Range extension and reproduction of the barnacle Balanus perforatus in the eastern English Channel

The distribution of the warm-water barnacle, Balanus perforatus, was surveyed along the south coast of England and the north-east coast of France between 1993 and 2001, repeating work carried out between the 1940s and 1960s. The species has recovered from catastrophic mortality during the severe winter of 1962–1963 and was found over 120 km (UK) and 190 km (France) east of previous records on both sides of the Channel. The presence of the species in the eastern Channel refutes suggestions in the 1950s that larvae, and hence adults, would not be found east of the Isle of Wight because of reproductive sterility close to the limits of distribution. Brooding of specimens translocated to Bembridge, Isle of Wight, commenced in May, earlier than previously observed in British waters, and continued until September. The stage of embryo development at Bembridge in mid-August was comparable to that of the large population at Lyme Regis, Dorset 100 km further west. However the size of brood per standard body weight was greater at Lyme Regis. Factors influencing the rate of colonization and further geographic range extension of the species as a possible result of climate change, are discussed.

Growth and breeding of a primitive stalked barnacle Leucolepas longa (Cirripedia: Scalpellomorpha: Eolepadidae: Neolepadinae) inhabiting a volcanic seamount off Papua New Guinea

A pedunculate barnacle, Leucolepas longa, occurs in densities over 1000 individuals m[minus sign]2 on the summit of a small seamount near New Ireland, Papua New Guinea. Most of the population grows on vesicomyid clams projecting from sulphide-rich sediments, or on their dead shells, but the barnacle also settles on rock and on tubes of a vestimentiferan. Collections of several hundred barnacles allowed comparison of population and reproductive characteristics. The barnacle is a suspension feeder with a lightly-armoured stalk that can grow to 40 cm above the bottom. Growth appears to be rapid and both reproduction and recruitment are continuous. The barnacles brood egg masses within the capitular chamber and 46% of one sample was brooding. Lecithotrophic nauplii released upon retrieval to the surface were cultivated for 45 days. Metamorphosis to Stage IV yielded an actively swimming larva about 1 mm long overall, which still contained lipid reserves, indicating capacity for wide dispersal

Prudent female allocation by modular hermaphrodites: female investment is promoted by the opportunity to outcross in cyclostome bryozoans

Many sessile, suspension-feeding marine invertebrates mate by spermcasting: aquatic sperm are spawned and gathered by conspecific individuals to fertilize eggs that are generally retained during development. In two phylogenetically distant examples, a cheilostome bryozoan and an aplousobranch ascidian, the receipt of allosperm has previously been shown to alter sex allocation by triggering female investment in eggs and brooding. Here we report experiments demonstrating that two species of cyclostome bryozoan also show restrained female investment in the absence of mating opportunity. In Tubulipora plumosa, the production of female zooids and progeny is much reduced in reproductive isolation. In Filicrisia geniculata, development of distinctive female zooids (gonozooids) begins but halts in the absence of mating opportunity, and no completed gonozooids or progeny result. Reduced female investment in the absence of a mate thus occurs in at least two orders of Bryozoa, but significant differences in detail exist and the evolutionary history within the phylum of the mechanism(s) by which female investment is initiated might be complex. The broadening taxonomic spectrum of examples where female investment appears restrained until allosperm becomes available may signify a general adaptive strategy among outcrossing modular animals, analogous to similarly adaptive sex allocation typical of many flowering plants.

Prudent female allocation by modular hermaphrodites: female investment is promoted by the opportunity to outcross in cyclostome bryozoans

Many sessile, suspension-feeding marine invertebrates mate by spermcasting: aquatic sperm are spawned and gathered by conspecific individuals to fertilize eggs that are generally retained during development. In two phylogenetically distant examples, a cheilostome bryozoan and an aplousobranch ascidian, the receipt of allosperm has previously been shown to alter sex allocation by triggering female investment in eggs and brooding. Here we report experiments demonstrating that two species of cyclostome bryozoan also show restrained female investment in the absence of mating opportunity. In Tubulipora plumosa, the production of female zooids and progeny is much reduced in reproductive isolation. In Filicrisia geniculata, development of distinctive female zooids (gonozooids) begins but halts in the absence of mating opportunity, and no completed gonozooids or progeny result. Reduced female investment in the absence of a mate thus occurs in at least two orders of Bryozoa, but significant differences in detail exist and the evolutionary history within the phylum of the mechanism(s) by which female investment is initiated might be complex. The broadening taxonomic spectrum of examples where female investment appears restrained until allosperm becomes available may signify a general adaptive strategy among outcrossing modular animals, analogous to similarly adaptive sex allocation typical of many flowering plants.