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Glimpsing the 2020 spring bloom in the Strait of Georgia (Canada) with autonomous ferry-based sensors

Liam MacNeil*, Maycira Costa, Julie LaRoche

*Corresponding author:

ABSTRACT: Spatiotemporal observations are data rich and offer insights into links between ecological patterns and underlying processes. We present fine-scale autonomous observations from repeated ferry transects in the Strait of Georgia (Canada) during the 2020 spring bloom period using a FerryBox system (temperature, salinity, chlorophyll-α fluorescence) and a digital inline holographic microscope. Despite instrument cleaning interruptions relating to COVID-19 restrictions, three periods from late winter (February) to springtime (March and April) contained 14 days of high-quality holograms (>70k) capturing >10.5k identifiable micro-mesoplankton using automatic object detection. The ferry setup provided automatic data storage through Ocean Networks Canada, which also automatized data flagging and guaranteed remote access. The highest quality holograms repeatedly covered the central and eastern Strait indicating aspects of bloom succession: Fast-growing diatoms (Skeletonema sp.) emerged first followed by a diverse assemblage including Chaetoceros sp., Ditylum sp., Eucampia sp., and by April larger centric cells prevailed. The combined approach captured local suppression of chlorophyll-α fluorescence and diatom concentrations in Fraser River plume waters during the freshet, suggesting fine-scale spatial patterns in seasonal planktonic community composition. This work is among the first of its kind to autonomously generate in-situ imaging and physicochemical data with spatiotemporal resolution.