. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 338 REUBEN LASKER AND ARTHUR C. GIESE may be commensals which use what is left by the digestive enzymes of the sea urchin or they may be symbionts. The tentative conclusion is drawn that the sea urchin possesses enzymes which hydrolyze protein and starches of algae and per- haps slowly decompose some of the more resistant algal polysaccharides. In the latter action they may be greatly aided by the bacteria present in the gut. Under normal nutritive conditions reducing sugar was almost always found in the body fluid of sea ur
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 338 REUBEN LASKER AND ARTHUR C. GIESE may be commensals which use what is left by the digestive enzymes of the sea urchin or they may be symbionts. The tentative conclusion is drawn that the sea urchin possesses enzymes which hydrolyze protein and starches of algae and per- haps slowly decompose some of the more resistant algal polysaccharides. In the latter action they may be greatly aided by the bacteria present in the gut. Under normal nutritive conditions reducing sugar was almost always found in the body fluid of sea urchins taken in the field or feeding in the laboratory, the amount being greatest just after active feeding and least after starvation. Lang and MacLeod (1920) also report that little reducing sugar is present in the body fluid of the echinoderms which they tested, although Myers (1920) reported an unusually large content in S\ franciscanus. The possibility exists that additional sugar is present in a combination with proteins or other nutrients as in some other invertebrates (Morel and Bellion, 1910). 18 J6 o Q. E O> O ® gonad index O Moss Beach • Stillwater Cove. 0 N 1952 M A M J 1953 .10 .08 o .06o o a. .04s a. CD .02 .00 FIGURE 3. The gonad index (volume of gonad divided by the wet weight of the sea urchin) correlated with the water temperature during the year at Moss Beach, a habitat chosen because it lies on the open ocean, and at Stillwater Cover, a habitat chosen because it is sheltered. The non-protein nitrogen (NPN) showed about the same variations throughout the entire year as the sugar but it was more closely regulated than reducing sugar during starvation. On starvation the NPN in the body fluid remained almost constant but the gonads shrank to a fraction of their former size. It would seem that the gonadal nitrogen was mobilized to maintain the NPN in the body fluid during starvation. The gonads vary in size during the year and instead of a single growth
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