The invasive red seaweed, Dasysiphonia japonica, forms harmful algal blooms: Mortality in early life stage fish and bivalves and identification of putative toxins

• Published in: Harmful algae 2022-10, Vol.118, p.102294-102294, Article 102294
• Main Authors: Young, Craig S., Lee, Cheng-Shiuan, Sylvers, Laine H., Venkatesan, Arjun K., Gobler, Christopher J.
• Format: Article
• Language: English
• Subjects: Allelopathy; Bivalves; Fish; Invasive species; Macroalgae; Toxicity
• ISSN: 1568-9883; 1878-1470
• DOI: 10.1016/j.hal.2022.102294

•Dasysiphonia japonica is an invasive red macroalga with a global distribution.•Decaying D. japonica directly caused rapid (24 h) and elevated (50–90%) mortality in early- to juvenile-stage fish and larval bivalves.•Mortality was not caused by low oxygen, low pH, or elevated ammonium.•No mortality was observed for fish or bivalves exposed to healthy D. japonica.•Compounds with m/z ratios similar to known toxins including caulerpin were detected in decaying alga. In recent decades, the rate of introduction of non-indigenous macroalgae has increased. While invasive seaweeds often outcompete native species for substrata, their direct effects on marine life are rarely described. Here, we describe ‘red water’ events caused by the decay of blooms of the invasive red seaweed, Dasysiphonia japonica, in Great South Bay, NY, USA, and the ability of water from such events to induce rapid and significant mortality in larval and juvenile fish (Menidia beryllina, Menidia menidia, and Cyprinodon variegatus) and larval bivalves (Mercenaria mercenaria and Crassostrea virginica). All species studied experienced significant (p7 mg L–1) and low ammonium levels (< 20 µM), with the exception of C. variegatus, which expired under conditions of decayed D. japonica coupled with reduced DO caused by the alga. Screening of water with decayed D. japonica using liquid chromatography-mass spectrometry revealed compounds with mass-to-charge ratios matching caulerpin, a known algal toxin that causes fish and shellfish mortality, and several other putative toxicants at elevated levels. Collectively, the high levels of mortality (50–90%) of larval and juvenile fish and bivalves exposed to decaying D. japonica under normoxic conditions coupled with the observation of ‘red water’ events in estuaries collectively indicate the red seaweed, D. japonic