CONTRIBUTIONS TO THE BIOLOGY OF THE SEA URCHIN EvelDARlS TRlBULOlDES (LAMARCK)l B. F. McPHERSON Institute of Marine Sciences, University of Miami ABSTRACT The sea urchin Eucidaris tribuloides (Lamarck) is found in several different habitats off southeastern Florida. This species appears to be particularly adapted for living in rocky and coral reef areas, using its primary spines to anchor itself under rocks or in crevices. It may move from these protective sites at night. On reefs it ingests hard particles of limestone, probably deriving nourishment from boring and encrusting organisims associated with this material. On the patch reefs of Margot Fish Shoal, growth of the gonads in the population took place during spring and summer ] 965-66. There was some gametogenetic activity throughout the year. Sex cells accumulated, forming ripe gonads in late summer and early fall of .I 965 and .I 966. Relative growth rate of the test decreased with increasing size of the urchin, and it also decreased during the slimmer. Urchins probably live at least four to five years. A.lthough the greatest population density was observed on shallow-water, outer reefs, the growth rate there was less than in areas closer to shore. Urchins from different habitats varied in size and in dimensions of the test. Eucidaris was reared from the egg through metamorphosis in 25 days. INTRODUCTION Recently a number of investigators have been working on the ecology and physiology of various sea urchins (Boolootian, ] 966). The work has centered around relatively few species and practically nothing has been done on any member of the cidaroids. Perhaps this is because areas where most of the work has been carried out (California, New England, and northern Europe) do not have cidaroids in shallow water. Even in places where there are shallow-water representatives, such as Barbados, BWI, the urchins may not be abundant or easily obtained (John Lewis, personal communication). In the West Indian region there are 12 species of cidaroids, one of which is littoral, the rest being found at moderate depth. The littoral species, Eucidaris tribuloides (Lamarck), is relatively abundant in some habitats off southeastern Florida, and this afforded an ideal opportunity to study a cidaroid urchin and to compare its biology with that of other tropical urchins. According to Mortensen (1928), Eucidaris tribuloides occurs from South Carolina and Bermuda to Bahia, Brazil, in the western Atlantic, being very common throughout the West Indian waters. Bernasconi 1 Contribution No. 904 from the Institute of Marine Sciences, University of Miami. This study was carried out under Grant No. WP-00573 from the National Institutes of Health. 1968] McPherson: Biology of Eucidaris 40 I (1955) reported that E. tribuloides was collected off Rio de Janeiro and the island of Trindade in the South Atlantic. In the northwestern Atlantic it has been collected as far north as Cape Hatteras, North Carolina (Cerame- Vivas & Gray, 1966), and in the Gulf of Mexico it has been reported on Alacran Reef, Campeche Bank (Kornicker et al., 1959), and from St. Petersburg, Florida, at 55 meters (Donald K. Serafy, Florida State Board of Conservation, personal communication). Mortensen also reported that it occurred off the African coast (variety africana), at the Cape Verde Islands and in the Gulf of Guinea, and in the mid-Atlantic at the Azores and Ascension Islands. Over much of its range E. tribuloides occurs from very shallow to relatively deep water; Mortensen (1928) reported that it occurs to 450 m. However, along the edge of its distribution, at least in the North Atlantic, it is absent from the shallow water (North Carolina; St. Petersburg, Florida) . Kier & Grant (1965) studied the distribution of a number of echinoids off Key Largo, Florida, in the Pennekamp Coral Reef State Park. They reported that Eucidaris tribuloides was solitary and widely but sparsely distributed in rocky "niches" and turtle grass (Thalassia testudinum) beds. In the area of study it was collected from the back reef channel, over a mile from shore, seaward to depths of at least 25 meters. STATIONS Sites were selected to represent several environmentally different habitats (Fig. 1). Long Reef is an outer "dead" reef, composed mainly of rubble and old coral rock. Margot Fish Shoal is located about 1/2 mile inshore from Long Reef and consists of a large expanse of "patch" reefs, each patch separated from others by areas of sand or "sea grass" and deeper water. On this site there was both living and dead coral. A third site was the seaward side of Virginia Key, off the sewage treatment plant. This area has been referred to as "Sewage Beach" (Moore et al., 1963a and b). It is a shallow area of "sea grass" (mostly Thalassia testudinum), sand, and rocks. Eucidaris was found throughout the area, but in small numbers. Regular monthly sampling was begun in May, 1965. Collections on Long Reef were discontinued in September, 1965, because urchins became very scarce, partly because of Hurricane Betsy. Sampling on Margot Fish Shoal was continued through 1 December, 1966, and on Virginia Key through 31 October, 1966. Before the regular monthly sampling was initiated on these areas, intermittent collections had been made. In addition to these three sites, sampling and observations were also conducted at irregular intervals at a number of other locations (Fig. I): Lake Worth jetties (northern inlet); French Reef (an outer reef of coral rubble and rock, mostly "dead"); seaward of Alligator Reef (45-55 402 Bulletin of Marine Science [18(2) LAKE WORTH _____~ JETTIES NI ..____SEWAGEBEACH, q VIRGINIA KEY < d f ..--LONG REEF ri/~F:~;~~~"5" 0 .~/ -----MOLASSIS HUMP 25 - P .~.ALLIGATOR REEF 06 c:/ ,e? ...-1 •• 0 •• G c.--' 800 I FIGURE 1. Chart of southern Florida, showing collection stations. meters, flat mud-sand bottom); and Molasses Hump, Molasses Reef, Key Largo (coral rubble, mostly "dead"). Urchins collected in all the above areas, except number six, were taken in shallow water (1-3 meters), in most cases by diving with mask and flippers. Collections were made off Alligator Reef with the use of a 10-foot otter trawl. In addition to the urchins collected from the above areas, some were obtained from other locations in the Atlantic in order to study variation in shape of the test (see Table 1). 1968] McPherson: Biology of Eucidaris 403 TABLE 1 COLLECTIONSITES FOR Eucidaris trihuloides USED IN STUDIES ONVARIATIONIN DIMENSIONOF THETEST1 1. Margot Fish Shoal. 2. Long Reef. 3. Alligator Reef. 4. Sewage Beach, Virginia Key. 5. Llama Piedrecitas, Cartagena, Colombia; "living" and "dead" coral reef, 1-2 meters (urchins supplied by Dr. R. Pfaff, University of Cartagena, Colombia). 6. Ascension Island; shallow, rocky area (urchins supplied by Mr. R. Kes- singer) . 7. West Africa (E. trihuloides, variety africana); collected from R/V PILLS- BURY;P-275 (1° 24'N, 5° 38'W, 5-38 fms); P-22 (5° 25'N, 0° 01'W, 28 fms). 1 Ecological information on the first four collection sites is given in the text. METHODS AND MATERIALS For studies on growth of the gonads and reproduction, approximately 15 urchins, ranging in size from 28 to 35 mm in test diameter (t.d.), were collected monthly on Margot Fish Shoal to estimate changes in gonadal size and sexual condition in the population during the year. In addition, urchins ranging from 8 to 39 mm t.d. were collected at this same station in October, 1965, and in August, 1966, to estimate changes in gonadal size with increasing test diameter, and the size at which the first ripe sex cells develop. Varying numbers of urchins were also collected at irregular intervals at Long Reef, Virginia Key, and Lake Worth, to compare with those collected on Margot Fish Shoal. For most of the urchins collected, the volume of the gonads was measured, and a gonadal smear was examined under a microscope to determine if there were ripe sex cells. In order to verify ripeness of ova or spermatozoa in doubtful cases, fertilization experiments were carried out by mixing ova and sperm. Fertilization was considered suc- cessful if any cleavage was observed. Volume of the gonads was expressed 100 gonad volume relatively as 1 . This is the gonad index~. Gonad volume test vo ume was measured by water displacement in a graduated cylinder. The test volume (including spines, which accounted for about 20 to 30 per cent of the test volume) was determined for 42 individuals from Margot Fish '10 gonad volume ~t~es-t -vo-Il-,m-e-has been used by some authors (Moore et aI., 1963 a and b). 404 Bulletin of Marine Science [18(2) Shoal by water displacement. The cubed diameter of these individuals was plotted against test volume and a straight line regression was cal- culated. In subsequent work the test diameter was measured and the test volume was calculated from this regression line. Histological sections were made from the gonads of most of the urchins collected in the regular monthly samples at Margot Fish Shoal and from some of the urchins collected in other areas. Gonads were fixed in Bouin's solution. Sections were made perpendicular to the axis of greatest length of a gonad at a thickness of 8,..., and were stained with hematoxylin and eosin or with Masson's trichrome stain, the latter being used in most cases. On a few urchins, sections were made through different parts of the same gonad to determine if there were differences in development of sex cells in different parts of the gonad. Microscopic examinations of smears were made on more than one gonad of some urchins to determine if there were differences between gonads in the same individual.