Drivers of a window of opportunity for Dinophysis acuminata in a mussel seed-bank hotspot in Northwestern Patagonia

Abstract

Chilean shellfish production is a significant contributor to the world´s marine aquaculture industry (∼22 % of the global mussel production). Most of this activity takes place in the Patagonian fjords system of southern Chile. Reloncaví Fjord (∼41°S), in northwestern Patagonia, represents the largest mytilid seed supply source for Chilean mussel aquaculture. In this fjord, Dinophysis acuminata —a lipophilic toxins producer— has been frequently found above detection levels (10² cells L⁻¹) during the regular monitoring program, reaching maximum densities in the spring and summer seasons. The bloom development of D. acuminata has been associated with the stratification of the water column and prey (Mesodinium spp.) availability. However, the drivers underlying D. acuminata spatial and temporal dynamics in the fjord are still poorly understood. From January 2019 to March 2020, measurements of physicochemical parameters and water samples (0 – 20 m depth) were collected weekly, biweekly, and monthly to analyse the spatiotemporal distribution of D. acuminata and the water column structure, at a fixed station at the head of Reloncaví Fjord. D. acuminata was observed in summer and spring of 2019, with a maximum of 2.1 × 10³ cells L⁻¹ in the early summer of 2019. In contrast, D. acuminata was absent in the summer of 2020. Results from a redundancy analysis (RDA) and generalized linear models (GLM) suggested that water salinity, and diminished nitrite and silicate probably enhanced by a moderate rainfall deficit in summer of 2019, explained the presence of D. acuminata. Thus, the results of the 15 months of sampling, including two summer seasons, allowed us i) to elucidate environmental drivers that provided a window of opportunity for D. acuminta population growth, and ii) to highlight that the abundance and distribution of a stress-tolerant species is a multifactorial response in which slight changes in specific environmental conditions can have a large influence.