Sea Sponge

Sponges are an ancient group of animals, and have been around for more than 543 million years!

The shape and the unmoving nature of sponges convinced early naturalists that they were plants. It was not until 1795, when their feeding method was described, that they were finally recognised as animals.

Sponges are large-bodied multicellular animals that feed by circulating water through a unique system of water canals to filter out food particles. About 5,500 species of sponge are known, ranging from the bath sponges which are harvested for human’s bathroom use, to the giant sponges over 2m in height that are found in Caribbean reefs and Antarctica.

Sponges display nearly every colour imaginable, including bright purples, blues, yellows, reds and white. Most types build internal skeletons of needle-like ’spicules‘, made of either Calcium or Silica. Some look round like bath sponges, some rope-like, and some form delicate glass-like structures (e.g. ’Venus Flower Basket‘).
Although they resemble plants, their cells can move and change their function. Some sponges have even been observed moving, albeit very slowly, from one place to another.

Sponges are the only animals that if broken down to the level of their cells, can reassemble themselves. Experiments have shown that a sponge can survive after being passed through a fine cloth to break apart its individual cells. When left in seawater over a few days, the cells still recognise each other and begin to come together again, reforming into a functional sponge and the original cells return to their respective functions.

Furthermore, if cells of two different species are mixed, they sort themselves out and reform individuals of each separate species. This process is known as reaggregation (Wilson, 1910).

Even a casual rockpool explorer will quickly notice that sponges are almost everywhere you look. They grow on rock or sometimes sandy surfaces, where they can be exposed to predators such as fish or molluscs like whelks and sea slugs (nudibranchs). They must clearly have some clever defence mechanisms against predators! Sponges appear to use 'chemical warfare', not only to reduce predation, but also to compete for space with other invertebrates such as corals and sea-squirts.

In recent years, a wide range of important bioactive compounds have been discovered in sponges, such as anti-microbial, anti-inflammatory, biotoxin and anti-fouling substances. These discoveries have led to a resurgence of interest in these fascinating resilient animals.