Science

All marine creatures need to extract oxygen from sea water and eliminate the carbon dioxide that they generate via their metabolism¹. As with fish, most larger species of invertebrates have gills of some sort to carry out this function. Invertebrates with gills or gill-like structures include crustaceans (eg crabs, prawns, crayfish, barnacles); molluscs (eg, clams, oysters, pipis, abalones, snails, whelks, squid, octopus, cuttlefish); echinoderms (eg, sea urchins, sea cucumbers, sea stars); ascidians (eg, sea squirts, sea tulips), most annelid worms (eg, sand worms, tube worms, sea mice). Some creatures, such as Sipunculid worms, lack conventional gills: they generally exchange oxygen and carbon dioxide with the water directly through their skin (cuticle). See the video below for a massive wash-up of Sipunculids.

Most invertebrates do not have a continuous circulatory system of arteries, capillaries and veins as seen in vertebrates such as fish (and humans!). Instead their blood (haemolymph) … Click here for more.

Some of the first signs of the 2025 harmful algal bloom were reports of surfers complaining of sore or irritated eyes, nose and throat after surfing in water that had or was near areas of thick discoloured foam around the southern beaches of the Fleurieu Peninsula. Indeed, I experienced those symptoms after a windsurfing session in large waves in Encounter Bay, Victor Harbor, in mid-March. Since then, surfers, swimmers and divers have reported comparable symptoms to varying degrees after being in the water at most places where the bloom is present. In addition, many people have reported similar symptoms, simply by being on or near a beach affected by the bloom.

These observations indicate that are two main ways that people can come into contact with harmful components of the bloom: direct contact with bloom-affected water, such as during swimming or surfing; or contact with air-borne agents carried in aerosols from bloom-affected water, typically while walking along or near an affected beach..

All of the surfaces of the body are lined with epithelium. The epithelium of the skin (epidermis) is toughened and made water-resistant by a complex suite of proteins, most notably keratin. … Click here for more.

One of the most characteristic observations during the algal bloom mortality is the appearance of varying degrees of blushing – red blotchy skin – in many of the rays and sharks (elasmobranchs) that have washed up. 

This is a very peculiar phenomenon, for which there is no clear cut explanation. Much of the research my colleagues and I did over 30 years was on the control of the blood circulation in the skin, mostly in mammals. In mammals like humans, this type of skin flushing is due to the small blood vessels in the skin (the capillaries) becoming leaky, so that blood cells, both red and white, end up in spaces between the cells of affected tissues. This is called extravasation and it is a normal part of an inflammatory response to injury or infection: it is the painful redness in the skin after sunburn or an insect sting or whatever. 

… Click here for more.

The gills of fish have two critical functions¹:
    (1) Respiration: taking up oxygen (O₂) from the water, transferring it to the blood, and transferring carbon dioxide (CO₂) back from the blood to the water.
    (2) Salt balance: ensuring that the body fluids and cells of the fish are not overwhelmed by salt (sodium chloride, NaCl) in the sea water.

The structure of gills is complicated and varies in detail between different types of fish. But they all follow the same basic plan.

The heart pumps blood via veins from the rest of the body into the gills. This blood is deoxygenated and contains high levels of carbon dioxide (CO₂) due to the metabolic activities of all the body tissues, such as muscles, gastrointestinal tract, reproductive organs, etc. This blood is pumped into four pairs of gill arches. Each gill arch bears rows of gill filaments and each filament is covered by rows of thin ridges called gill lamellae. The gill lamellae are covered with a thin layer of epithelial cells and a filled with a network of blood capillaries. The fish pumps … Click here for more.

A wide range of marine organisms produce a toxin of some kind. In many cases, a particular species may produce a cocktail of toxins with different biological actions. The exact nature or mix of toxins can vary considerably, even between closely related species. Toxins are most commonly used to subdue prey, as in the case of jelly fish, cone shells and sea snakes, for example. Some species, such as toad fish and stingrays, use toxins primarily for defensive purposes. In the case of dinoflagellates, toxins seem to serve both functions to varying degrees.

Toxins exist in a bewildering variety of molecular forms. Some are synthesised by relatively minor variations of other metabolic processes. Others require complex biochemical pathways for their formation. Some species, such as toad fish, do not synthesise their toxins but acquire them from other organisms, in this case, bacteria that reside in their digestive tract.

Neurotoxins target specific molecules necessary for the transmission of electrical impulses by nerve fibres to other nerves or to the muscles the nerves are controlling. Some toxins directly target molecules on the muscles themselves. Most of these neurotoxins are very resistant … Click here for more.

One of the dominant dinoflagellates originally identified in the 2025 bloom in South Australia is Karenia mikimotoi. It causes mortality across a wide range of species due to a cytotoxic action that leads to the destruction of susceptible cells and tissues with which it comes into contact¹. The maximum cytotoxic effect requires the dinoflagellate cells to be intact: once the cells break down, due to turbulent sea conditions, for example, the cytotoxic action is reduced². Nevertheless, sea foams containing high levels of Karenia mikimotoi may retain some of its cytotoxic properties.

The precise chemical nature of the toxin in Karenia mikimotoi is not known. However, its mode of action probably reflects the biochemical nature and modes of action of cytotoxins in other related dinoflagellate species that have been characterised, such as karmitoxin and karlotoxin from Karlodinium spp or brevisucenals from Karenia brevisulcata (see details below).

In November 2025, Karenia cristata was identified as a dominant species in the current bloom. It produces significant levels of brevetoxins, which are primarily neurotoxins. However studies on Karenia brevis, another major producer of brevetoxin, not found in South Australia, have shown that it also possesses a potent … Click here for more.

Nerve fibres transmit signals by a complex set of interacting biochemical and electrical processes. A nerve impulse (action potential) is generated by the rapid movement of ions across the cell membrane of the nerve. Initially sodium ions enter the nerve to generate the beginning of the electrical impulse, and then potassium ions leave the cell to effectively terminate the electrical pulse. These electrochemical pulses travel along the nerve fibres at speeds of 0.1m/sec to nearly 100m/sec depending on the type of nerve.

… Click here for more.