. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. POPULATION DYNAMICS OF ASCIDIA 631 granite rock walls is dominated by solitary ascidians, brachiopods, and tube-building Dolychaetes. Here annual ascidians temporarily reach high densities while perennial species show less pronounced fluctuations in density (Svane, 1983). Ascidia mentula O F Muller is a quantitatively important, perennial species found exclusively on hard substrates. It can reach high densities at depths greater than 15 m. It is rare y found above the 15 m level. A. mentula has a boreal-lusitanian distributi
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. POPULATION DYNAMICS OF ASCIDIA 631 granite rock walls is dominated by solitary ascidians, brachiopods, and tube-building Dolychaetes. Here annual ascidians temporarily reach high densities while perennial species show less pronounced fluctuations in density (Svane, 1983). Ascidia mentula O F Muller is a quantitatively important, perennial species found exclusively on hard substrates. It can reach high densities at depths greater than 15 m. It is rare y found above the 15 m level. A. mentula has a boreal-lusitanian distribution (Berrili, 1950) and is recorded as far north as the Trondheimsfjord on the west coast of Norway (Millar, 1966). , • ^ • r A detailed study of growth, reproduction, and long-term population dynamics ot A mentula at one station and depth is described by Svane and Lundalv (1981). The aim of the present study is to assess the role of reproduction, recruitment, and mortality in the spatial and temporal population dynamics of/I. mentula. An attempt has been made to correlate changes in physical environmental parameters with patterns ot recruitment, reproduction and mortality observed at three stations each at two depth levels over twelve consecutive years. Material and Methods A stereo-photogrammetrical analysis was undertaken on data obtained over a 12- year period (1971 -1982) from three stations, each at two depth levels, on the Swedish west coast (Fig. 1). Station SI is at an exposed locality (St. Sundskar 58 , 11°'E) in the Vadero archipelago off the Swedish west coast. Station G6 is in a \ SI N t 0 I— NORWAY SWEDEN GOTEBORG. 10 km —I FIGURE 1. Map showing the Skagerrak area (inset) and the stations: SI. the ^^P^^^^^^J^^ °"'" ^"^^f Vadero G6 and G4: the and sheltered stations ,n ^hV""^^^!"^^^;'P^^^^^ the GuUmarsfjord. 1. Kristineberg Marine Biological Station. 2. The town of Lysekil. 3. Bomo Hydrograph
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