Crop plants contain many hundreds of chemicals, some of which have beneficial nutritional consequences for humans if consumed, while others may result in adverse health consequences for humans. Some plant chemicals may be both beneficial and harmful, depending on the dose consumed and the context of the consumption event. Chemicals naturally present in plants or produced by the plant in response to environmental factors that can elicit adverse health effects in humans or animals are often referred to as natural plant toxins.

Paralytic shellfish poisoning (PSP) is caused by the accumulation by filter-feeding bivalves of potent neuro-toxins produced by some planktonic micro-algae (dinoflagellates). Paralytic shellfish poisoning has caused serious illness in recreational shellfish consumers in New Zealand (Murray, 2014) and it is an important quality assurance problem for the New Zealand shellfish aquaculture industry (MacKenzie, 2014).

Beginning in early March 2011, a bloom of the saxitoxin (STX) producing dinoflagellate Alexandrium catenella developed in Tory Channel and spread throughout the greater part of the Queen Charlotte Sound.

A bloom of Alexandrium catenella began to develop in Opua Bay, Tory Channel, in late January 2012 and, from growth projections, it appeared likely there would have been a repeat of the widespread shellfish closures in 2011.