<I>Ostrea Permollis</I>
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LIFE CYCLE OF OSTREA PERMOLLTS AND ITS RELATIONSHIP TO THE HOST SPONGE, STELLETT A GRUBIJl MILTON L. FORBES Lamar State College of Technology, Beaumont, Texas ABSTRACT Anatomical and functional relationships of the commensal oyster, Os/rea permollis, to its host sponge were studied and common associates, especi- ally predators, were identified. O. permollis larvae were reared for study of responses to: host sponge, non-host sponges, and shell. Recruitment in inshore waters was detected by presence of O. permollis spat on S. grubii during June and November of the years studied. Age-groups were identifi- able in size-frequency histograms for over a year following recruitment. INTRODUCTION Os/rea permollis Sowerby is a commensal oyster in the sponge Stelletta grubii Schmidt. Adult O. permollis live crowded on the surface of S. grubii or embedded with shell margins protruding. Occurrence of O. permollis in sponges implies a selective advantage for its ability to inhabit sponges. The present study inquires into the existence of dependence on the host sponge and adaptations of the oyster to its host. Review of the Literature.-A previous paper (Forbes, 1964) deals with identification and distribution of O. permollis and S. grubii. The oyster- sponge association is common subtidally in the northeastern Gulf of Mexico. O. permollis has been found only in S. grubii, except once in Halichondria, itself attached to S. grubii. Mantle margins and conchiolin of the relatively fragile shells are golden yellow; otherwise O. permollis resembles other Os/rea species in all essential anatomical features (Fig. 1). General aspects of the biology of Ostrea and the other oyster genera are thoroughly discussed by Korringa (1941,1952), Thomson (1954), Menzel (1955), Nelson (1957), Yonge (1960), and GaltsofI (1964). PROCEDURES Oyster-sponges (S. grubii with O. permollis) were collected at St. Teresa, Franklin County, Florida; in Alligator Harbor nearby; and near Buoy 26, in the Gulf of Mexico about 10 miles south of Alligator Point. The localities are described elsewhere (Forbes, 1964). Much of the 'Contribution No. 212 from the Oceanographic Institute. Florida State University. From a disser- tation submitted in partial fulfillment of the degree of Doctor of Philosophy at Florida State University. Part of the "ork was done during tenure of a predoctoral National Science Foundation fellowship and part during tenure of a Florida State University Graduate School fellowship. 274 Bulletin of Marine Science [16(2) I em I i vm rma h 9 1m Iv FIGURE 1. Anatomy of Ostrea permollis: right valve and mantle removed. a, anus; am, adductor muscle; cc, cloacal chamber; ds, dental socket; g, gills, occupying branchial chamber; h, heart; Ii, ligament; 1m, left mantle; Ip, labial palps; lv, left dissoconch valve; pc, pericardial cavity; pi, palliobranchial fusion; r, rectum; rmo, origin of right mantle; um, umbo; vm, visceral mass. 1966] Forbes: Life Cycle of Ostrea permollis 275 research was done at the Alligator Harbor Marine Laboratory of the Florida State University. Oyster-sponges and extracted oysters were kept alive in cages near the end of the Marine Laboratory pier between neap and spring low tide levels. When larvae were needed, 10-20 oysters were cleaned and placed individuaHy in 10 cm finger bowls of filtered sea water in the laboratory. Like other species of Ostrea, O. perm ollis is an incubatory protandric hermaphrodite with alternation of sexual phases. Dishes were checked daily for larvae when the water was changed. Throughout the year, about one in ten large oysters (20-40 mm) liberated a brood of thousands of straight-hinge larvae in about 5 days. Straight-hinge larvae were reared to metamorphosis by methods described by Loosanoff (1954), Davis & Guil1ard (1958), and Loosanoff & Davis (1963). Larvae were diluted to 20 per mI. Sodium sulfametha- zine (Sulmet, American Cyanamid Co.) was added as a bacteriostat in the ratio of 1: 10,000. The chrysomonad Monochrysis lutheri Parke was fed to the larvae at a final dilution of 100,000-200,000 cells per ml. Pediveligers (ready-to-set, or eyed, larvae) were identified by their foot, a pair of ocelJi, and occasionally by their creeping behavior. Pediveligers were selected with a fine pipette under a stereoscopic microscope (45 x) for studies on setting. Substrate samples were prepared for larval substrate specificity studies as foHows. Sponge cuttings of 5-10 mm dimensions were cut from Stelletta grubii, Microciona prolifera Verrill, and an unidentified keratosid that may be a Spongia. Fragments from a clean, dry shell of Crassostrea virginica (Gmelin) were designated "clean shell" and stored dry between experi- ments. Shell fragments with an algal coating were designated "fouled shell," Sponge cuttings and fouled shell were stored in sea water which was changed daily. The growth rate of O. permollis was estimated from size-frequency analysis of periodic collections and verified by periodic measurement of oysters in a sponge. The size-frequency method used here was adapted from the length-frequency method used in fish studies, where each age- group in a population is represented by a separate normal curve around a mean length (Lagler, 1952). Since oysters vary in shape, it seemed desirable in the present study to use a size index based on product of length times height, and then to take the square root to avoid exaggerating older age-groups. The size index, V L X H, approximates length since the length/height ratio is usually close to unity in O. permollis. Measure- ments were made in millimeters to two significant figures with vernier calipers. Length is the distance from the beak of the left valve to the posterior margin; height, the greatest dorsoventral dimension. Five collections were made for the size-frequency study: three from 51. Teresa, 276 Bulletin of Marine Science [16 (2) I em co --ch . '. ,... co A . , . ':::'::':~ ••......... /. ,':'..:.:'" ":':'~.:.: ~. ,".',. co B FIGURE 2, Ostrea permollis in sagittal section, right valves in situ in the host sponge. Arrows indicate inferred path of excurrent stream, am, adductor muscle; b, bill of sheIl; ea, canal in sponge choanosome; eh, choanosome; co, sponge cortex; g, gill; n, nacre; ss, surface of host sponge; V III , visceral mass. 1966] Forbes: Life Cycle of Ostrea permoLlis 277 and two from the north shore of Alligator Harbor. The two stations were about a mile apart. Results from the size-frequency study were verified by measurements on individual O. permollis in a sponge over a 10-month period. Length was used for the latter determination since height could not be measured without extracting oysters. OBSERVATIONSANDRESULTS Anatomical and Functional Relationships of O. permollis and S. grubii.- The specimens of Stelletta grubii were massive, usually spherical or elongated, and up to 20-30 cm in diameter. The surface was hispid, often strongly wrinkled, and usually encrusted with sand, broken shells, and algae. The cortex was 1-3 mm thick and densely packed with spicules (predominantly triaenes). The choanosome was relatively soft and full of canals. O. permollis and its empty valves were invariably located in or at the surfaces of oyster-sponges. All sponge centers were free of oysters and valves. Ostrea perm ollis specimens grew normally when isolated from S. grubii and maintained in Alligator Harbor or in sea water tables. Stomach contents consisted of phytoplankton, and O. permollis did not appear to depend on S. grubii for nutrition. ORIENTATIONOF OYSTERSIN S. GRUBH: Oysters appeared to be crowded haphazardly at the surface of the host sponge. Beaks lay near the sponge surface and pointed in all directions with respect to gravity. A stacking effect, several oysters lying parallel next to one another, was a frequent result of crowding. Orientations of 152 O. permollis in S. grubii were analyzed to determine whether oysters were arranged in any consistent way. Orientation was analyzed in terms of four variables: the angle of the oyster's longitudinal axis to the sponge surface; the angle of the dorsoventral axis to the sponge surface; whether the inhalant (ventral) region protruded or was embedded; and whether the exhalant region was exposed or embedded. These variables were estimated by eye. The longitudinal axes of all O. perm ollis were approximately paraJJel with the sponge surface. The dorsoventral axes of ] 38 oysters were 450 -900 to the surface. The dorsoventral axes of 14 oysters were 00 _450 to the surface. The inhalant regions of all oysters protruded from the sponge. Exhalant regions of 146 oysters were fully embedded; four were partly embedded; two were fully exposed. Hence, the essential factor in orientation of O. permollis is access of its inhalant region to the sea. WATER FLOW THROUGHO. PERM OLLIS ANDS. GRUBH: Sagittal sections of 30 preserved O. permollis and surrounding sponge were cut with a razor blade. Canals were clearly present in the sponge at the exhalant region of 278 Bulletin of Marine Science [16(2) TABLE 1 COMMON ASSOCIATES OF astrea permollis AND Stelletta grubii =·===================-=.c= _ Alligator Harbor Gulf of Mexico (Buoy 26) CRUSTACEA CRUSTACEA Neopanope texana texana Stimpson Balanus amphitrite Darwin Menippe mercenaria (Say) Synalpheus sp. Pilumnus dasypodus Kingsley Pilumnus sayi Rathbun Balanus amphitrite Darwin PeUa mutica (Gibbes) Balanus eburneus Bruguiere Petrolisthes galanthinus (Bose) Cilicaea caudata (Say) Zoeae and megalops larvae, Brachyura POLYCHAETA POLYCHAETA Leodice rubra (Grube) Sabel/aria