ANSWER 1

Written response:

Knowledge Gap identified: Some information is available on this topic but only to answer the question partially (limited data)

Details:
There will be winners and losers from climate change, with each of the 200 or so known HAB species responding differently in terms of growth and toxicological responses. It is a myth that all HABs all over the globe will respond in a uniform manner.
Painstaking research efforts are currently in progress by a handful of Australian and New Zealand scientists to produce unialgal cultures for light and electron microscopy, molecular sequencing, and ultimately analyses for brevetoxins and ichthyotoxins on bulk cultures. PIRSA have observed previous Karenia mikimotoi bloom events and fish kills in SA Coffin Bay eg in March 1995 and Feb 2014, both in response to cold water (15-16oC) offshore nutrient upwelling events. However, the March-Aug 2025 SA bloom morphed into a mixture of 4-5 Karenia species and its months long persistence in coastal waters and its propensity to cause marine mass mortalities are new to Australia. Karenia mass mortalities are best known from cold-water habitats such as Russia, northern Japan, Chile, New Zealand, but similar events are also known from warmer regions such as Kuwait, Tunesia and Florida. Sometimes the same morphospecies (but in the form of different phylotypes) are known from both cold-and warm-water habitats. That’s why the molecular sequences are critical to answer this question.

Another myth is that all HABs are driven by anthropogenic nutrients. Many Karenia species are mixotrophic, that is, they can feed on other algae or potentially even derive nutrients from dead fish. The persistence of the 2025 SA bloom points in this direction, and this is another approach planned for laboratory culture experiments.

An open science research meeting has been scheduled for Fri 5 December to be held at the University of Technology Sydney where all available information on the SA HAB will be synthesized. In general, little can be learned from studying the late bloom stages (in coastal waters) because it is the start of the bloom (most likely offshore) that we need to better understand. Hence we probably are too late to do much about the 2025 HAB but hopefully we are better prepared to predict and manage future recurrences.