• To be unicellular.
• To be golden-brown in colour.
• To have one long visible flagellum.
• To have a

silicoflagellates

Silicoflagellates are one of the lesser known types of photosynthetic protists found in the oceans. They are prominent because of their bizarre “skeleton” which consists of a rigid flattened basket of hollow tubes. Two to 8 spines project radially from the central basket. Because the construction of this skeleton is so robust, scientists can estimate abundances of this organism fairly easily. Fossils of the skeleton indicate that the diversity of silicoflagellates was once greater than the few species we have today. The cell itself is a lumpy bag containing golden-brown bodies (chloroplasts) that sits around the central part of the skeleton.

Silicoflagellates are found in sun-lit zones of the of the ocean and are generally more common in colder waters. During winter they can be found closer to the tropics, but they retreat to cooler waters again in the warmer months. The distribution of their fossilised skeletons is used to help determine sea-temperatures in earlier ages.

Silicoflagellates are photosynthetic, converting sunlight into chemical energy using their chloroplasts. All the chloroplasts found in protists and in plants were once symbiotic photosynthetic bacteria, although most of the bacterial features and genetic material has long been lost. Chloroplasts probably only evolved once, however they have since been ‘stolen’ by several different colourless protist groups. This explains why the ‘algae’ are not a natural group of close relatives, despite their similarity of nutritional mode.

Silicoflagellates are large enough to be eaten by large protists and small animals, such as copepods and the larval stages of larger crustaceans.

Most small protists reproduce by binary fission, with one parent cell splitting into two daughter cells. Silicoflagellates can be made to divide every two days, which is unremarkable among protists (smaller species can be much faster). In silicoflagellates the parent seems to manufacture a second skeleton before splitting up. A culture derived from a single cell can produce a wide variety of skeleton shapes, which makes it difficult to determine how many species of silicoflagellates there are.

Silicoflagellates are basically loners.

The ocean’s microbes, particularly the photosynthetic groups, are capable of making their presence felt in a way that belies their small size. Their rate of living is very fast, which means that a low overall mass of microbes can nonetheless support a large biomass of animals. This also means that they can respond rapidly to elevated nutrient levels, an event that is known as ‘blooming’. While low-level blooms can increase the food available to larger organisms, some blooms can result in harmful affects. Blooms can cause massive death of marine animals through high concentrations of toxins or through oxygen depletion. These events can devastate environments and fisheries. Long term raised nutrients levels can cause drastic changes to environments. It is thought that the coral reef ecosystem may rely on nutrient levels being fairly low. Unfortunately, erosion, use of fertilisers, ocean dumping of sewage and other human activities tend to increase the nutrient levels in the oceans.