Gastropod egg mass deposition on a temperate, wave-exposed coastline in New South Wales, Australia : implications for intertidal conservation

The identification and protection of known breeding grounds is a high priority for the conservation of marine biodiversity. Here, we examine the intertidal habitats used by marine gastropods for the deposition of benthic egg masses along a wave-exposed coastline in New South Wales, Australia. A total of 200 surveys were conducted on 13 intertidal reefs. The egg masses of 46 species were identified, with a further eight distinct types recorded but remaining unidentified. Over half of the gastropods were found to deposit egg masses exclusively on the underside of boulders. Other intertidal substrata used for gastropod egg mass deposition included vertical and horizontal exposed rock surfaces, algal fronds and sand. Only eight species were found to attach their egg masses to more than one type of substratum. Twelve reefs were classified into three categories according to exposure to wave action and habitat diversity. The mean number of species found depositing egg masses was compared using a standard eight surveys from each site. Sub-maximally wave-exposed reefs with maximal habitat diversity were found to support a significantly higher species richness of gastropod egg masses, compared with maximally wave-exposed reefs with either maximal or sub-maximal habitat diversity (p=0.000). Gastropods that deposit egg masses on the underside of boulders were more likely to be found on sub-maximally wave-exposed reefs, whereas species that deposit egg masses in all other microhabitats were equally likely to be found breeding on sub-maximally or maximally exposed reefs. Gastropods with pelagic larvae tended to occur at a greater number of sites than those that hatch post-metamorphosis. A significant difference was found between species grouped according to these two developmental modes for the mean number of sites at which egg masses were recorded (p=0.008). Variation in the species richness of gastropods found depositing egg masses on different intertidal reefs appears to be influenced by the availability of suitable boulders and exposure to wave action. These factors should be taken into consideration during the selection of locations for intertidal protected areas.