BULLETIN OF MARINE SCIENCE, 45(3): 708-712. 1989

NOTE

PREDATION OF ASCIDIANS BY CORONA (: ) IN THE NORTHERN GULF OF MEXICO

James E. Dalby, Jr.

The diets of several large gastropods from the northern GulfofMexico are well- documented (Table I). Despite this knowledge, Ihave noticed that in north Florida one of these , , regularly feeds on the solitary ascidian, Styela plicata, an interaction previously not reported (Table I). The only other snail known to prey on ascidians in these waters is Fasciolaria hunteria (Table I: Young, in press). The purpose of this study, therefore, was to determine how many of these large snails feed on solitary ascidians.

MATERIALS AND METHODS

Snails and solitary ascidians were collected in 1986-1987 from four locations in north Horida: St. Joseph Bay, Turkey Point, Turkey Point Shoal, and Bay Mouth Bar. The two species of solitary ascidians used in the study, S. pUcata and Mo/gu/a occidentaUs, are among the most common on the Gulf Coast of north Horida (Rudloe, 1971). The study was done at the Horida State University Marine Laboratory, Turkey Point, during the summer of 1987. In the laboratory experiment, each snail species was presented with S. pUcata, M. occidenta/is, and, as a control, one of its normal prey species. These control prey were: oysters (Crassostrea virginica) for Me/ongena corona; mussels (Modio/us sp.) for contrarium and F. hunteria; (Aequipecten irradians) for spiratum and F. tu/ipa; and snails (M. corona) for P/europ/oca gigantea. Snail length was measured as the distance from the tip of the apex to the tip of the siphonal aperture. Snail lengths (mm) were 74-101 (M. corona), 143-242 (B. contrarium), 84-117 (B. spiratum), 167- 282 (P. gigantea), 116-152 (F. tuUpa), and 63-77 (F. hunteria). Ascidian height was measured as the distance from the tip of the siphons to the base. Ascidian heights (mm) were 45-70 (s. p/icata) and 42-65 (M. occidenta/is). Bivalve height was measured as the distance from the umbo to the ventral margin. Bivalve heights were 43-55 (oysters), 32-65 (mussels), and 36-55 (scallops) and 71-81 (snails). Twenty 100-liter aquaria were set up in the laboratory, each with a separate supply of running seawater (25-30OC; 27-32 ppt). In each of 18 ofthese tanks, one snail was placed with one prey item (six snail species x three prey types). Those snails that fed on ascidians did so by insertion of the proboscis through the siphons rather than drilling through the test (pers. obs.). For this reason, it was impossible to tell whether dead ascidians were killed by snails or by bacterial degradation. Thus, as a control, I placed one S. pUcata in one of the two remaining tanks and one M. occidenta/is in the other. Ascidians were recognized as dead when necrotic tissue formed and when they did not contract their siphons when touched. In contrast, I could infer snail predation on the control prey when I found their empty shells. The experiment was run six times so that six specimens of each snail species were presented with each of the three prey types, and six individuals of each ascidian species served as controls. The assignment of snail-prey combinations to tanks was random in each run. Each run lasted 7 days and the interval between runs was 3-7 days. All 20 tanks were emptied and washed at the end of each run. When not being used in experiments, snails of each species were held in separate water tables with their normal prey (Table I). Likewise, when ascidians were not being used in experiments they were held in water tables with running seawater. Individual snails were either identified by their sizes and color patterns, or by numbers marked on their shells. Snails that died in experiments were replaced with new ones. Five snails across four species died of unknown causes.

708 NOTE 709

Table I. Diets of six large gastropods (Order Neogastropoda) in the northern Gulf of Mexico

Snail Prey References Family Melongenidae Melongena corona snails, bivalves, moribund Clench and Turner (1956); , carrion Gunter and Menzel (1957); Hathaway (1958); Menzel and Nichy (1958); Turner (1956; 1959); Hathaway and Woodbum (1961); Wells (1970); Wilber and Hermkind (1984) Busycon contrariurn bivalves, carrion Menzel and Nichy (1958); Nichy and Menzel (1960); Paine (1963); Peterson (1982); Kent (1983) Busycotypus spiraturn bivalves, snails, carrion Paine (1963); Kent (1983) Family Fasciolariidae Pleurop/oca gigantea snails, bivalves Paine (1963); Weldon (1981) Fascio/aria tulipa snails, bivalves Paine (1963); Wells (1970); Snyder and Snyder (1971); Engstrom (1982); lory (1985); Feifarek (1987) Fascio/aria hunteria snails, polychaetes, Wells (1958); Paine (1963); bivalves, ascidians Young (in press)

RESULTS All snail species, except M. corona, fed on the control prey in at least half of the trials (Table 2) suggesting that their feeding behavior was not significantly altered by captivity. All S. plicata placed in the presence of M. corona died while all those placed with other snails lived (Table 2). Since no S. plicata died in the absence of snails (Table 2), M. corona must have fed on this ascidian. Although one Molgula occidentalis died in the absence of snails (Table 2), all six of those placed with M. corona died suggesting that predation took place. It is unclear whether the death of M. occidentalis in the presence of the other five snail species was due to predation or bacterial degradation since few ascidians died in these trials (Table 2). In the intertidal zone at Turkey Point in 1986-1987, I observed on many occasions M. corona feeding on aggregations of S. plicata that had washed ashore from the subtidal zone. In the laboratory I frequently witnessed M. corona preying

Table 2. Predation of the ascidians S. plicata and M. occidentalis by snails in laboratory experiment

Number dead in six trials Snail Control prey S. p!icala M. occidentalis

Melongena corona I 6 6 Busycon contrariurn 6 0 I Busycotypus spiraturn 5 0 2 Pleurop/oca gigantea 4 0 2 Fascio/aria tulipa 5 0 3 Fascio/aria hunteria 3 0 I No snails (control) 0 I 710 BULLETIN OF MARINE SCIENCE, VOL. 45, NO.3, 1989

Table 3, Prosobranch gastropods that prey on ascidians (classification after Boss, 1982)

Taxa References Order Archeogastropoda Family Fissurellidae Kohn (1983) (not named) Family Trochidae Parry (1984) (Trochus) Family Turbinidae Parry (1984) (Turbo) Family Neritidae Kohn (1983) (Theodoxus) Order Mesogastropoda Family Cymatiidae Millar (1971); Laxton (1971); (Fusilrilon. Cabeslana, Mayena, Monoplex. Taylor et a1. (1980); Priene) Paine and Suchanek (1983); Kohn (1983); Young (1985; 1986); Underwood and Fairweather (1986) Family Lamellariidae Millar (1971); McCloskey (1973); (Larnellaria, Marsenina, Marseniopsis) Kohn (1983); Parry (1984) Family Yelutinidae Millar (1971); Young (1985) (Velutina) Family Cypraeidae Parry (1984) (Cypraea) Family Triviidae Millar (1971); Gulliksen (1975); (Erata. Trivia) Parry (1984) Order Neogastropoda Family Columbellidae Millar (1971); (Milrella) Taylor et a1. (1980) Family Buccinidae Taylor et a1. (1980) (not named) Family Fasciolariidae Young (in press) (Fascialaria) Family Muricidae DuBois et al. (1980); (Tha~. Canchakpas) Paine and Suchanek (1983); Underwood and Fairweather (1986) Family Melongenidae Present report (Melangena)

on both S. plicata and M. occidentalis. Never have I seen other snail species feeding on these two solitary ascidians, although Young (in press) reports that F. hunteria preys on M. occidentalis.

DISCUSSION Melongena corona represents the 14th family (Melongenidae) ofprosobranchs having members that prey on ascidians (Table 3). Besides ascidians, M. corona feeds on several species of bivalves, snails, mor- ibund animals, and carrion (Table 1). Likewise, in addition to M. corona, the predators of S. plicata include large fish (Sutherland, 1974; Mook, 1981, 1983) while the only other known predator of M. occidentalis is the snail, F. hunteria (Young, in press). Melongena corona is a predominantly intertidal snail occurring on sand bars, NOTE 711 oyster reefs and in salt marshes (Hathaway, 1958; Menzel and Nichy, 1958; Levy, 1979; Wilber and Herrnkind, 1984; Woodbury, 1986; Loftin, 1987). Conversely, S. plicata and M. occidentalis are mainly subtidal ascidians living attached to shells, seagrass, worm tubes, roots, and man-made structures, or rolling around on the bottom (Rudloe, 1971; Dalby, 1988; Young, in press). While experiments suggest that physical factors (e.g., desiccation, freezing) set the upper depth limit of these ascidians (Dalby, 1988; Young, in press), M. corona predation may also contribute to this limit. Predation by snails and sea stars may set the lower depth limit of the intertidal ascidian Pyura praeputialis in Chile (Paine and Suchanek, 1983). It is not known why M. corona is rare in the subtidal zone where its ascidian prey are common. Factors that may set the depth limits of intertidal gastropods include behavior, recruitment, physiological stress, predation and competition (Underwood, 1979).

ACKNOWLEDGMENTS

Drs. J. Hitron and W. Menzel provided laboratory space at the Florida State University Marine Laboratory. I thank D. Berschauer for collecting snails and S. Dall for laboratory assistance. Dr. C. Young offered advice on experimental design.

LITERATURE CITED

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DATEACCEPTED: June 14, 1989.

ADDRESS: Department of Biological Science. Florida State University, Tallahassee, Florida 32306; PRESENTADDRESS:Zoology Department, Melbourne University, Parkville, Victoria 3052. Australia.