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Competitive interactions in the epifaunal community at Portsea, Victoria.
The resource provides information on the rates of growth, competitive ability and life spans of species in the epifaunal community at Portsea. Estimates of rates of growth for all species were collected from panels immersed on 16/11/1977 except for the common barnacle (Elminius modestus) and ascidian (Didemnum augusti) which were collected from panels immersed on 24/10/1975. Length and average width of colonies or individuals and maximum height of arborescent bryozoans were made at regular intervals during the time of immersion. Colonial ascidians were the most rapid occupiers of space. In general, colonial ascidians and sponges attained a larger size and occupied space more rapidly than encrusting bryozoans. Competitive interactions between species were examined using the same panels as described in the record 'Patterns of development in the epifaunal community at Portsea, Victoria' (File identifier: a88f2d70-ebf6-11dc-a93a-00188b4c0af8). These panels had been immersed for 2 to 42 months and fixed in formalin-sea water solution. Approximately 5500 interactions were recorded between 52 species. An interaction was defined as the overgrowth or smothering of an organism by another organism of the same or different species. For each interaction the species involved were identified, the sizes of the interacting organisms were measured and the percentage of overgrowth, if any, was estimated visually in increments of 5% overgrowth of the colony or individual. There was no single competitively dominant species in the marine epifaunal community at Portsea. The competitive ability of a species depended on the rate of growth of the species and the maximum size they could attain. The relative size of interacting colonies was often important in determining the outcome of an interaction with larger colony generally winning. The maximum life span for each species was estimated from observations of communities on panels and on pier pilings over the 4 year period of the study (October 1975 to November 1979). The life spans of the major groups of epifauna on panesl at Portsea followed the order sponges (>24 months) > ascidians (~ 12 - 20 months) > bryozoans (~ 8 - 20 months) > barnacles, polychaetes, tubicolous amphipods and hydroids (4 - 12 months).
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Effects of predation by fishes on the epifaunal community at Portsea, Victoria.
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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.
Patterns of recruitment of epifaunal species at Portsea, Victoria.
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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.
The importance of predation in shaping marine sessile communities at Williamstown, Victoria
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Predation on newly settled individuals has been shown to shape sessile invertebrate communities of the northeast coast of North America. This study tests if this response can also be observed at other geographic locations that support different assemblage of sessile invertebrates. The effects of predation in early post-settlement assemblages were tested at two locations in Victoria; Workshops Pier, Williamstown and Queenscliff Pier, Queenscliff during the summer of 2005-2006. At each site, early post-settlement assemblages of sessile invertebrates were established and subsequently exposed to a series of predation exclusion treatments of varying durations. This dataset gives the abundances of sessile invertebrates on plates at Williamstown Pier after the initial 4 day settlement period, and after subsequent exposure to 3, 15 and 35 days exposure to three predation exclusion treatments. The predation treatments were i) uncaged, no predator exclusion, ii) full 2 mm mesh cage, total predator exclusion and iii) full 10 mm mesh cage, exclusion of large predators only. In addition two cage control treatments were established to identify if the cages themselves caused a change in the sessile invertebrate assemblages. Cage controls were partial cages constructed from both 2 mm and 10 mm mesh. The results indicated that, although predators were common, predation did not exert a strong influence on sessile invertebrate communities at Williamstown.
The importance of predation in shaping marine sessile communities at Queenscliff, Victoria
공공데이터포털
Predation on newly settled individuals has been shown to shape marine sessile invertebrate communities of the northeast coast of North America. This study tests if this response can also be observed at other geographic locations that support different assemblage of marine sessile invertebrates. The effects of predation in early post-settlement assemblages were tested at two locations in Victoria; Workshops Jetty, Williamstown and Queenscliff Pier, Queenscliff during the summer of 2005-2006. At each site, early post-settlement assemblages of sessile invertebrates were established and subsequently exposed to a series of predation exclusion treatments of varying durations. This dataset gives the abundances of sessile invertebrates at Queenscliff Pier after an initial 4 day settlement period, and 20 and 40 days after these initial assemblages were exposed to three predation exclusion treatments: i) uncaged, no predator exclusion; ii) full 2 mm mesh cage, total predator exclusion; iii) full 10 mm mesh cage, exclusion of large predators only. In addition two cage control treatments were established to identify if the cages themselves caused a change in the sessile invertebrate assemblages. Cage controls were partial cages constructed from both 2 mm and 10 mm mesh. The results indicated that didemnid ascidians may have been preyed upon by a small predator, but this predator was not identified. However, predation did not exert a strong influence on other taxa or on the overall structure of sessile invertebrate communities at Queenscliff.
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