Arenicola sp. egg mass - Solent, UK

Описание: Species: Arenicola sp (lugworm)
Date: 12th August 2020
Location: The Solent, UK
Activity: Reproductive effort (egg mass production)

I took this video on August 12th 2020 during a snorkel over my intertidal study site in the Solent. It principally shows an egg mass of my case study species Arenicola sp.

This first freeze frame just shows the siphons of one of the dominant bivalves on the shore here, Cerastoderma edule or the common cockle, the sediment is littered with these in many areas.

The Arenicola species is tentatively, brasiliensis, but either way it is a non-native lugworm now living and breeding for a number of years here on the south coast of the UK.

The egg mass was being thrown around by the tidal currents on this calm day and I’ve slowed the video down and studded in a few freeze frames so hopefully you don’t get too queasy with the poor filming!

This particular egg mass has been in place for several days as indicated by the absence of transparency. When first produced the egg masses are clear and the developing larvae within can easily be seen. But the outer surface soon becomes rougher and begins to get a diatom coat which completely obscures the contents. A characteristic frill, or ring can often be seen towards the top of the egg mass.

The egg mass itself is tied back into the sediment not by a single thread but by branching rootlets which I believe is why they can remain tethered in place even in quite rough conditions. Though they naturally detach after a period of about 4 to 5 days or so. The tie-back is not to the tail end where the casts are produced. My guess is that they are produced either from the head end of the burrow or that a dedicated egg-exit point is created and a new head tunnel dug for the burrow. I have recorded many instances of dual egg masses clearly suggestive of single females producing more than one egg mass consecutively.

This is interesting in the context of the video because of the large smooth mound visible just left of the egg mass here. It is speculative of course but I suggest it is possible this conceals another egg mass being formed by the lugworm living here.