Using the Red Band Difference Algorithm to Detect and Monitor a Karenia spp. Bloom Off the South Coast of Ireland, June 2019

Catherine Jordan,Michelle C Tomlinson,Peter L Croot,Andrew Meredith,Clynton Gregory,Caroline Cusack,Rafael Salas,Ryan Mcgeady

doi:10.3389/fmars.2021.638889

Abstract

During the months of May, June, July and August 2019 the Red Band Difference algorithm was tested over Irish waters to assess its suitability for the Irish harmful algal bloom alert system. Over the 4 weeks of June an extensive localised surface phytoplankton bloom formed in the Celtic Sea, south of Ireland. Satellite imagery from the Sentinel-3a’s Ocean and Land Colour Instrument, processed using the Red Band Difference algorithm detected the bloom in surface shelf waters and helped monitor its movement. Daily satellite images indicated that the bloom appeared at the sea surface on the 2nd June 2019 and peaked in size and surface abundance in offshore shelf waters within 4 weeks, remnants remained at the surface into July. A particle tracking approach was used to replicate oceanic circulation patterns in the vicinity of the observed algal bloom and estimate its trajectory. The initial horizontal distribution of particles in the tracking model were based on a satellite imagery polygon of the bloom when it first appeared in surface waters. Good agreement was observed between satellite imagery of the bloom and the particle tracking model. In situ sampling efforts from a research cruise and the national inshore phytoplankton monitoring programme confirmed that Karenia mikimotoi was the causative organism of the bloom. This pilot study shows great potential to use the Red Band Difference algorithm in the existing Irish harmful algal bloom alert system. In addition, satellite ocean colour data combined with particle tracking model estimates can be a useful tool to monitor high biomass harmful algal bloom forming species, such as Karenia mikimotoi, in surface coastal waters around Ireland and elsewhere.

Highlights

Aquaculture is extremely important for providing food, nutrition and employment around the world
The Red Band Difference (RBD) algorithm was tested in Irish waters for the first time during the months of May, June, July, and August 2019 to assess its suitability for adding to the established Harmful Algae Blooms (HABs) monitoring system
The results we have presented here show the RBD algorithm was proficient in assessing the timing of the initiation, movement, geographical extent, locations of the peak abundances and duration of the bloom

Summary

Introduction

Aquaculture is extremely important for providing food, nutrition and employment around the world. There has been a 527% increase in global aquaculture production from 1990 to 2018. Production in Ireland had a net gain from under €100 million in 2009 to €180 million in 2018 with aquaculture outputs between 30,000 and 50,000 tonnes mainly from salmon and bivalve farming (Dennis and Jackson, 2019). Harmful Algae Blooms (HABs) are a concern for both finfish and bivalve aquaculture (Callaway et al, 2012). The proliferation of microscopic algae is beneficial to the overall ecosystem, e.g., as a source of food for wild fisheries and aquaculture (Tweddle et al, 2018). HABs, caused by either small or large biomass blooms, and depending on the species, can result in serious economic losses to marine sectors such as tourism, aquaculture and fisheries with additional, often unquantifiable, impacts on ocean health (Anderson et al, 2015)

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