The catastrophic 2008–2009 red tide in the Arabian gulf region, with observations on the identification and phylogeny of the fish-killing dinoflagellate Cochlodinium polykrikoides

Harmful algal blooms (HABs) caused by the marine ichthyotoxic dinoflagellate Cochlodinium polykrikoides Margalef are responsible for mass mortalities of wild and farmed fish worldwide, with catastrophic impacts to aquaculture and local economies. Here we report on the Cochlodinium species responsible for a severe and widespread HAB in the Arabian Gulf and Gulf of Oman that has lasted for more than eight months at this writing, killing thousands of tons of fish and limiting traditional fishery operations, damaging coral reefs, impacting coastal tourism, and forcing the closure of desalination plants in the region. To identify the causative organism, cultures were established from cells isolated along the Arabian Gulf shore of the United Arab Emirates. Taxonomic analyses using scanning and light microscopy, and partial analysis of the large subunit (LSU) ribosomal RNA (rRNA) gene confirmed the C. polykrikoides classification. rRNA gene sequences of C. polykrikoides isolates from the Arabian Gulf were identical to isolates from the northeastern USA, Puerto Rico, Mexico, and Malaysia, known as the “American/Malaysian” ribotype. To our knowledge, this is the first HAB event associated with C. polykrikoides in the Arabian Gulf or the Gulf of Oman. The sudden emergence of C. polykrikoides in these Gulfs coincides with an apparent global expansion of this taxon, as well as a recent increase in HAB impacts observed in this region. The mechanisms underlying this expansion require further investigation, and may include increased nutrient enrichment of coastal waters in the Arabian Gulf and Gulf of Oman from domestic and industrial inputs, natural meteorological and oceanographic forcings, and the recent introduction of this species through ballast water discharge. A pattern of subsequent recurrence of C. polykrikoides blooms following an initial outbreak has been observed in other parts of the world, suggesting that this species may become a persistent HAB problem in this region. As Arabian Gulf countries rely on desalination plants as the primary source of freshwater, the disruption of plant operations by recurring Cochlodinium blooms poses a serious threat to the drinking water supply in the region, and represents an unprecedented HAB impact.