The fate of Lyngbya majuscula toxins in three potential consumers

Abstract

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 ᠰ.31 mg/kg-1) and B. leachii (156.39 ᠴ6.92 mg/kg-1). D. dentifer showed high variability in the distribution of sequestered compounds. Lyngbyatoxin-a was detected in the digestive gland (3.56 ᠳ.56 mg/kg-1) but not in the head and foot, while debromoaplysiatoxin was detected in the head and foot (133.73 ᠱ29.82 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.