Biodiversity and historical ecology of marine gastropod assemblages from subtropical Moreton Bay, Queensland, Australia

Abstract

Climate change and anthropogenic impacts are adversely affecting the biodiversity of ecological communities around the world. Coastal marine ecosystems in particular are increasingly subjected to stressors from human activities. Furthermore, there is a lack of historical studies that directly assess how human settlement patterns affect these ecosystems. Microgastropods (<5mm) found as fossils in sedimentary cores and in modern death assemblages were collected at Wellington Point, Peel Island and Myora Reef in Moreton Bay (Southeast Queensland, Australia). We established the temporal and spatial variability of species diversity and taxonomic composition prior to and following European settlement (mid 19th century) of the southeast Queensland coastline. A total of 53,260 specimens belonging to 56 families were collected and identified from fossil assemblages (sediment cores) and modern death assemblages (grab samples) from Moreton Bay. From the death assemblages we identified 219 species belonging to 115 genera and 46 families, and from fossil assemblages we recorded 51 families. The variation in the distribution of taxonomic composition of microgastropod assemblages in the bay is in part explained by substrate, total nitrogen, temperature, turbidity and depth. Environmental conditions were associated with species traits: 1) species with discoidal shape and nodulose sculpture exhibited the most pronounced preference for western sites, near the Brisbane River, linked with turbidity and high nitrogen concentrations; 2) ectoparasite species on echinoderms or actinarians, anemones, and corals were associated with western central bay sites associated with high phosphorous and chlorophyll a; 3) tropical, subtropical and temperate species of small to medium size, fusiform shape, carnivorous, and found in the lower intertidal zone were associated with eastern central bay sites linked with good light penetration, high oxygen concentrations and normal marine salinity; and 4) globose species of medium size, herbivore-grazers found in the upper intertidal zone exhibited a preference for eastern sites, off the Brisbane River mouth, with relatively constant temperature and pH. The Holocene assemblages were stable from ca7500 yr BP to around 160 yr BP after which the modern death assemblages differed from fossil assemblages and the ‘shallow’ assemblage from Myora Reef shifted into deeper subtidal waters. The differences between fossil and modern death assemblages are presumably a result of declining water quality due to the cumulative effect of human impacts. This is the first palaeoecology and modern ecology study to identify community shifts on microgastropods that can help to better understand the future response of marine invertebrate species to human impacts.