Lunar Periodicity in Sea Urchins

Home , Paracentrotus lividus, Sphaerechinus granularis

1100 S. KECKES

S t je p a n K e Čk e Š

Institute „Ruder Boskovic“, Rovinj and Zagreb, Yugoslavia

(Z. Naturforschg. 21 b, 1100— 1101 [1966] ; eingegangen am 9. April 1966)

The lunar periodicity in Paracentrotus lividus (Lam.) and Sphaerechinus granularis (Lam.) was studied at several stations in the North Adriatic during four years. No correlation was found between the moon cycle and the maturity of the investigated species.

Investigators using sea urchin gametes as ex Results and Discussion perimental objects are familiar with the fact that even during the season when normally the animals The results of all measurements are shown to should be ripe, sometimes nearly all gonads are gether in Fig. 1, where the percentage of ripe „empty“, i.e. without any ripe sperm or eggs. specimens are plotted versus time. Some authors 2 described the influence of lunar Generally it may be concluded that sea urchins cycle on the spawning of Diadema setosum at Suez are ripe in the investigated area from March to and in the Java Sea. They have found that during September. Furthermore, it is evident that there is its breeding season the gonads become empty at full no lunar periodicity in the investigated species. moon, but M o r t e n s e n 3 could not confirm this lunar periodicity. In Paracentrotus lividus at Woods Hole 100 the lunar periodicity was not observed4. An ex- 1960 celent review of lunar periodicity is given by Korringa 5. 50 Having these, sometimes controversial, results at our disposal, we tried to test the correlation be I I I I I I______I______I______I______I______L tween the moon phases and the maturity of Para X .x 1961 v * r * .* • > centrotus lividus Lam. and Sphaerechinus granularis X•x V• X * * x x; Lam. i : X 50 - Material and Methods 1 •.* i i 1 i £ I I IV V vi vn vm U s x In regular intervals during four years (1960 — 1963) \ ID % xs the ratio of ripe and unripe specimens was determined 1 1962 V *• « *• X and compared with the moon cycle. Owing to general < I lade of ripe animals in the winter the greatest number' * of observations refer to the spring, summer and; / X autumn periods. ; • «* 'x • •X* X • Sea urchins were collected by free diving technique! i 4 1 1 l"x • 1 rx • 1 I PI rr v vi vn vm IX % XI xn or dredging. The number of specimens in each catch 1 •; x-. *ji ;. i • x • was large enough to ensure a representative result. 1963 $ X Normally the animals were opened by a circular cut X and their sex and maturity were checked immediately 50 - « after their removal from the bottom. Some results were X obtained on animals opened in the laboratory as soon •* l * V i i 1 1 I 1 i . *• as possible after their removal from the sea. i nmwvvivivfflixxxixn The sites of sampling were chosen in the North MONTHS Adriatic, near Rovinj, so that the unexpected local Fig. 1. Variations of the percentage of secually ripe Para influences could be avoided. centrotus lividus (• ) and Sphaerechinus granularis (X).

1 H. M. Fox, Proc. Roy. Soc. [London], Ser. B 95, 523 4 E. B. H a r v e y , The American Arbacia. Princeton University [1924]. Press (1956). 2 M. Y o s h i d a , Annotnes zool. jp. 25, 117 [1952]. 5 P. K o r r i n g a , Ecolog. Monogr. 17, 349 [1947]. 3 T. Mortensen, III. Kgl. danske Vidensk. Selsk. Skr., natur- vidensk. math. Afdel. Ser. 9. 7,1 [1937]. LUNAR PERIODICITY IN SEA URCHINS 1101

In June 1961 a sudden fall in the number of ripe sperm and eggs. During the whole year the oxygen Paracentrotus was observed which was not followed content is close to saturation or even above it. by a decrease of ripe Sphaerechinus, indicating that Variations in salinity are also not in correlation the stimulus for shedding acted specifically only on with the percentage of ripe animals. the Paracentrotus. Another sudden decrease of ripe The sudden decrease of ripe Paracentrotus in animals observed in August 1962 was common to June 1961 and of both the investigated species in both species. August 1962 can perhaps be to some extent attribu From the results obtained in the period June to ted to the influence of spawning individuals on the August 1961 it seems that in Paracentrotus lividus ripe members of sea urchin populations 6. However, it takes about two months to develop ripe genital the reason for the long lasting lack of ripe animals products. during the second half of 1962 is without ex The knowledge of the physical and chemical para planation. meters of the sea in the area where sea urchins were M o n r o y 7 reported that at Naples sea urchins collected, does not offer any indication about the usually shed after storm or the sirocco. Unfortunately mechanism which governs the appearance and dis we did not register the winds and we cannot analyze appearance of sexually ripe specimens. Thus the our results in this respect. average temperature of the surface layer of the sea The author wishes to express his sincere gratitude is below 10 °C in March, when sea urchins are to thes taff of the Institute of Marine Biology, Rovinj, already ripe, while it is about 15 °C in November, Institute for supplying him with the material in 1960 when the gonads of nearly all specimens are without and 1961.

8 S. K e c k e ? , B. O z r e t i c , and C. Lucu, Experientia [Basel] 7 A. M o n r o y , cited as personal communication in H a r v e y ’s 22, 146 [1966]. The American Arbacia.