Algal bloom

Event Date: 
Wednesday, March 27, 2013 - 19:15 - 20:00
Institution: 
Alfred Wegener Instute for Polar and Marine Research
Title: 

Alexandrium: Evolutionary and ecological insights into the most prominent toxigenic dinoflagellate

Abstract: 

Dinoflagellates are a major cause of harmful algal blooms, with consequences for coastal marine ecosystem functioning and services.  Representatives of Alexandrium tamarense species complex are of the most abundant and widespread toxigenic species, and produces paralytic shellfish poisoning toxins as well as allelochemical substances.  This species complex consists of four to five species. The debate of the separation of this complex into real species in long on going and here a concept for the divorce of this group will be proposed.  Problems with identification of a toxic member of this species complex in November 2012, which led to the accidental export of toxic mussels to Japan, has now led to severe restrictions on Australian shellfish exports to Japan for a year, and resulting losses of many million $. Furthermore, population genetic insight and adaptive strategies in species interaction processes will be presented. Allelochemical mediated intra-population facilitation, may explain at least partly the high genotypic and phenotypic diversity of Alexandrium populations. Consequently, multiple traits within a population potentially allow mutual facilitation, and may promote the success of microbial planktonic populations.

Event Date: 
Wednesday, October 31, 2012 - 06:00 - 06:15
Institution: 
UTS
Title: 

Sulfur scent for a harmful algae killer

Abstract: 

 
Marine harmful algal blooms (HABs) are dense ephemeral proliferations typically of dinoflagellates, cyanobacteria or diatoms. These HABs can cause illness and death in humans and marine life, or ecosystem alterations affecting food provision and recreational activities. Despite being recognised as a major environmental challenge, little is known about what makes HABs thrive and vanish. For dinoflagellates, which account for 75% of HAB-forming phytoplankton species, bottom-up factors (including: eutrophication, climate change and species dispersal) are common triggers, yet the causes of bloom termination remain obscure.
Parasitoids have been identified as a major cause of termination of coastal harmful algal blooms, but the mechanisms and strategies they have evolved to efficiently infect ephemeral blooms are largely unknown. This study investigated the potential cues for parasite infection by the generalist dinoflagellate parasitoid Parvilucifera sinerae (Perkinsozoa, Alveolata). It showed that P. sinerae was activated from dormancy by Alexandrium minutum cells. Further investigation identified the algal metabolite dimethylsulphide (DMS) as the density-dependent chemical cue for the presence of potential host cells. The presence of DMS allowed the parasitoid to alternate between a sporangium-hosted dormant state and a chemically activated, free-living virulent state. DMS-rich exudates from infection-resistant dinoflagellate species also induced parasitoid activation, which can be interpreted as an example of a co-evolutionary arms race between parasitoid and host. These results further expand the involvement of dimethylated sulphur compounds in marine chemical ecology, where they have been described as foraging cues and chemoattractants for mammals, birds, fish, invertebrates and plankton microbes.

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