Large mass of boring sponge , the tall hydroids provide some scale .
The vents of an excavating sponge can be very unobtrusive ; a large black goby looks on
When you look back at your photographs or videos of attractive reef vistas around Britain , have you noticed how often large yellow mounds of sponge form part of the scenery ? As I was looking at images for this piece , I was struck by how often they were there among the sea fans , anemone patchworks or other sponges that I was concentrating on when I took the pictures . And it made me wonder if this is somehow one of our most obvious but ignored species .
Ironically , those oftenoverlooked bright yellow masses are the most prominent form of the sponge . It also has an alternative lifestyle where it lives up to its name ( but only in one sense !) by digging into calcareous rock . This boring has been likened to a mining operation , with tiny chips of rock being undermined and broken away with an acidic by-product of the sponge ’ s respiration , then transported to the surface by its water current and ‘ spat out ’.
Using that technique , the sponge can excavate extensive chambers and galleries , so a large section of rock or an entire boulder is destroyed . When leading this subterranean lifestyle , just the sponge ’ s water inlet vents and outlet ‘ chimneys ’ are visible at the surface of the rock . These characteristic structures also cover the surface of the obvious yellow masses because , like all sponges , it makes its living from continuously drawing in prodigious volumes of seawater by creating water currents with vast armies of beating cilia ( tiny whip-like hairs ) and filtering out particulate material for food , before expelling the water .
The ‘ mining ’ and ‘ massive ’ versions of the boring sponge are actually considered to be distinctly different forms of the species and may even be two separate species . I had previously assumed that the prominent masses had simply ‘ outgrown ’ their chambers , but it is interesting to note how , when the two forms are right next to each other , they are often different shades of yellow , for example .
The boring sponge isn ’ t fussy about what calcareous material it invades , and it also excavates into the shells of molluscs . Oysters and scallops , for example , can be seriously afflicted . When infested by this sponge , they react by producing extra shell material to stem its progress , but that reduces their living space within the shell and takes their energy away from important tasks such as reproduction .
By contrast , other sponges can be most welcome guests on the shells of molluscs . The orange sponge you see on so many queen scallops , for example , provides a slippery coat that makes them more difficult for a predatory starfish to grasp . Indeed , research has shown that the shell surfaces of some mollusc species have even adapted to become more attractive to settling sponge larvae . Does this all go horribly wrong for the unfortunate shellfish that entice boring sponge occupation , or is there even an evolutionary impetus for them to appeal only to the ‘ right kind of sponge ’? To me , it ’ s utterly fascinating and most definitely not ‘ boring ’! �
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