Estimating the abundance of clustered and cryptic marine macro-invertebrates in the Galápagos with particular reference to sea cucumbers

Estimating the abundance of marine macro-invertebrates is complicated by a variety of factors: 1) human factors, such as diver efficiency and diver error; and 2) biological factors, such as aggregation of organisms, crypsis, and nocturnal emergence behavior. Diver efficiency varied according to the detectability of an organism causing under-estimation of density by up to 50% in some species. All common species were aggregated at scales from 10-50 m. Transects need to be long enough to transcend the scale of patchiness to improve accuracy. Some species of sea urchins and sea cucumbers (pepinos) which are cryptic by day emerged at night so that daytime censuses underestimated their abundance by up to 10 times. In the sea cucumber fishery, estimates of abundance need to be made at the scale of the population, i.e. at hundreds of km. A strategy for this is proposed

Investigator group expedition 2006: Habitat-dependent foraging behaviour and diet of the scalyfin, Parma victoriae, in South Australia

The foraging behaviour, territory size and diet of the scalyfin, Parma victoriae, were studied at three sites in South Australia. Two sites were in Ecklonia habitat on an exposed coast, one of them, Site 1, in a marine reserve at West I., and the other, Site 2, in an intensely fished area at The Bluff, Victor Harbor. The third, Site 3, was sheltered, in a fucoid community in Groper Bay, Flinders I., in the eastern Great Australian Bight. The algal food supply was highest at the reserve site (1), and lowest at the sheltered site (3). The scalyfin spent a greater proportion of time foraging, and a lower proportion of time sheltering, at the reserve site (1), than at the Bluff site (2). At Site 3, territories were about seven times larger than at the other two sites, and fish spent a higher proportion of time in defence and aggressive interactions than at the other sites. The diet at all sites was predominantly browsed rhodophytes, but at Site 3 the rhodophytes eaten were almost entirely epiphytic on fucoid algae and in low abundance. At the exposed sites (1, 2), where food algae were patchy, scalyfin removed Ecklonia sporophytes experimentally placed in their territories, but not at Site 3, dominated by fucoids. At the exposed sites they employed a saltatory foraging mode, whereas at Site 3 they adopted a cruise search foraging behaviour over their larger territories. Both modes seem optimal in their respective habitats.Shepherd, S.A.; Clark, M. and Ferguson, G.http://adelaideaus.library.ingentaconnect.com/content/rssa/trssa/2008/00000132/00000002/art0000

Long-term changes in macroalgal assemblages after increased sedimentation and turbidity in Western Port, Victoria, Australia

The long-term impacts of declining water quality from coastal development on macro-algal communities can be devastating, but are rarely known because of lack of baseline studies. This study examines the effect of increased sediment and reduced water quality over 35 years in an Australian temperate coastal embayment. The algal assemblage on Crawfish Rock in northern Western Port was surveyed in 1967–1971 and in 2002–2006. During the 1980s, water quality declined following large-scale seagrass loss. In 1971, the Rock had a rich algal flora with 138 recorded species, including 97 species of Rhodophyta. The biomass and cover of canopy and understorey species were measured at sites of strong and slight current on a depth gradient. In 1971, fucoid or laminarian canopy species were dominant from ~1–8 m depth, and an algal understorey extended from the intertidal zone to ~12–13 m depth. In 2002–2006 the canopy species extended to only 3 m depth and the algal understorey to ~4 m depth, and 66% of the algal species had disappeared, although a few additional species were present. Persistent, sediment-tolerant species included several phaeophycean canopy species, some chlorophytes (Caulerpa spp.) and a few rhodophytes.Scoresby A. Shepherd, Jeanette E. Watson, H. Bryan S. Womersley and Janet M. Care

Climate change cascades: Shifts in oceanography, species' ranges and subtidal marine community dynamics in eastern Tasmania

Several lines of evidence show that ocean warming off the east coast of Tasmania is the result of intensification of the East Australian Current (EAC). Increases in the strength, duration and frequency of southward incursions of warm, nutrient poor EAC water transports heat and biota to eastern Tasmania. This shift in large-scale oceanography is reflected by changes in the structure of nearshore zooplankton communities and other elements of the pelagic system; by a regional decline in the extent of dense beds of giant kelp (Macrocystis pyrifera); by marked changes in the distribution of nearshore fishes; and by range expansions of other northern warmer-water species to colonize Tasmanian coastal waters. Population-level changes in commercially important invertebrate species may also be associated with the warming trend