The study presents dry mass and body measurements of the larval stages of five common barnacle species occurring in mesozooplankton catches of Southampton Water and the central Solent area of the south coast of the UK. Quantitative samples were collected with conventional 120-μm mesh plankton nets. Species-specific regression equations relating carapace width and total length with dry mass were obtained for stage II to stage VI nauplii and cyprids of Austrominius modestus, Amphibalanus improvisus, Balanus crenatus, Semibalanus balanoides and Verruca stroemia. Width–dry mass and length–dry mass regressions obtained in the present study accounted for more than 98% of the variability for naupliar stages, and length–dry mass for 80% of the variability for cyprids. The dry mass of barnacle larvae predicted from carapace width equations determined here differed by only –6% from the measured dry masses of an independent data set, suggesting these first-reported equations of barnacle larvae are useful additions to zooplankton production studies.

Barnacles are one of the dominant macrofouling organisms found in the intertidal region throughout the world. Among the different species of barnacles Balanus amphitrite (=Amphibalanus amphitrite) is a favoured candidate organism used in experimental studies. Larval development in this barnacle includes planktotrophic naupliar stages followed by pre-settling cyprid instar. Studies have shown that availability of food during naupliar development is of critical importance to successful metamorphosis of the cypris larva. Traditionally barnacle larvae are raised in the laboratory providing mono-algal cultures of diatoms as food organisms. Such a luxury is not a reality in the wild. Observations to quantify the food available for the nauplii deliberated by monitoring the faecal pellets egested by freshly captured larvae from a tropical estuarine environment (Dona Paula bay, Goa, west coast of India) influenced by monsoon and characteristic temporal variations in the phytoplankton abundance and diversity indicated that the percentage of defaecating larvae (an indicator of food consumed) was comparatively higher during the pre-monsoon season. Generally this season is characterized by lower chlorophyll-a concentration. However, the average number of faecal pellets defaecated by a larva remained constant irrespective of the season. Earlier work in the study area depicts temporal changes in phytoplankton community structure; diatoms dominate during the post-monsoon season whereas dinoflagellates dominate during the pre-monsoon season. These observations indicate a possible shift in the food available for the larvae. As the faecal pellets did not always have remnants of diatom frustules, it is possible to say that the larvae survived on food material other than diatoms. Settlement of barnacles on panels of aluminium in the vicinity was monitored throughout the year and peaked during the pre-monsoon season. It is thus possible to infer successful larval development and metamorphosis in this barnacle species on varying forms of food.