. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 128 HAMEL ET AL using the combined discharges from the Montmorency, Bastiscan, Saint-Anne and Chaudiere rivers. Phytoplankton cells abundance control the spawning of a number of marine invertebrates in the Estuary, but regular phytoplankton measurements could not be made during our study. As an indirect signal of the spring phy- toplankton bloom, we determined, in 1989. the time of spawning in the green sea urchin Strongylocentrotus droe- bachiensis. This species spawns when the adults detect the rapid growth of phytop
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 128 HAMEL ET AL using the combined discharges from the Montmorency, Bastiscan, Saint-Anne and Chaudiere rivers. Phytoplankton cells abundance control the spawning of a number of marine invertebrates in the Estuary, but regular phytoplankton measurements could not be made during our study. As an indirect signal of the spring phy- toplankton bloom, we determined, in 1989. the time of spawning in the green sea urchin Strongylocentrotus droe- bachiensis. This species spawns when the adults detect the rapid growth of phytoplankton during the spring bloom (Himmelman, 1981; Starr, 1990; Starr elal, 1990, 1992). Thus, from March to August, when spawning was anticipated, gonadal indices (percentage gonadal mass) were determined for 15 adult urchins ( cm in di- ameter) of both sexes at each sampling date. We used two approaches to examine seasonal changes in the intestinal contents of Psolus fabricii. First, for each date, the contents of the first centimeter of the intestine of each of the 30 individuals were suspended in 5 ml of 10% formalin, and the various types of undecomposed organisms present in a 1 ml subsample were identified and counted with a hemacytometer. Large cells were ex- amined under white illumination, and the presence of small phytoplankton cells was determined by the fluo- rometric method of Yentsch and Menzel (1963). Second, the contents of the following 30 g portion of the digestive tract was emptied into a Petrie dish, examined with a binocular scope, and the proportion of living phytoplank- ton cells (green in color) to non living materials (decom- posed cells and inorganic materials) was estimated. The phytoplankton cells in the first centimeter of the intestine seemed virtually undigested (green in color and intact). Buoyancy ofoocytes Forty oocytes were collected from five mature females (measuring 25-34 g in dry body wall mass) collected on 14 July 1990. The oocytes
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
