Brevetoxin accumulation and persistence during a Karenia Brevis (Red Tide) bloom in South Texas

Red tide blooms composed of the harmful microalgae, Karenia brevis, are bi-annual events along the South Texas coast that cause marine and terrestrial animal mortalities. On September 13, 2015, a red tide bloom occurred from Port Aransas, TX to South Padre Island, TX and persisted in Corpus Christi Bay, TX until November 23, 2015. The objective of this study was to determine if brevetoxin (PbTx), produced by K. brevis, was passively or actively accumulated in macroalgae and if so, determine persistence time and depuration rates.

Sargassum was collected from Padre Island National Seashore on September 26, 2016 and co-cultured with seawater containing K. brevis. Accumulation of PbTx was measured for a 72-hr exposure period. The PbTx concentration was determined using ELISA (reported as PbTx-3 equivalents) and confirmed by HPLC-MS/MS (normalized to PbTx-1 standard). The Sargassum community was partitioned mechanically to include epiphytic algae (with concentrations as high as 26 ng/mL PbTx-3 equivalents) and toxin adsorbed on Sargassum (up to 51 ng/mL PbTx-3 equivalents). Concentrations as high as 100 ng/g PbTx-3 (by ELISA) and 934 ng/g PbTx-1 (by HPLC-MS/MS) were detected in Sargassum tissue.

As little information is available on PbTx in plant vectors; a second study assessed toxin depuration and persistence in macroalgae after the K. brevis bloom subsided. Ulva intestinalis was collected from Corpus Christi Bay on November 6, 2015 and incubated in f/10 media for a 30-day period to assess depuration. The epiphytic fraction contained over 17 ng/mL PbTx-3 equivalent and above 3 ng/g PbTx-3 equivalent in adsorbed PbTx over the 30-day period. U. intestinalis tissue PbTx concentration remained above 110 ng/g PbTx-3 equivalent. These results confirm that PbTx can be present in the macroalgal community for at least one month after a K. brevis bloom subsides.

This study is the first to assess macroalgae as a vector for PbTx trophic transfer. Pelagic forms of macroalgae can accumulate and transfer PbTx into regions not experiencing red tides while toxin in attached forms can persist and be released to the environment after a bloom has disappeared. In future studies, examination of accumulation, depuration, and persistence of toxins in other macroalgal species should be considered. Studies on the transfer of marine algal toxins to different communities (i.e. beaches) could provide a better understanding of post-bloom effects.