Abstract

Climatic phenomena like “El Niño” and “La Niña”, produce changes in the abiotic and biotic environmental conditions, varying sun radiation, seawater temperature, and rainfall patterns, which in addition to the availability of nutrients, are considered key components of pathogenic Vibrios species (PVS) outbreaks, which affect both marine organisms and humans. In Chile, V. splendidus strains have been associated with massive mortalities on the commercially reared larvae Argopecten purpuratus, representing a high economic risk for the Chilean aquaculture industry. Additionally, in the last decade, harmful algal blooms (HAB) have increased substantially in southern Chile, being responsible for the mortality of vertebrate and invertebrate marine animals. Although no direct relation has been stablished between HAB and mortality of shellfish, recent studies indicated that paralytic shellfish toxins (PSTs), increases the susceptibility of the mollusks to both pathogens and their predators. Therefore, the main objective of this study is to assess the development and survival of natural and farmed mollusks, exposed to the HAB and PVS interaction effects, under variable environmental conditions. First, this proposal attempt to determine which species of the genus Vibrio belong to the microbiota associated to mussels (Mytilus chilensis), one of the most economically important specie of Chilean marine ecosystems, and are present in seawater. This objective will be developed in two marine areas (one, in Carelmapu/Maullín, in De Los Lagos Region, and the other northern Corral Bay, in De Los Rios Region) during summer season. For this task, Illumina MiSeq barcoding 16S approach will be performed to distinguish the spectra of species, providing global biodiversity patterns of the microbiota community. In addition, a longitudinal field study (18 months) will be carried to determine the prevalence, spatial distribution and temporal change of selected PVS associated to M. chilensis, and their dynamic in the surrounding water, in the two marine coast areas described previously. Moreover, this study will also assess the association between PVS and environmental parameters, such as temperature and salinity. Complementarily, the presence and abundance of local phytoplankton (that include HAB’s species) and zooplankton species in the water column will be determinate at the same time, to study potential in situ interactions between PVS and local plankton species which could act as potential PVS reservoirs. Therefore, these results should greatly increase the knowledge on the abundance, ecology and characteristics of PVS associated with mussels and present in the surrounding waters of the De Los Lagos Region and the De Los Rios Region, which are the main shellfish producing areas in the country. Additionally, these results could potentially help to improve Environmental Monitoring and Assessment Program of PVS presence in Chile. Finally, an experimental infection in a controlled environment with a toxic dinoflagellate (Alexandrium catenella) will be carried out to study their impact on mollusks susceptibility to respond to pathogenic vibrio species. For that, three environmental conditions (unexposed to algae, or exposed a toxic or non-toxic dinoflagellate) will be studied. The transcriptomic analysis will allow to compare bivalve unexposed to algae, or exposed for 48 h a toxic or non-toxic dinoflagellate before and after bacterial infection. Next-Generation Technologies will be used to obtain genomic information to understand how two bivalve mollusks (M. chilensis and Mesodesma donacium) respond to PVS infection. Results will show relative genes and pathways against selected environmental conditions and bacterial infections, which could solve important problems in the bivalve production such as the “summer mortality”, which may have serious economic and social repercussions.