The reproductive cycles and geographical distribution of some common eastern Australian prosobranchs (Mollusca: Gastropoda)

Abstract

The taxonomic positions and Australian distributions of 10 common species of intertidal prosobranchs from eastern Australia were established from museum collections and published records. Patellanax peroni (Blainville), Subninella undulata (Solander) and Littorina unifasciata Gray have a southern distribution (from latitude 43º 30'S.) reaching as far north as 26º S., but not to the tropic of Capricorn. Austrocochlea constricta (Lamarck), Nerita atramentosa Reeve and Bembicium nanum (Lamarck) have the same southern limit as the former species but extend northwards to the tropic of Capricorn. Montfortula rugosa (Quoy & Gaimard) and Cellana tramoserica (Sowerby) extend further north to northern Queensland (17ºS.). Nodilittorina pyramidalis (Quoy & Gaimard) and Morula marginalba Blainville have a northern distribution, occurring throughout the Pacific, and extend southwards to southern New South Wales (37º 30'S.). These four types of distribution are briefly discussed in relation to the Australian faunistic provinces.

Monthly samples from March 1972 to May 1973 of the ovaries of the 10 species were fixed for examination by light microscopy. The numbers of immature and mature oocytes were recorded to establish the times and seasonal duration of gametogenesis, vitellogenesis and spawning. The time of spawning for most species was confirmed from the presence on the shore of egg capsules or newly settled juveniles. The external appearance of male and female gonads proved unreliable for estimation of the phases of reproductive cycle. The 10 species showed a wide variety of pattern and timing of reproductive cycle at one locality, which did not correlate with their overall geographical distributions, zonation pattern on the shore or phylogenetic relationships.

The possible importance of seawater and air temperatures as stimuli for initiation and cessation of phases of the reproductive cycles is discussed. Some species are influenced by temperature changes.

The spawning periods of N. pyramidalis, L. unifasciata, M. marginalba and B. nanum fell within the period of maximum availability of phytoplankton (August to March). All these species have long-term planktotrophic larvae. With the possible exception of Nerita atramentosa, which breeds during the same period as the previous species, all the other species are archaeogastropods with short-term lecithotrophic larvae, which are independent of the availability of phytoplankton food sources. Austrocochlea constricta breeds throughout the year, Patellanax peroni either from June to September or from February to May. Cellana tramoserica breeds from March to October and Subninella undulata and Montfortula rugosa from October/November to May.

All of the archaeogastropods, especially Patellanax peroni, retain unshed mature oocytes from one year to the next. Nodilittorina pyramidalis, Littorina unifasciata, Bembicium nanum, Nerita atramentosa and Morula marginalba all show cytolysis and resorption of unshed oocytes.