Sponges

Sponges are primitive multicellular colonial animals that make up the phylum Porifera. When one thinks of sponges, it is usually of those that are harvested for domestic use. These are from tropical seas, the sponges found locally do not look like this, instead are smaller or encrusting forms. It is not surprising that sponges are mistaken for a type of plant, as many sponge species are encrusting forms and the fact that sponges exhibit no noticeable movement.

Sponges are divided into three classes; Calcispongiae, Hyalospongiae and Demospongiae. The division into the classes depends on the make up of their skeletal structures.

Physiology

Sponges belong to the phylum Porifera the term derived from Latin meaning the bearer of pores. Sponge species come in a diverse range of forms and can have a specific shape including urn shaped, tubed, or branched, but also can be shapeless encrusting forms.

Further, differing environmental conditions will produce different forms within an individual species. The degree of shelter and currents affect the shape and dimensions. The amount of light available can determine the colouring. Such factors lead to sponges of the same species appearing different depending on where they are found.

Sponges are filter feeders. Water is drawn through the sponge’s pores into a cavity. Lining this cavity are flagella. Water flow through the sponge is sustained by the continual movement of the flagella. The water flowing through the sponge brings in organic material such as debris and bacteria; nutrients that sponges requires. The water is expelled via the osculum carrying away waste products.

Sponges have not evolved specialised respiratory organs, instead they absorb oxygen through direct exchange between their tissue and water. The water flow increases the amount of water passing the tissue and hence increases oxygen available to the sponge.

Purse Shaped Sponges

Reproduction

The majority of sponge species are hermaphrodite, possessing both male and female reproductive organs. Sponges reproduce by releasing sperm, which are carried by the tide until they reach another sponge. Fertilization occurs, the resulting larvae are free swimming and go through several stages until eventually the larvae settle and mature into adult sponges.

Sponges also reproduce asexually by growing buds that become detached and form sponges themselves. Due to sponges’ impressive capacity to regenerate, fragmentation of a sponge can lead to the individual pieces forming sponges themselves.

Associations

Sponges have a variety of associations with other marine creatures. To what degree this arrangement advantages each animal involved depends on the specific association.

The sponge crab has a sponge growing on it its carapace, this is a mutualistic association with both sides gaining. The sessile sponge is now mobile being carried by the crab. The crab is camouflaged plus there is the additional benefit of the sponge’s unpleasant taste and smell which deters predators.

The sponge, Cliona celata, bores into oyster shells. This association will provide protection for the sponge but it is detrimental to the oyster’s shell strength.

However the most important association which is often overlooked is the symbiotic relationship between sponges and green algae. The algae lives close to the surface of the sponge, and photosynthesises light. The algae is provided with a beneficial habitat, protected from predators. The sponge benefits from the by-product of photosynthesis, oxygen.

Identification

Appearances of sponges vary, they can be encrusting, forming patches such as the Breadcrumb Sponge, Halichondria panicea or have a vase shape like the Purse Sponge, Grantia compressa.

Identification of sponges is not always straight foreward as one species can exist in various forms. As is the case of the Breadcrumb Sponge Halichondria panicea, a well known encrusting sponge with its distinctive volcano like mounds; this also exists in variable forms including finger like projections.

The colour can be a good indicator in identifying species. However in some species colour can vary depending on environmental factors such as in the case of the Breadcrumb Sponge. When situated in well lit conditions the sponge is green. The sponge contains algae which utilize the light and can photosynthesise. Where the light is not sufficient this will not occur and the sponge is a light yellow.

The skeletal structure of a sponge is comprised of spicules, which are scattered throughout the sponge’s body. Spicules can be calcium or silicon based; and can be rigid, or fibrous and soft. Spicules’ differing shape and size are vital in identifying individual species. This is particularly relevant in the case of sponges as the morphology in a single species can be varied. The only problem using spiracles for identification is it is not appropriate to do so in the field as they are too small for the naked eye and a microscope is required.

Sponges Found on Cornish Shores

Sponges are so often overlooked, but they are extremely common, and are easily found if looked for. They are found on rocky overhangs where they form a colourful cover on the undersides. Another place to find them is on kelps, thrown ashore after a storm.

Sponges either exist as simple individual sponges like the Purse Sponge Grantia compressa or as colonies as is the case of the Breadcrumb Sponge Halichondria panacea.

The most common sponge found locally is the Breadcrumb Sponge Halichondria panacea. Other common species include the Purse Sponge, Grantia Compressa and Hymeniacidon perlevis.

Species of Sponges Found In Cornwall

    Breadcrumb Sponge Halichondria panicea

  Purse Sponge Grantia compressa

     Hymeniacidon perlevis

  Boring Sponge Cliona celata

Breadcrumb Sponge Halichondria panicea  

The breadcrumb sponge is found on rocks, kelp holdfasts and stipes.

The colour varies from green, red, yellow, orange to brown.

In situations where there is good light, the sponge tends to be green. While in darker areas such as on kelps, where the fronds have cut out most of the light it is a whitish yellow.

It is commonly an encrusting sponge forming small patches of about 1cm in depth. It is easily identified by its “volcano like” mounds. Each volcano housing an osculum.

Hymeniacidon perlevis

This sponge is very common on the kelp holdfasts and stipes, but it can also be seen in rock crevices. It is coloured red to orange.

Purse Sponge Grantia compressa   

This purse shaped sponge is a simple sponge. It is found in small groups found under overhangs, clinging to the rock with a basal attachment. It is coloured yellow to white.

Boring Sponge Cliona celata   

This sponge bores into mollusc shells particulary those of scallops and oysters . The sponge can be seen in the holes as yellow, blue or green specks. It can become a serious pest in commercial oyster beds.