Environmental drivers of population variability in colony‐forming marine diatoms

Abstract

Many aquatic microbes form colonies, yet little is known about their abundance and fitness relative to single-celled taxa. The formation of diatom chains, in particular, has implications for diatom growth, survival, and carbon transfer. Here, we utilize an autonomous underwater microscope, combined with traditional microscopy, to develop a novel, multiyear record of the abundance of single-cell and colony-forming diatoms at Scripps Pier, a coastal location in the Southern California Bight. The total abundance of diatoms was lower during the warmer and more stratified conditions from 2015 to early 2016, but increased in cooler and less stratified conditions in mid-2016 to late 2017. Diatom blooms were dominated by chain-forming taxa, whereas solitary diatoms prevailed during low-biomass conditions. The abundance of dinoflagellates, some of which are important diatom predators, is highest when colonies (chains) are most abundant. These observations of the diatom assemblage are consistent with a trade-off between resource acquisition and predator defenses. Solitary diatom cells dominated during conditions with weak nutrient supply because they have a greater diffusive catchment area per cell in comparison to cells living in colonies. In contrast, during bloom conditions when nutrient supply is high and predators are abundant, forming a colony may reduce predation losses to quickly growing microzooplankton predators, and afford chains a higher fitness despite the costs of sharing resources with neighboring cells. These results highlight the contrasting ecology of single-cell and chain-forming diatoms, and the need to differentiate them in monitoring campaigns and ecological models.

Semi‐ and fully supervised quantification techniques to improve population estimates from machine classifiers

“…A human plankton expert examined data from the 5X SPCS microscope in search of diatom chains (Kenitz et al 2020). They grouped all diatom species into a single class for the sake of simplicity.…”

“…The complete resulting time series, corrected with the supervised quantification approach, was used by Kenitz et al (2020) to examine ecological drivers of chain formation. For the remainder of this paper, we restrict the target domain to data from August to November of 2017 for the sake of clarity and brevity.…”

“…With digital imaging instruments, scientists are able to interrogate the environment at high spatiotemporal resolution, amassing huge amounts of data (Gorsky et al 2000;Olson and Sosik 2007;Cowen and Guigand 2008;Beijbom et al 2012;French et al 2019). Imaging technologies have led to fascinating discoveries, enabled new experimental designs, and facilitated many in situ studies of diverse organisms: parasites of plankton, coral polyps, global-scale protist populations, the role of larvaceans in carbon cycling, and ecological drivers of colony formation to name a few (Peacock et al 2014;Biard et al 2016;Mullen et al 2016;Katija et al 2017;Kenitz et al 2020). But the volume of data is unwieldyno human, or team of humans, could feasibly taxonomically classify all the data collected by a single instrument.…”

Underwater dual-magnification imaging for automated lake plankton monitoring

“…Automated image classification was achieved for plankton with the 0p5x magnification in this study (Supplemental methods) and elsewhere (Campbell et al, 2020;Orenstein et al, 2020). The training of a phytoplankton classifier will be manageable with relatively low effort (Kenitz et al, 2020), however more tedious due to the larger number of taxa to annotate. An approach based on imaging has the potential to yield high frequency and standardized plankton monitoring data (Lombard et al, 2019) and, boosted by continuous (and opensource) advances in image processing and artificial intelligence, offers the prospect to automate and standardize also taxonomic classification of plankton (MacLeod et al, 2010).…”

The Scripps Plankton Camera system: A framework and platform for in situ microscopy

“…The SPC was originally developed to augment the Scripps Pier plankton time series currently maintained by the Southern California Coastal Ocean Observing System (SCCOOS) through the Harmful Algal Bloom Monitoring and Alert Network (HABMAP) (Kim et al 2009; Kenitz et al 2020). The SCCOOS time series, dating back to 2005, was built from weekly hand‐collected net tows and discrete water samples.…”