Devastating farmed abalone mortalities attributed to yessotoxin-producing dinoflagellates

Area of Science:

• Marine Biology
• Ecotoxicology
• Aquaculture Science

Background:

• A large dinoflagellate bloom occurred in Walker Bay, South Africa, in January 2017.
• This bloom significantly impacted three land-based abalone farms, leading to substantial animal mortality.

Purpose of the Study:

• To identify the dinoflagellate species responsible for the bloom.
• To determine the source of yessotoxins (YTX) found in affected abalone.
• To investigate the pathological effects of the toxins on abalone.

Main Methods:

• Satellite imagery (Ocean and Land Colour Imager - OLCI) was used to monitor bloom dynamics.
• Dinoflagellate species were identified using light microscopy and confirmed with phylogenetic analysis of rDNA sequences.
• Yessotoxin levels in plankton and abalone were quantified, and abalone tissues were examined for pathology.

Main Results:

• The bloom was dominated by Gonyaulax spinifera and Lingulodinium polyedrum.
• Yessotoxin concentrations in abalone correlated with dinoflagellate abundance, with homo-YTX and 45-hydroxy-YTX being dominant analogues.
• Gonyaulax spinifera was identified as the probable source of YTX, as toxins were absent in L. polyedrum cultures.
• Abalone gills exhibited severe pathological changes, including epithelial disruption, degeneration, and necrosis.

Conclusions:

• Gonyaulax spinifera blooms can produce yessotoxins, posing a significant threat to aquaculture.
• Yessotoxin accumulation in abalone causes severe gill pathology, leading to mortality.
• Understanding bloom dynamics and causative agents is crucial for mitigating aquaculture losses.