Toxic blooms

When environmental conditions for growth are optimal, photosynthetic Archaeplastida, excavates, and chromalveolates can grow exponentially, leading to high local populations. This can occur in several species of marine dinoflagellates that contain poisons that are toxic to fish, invertebrates or mammals, depending on the species of alga and the class of compound they produce. The toxins are accumulated in the digestive glands of shellfish and when consumed by man cause paralytic shellfish poisoning. Many of these compounds are neurotoxic. Saxitoxin, accumulated in shellfish and accidentally consumed, causes numbness of the mouth, lips, and face, which reverses after a few hours.

Toxins can also accumulate in higher animals like fish.  For example ciguatoxin from Gambierdiscus toxicus accumulates in muscle tissue of grouper and snapper and when eaten causes gastric problems, central nervous system damage, and respiratory failure.Toxins can also be formed by other species. Some species of diatoms can produce domoic acid, which can accumulate in mussels and, when consumed by humans, causes amnesic shellfish poisoning, a short-term loss of memory that can occasionally cause death. Some of the golden-brown species that give rise to these types of poisoning are highly pigmented members of the Chrysophyceae, and high cell densities can be seen as so-called red tides in the sea. Other toxins from species of the Prymnesiophyceae can affect gill function of fish and molluscs.