Machine learning techniques to characterize functional traits of plankton from image data.

Plankton imaging systems supported by automated classification and analysis have improved ecologists' ability to observe aquatic ecosystems. Today, we are on the cusp of reliably tracking plankton populations with a suite of lab-based and in situ tools, collecting imaging data at unprecedentedly fine spatial and temporal scales. But these data have potential well beyond examining the abundances of different taxa; the individual images themselves contain a wealth of information on functional traits. Here, we outline traits that could be measured from image data, suggest machine learning and computer vision approaches to extract functional trait information from the images, and discuss promising avenues for novel studies. The approaches we discuss are data agnostic and are broadly applicable to imagery of other aquatic or terrestrial organisms.

Role of small-sized phytoplankton in triggering an ecosystem disruptive algal bloom in a Mediterranean hypersaline coastal lagoon.

Monthly samplings carried out in 2016-2019 and satellite color images from 2002 to 2019 have been combined to determine the onset and causative species of the ecosystem disruptive algal bloom (EDAB) that affects the Mar Menor coastal lagoon (Western Mediterranean Sea) since 2015. Substantial changes in satellite spectral reflectance attributable to increasing abundance of Synechococcus were registered in 2014. Furthermore, cell abundances of this species in 2016 were the largest ever obtained in the lagoon (6 106 cells mL-1), with values similar to those reported for other Mediterranean hypertrophic estuaries and coastal lagoons. These results suggest that the early changes leading to the EDAB started in 2014 and that Synechococcus played a relevant role in its development. Moreover, diatom and dinoflagellate abundances changed substantially in 2016-2019, ranging from 102 to more than 104 cells mL-1. Some of these changes were linked to flood, suggesting that EDAB has modified substantially the homeostatic capacity of the lagoon.

Shifts in the protist community associated with an anticyclonic gyre in the Alboran Sea (Mediterranean Sea).

The diversity of protists was researched in the Alboran Sea (SW Mediterranean Sea) by means of high-throughput sequencing technologies based on the amplification of the V9 region of 18S rRNA. Samples were collected at different depths in seven stations following an environmental gradient from a coastal upwelling zone to the core of an oligotrophic anticyclonic gyre (AG). Sampling was performed during summer, when the water column was stratified. The superphyla Alveolata, Stramenopila and Rhizaria accounted for 84% of the total operational taxonomic units (OTUs). The most diverse groups were Dinophyceae (21% of OTUs), Marine Alveolates-II (MALV-II; 20%), Ciliophora (9%) and MALV-I (6%). In terms of read abundance, the predominant groups were Dinophyceae (29%), Bacillariophyta (14%), MALV-II (11%) and Ciliophora (11%). Samples were clustered into three groups according to the sampling depth and position. The shallow community in coastal stations presented distinguishable patterns of diatoms and ciliates compared with AG stations. These results indicate that there was a strong horizontal coupling between phytoplankton and ciliate communities. Abundance of Radiolaria and Syndiniales increased with depth. Our analyses demonstrate that the stratification disruption produced by the AG caused shifts in the trophic ecology of the plankton assemblages inducing a transition from bottom-up to top-down control.

Potential polyunsaturated aldehydes in the Strait of Gibraltar under two tidal regimes.

Diatoms, a major component of the large-sized phytoplankton, are able to produce and release polyunsaturated aldehydes after cell disruption (potential PUAs or pPUA). These organisms are dominant in the large phytoplankton fraction (>10 µm) in the Strait of Gibraltar, the only connection between the Mediterranean Sea and the Atlantic Ocean. In this area, the hydrodynamics exerts a strong control on the composition and physiological state of the phytoplankton. This environment offers a great opportunity to analyze and compare the little known distribution of larger sized PUA producers in nature and, moreover, to study how environmental variables could affect the ranges and potential distribution of these compounds. Our results showed that, at both tidal regimes studied (Spring and Neap tides), diatoms in the Strait of Gibraltar are able to produce three aldehydes: Heptadienal, Octadienal and Decadienal, with a significant dominance of Decadienal production. The PUA released by mechanical cell disruption of large-sized collected cells (pPUA) ranged from 0.01 to 12.3 pmol from cells in 1 L, and from 0.1 to 9.8 fmol cell⁻¹. Tidal regime affected the abundance, distribution and the level of physiological stress of diatoms in the Strait. During Spring tides, diatoms were more abundant, usually grouped nearer the coastal basin and showed less physiological stress than during Neap tides. Our results suggest a significant general increase in the pPUA productivity with increasing physiological stress for the cell also significantly associated to low nitrate availability.