Drivers of dinoflagellate benthic cyst assemblages in the NW Patagonian Fjords System and its adjacent oceanic shelf, with a focus on harmful species

Abstract

In recent decades, the alteration of coastal food webs (via aquaculture, fishing, and leisure activities), nutrient loading, and an expansion of monitoring programs have prompted an apparent worldwide rise in Harmful Algae Blooms (HABs). Over this time, a parallel increase in HABs has also been observed in the Chilean southern austral region (Patagonia fjords). HAB species like Alexandrium catenella—responsible for Paralytic Shellfish Poisoning (PSP)—are of great public concern due to their negative socioeconomic impacts and significant northward geographical range expansion. Many toxic dinoflagellate species (like A. catenella) produce benthic resting cysts, yet a holistic understanding of the physical-chemical and biological conditions influencing the distributions of cysts in this region is lacking. In this study, we measured a combination of hydrographic (temperature, salinity, and dissolved oxygen) and sediment physical-chemical properties (temperature, pH and redox potential), in addition to meiofaunal abundances –as sediment bioturbators and potential cyst predators– to determine the factors influencing dinoflagellate cyst distribution, with emphasis on A. catenella in and around a “hotspot” area of southern Chile. An analysis of similarities (ANOSIM) test revealed significant differences (p < 0.011) in cyst assemblages between the fjords and oceanic environments. Permutational Analysis of Variance (PERMANOVA) showed significant effects of sediment temperature and silt proportion in explaining differences in the cyst assemblages. A generalized linear model (GLM) indicated that sediment temperature, silt/sand, anoxic conditions, and low abundances of Harpacticoida —a meiofauna herbivore group and potential bioturbator— are associated with the higher resting cyst abundances of the harmful species A. catenella. The implications for A. catenella resting cysts dynamics are discussed, highlighting physical-chemical and biological interactions and their potential for PSP outbreak initiation.