STUDIES ON THE BIOLOGY OF THE TROPICAL SEA URCHINS, LUCUNTER AND ECHINOMETRA VIRIDIS1

B. F. McPHERSON Institute of Marine Sciences, University of Miami

ABSTRACT The sea urchins, (Linnaeus) and E. viridis A. Agassiz, are found in the same habitat on Margot Fish Shoal, a "patch" reef off the Florida Keys. The former , however, is more widely distributed off southeastern Florida than the latter. In addition to the patch reef environment, E. lucunter also is found commonly on some rocky, inshore areas. In both species, growth of the gonads occurred during spring and summer. Spawning probably occurred in late summer or early fall. There was some indication that gametogenesis and spawning began slightly later in 1965 for E. viridis than for E. lucunter. Although individuals of E. lucunter from different habitats manifested a similar reproductive cycle, relative growth of the gonads and size of the test were greater in inshore areas than on offshore patch reefs. Young specimens of E. lucunter were found in large numbers on several sites in the summer of 1965, and in fewer numbers in the summer of 1966. These urchins failed to survive to sexual maturity on the outer reefs.

INTRODUCTION Echinometra lucunter (Linnaeus) is a widely distributed tropical occurring throughout the West Indies. It occurs as far north as southern Florida and Bermuda, and as far south as Desterra on the Bra- zilian coast. It is found on Ascension and St. Helena islands and on the West African coast from Dakar to Angola (Mortensen, 1943). It is usually found in very shallow water (intertidal to five meters), but Mortensen (1943) reported specimens from as deep as 45 meters. Off southeastern Florida, Echinometra lucunter occurs on shallow rocky areas, coral reefs, and occasionally in beds of turtle grass (Thalassia tes- tudinum). It may be found under detached slabs of rock, beneath coral heads, and at the base of loggerhead sponges (Spheciospongia vesparia), and it is very common on rocky areas just below the intertidal zone off the Florida Keys where it usually occupies holes or crevices in the rock which are slightly larger than the urchin (Kier & Grant, 1965). A. Agassiz has a smaller geographic range than E. lucunter. It occurs through the West Indies, from southern Florida to Venezuela, although it is not found east of the Virgin Islands (Mortensen, 1943). Off southeastern Florida, E. viridis is found from the shoreline to

1 Contribution No. 989 from the Institute of Marine Sciences, University of Miami. This study was carried out under Grant No. WP-00573 from the Department of Health, Education, and Welfare. 1969] McPherson: Biology of Tropical Sea Urchins 195

N

VIRGINIA KEY

,

I.-LONG REEF

it.' ,::t~~""25" - ;ft! .c:J c? ~~ """,,o.c' :£' o&0\f'O· '~PIGEON KEY 81· 80· I I FIGURE1. Chart of southern Florida showing collection sites. the outer edge of the main reef at about 12 meters and possibly deeper (Kier & Grant, 1965). It is often absent from inshore rocky areas along the Florida Keys, where great numbers of E. lucunter are found. Kier & Grant (1965) reported, however, that E. viridis occurs in the intertidal zone off Molasses Key where it occupies holes in the rock. In this study, E. viridis was found in greatest numbers several miles offshore on "patch" coral reefs.

STATIONS Studies on density, growth, and reproduction were made on the follow- ing sites off southeastern Florida: (1) Pigeon Key, about three miles west of Marathon; (2) the northeast tip of Virginia Key, off the sewage treat- ment plant; (3) Margot Fish Shoal; (4) Long Reef; and (5) French Reef (Fig, 1). Echinometra lucunter was collected at all the above sites. E. viridis was collected only at Margot Fish Shoal. Margot Fish Shoal consists of a number of "patch" coral reefs located several miles east of Elliot Key, Florida, and about a mile shoreward from the outer reefs. Each patch is separated from other patches by areas of 196 Bulletin of Marine Science [19(1) sand and sea grass (mostly Thalassia testudinum) and deeper water. There are both living and dead coral rock in this area. Urchins were collected at several inshore patches, beneath rocks or coral heads, in water approxi- mately one meter deep. Long Reef and French Reef are outer, "dead" reefs composed mainly of rubble and old coral rock. Urchins were col- lected from beneath rocks, on shallow parts of the reef, in depths similar to those on Margot Fish Shoal. Off Pigeon Key, urchins were collected on a rock platform just below the intertidal zone. Off Virginia Key, urchins were collected on a rocky area about one hundred meters from shore in water about one meter deep.

METHODS Estimates of density were made at several stations in areas where urchins were most abundant. This was done by dropping a one-meter-square iron frame fifty times at random over the area to be sampled, and counting the urchins within each square meter. The density was then expressed as the mean number of urchins per square meter plus two standard errors of this mean. The total number of urchins in a particular area was estimated for the Pigeon Key station. This was done by determining the 95 per cent confidence interval for the mean number of urchins within this measured area. An estimate of the maximum number of urchins per square meter at a particular station was sometimes made by selectively placing the iron frame on the bottom, and counting the urchins within this sample. The selective placement of the iron frame was made on a site where the urchins appeared most abundant, as determined from a visual examination of the station. Size frequency analyses were made to estimate the range and the mean size of the test on each station. Urchins were collected, measured, and returned to the sea. Maximum diameter of the test, measured to the nearest 0.1 mm, was used as a measure of the size of the test. In addition, several other measurements were made on urchins from Margot Fish Shoal to determine variations in dimensions of the test between the two species. Urchins were examined periodically to determine gonadal growth and reproductive condition at Pigeon Key, Virginia Key, and Margot Fish Shoal. They ranged in size from 35 to 65 mm in test diameter at the first two sites, and from 25 to 40 mm at the last site. In addition to the urchins that were collected periodically throughout the year, a number of indi- viduals of both species were collected on Margot Fish Shoal during periods of maximum ripeness to determine the size of the test at first sexual ma- turity. Most of the urchins from Long Reef and French Reef were sexually immature. Urchins collected for studies on reproduction and growth were cut open and a gonadal smear was examined under a microscope to determine if 1969] McPherson: Biology of Tropical Sea Urchins 197

there were ripe sex cells. In order to vertify ripeness of ova or spermatozoa in doubtful cases, fertilization experiments were carried out. Fertilization was considered successful if any cleavage was observed. For most of these urchins, volume of the gonads was measured by displacement of water in a graduated cylinder and was then expressed relatively as a gonadal index (Gonadal index = 100 x gonad volume/test volume). The test volume (including spines) was determined for 34 individuals of Echinometra lu- cunter and 30 individuals of E. viridis by water displacement. The cubed diameter of these individuals was plotted against the test volume, and straight-line regressions were calculated. In routine work the maximum diameter of the test was measured and the volume of the test was calculated from the regression line of that particular species. Histological sections were made from the gonads of some urchins from each sample. Gonads were fixed in Bouin's solution. Sections were made perpendicular to the axis of greatest length of the gonad at a thickness of 8 p., and were stained with Massons trichrome stain.

IDENTIFICA TION According to Mortensen (1943), Echinometra viridis differs from E. lucunter in having fewer pore-pairs per are, fewer ambulacral and inter- ambulacral plates, a more naked apical system, and more slender tridentate pedicellariae. In addition, in E. viridis the spines are almost always tipped with violet, a pattern seldom seen in the other species. Mortensen (1943) stated that E. lucunter might manifest anyone, but not all, of the above characteristics of E. viridis. The color pattern is useful in distinguishing Echinometra viridis from E. /ucunter. As mentioned, the spines of the former species are tipped with a dark color, usually violet. In addition, each spine has a thin, white ring at its base. In no case during this study did individuals of E. lucunter have spines with color patterns resembling those of E. viridis. The color pattern of E. /ucunter is quite variable. Most individuals observed in this study were black or bluish-black aborally. Colors tended to be lighter on the oral surface. In some cases the apical system and adjacent test were bright red, with the spines and lower parts of the test being the characteristic black. The oral spines of most individuals were colored purple near their points. A few urchins were dull red over most of their test and spines. The test of E. viridis tended to be brown. No individual with red color was observed. All the individuals of Echinometra viridis examined from Margot Fish Shoal had five pore-pairs at the ambitus and a relatively naked apical sys- tem with only a few spines or tubercles. The specimens of E. lucunter had a variable number of pore-pairs, ranging from four to seven, and an apical system with many spines. These observations agree with those of Morten- sen (1943). 198 Bulletin of Marine Science [19(1)

LL E o E 0:::- w::2: I- W 10 Ecl1inomefro /ucunfer ° ,23 WI- ::2:(/) E. viridis 8 ,29 «>- 2)(/) ::2:

FIGURE 2. Maximum diameter of the apical system and test of Echinometra lucunter and E. viridis from Margot Fish Shoal.

Individuals of Echinometra lucunter and E. viridis collected on Margot Fish Shoal manifested some specific differences in dimensions of the test. In E. viridis the maximum diameter of the apical system tended to be rela- tively larger than that of E. lucunter (Fig. 2). Within the apical system, the periproct of the former was relatively smaller than that of the latter (Fig. 3).

E .s 5 I- o o 0::: 0- ° ° ii: 4 Ecllinomefro /ucunfer 0,19 W a.. E. v/rdis 8,29 o ° W 6lf; 6 66 :r: 0008/!:,66f,° 6 I- 3 0r:P06 ° /}j oLL 0::: °6 W I- 0006 8 W 2 8 8 «:2 00 2) ::2: ::) I ::2: «x ::2:

o 234 5678 MAXIMUM DIAMETER OF THE APICAL SYSTEM (mm)

FIGURE 3. Maximum diameter of the apical system and the periproct of Echinometra lucunter and E. viridis from Margot Fish Shoal. 1969] McPherson: Biology of Tropical Sea Urchins 199

PIGEON KEY N= 56 117 150 142 130 .sE • • 0:: 60 w I- W :::;:

26 JAN 8 MAY 29 AUG 4DEC II AUG 1965 VIRGINIA KEY 1966 N= 18 25 78 128 127 34 E ~ E 0::60 w ~ l l- W :::;: ~

18JAN 28APR 10JUN 21JUL 20AUG 40CT 1965 FIGURE 4. Size frequency analyses of Echinometra lucunter from Pigeon Key and Virginia Key.

SIZE AND ABUNDANCE Size frequency analyses indicated that Echinometra lucunter tended to be larger off Virginia Key and Pigeon Key than on Margot Fish Shoal. In the former areas the mean sizes of the adult populations were consistently larger than 40 mm in test diameter (t.d.), and urchins reached maximum sizes of about 70 mm. On Margot Fish Shoal the mean size ranged between 20 and 30 mm, and only a few urchins were larger than 40 mm (Figs. 4 and 5). Small, immature specimens of Echinometra lucunter (less than 20 mm) were observed at all stations during summer and fall, but were usually absent at other times. In October-November a group of small urchins from Margot Fish Shoal had a mean size of 15 mm. Size frequency analyses indicated that the mean size of this group had increased to 20 mm in 200 Bulletin of Marine Science [19(1)

N; 52 48 52 16 37 37 53 ~48 48

40 E 5 a: lJJ 30 f- lJJ :E

10

MJJAS ONDJFMAMJJA 1965 1966 FIGURE5. Size frequency analyses of Echinometra lucunter from Margot Fish Shoal (percentage).

February, 1966, and 23 mm in June (Fig. 5). Small urchins were very abundant on French Reef and Long Reef in the summer of 1965 (Fig. 6). The mean number of individuals on the former area was estimated at 1.4 ± 0.6 urchins per square meter on 9 August. The maximum number of urchins per square meter recorded during that summer was 7 on French Reef and 15 on Long Reef. On both locations most urchins were removed by Hurricane Betsy on 8 September 1965, so that only a few individuals could be found after the storm. Small urchins were not as abundant dur- ing the summer of 1966 as in 1965. Echinometra lucunter was quite abundant off Pigeon Key and Virginia Key in the summer of 1965, but there was a significant decrease in the numbers of this species during the following year. The mean density off Pigeon Key on 29 August 1965 was 2.7 ± 0.6 urchins per square meter. Urchins were confined primarily to a rocky platform on the northern coast of the key. Since the part of the rocky platform they occupied was about 1,270 square meters, the total number for this area could be estimated with 95 per cent confidence to be between 2,540 and 4,318. On 11 August 1966 the mean density in this area was estimated as 0.9 ± 0.3 urchins per square meter, or between 762 and 1,524 individuals. Off Virginia Key a maximum density of 12 urchins per square meter was recorded on 19 August 1965. The number of urchins decreased markedly during the fall so that only a few individuals could be found during the following year. 1969] McPherson: Biology of Tropical Sea Urchins 201

FRENCH REEF N= 45

E 20 S c::: W ~ I- w 0 ::i< N= 50 47 35

The significant decrease in urchins may have resulted from mortality suf- fered during or after Hurricane Betsy. Echinometra lucunter and E. viridis were common on some patch reefs on Margot Fish Shoal, while on others they were quite rare. Greatest abun- dance for both species was among bunches of stag horn coral, Acropora cervicornis. Both dead and living branches of this coral offered a protec- tive cover for these urchins as well as for other species, such as Eucidaris tribuloides and Tripneustes ventricosus. A maximum density of 21 indi- viduals of E. viridis and 6 individuals of E. lucunter per square meter was measured in one such area of staghorn coral on 15 July 1965. Most of these urchins were sexually mature, ranging in size from about 20-30 mm. Size frequency analyses gave no clear indication of when the young of Echinometra viridis entered the population, or of growth within the popu- lation. The greatest number of young urchins of this species was found during the summer and fall of 1965. Three small individuals of Echinometra viridis (3 mm) were found on Margot Fish Shoal on 6 April 1966. They were placed in aquaria where they grew to 8 mm by 14 June, 11 mm by 16 November, and 16 mm by 15 November. Larger individuals of Echinometra viridis and E. lucunter showed little or no growth in aquaria.

GROWTH OF THE GONADS AND REPRODUCTION Growth of the Gonads.-Gonadal indices of specimens of Echinometra lucunter collected on Virginia Key and Pigeon Key are given in Figures 7 and 8. Significant increases in the mean indices occurred during spring 202 Bulletin of Marine Science [19(1)

•• = MEAN , = MEAN x = MEAN OF All INDIVIDUALS VIRGINIA KEY 30 • = SEX UNKNOWN

25

~ 20 o z o

10

5

J F M A M ASONDJ FMAMJ 1965 1966

FIGURE 7. Gonadal indices of Echinometra lucunter collected off Virginia Key.

tI' = MEAN GONAD INDEX , = MEAN GONAD INDEX x = MEAN OF All INDIVIDUALS PIGEON KEY 15 • = SEX UNKNOWN

M A M ASONDJFMAMJ A 1965 1966

FIGURE 8. Gonadal indices of Echinometra lucunter collected off Pigeon Key. 1969] McPherson: Biology of Tropical Sea Urchins 203

~=MEAN GONAD INDEX , = MEAN GONAD INDEX 10 l:i =MEAN OF ALL INDIVIDUALS • = SEX UNKNOWN o E lucunter.

o « z 10 o (!)

M J J A SON OJ F M AM J J A 1965 1966 FIGURE9. Gonadal indices of Echinometra lucunter and E. viridis collected on Margot Fish Shoal. and early summer in both 1965 and 1966. Off Virginia Key, the greatest mean index in 1965 was 15 for the females and 14 for the males (21 July), and in 1966 it was 23 for the females and 18 for the males (15 June). Off Pigeon Key, the greatest mean index in 1965 was 10 (29 August), and in 1966 it was 13 for the females and 9 for the males (11 August). Significant decreases in the mean gonadal indices occurred during the fall and resulted in values of 5-6 at these sites during winter. Mean gonadal indices on Margot Fish Shoal were significantly lower than those recorded off Virginia Key and Pigeon Key. Values were maximal at the former location on 12 May 1965 (4) and on 1 June 1966 (6), and were generally low during the rest of these years (1-3). The mean monthly gonadal indices of Echinometra viridis collected on Margot Fish Shoal are given in Figure 9. The mean increased from a value of three in March, 1965, to a maximum value of six in August and Sep- tember. Significant decreases in the index occurred after 12 October, with the mean decreasing to about one in November. The gonadal indices in- creased slowly over the winter and spring reaching values of six or seven during the following summer. Reproduction.-During anyone season of the year developmental stages of the gonads of Echinometra lucunter appeared quite similar in all areas 204 Bulletin of Marine Science [19(1) sampled. For this reason, the description of the reproductive cycle given below is for all three areas studied. The sex could not be determined from gonadal smears for most indi- viduals of Echinometra lucunter collected during winter and early spring (December to April, 1965-66). Histological sections of gonads from urchins collected during this period revealed varying amounts of nutritive material, but few sex cells in the germinal layer. The term, germinal layer, is used for both germinal and non-germinal cells contained inside the mid- dle layer of connective and muscle tissue in the acini (after Holland & Giese, 1965). The nutritive material of the germinal layer contained vac- uoles and globules of various sizes which are characteristic of nutritive phagocytes found in the gonads of other sea urchins (Holland & Giese, 1965) (Fig. 10,A). During late spring (April to June, 1966) the number of sex cells in- creased so that it was possible to identify the sex of most individuals from gonadal smears. Histological sections indicated that most gonads during this time contained developing sex cells and nutritive material. Early stages of developing cells were seen around the base of the germinal layer, ad- jacent to the layer of connective and muscle tissue. Later stages of these sex cells, such as oocytes and spermatids, were often scattered throughout the germinal layer (Figs. 10,B, C; II,A). In some cases, spermatozoa or ova tended to accumulate in the center of the acini (Figs. 10,C; II,B). The nutritive material consisted of numerous round globules (5-8 p- in diameter), which stained green with Massons trichrome stain. In some cases, these globules appeared to be free in the acini and not included in cellular structures. In other cases the globules appeared to be contained in cells, presumably globulated nutritive phagocytes. Miller & Smith (193 I) reported a similar observation in the ovary of Echinometra lucunter. They believed that these globules, which they called nutritive bodies, surrounded developing oogonia and passed their nutritive material to these cells. Urchins were ripe in July and August of 1965 and 1966, with germinal layers of the gonads containing predominately spermatozoa or ova (Figs. 1O,D; 1l,C). Gonadal volumes were generally maximal. In a number of cases, urchins brought in from the field at this time spawned within a few hours after being placed in aquaria. During the fall (October to December, 1965) most urchins contained ripe sex cells, but these were presumably relict. Histological sections in- dicated that gonads during this period were characterized by acini which were partially empty. In many cases the lumen was quite conspicuous, containing only a few ova or spermatozoa (Fig. II,D). The amount of nutritive material was reduced; it stained gray with Massons trichrome stain, instead of the green color seen earlier in the summer. The annual reproductive cycle of Echinometra viridis was quite similar 1969] McPherson: Biology of Tropical Sea Urchins 205

D FIGURE 10. Histological sections through the gonads of -Echinometra lucunter (scale line is 100 fl.): A, gonad sampled in early spring showing absence of sex cells (nutritive material is probably deglobulated nutritive phagocytes); B, testis, 17 June 1965; C, testis, 17 June 1965; D, ripe testis, 20 August 1965, showing spermatozoa which fill the acini. Marine Science [19(1 )

FIGURE 11. Histological sections through the gonads of Echinometra lucunter (scale line is 100 p,): A, ovary, 17 June 1965, showing an early ripening stage; B, ovary, 21 July 1965; C, ripe ovary, 20 August 1965; D, spent ovary, 4 Oc- tober 1965. 1969] McPherson: Biology of Tropical Sea Urchins 207

FIGURE 12. Histological sections through the gonads of Echinometra viridis (scale line is 100 p.): A, gonad, 1 March 1966, showing absence of sex cells (gonad filled with nutritive material); B, testis, 15 July 1965, showing a ripening male; C, ripe testis, 12 October 1965; D, ovary in early gametogenic stage, 15 July 1965. 208 Bulletin of Marine Science [19(1) -:?;.

FIGURE 13. Histological sections through the gonads of Echinometra viridis (scale line is 100 p.): A, ovary, 15 July 1967; B, ovary, 17 August 1967; C, ripe ovary, 12 October 1965; D, spent gonad, 16 November 1965. 1969] McPherson: Biology of Tropical Sea Urchins 209 to that of E. lucunter, but studies of gametogenic development and spawn- ing indicated that these processes occurred slightly later in E. viridis. The sex was not determinable in smears for most individuals of Echino- metra viridis collected during winter and spring (December, 1965, to June, 1966, and in May, 1965). Sections of gonads during this period revealed varying amounts of nutritive material, but few sex cells. The nutritive ma- terial contained vacuoles and globules of various sizes (Fig. 12,A). Evidence of active gametogenesis was first observed on 23 June 1965 and 1 June 1966 in a few individuals (Fig. 12,D). In these urchins early stages of sex cells were observed at the base of the germinal layer, which still consisted primarily of nutritive material. Sex cells became more common during the next month. On 15 July 1965 and 5 July 1966 most individuals were ripening (Figs. 12,B; 13,A,B). The germinal layer consisted of globules similar to those described for E. lucunter. Ovaries contained ova, oocytes, and earlier stages of sex celIs, the latter being found mainly around the base of the germinal layer. Testes contained spermatozoa and earlier stages of male sex cells. Spermatozoa tended to accumulate in the center of the acini. Most urchins sampled on 12 October 1965 were ripe (Figs. 12,C; 13,C). The acini were filled with ripe sex cells replacing most of the nutritive ma- terial. Gonadal indices were high during summer but decreased sharply after the sampling in October. Histological sections after October indicated that the acini were mostly empty (Fig. 13,D). There was, however, some sparsely distributed nutritive material resembling that described for E. lucunter during the fall. Ripe sex cells were evident in some gonads in November, but these were few and were presumably relict. Forty-five individuals of Echinometra lucunter and 49 individuals of E. viridis ranging from 10 to 36 mm in test diameter were examined during periods of maximum ripeness in the adult population to estimate the size at which the first ripe sex cells were developed on Margot Fish Shoal. Ripe sex celIs were absent from all individuals of E. lucunter smaller than 18 mm and from all individuals of E. viridis smaller than 15 mm (Table 1).

FEEDING AND BEHAVIOR Most of the urchins examined from all stations and at all seasons con- tained algae in their guts. This appeared to be the predominant food, al- though many urchins also contained varying amounts of fine particles of calcium carbonate. Observations on feeding were made during the day at Pigeon Key on 5 December 1965. Urchins were considered to be feeding if they had material between their teeth. Of the 105 individuals of Echino- metra lucunter examined, 51 per cent were feeding on algae (a number of 210 Bulletin of Marine Science [19(1)

TABLE 1 THE SIZE AT FIRST SEXUAL MATURITY OF URCHINS ON MARGOT FISH SHOAL

Test, Echinometra Jucullter Echinometra viridis diameter (mm) Unripe Ova Sperm Unripe Ova Sperm 10 2 2 11 2 1 12 2 3 13 2 4 14 2 I 15 1 1 16 1 1 1 17 1 I 1 18 2 1 2 1 19 2 3 20 2 I 21 1 2 1 2 1 22 1 1 23 2 1 2 24 1 1 25 1 1 26 1 27 1 28 2 1 29 1 1 30 1 1 31 1 3 2 32 2 1 33 2 34 2 1 35 36 2 these were feeding on Laurencia papillosa) and 14 per cent were feeding on calcium carbonate sediment. Thirty-four per cent were not feeding. During the day all individuals of Echinometra lucunter and E. viridis were under rocks or in crevices or holes. Urchins were sometimes hard to remove from these protective locations since they anchored themselves firmly with their spines whenever they were disturbed. Observations made several times during the nights of 31 August and 4 December 1965 and 11 August 1966 off Pigeon Key indicated that E. lucunter did, on occa- sions, move from its protective hole. On these nights, however, only small percentages of the several hundred urchins observed moved onto the open surfaces of the rocks. Many urchins appeared to be as deeply situated as they were during the day. Others moved only partially out of their holes. 1969] McPherson: Biology of Tropical Sea Urchins 211

DISCUSSION Both Echinometra lucunter and E. viridis showed a definite annual re- productive cycle in 1965-66. Both species accumulated nutritive material during the spring, but showed little evidence of gametogenic activity until early summer. Gametogenic activity began at all locations in May-June (1965 and 1966), suggesting that this process might be initiated by such external factors as increasing temperature, light, or length of day. Urchins became ripe during summer. In 1965, E. lucunter spawned in late summer and E. viridis spawned in early fall. Significant differences in the mean gonadal index from year to year or from one area to another may reflect either differences in individual growth of the gonads or in the degree of synchronization of gonadal development in the population. If individuals in the population are synchronized, that is if they all grow and ripen together, changes in the mean gonadal index will reflect individual gonadal growth. If the gonads grow and mature at different times, however, increases in the mean gonadal index of the popu- lation will give low estimates of individual gonadal growth. The evidence indicates that individuals of Echinometra lucunter and E. viridis were syn- chronized in their respective reproductive cycles, since, in each sample, in- dividuals of a species were in similar stages of gametogenic development. Mean gonadal indices were larger during the summer of 1966 than in 1965 (except for males of E. lucunter at Pigeon Key). Other investigators have pointed to a correlation between mean temperature and amplitude of the gonadal index. Strongylocentrotus purpuratus had a greater amplitude in its gonadal index in the northern populations than in the southern ones (Boolootian, 1966). Moore et al. (1963) and Moore et al. (1963) re- ported that the gonadal indices of Tripneustes esculentus and Lytechinus variegatus were greater after cold winters. McPherson (1968) noted that Eucidaris tribuloides off Miami had a larger mean gonadal index during 1966 than in 1965, and that 1966 was a somewhat cooler year. Absolute sizes of the test and gonads of Echinometra lucunter were larger on inshore areas off Pigeon Key and Virginia Key than on offshore areas at Margot Fish Shoal, suggesting that either growth rate or longevity was greater at the former locations. In support of the suggestion of a higher growth rate inshore than offshore is the fact that the amplitude and size of the gonadal index were also significantly greater in the former habitat than in the latter. Echinometra lucunter may settle from the over an area much wider than that in which it survives as an adult. Sexually mature individ- uals of this species were rarely observed on outer, dead reefs of rubble, such as French Reef or Long Reef. It was noted, however, that during the summer this species did settle on these areas, but failed to survive in any numbers. The settlement during the summer of 1965 was large, but few 212 Bulletin of Marine Science [19(1) of these urchins survived through the fall. Undoubtedly hurricanes and other storms which sweep the outer reefs make survival difficult, since most of the rocks on these areas are small and unstable. Echinometra appears to be able to survive strong wave action only if it is living in a crevice or hole in a stable rock. Echinometra lucunter and E. viridis sometimes appear to occupy the same ecological niche. Individuals of both species occur together under the same rocks on Margot Fish Shoal, where they manifest no significant differences in their food or habits. A number of other closely related species of echinoids also apparently share the same niche (Mortensen, 1928; 1943; Chesher, 1967). Since many echinoids are omnivorous, and usually have a large supply of food, interspecific competition for food may be low and thus allow species with similar ecological requirements to live in the same habitat when other conditions are suitable.

SUMARIO ESTUDIOS DE LA BTOLOGlA DE LOS ERTZOS TROPICALES, Echinometra lucunter y E. viridis Los erizos Echinometra lucunter (Linnaeus) y E. viridis A. Agassiz se encuentran en el mismo habitat en Margot Fish Shoal, una "mancha" de arrecife frente a los Cayos de la Florida. La primera especie, sin embargo, esta mas ampliamente distribuida frente al sudeste de la Florida, que la ultima. Ademas del ambiente de mancha de arrecife, E. lucunter tambien se encuentra comunmente en algunas areas rocosas cerca de la costa. En ambas especies, el crecimiento de las g6nadas tiene lugar durante la prima- vera y el verano. El desove probablemente tiene lugar al final del verano o a principios del otono. Hubo cierta indicaci6n de que en 1965 la game- togenesis y el desove fueron algo mas tarde en E. viridis que en E. lucunter. Aunque ejemplares de E. lucunter procedentes de diferentes habitats pre- sentaron un cielo reproductor similar, el crecimiento relativo de las g6nadas y el tamano de la concha fueron mayores en areas cerca de la costa que en las manchas de arrecifes lejos de la costa. Ejemplares j6venes de E. lucunter se encontraron en gran numero en varios lugares durante el verano de 1965 y en menor numero en el verano de 1966. Estos erizos no lograron sobrevivir hasta la madurez sexual en los arrecifes exteriores.

LITERATURE CITED BOOLOOTIAN, R. A. (Editor) 1966. Physiology of echinodermata. John Wiley and Sons, New York, 822 pp. CHESHER, R. H. 1967. The systematics of sympatric species in West Indian spatangoids: A revision of the genera Brissopsis, Plethotenia, Palaeopneustes, and Saviniaster. Doctoral dissertation, University of Miami, 537 pp. 1969] McPherson: Biology of Tropical Sea Urchins 213

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