Effects of food type and ration on reproductive maturation and growth of the sea urchin Strongylocentrotus droebachiensis

We investigated the effects of food quality and quantity on reproductive ma turation and growth of juveniles of Strongylocentrotus droebachiensis (Mull er) in a 22 month laboratory experiment in which we fed sea urchins four di ets: (1) kelp (Laminaria spp.) for 6 d wk(-1) and mussel (Mytilus spp.) fle sh for 1 d wk(-1) (KM); (2) kelp for 7 d wk(-1) (high ration, KH); (3) kelp for id wk(-1) (low ration, KL) and (4) no food other than encrusting coral line algae (NF). At their first and second opportunity for reproduction, al l sea urchins in the KM and KH treatments, and most in the KL treatment wer e reproductively mature, whereas all sea urchins in the NF treatment remain ed immature. Gonad index differed significantly among all fed treatments at first and second reproduction, and was highest in the KM and lowest in the KL treatment. Gonad index was similar in both sexes at first reproduction, but it was higher in females than in males at second reproduction. Diet ha d little or no effect on the relative abundance of spermatocytes, spermatoz oa, or nutritive phagocytes in testes at first and second reproduction. In ovaries, nutritive phagocytes were significantly more abundant in females i n the KM and KH treatments than in the KL treatment at first reproduction, and significantly more abundant in unfed (NF) than fed (KM, KH, KL) females at second reproduction. Mean oocyte size was similar in all fed females at first reproduction, but significantly larger in fed than unfed females at second reproduction. Mean ovum size was similar in all fed females in both reproductive periods. Increase in test diameter was greatest in the KM trea tment and smallest in the KL treatment; sea urchins in the NF treatment dec reased slightly in size. Survival was 95 to 100% in all fed sea urchins but significantly lower in unfed ones. The feeding rate on kelp was significan tly greater in the KL than the KM and KH treatments. In the KM treatment, t he feeding rate on kelp increased significantly over a 6 d period after mus sel flesh was provided. Our results demonstrate that a diet of high food qu ality and quantity accelerates reproductive maturation and growth rate, and enhances gonad production and survival in juvenile and young adult S. droe bachiensis. These findings contribute to our understanding of the reproduct ive ecology of S. droebachiensis in habitats with differing food supplies ( e.g., kelp beds and barrens). Our results also can be used to improve aquac ultural practices for sea urchins.