Barnacles in corals
 

I have noticed barnacles that are incorporated in the skeleton of several of my corals (acropora and LPS too). I am trying to learn more about the relationship between the two. What possibly is the species I am observing (they have white eyelash-like legs and are about 5 mm or so across)? How does the barnacle settle there and why does the coral allow this? Does the barnacle excrete substances that stop the coral from growing over it or reacting defensively towards it? If anyone can direct me towards info about barnacles it would be helpful.

[quote]How does the barnacle settle there and why does the coral allow this?[/quote]
The larvae must somehow avoid the coral's receptors. To my best knowledge, this is poorly (= isn't) researched, just like in some featherduster worms that settle, on say, [i]Porites[/i].

Hi,

There are actually several groups of related barnacles that live under the tissues on corals; the major group is called the "Family Pyrgomatidae." The barnacle larave find their host coral, settle on the tissue, and cut through the tissue to the skeleton beneath. They fasten onto the skeleton and metamorphose, from a larva into a juvenile barnacle.

The coral doesn't "allow" this anymore than you allow the parasites that you have living on your skin to be there (and yes, you have a lot of small animals living on your skin. :D).

The wound in the coral's tissues heals and it grows up to the edge of the barnacle's opening. In most cases, I think researchers feel that simple mechanical action of the barnacle's feeding motions prevents the coral from growing over the barnacle. If something kills the barnacle or it dies, the coral will quickly grow over it and nothing will be visible of the barnacle but a bump under the coral's tissues.

How do these barnacles and other smaller non-colonial sessile inverts reproduce (tube worms, vermatids)? Do they release gametes into the water column, or do they have some form of asexual reproduction? I know tube worms can reproduce asexually since I have observed this. If it is sexual, is this process driven by the moon as in cnidarians?

Hi,

Your question is really impossible to answer; there are simply too many types of organisms covered in the phrase "smaller non-colonial sessile inverts" to form a coherent answer.

Specifically, barnacles reproduce only sexually. They have a long lived larvae which may (or may not - it depends on the species) be able to travel great distance prior to settlement.

A point of order as well, although reproduction in some corals (not all) may show timing correlated to lunar periodicity, it is likely actually cued by tidal changes and temperature variations than lunar illumination. :D