Cyprid

The barnacle cyprid (syn. cypris larva) is the final, lecithotrophic, larval stage of barnacles. Metamorphosis into a cyprid usually follows 5 or 6 planktotrophic nauplius stages and the time that the cyprid spends in the plankton can range from a few days ("Balanus amphitrite") to weeks ("Semibalanus balanoides").

The role of the cyprid is to successfully locate, and attach to, surfaces conducive to adult growth and survival. It achieves this by exploring immersed surfaces using modified antennular structures and, finally, uses a proteinaceous adhesive to attach permanently prior to metamorphosis into an adult. This process has economic implications for the maritime industry where barnacles are a serious problem as a biofouling organism.

Surface Exploration

Although many people are familiar with adult barnacles, being a feature of rocky shorelines around the world, few are aware of the processes that lead to the visible 'clustering' of individuals in certain locations. In fact, the grouping of sessile adults is not a random process.

After the nauplii have fed in the water column and accumulated an energy store in the form of lipid, they undergo their final metamorphosis to a cyprid. Cyprids are unlike nauplii in morphology and are highly specialised for location of suitable settlement sites and subsequent attachment. Cyprids are able to swim actively in the plankton and have numerous adaptations designed to help the organism locate surfaces to explore.

Once a cyprid encounters an immersed surface, it attaches via a poorly understood mechanism of temporary adhesion. This adhesion is facilitated by the 3rd segment of the antennules that each present an adhesive disc, reminiscent of the tarsal structures of flies. A glycoproteinaceous secretion, originating from glands within the 3rd segment is involved to some degree in temporary adhesion but, again, its role is not well understood.

SIPC

What is known is that 'footprints' of this proteinaceous secretion are deposited onto surfaces that have been explored by cyprids, increasing their attractiveness to subsequently exploring cyprids. This attraction to conspecific factors is attributed to a settlement inducing protein complex (SIPC), also present in adult barnacles. This is probably the principle driving force for gregariousness in barnacles.

Other Cues

As well as conspecific cues, cyprids are sensitive to numerous physical surface factors that combine to reduce, or increase, the likelihood of their settlement in any one location. These factors include surface texture, chemistry, relative wettability, colour and the presence/absence and composition of a surface biofilm. As cyprids age and deplete their finite energy reserves, they become more likely to settle on surfaces that may have been rejected at an earlier juncture.

Permanent Adhesion

Eventually, cyprids select a surface and attach permanently via the explosive secretion of another proteinaceous adhesive, originating from glands within the body, that hardens and embeds the antennules - tethering the cyprid to its selected surface. Metamorphosis into a juvenile barnacle then occurs within a matter of hours depending on species.

External links

1. Barnacle and biofouling related information at http://www.ncl.ac.uk/barnacles