have relied on filament lamps that had a tendency to over-represent light within the infrared parts of the spectrum, causing heating to the cosm surface and various thermal lid effects (Båmstedt and Larsson, 2018). Conversely, filament lamps underrepresent the UV component of sunlight and, while UV light is attenuated quickly in the water column, it can still have an influence on cosm ecology.…”

“…If using a natural planktonic population, it is possible to omit microzooplankton by filtering the water used prior to filling the cosms (Båmstedt and Larsson, 2018). While this is not suitable for predatorprey interaction studies, the removal of grazing should allow the subtle impacts of turbulence interactions on the phytoplankton community to be more easily observed.…”