(Echinodermata) from a Shallow Back-Reef Lagoon, Discovery Bay, Jamaica
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BULLETIN OF MARINE SCIENCE, 32(2): 549-571,1982 CORAL REEF PAPER PATTERNS OF FEEDING AND ACTIVITY IN DEPOSIT-FEEDING HOLOTHURIANS AND ECHINOIDS (ECHINODERMATA) FROM A SHALLOW BACK-REEF LAGOON, DISCOVERY BAY, JAMAICA L. S. Hammond ABSTRACT The holothurians Isostichopus badionotus Selenka, Holothuria mexicana Ludwig, H. thomasi Pawson and Caycedo, Actinopyga agassizi Selenka and Euapta lappa Miiller, and the c1ypeastroid echinoid Clypeaster rosaceus L., had distinctly nocturnal patterns of activ- ity and feeding. The spatangoid echinoid Meoma ventricosa Lamarck was more active at night than by day. Except in E.lappa, which was strictly nocturnal, activity increased during the afternoon, peaked before midnight, then declined to a minimum before midday. All species exhibited some form of diurnal concealment except I. badiono/Us and H. mexicana, which remained fully exposed at all times. These and other data suggest nocturnal activity, which may have evolved as a predation avoidance mechanism, as the paradigm of ancestral holothurian behavior. Evidence in support of a similar explanation for the behavior of the irregular echinoids is slight. Of the "permanently" infaunal species, the holothurian H. arenicola Semper did not vary its feeding throughout the 24-h cycle, while data suggesting diel variations in activity in the spatangoid echinoid Plagiobrissus grandis Gmelin were equivocal. The two spatangoid species and H. arenicola were major agents of bioturbation where they occurred at maximum densities, but the other holothurian species did not disturb or transport large quantities of sediment. In the short-term «I day), movements of I. badionotus, H. mexicana, M. ventricosa and P. grandis were random. Over a IO-day period, I. badionotus and H. mexicana moved less than predicted by the random walk theorem; this was attributed to boundary effects in an heterogeneous environment, and may explain how the patchy dispersion of each species is maintained. Over 9 days, in an apparently uniform environment, both species of spatangoid moved distances similar to those predicted for random walking. The density of the cryptic H. thomasi in a patch of coral heads may have been limited by the number of available, suitable crevices; the frequency with which animals changed crevices was considered an index of microhabitat suitability. The stability of burrows of H. arenicola over long periods of time can be related to their association with buried rubble, which provides a physical refuge from disturbance by bioturbation. Patterns of predominantly nocturnal activity, usually associated with feeding, are widespread in the Phylum Echinodermata (Reese, 1966). Semper (1868) pos .. tulated that nocturnal activity and feeding characterized most holothurians, and there is much evidence to support this generalization (Crozier, 1915; Stier, 1933; Yanamouti, 1939; Crump, 1965; Berrill, 1966; Bakus, 1968; Konnecker and Kee .. gan, 1973). However, some species are thought to feed uniformly both day and night (Yanamouti, 1939; Bakus, 1973). Diel rhythms of feeding and activity an: also widely known in echinoids (Thornton, 1956; Sinclair, 1959; Ogden et aI., 1973a; Abbott et al., 1974; Nelson and Vance, 1979), but have been recorded in few species of deposit-feeding echinoids (Chesher, 1969; Gladfelter, 1978). Despite recognition of the general prevalence of diel rhythms of activity and feeding, previous studies of holothurians have attempted only gross assessments of movement or sediment processing through the guts, with varying degrees of exactitude (Guppy, 1882; Crozier, 1918; Mayor, 1918; Yanamouti, 1939; Trefz, 1958; Yingst, 1974; Webb et al., 1977). None of these studies, nor the more 549 550 BULLETIN OF MARINE SCIENCE, VOL. 32. NO.2. 1982 detailed ones of Chesher (1969) and Gladfelter (1978) on echinoids, involved continuous monitoring in the field, Traditionally, such studies were concerned with elucidating the role of deposit feeders in modification of reef sediments, by dissolution and attrition, and their influence on the physical disposition of sedi- ments, by bioturbation and transport. However, there are further consequences of deposit feeding for which detailed studies of the diel variation of activity and feeding have major implications. These include the structuring of infaunal com- munities through predation and disturbance (Rhoads and Young, 1970; Woodin, 1978), and regulation of nutrient fluxes between sediments and the overlying water through either physical disturbance (Rhoads, 1973; Aller, 1978), or influ- ence on the activities of the microfauna (Aller, 1978; Gerlach, 1978). Definition of optimum feeding strategies for deposit feeders, and of mechanisms of resource partition.ing between co-existing species (Levinton, 1972; Levinton and Lopez, 1977; Taghon et aI., 1978) require detailed knowledge of feeding patterns and processes. This study examined patterns of activity and feeding in six species of holothu- rians and two spatangoid and one clypeastroid echinoid species in the shal10w back-reef lagoon, Discovery Bay, on the north coast of Jamaica. MATERIALS AND METHODS Study Area and Species A useful description of the marine habitats of Discovery Bay may be found in Woodley and Rob- inson (1977). The dispersion patterns and habitat associations of the aspidochirote holothurians Ho- lothuria mexicana Ludwig, H. arenicola Semper, H. thomasi Pawson and Caycedo, Isostichopus badionotus Selenka and Actinopyga agassizi Selenka, the apodous holothurian Euapta lappa Miiller, and the spatangoid echinoids Meoma ventricosa Lamark and Plagiobrissus grandis Gmelin in the western lagoon (Fig. I) were reported by Hammond (in prep!). The c1ypeastroid echinoid Clypeaster rosaceus L. was found only in the eastern lagoon. The study utilized two areas in the western lagoon (Fig. I): Site I, an "heterogeneous" habitat (Hammond, in prep.)' consisting of a mosaic of mounded sand, rubble, coral heads and light macro- algal growth, and; Site 2, an open, relatively homogeneous sandy area, adjacent to which were large patches of dead coral heads and mounds formed by the infaunal funnel feeder, H. arenicola. Site 3, in the eastern lagoon (Fig. I), comprised a stand of the seagrass, Thalassia testudinum. surrounded by sand and coral heads. Site 4, also in the eastern lagoon, was a lithified Pleistocene pavement covered by a felt-like algal turf, with intermittent coral heads and crevices. All sites were in 1-3 m of water. Twenty-four-hour Surveys Similar approaches were employed for six species; these are summarized in Table I. The straight line distance traveled by each specimen of each species was measured at approximately 4-h intervals during the 24-h survey. All surveys of each species were done on different dates, at approximately the same phase of the moon, except the last four surveys of P. grandis, in which two groups of 10 animals were followed for 2 consecutive days. H. arenicola showed no detectable daily movements, except irrigation of its burrow and defecation. The cylindrical feces of J. badionotus were collected at each interval, dried and weighed. Holothuria mexicana and H. arenicola produce regular sized fecal pellets. Within a sample of 10 animals of each species, it was found that pellet number and dry weight were highly correlated for each animal (r from 0.92 to 1.0, P <0.01), so on all surveys counts of pellets were recorded and the dry weight of a sample of pellets from each animal was used to calculate weight defecated in each interval. Since the echinoids do not produce discrete feces, bound by a mucous envelope, and the spatangoids defecate below the sediment surface, the amount of sediment passed was not determined. The length of all animals, except the infaunal H. arenicola, was measured. The echinoids posed no problems, but holothurians contract markedly and unpredictably when handled. Several times during each survey the length of each holothurian was measured by holding a flexible tape above it, avoiding disturbing the animal. The length was taken as the average of these measurements . • Hammond, L. S. Dispersion and habitat relations of deposit·feeding holothurians and echinoids (Echinodermata) from a shallow reef lagoon, Discovery Bay. Jamaica. In preparation. HAMMOND: ACTIVITY AND FEEDING IN DEPOSIT-FEEDING ECHINODERMS 551 , \ \ \ \ DISCOVERY BAY \ t -' "'- .... , I I / / .•. / - ---'" , . 300 M Figure I. Map of Discovery Bay, showing the eastern and smaller western lagoon behind the fringing reef (cross-hatched), bounded by the -10 m contour. The locations of the study sites 1-4 are marked. On each survey, the number of changes of direction greater than 450 made by individuals of five species (Table I) was recorded. Smaller changes were often ambiguous, so were excluded. Direction changes were detected by the trail of disturbed sand left by the burrowing spatangoids, or by the feces trail and orientation of the animal in the other three species. To test for randomness, on one survey for each species in which long term patterns of movement were studied (below), the net direction of travel by an individual during each interval was allocated to one of the four quadrants of an underwater compass. Travels along the north-south or east-west axes were assigned to the next quadrant clockwise. A Chi-squared analysis was constructed, to test the hypothesis that the direction of travel did not deviate from that predicted by randomness (i.e., an equal number in each quadrant). In only one interval for each of M. ventricosa and P. grandis,