First Report of Accumulation of Lyngbyatoxin-A in Edible Shellfish in Aotearoa New Zealand from Marine Benthic Cyanobacteria

Abstract

This study reports the first documented accumulation of lyngbyatoxin-a (LTA), a cyanotoxin produced by marine benthic cyanobacteria, in edible shellfish in Aotearoa New Zealand. The study investigates two bloom events in 2022 and 2023 on Waiheke Island, where hundreds of tonnes of marine benthic cyanobacterial mats (mBCMs) washed ashore each summer. Genetic analysis identified the cyanobacterium responsible for the blooms as Okeania sp., a genus typically found in tropical marine ecosystems. Analysis by liquid chromatography-tandem mass spectrometry indicated that the cyanobacteria produced a potent dermatoxin, lyngbyatoxin-a (LTA), and that LTA had accumulated in marine snails, rock oysters and cockles collected near the mats. Snails contained the highest levels of LTA (up to 10,500 µg kg^-1). The study also demonstrated that the LTA concentration was stable in composted mats for several months. The presence of LTA in edible species and its stability over time raise concerns about the potential health risks to humans consuming LTA-contaminated seafood. This underlines the need for further studies assessing the risks of human exposure to LTA through seafood consumption, particularly as climate change and eutrophication are expected to increase the frequency of mBCM blooms. The study highlights the need to develop public health risk management strategies for mBCMs.

Keywords: bioaccumulation; cyanoHAB; degradation; food safety; harmful algal blooms; liquid chromatography–tandem mass spectrometry; marine cyanotoxins; public health risk; toxicity.

Figure 1

Light micrographs of Okeania sp. filaments isolated from Waiheke Island, New Zealand. (A) Trichomes are enveloped in sheaths to which epiphytic bacteria are attached. (B) Photograph showing the empty sheaths at the end of the filaments (black arrows).

Figure 2

Phylogenetic tree based on 16S ribosomal RNA (rRNA) gene sequences of the Waiheke Island (New Zealand) cyanobacterial mats. The tree was based on the Jukes–Cantor model, using the UPGMA tree-building method. The percentage of trees in which the associated taxa clustered together is shown next to the branches. GenBank submission number: SUB14717735.

Figure 3

Total ion chromatograms of the multiple reaction monitoring channel analysing for (A) lyngbyatoxin-a in a standard and extracts from (B) an Okeania sp. mat and (C) a marine snail (Lunella smaragda) collected from the vicinity of Okeania sp. mats.

Figure 4

Mean concentrations of lyngbyatoxin-a (LTA) for the composting samples collected from (A) Surfdale Beach and (B) Blackpool Beach. The error bars represent the standard error for four replicate subsamples. (C,D) Linear regression analysis of mean LTA concentrations in Okeania sp. mat composting samples from 8 to 127 days (t = 1 to t = 7; the shaded region indicates the 95% confidence interval).

Figure 5

Locations of benthic cyanobacterial mat collection sites from Waiheke Island and the Auckland region (Aotearoa New Zealand).

Figure 6

Images from Waiheke Island. (A) Tonnes of benthic marine cyanobacterial mats (BCMs) washed up on Blackpool Beach 2023 in March; (B) BCMs washing up on shellfish beds on Shelley Beach in March 2023; (C) BCMs floating to the surface near Blackpool Beach in January 2024 (credit: Merrie Hewetson); and (D) washed-up BCMs on Surfdale Beach in December 2023 (credit: Auckland Council).