I recently found this large sponge on the lower aspect of a jetty pile at the Rapid Bay jetty: –
It is a good example of the degree of injury, and often death, that many types of inshore sponge (and some from deeper water too) incurred from exposure to the prolonged toxic algal bloom affecting the Fleurieu Peninsula and elsewhere in SA, and the recent major storm event hasn’t helped things.
This sponge is thought to be Spheciospongia papillosa, a member of boring sponges, Family Clionaidae.
I have posted details to iNaturalist.
The sponge looks like it is still alive for the most part, but it has lost a big amount of tissue from the upper aspect, as seen best in this 2nd image: –
Why the top part has been so severely affected is unclear to me, but I can think of a few possible reasons. Perhaps the tendency of the dinoflagellate cells to descend the water column overnight, or whenever that occurs, means that maximum concentration of toxin would settle on the upper part of the sponge. And if that’s the weaker, softer part, then sponge eating animals may start munching there. Or even strong wave action might be enough to tear off chunks, although quite how that would cause a crater like defect escapes me.
The settling of the toxin on top seems likely to have been the main factor here. (I can’t exclude entanglement from a fishing line’s tackle, either, but this sponge is a fair distance away from the main recreational fishing platform, the new jetty. And I saw no snagged hooks, etc.. on the sponge. Heavy gear like shark and ray fishers use would be hard to fully exclude, but I think that is unlikely in this instance).
FWIW on review I can’t tell what the little dark grey sphere on the damaged matrix in 2nd image is. I suppose it could be a small lead sinker that was part of fishing gear. I just don’t know. I should’ve checked at the time, but I had to keep my buddy in view to avoid separation in the gloom!
Hi David, were there any other examples of this anywhere else? I saw the mapped location on iNaturalist and could not help thinking maybe the initial damage was caused through fishing? As a occasional squid fisher myself, if the location on the map is accurate, ie midway between jetties, this spot is popularly focused on for squid fishing, etc (the squid ink stains on the jetty show this). A squid jag cast out could snag a sponge on its top side as shown, and often the lines typically used are capable of not breaking despite being snagged (eg braided line), which then could be carefully pulled free by ripping/damaging the sponge and exposing the inner tissue. With a chunk ripped away the sponge’s inner tissue is now highly vulnerable to all sorts of further damage as you explained. I will keep an eye out for any sponge damage I may come across.
It also reminded me of a large sponge at one of my regular spots I was using as a marker that suddenly vanished altogether, but did not have a really close inspection of the site for any remnant signs of it, as unfamiliar of sponge life cycles.
PS When squidding using a squid lure the jag/jig is cast out, most often then left to sink through the water column to get closer to the bottom and then trawled along near the bottom, while trying not getting snagged. In more recent times it seems to be many people are also leaning to favouring attaching a small sinker on a short <30cm leader which will drag/bounce along bottom causing unintentional damage along its path to plants etc. This can really decimate any weed growth on the sea floor area around popular jetties.
Hi Chris,
Your points are valid. I’m familiar with squid fishing techniques and gear, also,mainly from observing recreational fishers in action above and below surface but also from catching some with jags myself earlier in life.
But this big sponge has been subjected to attacks by squid jags etc for many years, and on occasions pre HAB I’ve seen hooks caught in it and in ones like it elsewhere on the old jetty. But the damage didn’t ever seem to progress, or ‘self propogate ‘/extend to make the greater sponge tissue mass look sick. So the bottom line (unintended pun) is that I am as certain as I can be that the sponge is badly affected by the toxic algal bloom. Irrespective of whether it was predisposed, by anthropogenic tackle trauma.
Thanks again for your feedback,
David