Flow cytometry is widely used to assess phytoplankton populations, yet opportunities remain to improve and simplify the extraction of ecologically meaningful cellular properties such as biovolume. We assessed the relationship between microscopy measurements and flow cytometry signals in phytoplankton samples and calibration beads to estimate biovolume and validate the extent to which "conventional" (i.e., medical) flow cytometers can be used to measure biovolume. Microscopy-based biovolume showed a strong correlation with flow cytometry signals and was best described by a forward scatter-area (FSC-A) power-law model (R-2 = 0.89, p < 0.01). FSC-A was therefore used to define the biovolume-flow cytometry relationship for phytoplankton cells. This relationship was consistent with that observed between calibration bead volume and FSC-A; however, both cells and beads <= 2 & micro;m in diameter (4.19 & micro;m(3)) deviated from the main correlation. Cell morphology did not significantly affect the FSC-A-biovolume model but did influence bead-based biovolume predictions. This study presents a simple approach for estimating phytoplankton biovolume using widely accessible medical flow cytometers and demonstrates that calibration beads provide reliable biovolume estimates for cells >5 & micro;m(3). As biovolume is central to phytoplankton ecology and ocean biogeochemical fluxes, this approach enhances the utility of flow cytometry for biovolume assessment.
Abstract Documenting operational setbacks is essential for refining marine conservation strategies. We present the lessons learned from an experimental restoration trial of habitat-forming Cystoseira sensu lato species under intense grazing pressure in Gökova Bay, eastern Mediterannean Sea. Transplanted thalli placed inside protective PVC-and-metal mesh exclusion-cages exhibited rapid growth and recruitment. However, upon cage removal, invasive Siganus spp. entirely consumed the macroalgae within 48 h. Operational constraints included wave-induced cage deformation, mesh clogging, and temperature-driven donor mortality (ΔT = 3 °C). These practical reflections demonstrate that direct transplantation is ecologically unviable without prior mitigation of widespread biotic stressors.
Abstract Iron is a key component of many enzymes and thus helps set the magnitude of primary production and nitrogen fixation. Other trace metals have essential metabolic functions but probably play lesser roles relative to iron. Studies report that manganese can, in certain ocean provinces and during some seasons, play an influential role in regulating phytoplankton metabolism. Evidence is based on nutrient amendment in shipboard incubations or manganese/iron stoichiometric patterns in resupply from depth. Iron recycling underpins primary production in High Nutrient Low Chlorophyll regions over most of the year. In contrast, less is known about manganese recycling. Here we compare Southern Ocean iron and manganese recycling using combined approaches to construct an ecological stoichiometric framework of the epipelagic (0–200 m depth) ocean. Our findings point to important differences in the stoichiometry of resupply of iron versus manganese, with manganese likely more efficiently recycled and hence retained in the upper ocean. In particular, the export of iron-rich copepod faecal pellets drives less retentive recycling by the “ferrous wheel” relative to the “spinning manga”. Such preferential retention of recycled manganese may offset observed differences in the stoichiometric supply of new iron compared with manganese and contribute to observed patterns of iron versus manganese limitation in the Southern Ocean.
Abstract Calcification by coccolithophores represents a major biogeochemical process in the oceans. Calcification involves the formation of calcite coccoliths within a Golgi-derived compartment inside the cell. These are secreted to the cell surface where they form the coccosphere. Coccolithophore calcification is underpinned by membrane transport processes that deliver the inorganic carbon and calcium substrates from the external seawater to the site of calcification and by the removal of products, namely protons produced in the calcification reactions. Understanding these critical aspects of calcification will provide clearer insights into the responses of coccolithophores to chemical and physical conditions, both in terms of short-term acclimation and long-term adaptation to a changing ocean. In this review we consider these processes, their localization and the specific transporters likely to be involved. We also consider how transport processes are linked to structural aspects of the cell, providing specialized pathways for the substantial ion fluxes involved.
