Materials and methods Directory UMM :Data Elmu:jurnal:J-a:Journal of Experimental Marine Biology and Ecology:Vol252.Issue1.Sept2000:

C .J. Jeffery J. Exp. Mar. Biol. Ecol. 252 2000 15 –26 17 response to more concentrated conspecific cues Minchinton, 1997. It may be, however, that reduced area of patch will intensify settlement Pineda and Caswell, 1997 despite other influences. At Cape Banks, Botany Bay, New South Wales, Australia, contrary to previously documented cases, few larvae of the small gregarious barnacle Chamaesipho tasmanica arrive and settle relative to the space available Jeffery, 1997. The barnacles often form continuous sheets of joined individuals or occur in isolated groups of joined or separate individuals on mid-littoral areas. In the more wave-exposed areas at Cape Banks, a patchy distribution is prevalent whereas, in sheltered areas, cleared spaces may be scattered throughout aggregations of barnacles. Despite the amount of space differing from place to place, there were consistent patterns in numbers of cyprids arriving from 1990 to 1993. Although the numbers of cyprids varied among places, they were correlated with the distributions of juveniles on the substratum Jeffery, 1997; Jeffery and Underwood, 2000. Obviously, the suggestions of Pineda and Caswell 1997 that consistent differences in rate of settlement might be explained by the proportion of the substratum available, cannot be substantiated by Chamaesipho. Other processes must also be operating. For example, because Chamaesipho settle gregariously in response to the presence of adults Otaiza, 1989; Jeffery, 1997, if different-sized patches were cleared within aggregations of barnacles, it was hypothesised that the degree of exposure to adults along perimeters of patches, rather than the amount of space available, would influence settlement of cyprids. It was therefore predicted that in plots of 6, 3 or 1.5 cm diameter cleared daily of newly-settled barnacles, there would be proportionally greatest settlement in the smallest plots with the greatest relative exposure to adults along perimeters. This study therefore tested the hypotheses that increased availability of substratum and or exposure to conspecific adults would influence settlement of Chamaesipho. If free space contributed to numbers settling, it would be expected that there would be no differences in numbers settling per unit area in patches of different sizes. Alter- natively, if adults around the perimeter of a patch influence settlement, there should be no differences in settlement per unit length of perimeter around patches of different sizes.

2. Materials and methods

2.1. Study area Chamaesipho tasmanica were studied from July to December in 1991 and 1992 at two sheltered sites hereafter called Sites 3 and 4 as originally named during a long-term study of six sites at Cape Banks on mid-shore levels of the Cape Banks Scientific Marine Research Area at the northern head of Botany Bay, New South Wales, Australia 34 8009S, 1508159E. This is a relatively undisturbed location with highly diversified intertidal assemblages similar to those on other areas of the New South Wales coast. The study area faces south and is subjected to strong South-East winds, especially in winter 18 C .J. Jeffery J. Exp. Mar. Biol. Ecol. 252 2000 15 –26 Short and Trenaman, 1992, which contribute to conditions of variable exposure. Tides are semi-diurnal and range over 2 m. 2.2. Influence of substrate availability and conspecific adults on gregarious settlement In July 1991 and 1992, 6, 3 and 1.5 cm diameter patches n 5 3 were cleared on the substratum within aggregations of barnacles at Sites 3 and 4 at each Low, Mid and Upper height of Chamaesipho’s distribution. From July to December each year, in 1991 and 1992, settlers were removed daily from each different-sized patch for approximately 6 days during each new and full moon. Very few, if any, barnacles settled during the intervening period Jeffery, 1997. Daily removal was necessary to negate possible confounding by gregariousness as neighbouring settlers aged Jeffery, 1997, and to ensure that only free space and conspecific adults on perimeters could act as cues for settlement. Numbers of barnacles settling in these patches were recorded until December of each year of the experiment. Total numbers of settlers in the patches in each experiment in 1991 and 1992 were compared. Because different-sized patches were used in this investigation it was necessary to separate the influences of the availability of substratum and numbers of adults along perimeters of patches. Numbers of larvae settling on different-sized patches were manipulated in two ways. To test the hypothesis that amount of available free space will influence settlement, the total numbers of settlers recorded each year on plots where larvae were removed daily were divided by the appropriate areas 28.28, 7.07 and 2 1.77 cm . To test the hypothesis that larval choice will influence settlement near conspecific adults, the numbers of barnacles settling were divided by the appropriate perimeters 18.85, 9.43 and 4.71 cm.

3. Results