An experiment was conducted to compare the effects of the introduced bryozoan, Bugula neritina, and the native bryozoan, Bugula dentata, on sessile invertebrate assemblages. Individuals of both species were collected from Workshops Jetty and Altona Pier prior to the experiment and transported back to the laboratory. Two colonies of either B. neritina or B. dentata were attached to each plate using sponges that expanded when wet. The plates were then transported to Workshops Jetty and attached to plates and left for 12 days. At the conclusion of the experiment plates were collected and abundances of species on the plates were counted and identified.

Study of the genetic structure, demography and recruitment of several species of marine invertebrates.

Larval supply and recruitment of reef fish at 5 sites around Lord Howe Island were measured during November/December 2003 and January/February 2004. Light traps, artificial reef units (ARUs), and underwater visual censuses were used simultaneously. Two types of ARUs were trialed, Standardised Monitoring Units for the Recruitment of Fishes (SMURFs) and crevice collectors. Visual censuses involved taking photos of the habitat every 5m along a 25 x 2m fixed transect. The results indicated that the catch efficiencies of the 2 ARUs varied depending on species. For example, Eviota spp. preferentially settled into crevice collectors, while Enneapterygius rufopileus (blackcheek threefin) preferred SMURFs. Spatial patterns of recruitment were influenced by larval supply only for E.rufopileus. The amount of suitable habitat was a good predictor of recruitment for Neoglyphidodon polyacanthus (multispine damsel).

Study on genetic structure, demography and recruitment of several species of marine invertebrates.

The population dynamics of the infaunal bivalve Soletellina alba were investigated at three sites situated in close proximity to the mouth of the Hopkins River estuary from 1997 to 1999. The distribution and abundance of juvenile and adult S.alba was very variable across all dates, sites and channel elevations (i.e. water depths). An experimental test comparing the recruitment of juveniles at different channel elevations and in sediments of varying particle size was conducted during 1999. The results of these tests showed that recruitment was greatest at the shallowest channel elevation and there was little evidence that sediment particle size influenced recruitment. In contrast to 1999, recruitment during 1997 or 1998 was very low. Growth rates were monitored using tagged individuals held in caged and uncaged plots, which revealed that growth was highly variable among individuals, but not between sites. These tests also revealed that growth was negligible during the colder, winter months, and that the fastest growing individuals were capable of growing 0.2 mm/day. Salinity tolerance experiments showed that bivalves exposed to low salinities (< 6 ppt), exhibited poorer condition and took longer to re-burrow into sediments than those exposed to greater salinities (> 14 ppt), while death of bivalves exposed to salinities < 1 ppt occurred after 8 days of exposure. These tests provide evidence that low salinities are probably the principal cause of mass mortalities that are observed during winter flooding, although the interaction between salinity, temperature and turbidity also deserve consideration in the future. It is hypothesised that the survival of very young juveniles (between 0.5mm and 1mm shell length) and rapid growth rates are important features of the life history of S.alba that explain its successful persistence within the Hopkins River estuary. It is highly likely that this species is capable of completing its entire life cycle within the estuary. The absence of other nearby populations, and periods of mouth closure, are likely to greatly limit the potential contribution made by larvae entering from the surrounding marine environment. This study has added to our knowledge of how an infaunal bivalve copes with life in the intermittently closing estuaries that typify semi-arid coastlines in the Southern Hemisphere.

Metadata record for data expected from ASAC Project 2163 See the link below for public details on this project. Records of observations of kelp rafts passing within 50 m of one side of the vessel over replicated periods of 1 hour. Data collected over subantarctic latitudes only. Records include: size, species, presence/absence of holdfast, latitude and longitude, ship speed.

Exclusions were attached to artificial substrata to investigate the relative effects of predation on the development of epifaunal communities at Portsea. Exclusions were black plastic mesh cages enclosing panels that were attached to rigs under the Portsea Pier. Bare control panels and cage controls where included in the experimental design. Cage controls had the bottom and half of the roof on the cage removed. There were 2 replicate panels of each treatment that were immersed for 2, 4 or 7 months and there were 6 runs of the experiment from October 1975 to November 1977. At the conclusion of each run of the experiment the panels were fixed in 4% formalin-seawater solution. In the laboratory, the number of individuals and percent cover of colonial species on each panel were recorded. Surveys identified that grazing fish were the most abundant predator of the epifaunal community at Portsea during the experiment. Predation significantly affected the pattern of establishment of the epifaunal community. There were fewer ascidian recruits and more diverse communities on bare control panels because fish predation prevented monopolisation of space by dominant ascidian competitors. On caged panels were there was no fish grazing, the survival of colonial ascidians was greater and the panels were dominated by arborescent bryozoans and ascidians.

This study investigated the temporal and spatial patterns of recruitment of epifaunal species at Portsea. Recruitment panels were immersed at depths of 1 - 2.2 metres for 10 months (25/10/1975 - 11/9/1976) and 24 months (16/11/1977 - 14/11/1979) and at depths of 3 - 3.8m for 18 months (11/9/1976 - 18/5/1978). Each panel was divided into four quadrats (9 x 9cm) and the number of larvae recruits in each quadrat was recorded every 2 months using a binocular microscope. The replicate number of quadrats sampled every 2 months varied between 1 and 30 replicates. The mean number of larval recruits per quadrat for each period was calculated for each species at each depth. An additional treatment ('complex substratum' treatment) was added to 2 panels for 2-month periods from 13/10/1976 to 12/10/1977 to assess the effects of substratum complexity on the recruitment of epifauna. The complex substratum treatment simulated the physical structure of a barnacle and arborescent bryozoan community. On each panel there was 1 quadrat that was a complex substratum treatment and 1 quadrat that was randomly chosen from the 3 remaining to be analysed as the control. Thus, there were 2 replicate quadrats of each treatment (complex substratum and control) per 2-month period. At the completion of each period all individuals and colonies of each species were counted in each quadrat. Availability and abundance of settling larvae varied seasonally and annually. Rates of recruitment of larvae were greatest during spring, summer and autumn. Polychaetes, barnacles, hydroids, tubicolous amphipods and bryozoans recruited in greater abundance and more consistently throughout each year than did ascidians or sponges. A greater diversity of species settled on the complex substratum treatments and the density of settlement of some species was also higher.

Sabella spallanzanii is an introduced sabellid ploychaete that is thought to be native to the Mediterranean and east Atlantic coast. Since its first identification in Port Phillip Bay in 1992 it has spread rapidly and occurs in most parts of the bay. This thesis examines the ecological impact of Sabella spallanzanii aggregations on hard substrate epifaunal assemblages in south eastern Australia. Specifically the effects of Sabella on: a) recruitment of sessile invertebrates; b) development of epifaunal assemblages; c) distribution of larvae and other planktonic organisms and d) growth and survival of sessile animals are examined. These effects are evaluated in relation to spatial and temporal changes in Sabella canopies resulting from changes in populations and patterns of fan deployment. Studies were carried out between 1995 and 1998 at four sites within Port Phillip Bay, Victoria (Geelong Marina, Breakwater Pier, Victoria Dock and St Kilda Marina) and at Outer Harbour, within the Gulf of St Vincent, South Australia. The effects of Sabella on recruitment of sessile taxa were complex, but a number of generalisations could be made. Recruitment of some barnacles, bryozoan, spirorbid and ascidian taxa to large experimentally cleared (pilings) areas was higher than on uncleared areas. On the scale of individual 20 by 20 cm settlement plates, where the effects of physical structure was controlled using fanworm mimics, most of the effects were caused by the presence of physical structure on the plate. Positive and negative responses of some taxa were observed but responses were not consistent across experiments. Recruitment onto tubes increased the abundance of several taxa on plates with fanworms, but not all taxa recruited onto tubes. Results were not consistent within taxonomic groups or between sites. Longer term experiments revealed fewer changes to the structure of the understorey assemblage. The apparent disappearance of canopy effects with time could be caused by processes associated with assemblage development such as overgrowth and senescence of early recruits. Alternatively it could simply be caused by differences in the composition of assemblages between experiments. Multivariate analyses showed that spatial variation in recruitment on the scale of 10's of metres was important in determining the composition of the assemblage in both early and later stages. The planktonic abundances of larval solitary ascidian, spionid polychaetes and pooled larval taxa adjacent to the substratum were significantly reduced by the presence of a fanworm canopy, suggesting that larval flux to these areas may be lower. Little difference in larval recruitment between cleared and uncleared areas suggests that settlement rates may be enhanced or post-settlement mortality rates might be lower beneath canopies. Growth of the arborescent bryozoan Bugula stolonifera and an encrusting bryozoan Watersipora subtorquata were affected by the presence of a canopy, but these effects were not consistent between experiments. This variability suggests that canopies may act in different ways at different times. The overall impact of Sabella spallanzanii on other species at the scales examined in this thesis can not be explained by its modification of the habitat. The use of tubes as settlement sites, and the predominance of small scale responses to physical structure support this idea. Any impact of Sabella spallanzanii must also be evaluated in the light of observations that the canopy was not constant though time, due to population crashes that occurred at a number of times and places.