Day 4 of Life Beneath the Keel

On Sunday 13 September, at 1800 BST, The Island Trust is live streamingLife Beneath the Keel’ from Plymouth Yacht Haven as part of the Ocean Institute’s virtual Maritime Festival. This is the fourth in a series of blogs about the marine life we hope to discover then.

Day 4:  3 September 2020 | Worms

“The Sailors’ Prayer” in the Book of Common Prayer asks the Almighty to “Preserve us from the dangers of the sea, and from the violence of the enemy.” We tend to think of the dangers of the sea in terms of tempest and shipwreck, but in former times lack of wind and a foul bottom could bring the risk of death from thirst or starvation, and disease was ever present. Also, the fabric of the ship faced the perils of marine boring worms. Modern technology has largely removed that threat (not without environmental costs), but we can still find worms on and around our ships and boats, in the marina and on the sea bed.

The worms we are familiar with on land wriggle about underground, and there are those who do that in the sea, although we are not likely to see them in the marina unless they emerge from the seabed to be seen on the BRUV mentioned in the introductory blog (image 1).

Other active worms patrol the jungle that grows up on marina pontoons or those boats with foul hulls (image 2a & 2b). They can be difficult to identify!

More fun to find are the sessile worms, at least they don’t run away as soon as you try to follow them under the microscope. Many of them create a tube to protect themselves from predators, and like the cnidarians I mentioned yesterday, although they don’t have stinging cells, they deploy a shuttlecock-like array of tentacles to filter plankton, dead stuff and poo out of the water (image 3)

Those who dive or snorkel in tropical waters will be familiar with the Christmas tree worm (image 4) which hides its body inside a coral head, and has a filtering mechanism more like an inverted shuttlecock. But it can withdraw it at lightning speed if threatened. We have less exotic worms in our marinas, but they are still worth seeking out. The keel worm makes a hard casing with a ridge along the top firmly attached to something like a mussel shell. The filters are generally brown, but you might find the occasional bright blue one (image 5). At only a couple of millimetres across, less than the width of the keel worm’s case, is the spiral worm, which grows on hard surfaces and on sea weeds, but it’s life strategy is the same (image 6). You can really see the similarity with a shuttlecock on this unidentified fan worm in Panama City (image 7).

These worms will affect your boat’s performance, but not to the extent of the invasive non-native (in UK) species, Ficopotamus enigmaticus, which forms dense, complex colonies of twisted individual tubes (image 8). They will slow you down!

John Hepburn, Ocean Discoverability Project Manager
3 September 2020