Can photoperiod manipulation affect gonad development of a boreo-arctic echinoid (Strongylocentrotus droebachiensis) following exposure in the wild after the autumnal equinox?

摘要

A laboratory experiment was conducted in the winter of 2003-2004 to assess the effect of varying photoperiod regime on consumption rate, assimilation rate, absorption efficiency, and gonad development of the green sea urchin, Strongylocentrotus droebachiensis. Adult individuals were collected from the wild after they had been exposed to the ambient autumn photoperiod cue (which is the extraneous trigger thought to elicit gametogenesis in this species) and placed at ambient temperature for 12 weeks under five different photoperiod regimes: (1) 24 h light:0 h dark = "0D", (2) 16 h light:8 h dark = "8D", (3) 8 h light: 16 h dark = "16D", (4) 0 h light:24 h dark = "24D", and (5) ambient photoperiod (range: 10.50-15.25 h dark). Urchins in these five treatments were fed ad libitum with bull kelp, Ne-reocystis luetkeana. A sixth treatment consisted of starved individuals held under 0D conditions. Various gonad factors including gonad index, percent gonad water, gonad colour (CIE lightness or L~*, CIE hue or a~*, and CIE chroma or b~*), percent area occupation of the gonad by various cell types (nutritive phagocytes, spermatozoa, and secondary oocytes/ova), and stage of development were assessed at the beginning of the experiment and at weeks 4, 8, and 12 of the study.