The fate of Lyngbya majuscula toxins in three potential consumers

Blooms of Lyngbya majuscula have been reported with increasing frequency and severity in the last decade in Moreton Bay, Australia. A number of grazers have been observed feeding upon this toxic cyanobacterium. Differences in sequestration of toxic compounds from L. majuscula were investigated in two anaspideans, Stylocheilus striatus, Bursatella leachii, and the cephalaspidean Diniatys dentifer. Species fed a monospecific diet of L. majuscula had different toxin distribution in their tissues and excretions. A high concentration of lyngbyatoxin-a was observed in the body of S. striatus (3.94 mg/kg⁻¹) compared to bodily secretions (ink 0.12 mg/kg⁻¹; fecal matter 0.56 mg/kg⁻¹; eggs 0.05 mg/kg⁻¹). In contrast, B. leachii secreted greaterconcentrations of lyngbyatoxin-a (ink 5.41 mg/kg⁻¹; fecal matter 6.71 mg/kg⁻¹) than that stored in the body (2.24 mg/kg⁻¹). The major internal repository of lyngbyatoxin-a and debromoaplysiatoxin was the digestive gland for both S. striatus (6.31 ± 0.31 mg/kg⁻¹) and B. leachii (156.39 ± 46.92 mg/kg⁻¹). D. dentifer showed high variability in the distribution of sequestered compounds. Lyngbyatoxin-a was detected in the digestive gland (3.56 ± 3.56 mg/kg⁻¹) but not in the head and foot, while debromoaplysiatoxin was detected in the head and foot (133.73 ± 129.82 mg/kg⁻¹) but not in the digestive gland. The concentrations of sequestered secondary metabolites in these animals did not correspond to the concentrations found in L. majuscula used as food for these experiments, suggesting it may have been from previous dietary exposure. Trophic transfer of debromoaplysiatoxin from L.majuscula into S. striatus is well established; however, a lack of knowledge exists for other grazers. The high levels of secondary metabolites observed in both the anaspidean and the cephalapsidean species suggest that these toxins may bioaccumulate through marine food chains.\u

Plankton Community Changes and Nutrient Dynamics Associated with Blooms of the Pelagic Cyanobacterium <i>Trichodesmium</i> in the Gulf of Mexico and the Great Barrier Reef

Blooms of the harmful dinoflagellate Karenia brevis on the West Florida Shelf (WFS), Gulf of Mexico, are hypothesized to initiate in association with the colonial cyanobacterium Trichodesmium spp. and benefit from dissolved organic nitrogen (DON) release derived from N2-fixation by the cyanobacteria. Previous studies have detected DON release using direct experimental measurements, but there have been few studies that have followed nutrient release by in situ blooms of Trichodesmium and the associated plankton community. It was determined that long-term Trichodesmium spp. and Karenia brevis abundances on the WFS were related, following a 2-month lag. A separate Eulerian study of a Trichodesmium erythraeum bloom event was conducted over 9 days on the Great Barrier Reef. Concentrations of T. erythraeum increased over the course of the study, with coincident increases in dinoflagellate abundance and decreases in diatom abundance. Inside the bloom, concentrations of NH4+, PO43−, and DON increased significantly. The copepod grazer Macrosetella gracilis also increased in abundance as T. erythraeum numbers increased, contributing to nutrient release. Copepod grazing rates were measured, and N release rates estimated. Together, these studies show that Trichodesmium blooms have consequences for dinoflagellate abundance at both seasonal and ephemeral scales via direct and indirect N release

Microbial production along the West Florida Shelf: Responses of bacteria and viruses to the presence and phase of Karenia brevis blooms

Bacterial abundance, production, protein and nucleic acid synthesis, growth, and viral abundance were measured in waters associated with three bloom stages of the “red tide” dinoflagellate Karenia brevis along the south West Florida Shelf (WFS). Measurements were taken: (1) when no bloom was present; (2) during the initiation stage of a bloom; and (3) during the maintenance stage of a bloom. Results indicate that the bacterial community was nutrient limited in the non-bloom period, with highest abundance and production rates occurring near and within estuaries. Abundance of virus like particles (VLPs) was higher within estuaries, but we hypothesize VLPs were not a high source of bacterial mortality, possibly due to high decay rates due to UV degradation or extracellular nucleases. High bacterial production, balanced protein to nucleic acid synthesis, and statistically similar bacteria abundances measured on consecutive days within the initiating bloom suggest a highly productive community with equally high mortality. VLP abundance declined during the first 48h within both bloom stages, suggesting that viral genomes were either within host cells (not evident in water column samples), or bacterial mortality was due to mixotrophic grazing by K. brevis. Using a conservative grazing rate of 1bacteriaK. brevis−1h−1, K. brevis grazing could account for >100% of bacterial mortality during an initiating bloom. Bacterial abundance and production were significantly decreased and protein to nucleic acid synthesis became unbalanced during the maintenance phase bloom. An increase in VLP abundance during the maintenance phase was most likely the cause of bacterial mortality as mixotrophic grazing could only account for ∼4% of the change in bacterial abundance. Together, these data suggest that the associated bacteria and viruses play a critical role in the formation and termination of K. brevis blooms

Treatment-related adverse events.

<p>Treatment-related adverse events.</p