A Comparison of Two Versions of an Individual Based Particle Tracking Model for Harmful Algal Blooms (HABs)

Early warning is crucial for mitigating the harmful effects of HABs. An individual-based model (IBM) to identify bloom origins was developed utilizing model outputs, e.g. salinity, temperature, mixed layer depth (MLD), from Gulf of Mexico (GOM) HYCOM (exp_32.5). The GOM HYCOM was recently updated (exp_90.1), which required an update to the IBM. To test if the IBM using the two GOM HYCOM versions would produce similar outputs (i.e. cell distributions), the two were compared by seeding each with individuals representing three different species of plankton (a dinoflagellate, a ciliate, and a cryptophyte) and running the model for the first 60 model days of 2017. However, final cell distributions between the two model outputs differed considerably, necessitating a closer look at the differences between the two GOM HYCOM outputs. Time series of salinity, temperature and current velocities (u, v) were created from hourly model outputs from both exp_32.5 and exp_90.1 and compared to data collected at buoys (B, D, R) in the Texas Automated Buoy System (TABS). Salinities at B, D, and R were found to be higher in exp_90.1 when compared to exp_32.5; temperatures at B, D, and R were found to be similar. To further test the accuracy of exp_90.1, individual particles were inserted into the model based on cell counts collected by two Imaging FlowCytobots (IFCB) located at Port Aransas, TX and Surfside Beach, TX. Particles were stepped forward in time and their locations tracked for 60 days. A time series of cell abundance at the two IFCB locations was then generated from the IBM outputs and compared to the IFCB time series of abundance at both sites. The IBM output differed from observed cell abundances. We hypothesize this is due to the differences between exp_32.5 and exp_90.1 In exp_32.5, MLD was included and was used to determine nitrate values; whereas exp_90.1 lacked MLD output. Understanding why IBM outputs differ and their accuracy is significant because they contribute to the process of early detection of HABs.