<I>Chione Cancellata</I>

THE ECOLOGY OF CHIONE CANCELLATA1 HILARY B. MOORE AND NELIA N. LOPEZ Institute of Marine Sciences, University of Miami ABSTRACT Chione cancellata occurs intertidaIly and sublittorally. It is mature at a length of about fifteen millimeters and an age of one year. There is little growth after four years. Chione spawns twice a year, in the winter and summer. Shell growth is positively correlated with temperature in im- matures, but is depressed in summer in adults. The annual productivity is about 83 per cent of the standing crop, and half the productivity is in the form of spawn. A rich intertidal community produces a dry weight of tissue of 7.9 gm per square meter per year. An account of habitat and behavior is given. INTRODUCTION The family Veneridae, including the genus Chione, is of worldwide dis- tribution, and its species are important constituents of various bottom communities. The species Chione cancellata Linne ranges from Cape Hat- teras to Brazil, including Bermuda and the West Indies (Abbott, 1954; Dall, 1903). In view of its importance, it is unfortunate that almost noth- ing is known of its ecology. A long-term study is in progress on the communities in Biscayne Bay, Florida. This is considered to be a typical tropical shallow-water estuary; basic information is needed on the ecology of such an area, and particularly on its productivity. In a study of the infaunal communities in the soft bottom in this area (McNulty et al., 1962), C. cancellata was found in all but the coarsest sediments. The following mean numbers of animals per square meter were found at the corresponding median diameter of sedi- mental particles: 0.31 « 0.2 mm), 0.36 (0.2-0.4 mm), 0.83 (0.4-0.6 mm), 0.0 (> 0.6 mm). At an intertidal station referred to later, a density as high as 162 per square meter was recorded. We are indebted to the Department of Health, Education and Welfare for supporting this study (grant No. WP-00573). Several graduate students studied this species in a course on marine ecology, and their reports have proved of great value. We wish to thank R. L. Aaron, C. N. D'Asaro, G. Reyes and A. D. Mathias for allowing us to use their data. We are also grateful for help from many other members of the laboratory. MATERIAL AND METHODS The community survey led to detailed quarterly sampling of two selected areas in 1957 and 1958. This used a one-tenth-square-meter Van Veen 1 Contribution No. 987 from the Institute of Marine Sciences, University of Miami. 132 Bulletin of Marine Science [19(1) grab. Numbers per square meter were estimated, as well as size frequency. A single series of tissue-weight determinations was made, and from these the seasonal variation in tissue weight per square meter was estimated. In the present study it was considered more desirable to obtain large quantities of material than to know precisely from what area of bottom it was taken. We therefore used a mud bucket for collecting. An approximate calibra- tion of the bucket (Moore & Lopez, 1966) gave a value of 6.24 buckets per square meter of surface, so the results of this series are roughly quan- titative. In the summer of 1965, a series of transects were made down the intertidal zone on the Seaquarium flats, close to the laboratory (Moore, et al., 1968). These have provided a good estimate of the general abund- ance of Chione in such a habitat. Finally, sampling on a selected intertidal location of these flats was commenced in July, 1964, and repeated at frequent intervals up to July, 1966. It is the work at this location which has produced most of the following data. This location is shown as station F on transect 1 in Figure 2 of Moore et al. (1968). This is slightly below mean low water of equinoctial spring tides. At approximately monthly intervals, a sample of about two hundred Chione from this station was brought to the laboratory where the size frequency was recorded. About thirty animals covering the full size range were then opened. The length and width of the gonad of each were mea- sured, and a small fragment of the gonad removed to make a smear prepa- ration. The sex of this was recorded, together with the degree of ripeness of the gonad. Finally the tissues were removed from the shell, dried for 72 hours at 105 °e, and weighed. The gonads were found to mature at a shell length of about 16 mm. For the animals above this size in each sample, the regression of dry tissue weight on the cube of gonad length length + breadth) 3 and on ( 2 were determined. The regression of weight on shell length cubed was also determined. Tagging was performed with very small, numbered plastic tags cemented to the shells with "Plasspar," an epoxy resin which has the advantage of adhering to a wet surface. Tagged animals were released both free on the shore and in pens, but losses occurred sporadically because of storms, in- terference, and other reasons. We ended up with data for about a hundred free animals. In addition we have growth data for about 350 tagged individuals kept in a tank in the laboratory. Identification presented no problems, since no other species of Chione occurs more than rarely in the area, and there are no other species with which C. cancellata is likely to be confused. In discussing productivity, spawn production is used to include both eggs and sperm. 1969] Moore & Lopez: Ecology of Chione cancel/ala 133 100 1964 50 9 0 WIOO t9 <i I- Z ~ 50 a:: W Q.. 0 100 c::::J UNRIPE r:::=:J RIPENING 50 RIPE -c::::J SPENT 0 J F M A M A S 0 N 0 FIGURE 1. Seasonal changes in condition of gonads of females. GONADS Gonads were examined from unstained smears. When fully ripe the eggs lose their nuclear membrane and appear non-nucleate. Gonads con- taining nearly all non-nucleate eggs were never found, as they are in many species. In the whole series examined, only three individuals were seen with more than fifty per cent non-nucleate eggs, and one additional speci- men with more than 25 per cent. We have therefore described as ripe those individuals with more than ten per cent of non-nucleate eggs. Those with less than this percentage, but with generally large eggs, were described as ripening. Those with predominantly small eggs were described as unripe, and those with a few large eggs and much debris as spent. Males with testes full of active sperm were recorded as ripe, those with large gonads but little activity as ripening, those with large gonads but no activity as unripe, and those with only a few active sperm and much debris as spent. The smallest identifiable male was one with a shell length of 8.3 mm taken in December, and the smallest female (10.8 mm) was taken in 134 Bulletin oj Marine Science [19(1) 100 1964 50 d o wlOO C) <l I- Z 50 W (.) a:: w a. o 100 c=J UNRIPE ~ RIPENING 50 _ RIPE C=:J SPENT o J F M AM J J AS 0 NO FIGURE 2. Seasonal changes in condition of gonads of males. January. When between 14 and 16 mm in shell length, all individuals of both sexes develop a gonad. For seasonal comparisons of the tissue weight and gonadal size we selected a standard size of 23 mm. The spawning seasons are shown most clearly by the females, since in the males some ripe individuals are found throughout the year (Figs. 1, 2). In both 1965 and 1966 there was a definite winter spawning in the period January-February or January-March. The ovaries then ripened again, and there was a second spawning in the summer. The end of this summer spawning was caught in 1964, when it terminated in October. In 1965, it terminated in July, and in 1966, it had not yet commenced when the last sample was examined in July. The males, which are always more difficult to classify precisely, do not show a clear seasonal picture. For each sample, tissue weights were determined at a range of sizes, a regression was fitted to the data relating dry tissue weight to shell length cubed, and the weight of a standard-sized individual of 23 mm was read from this. Figure 3 shows the seasonal pattern of tissue-weight change in 1969] Moore & Lopez: Ecology of Chione cancellata 135 E Cl E l- I (!) W ~ 110 W :J A---A = 1964 (J) (J) 0----0 = 1965 I- x·· ..·..····x = 1966 100 >- a: 0 90 JFMAMJJ ASOND FIGURE 3. Seasonal change in dry tissue weight of a 23-mm Chione in suc- cessive years. a standard animal. The winter spawning shows clearly in both 1965 and 1966, with about a 17 per cent weight loss in 1965. The graph indicates that the spawning commenced much earlier, in about September, in 1965- 66, and in this case the weight loss was 26 per cent. The summer spawning was not recorded completely in 1964, but was clear in the two succeeding years when it represented weight losses of 17 and 26 per cent respectively. Averaging the two years, the total annual loss of weight in spawning was 43 per cent. An attempt was also made to determine the gonadal changes from linear measurements of the gonad in situ.

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