AN ANTIPREDATION MECHANISM OF THE POLYCHAETE PHYLLODOCE MUCOSA WITH NOTES ON SIMILAR MECHANISMS IN OTHER POTENTIAL PREyl

ROBERT S. PREZANT2

ABSTRACT

The polychaete Phyllodoce mucosa exhibits an antipredation response via the extrusion ofa repulsive mucoid secretion. The mucus, secreted by large glandular regions ofthe dorsal and ventral parapodial cirri, prevents immediate ingestion of the worm by several species of small or juvenile fish. A sipunculid, Phascoleopsis gouldi; a nemertean, Lineus ruber; and a large flatworm, Stylochus zebra, arealso distasteful to some potential predators. Antipredation responses found in some organisms may play an important role in regulating benthic community dynamics by mediating the feeding habits of certain predators during at least some stage of their development.

Feeding habits of many species of fish have been community to thwart extensive predatory crop­ well established, but few studies have extended ping by using inherentprotective devices may also analyses beyond stomach contents. nesults ofsuch affect community structure. research frequently lead to labeling food found in An accurate picture of community dynamics the stomach as "preferred" (Onyia 1973; Smith demands a closer examination of direct interac­ and Daiber 1977). Reports ofselective feeding be­ tions between potential prey and predatory havior based mainly on stomach contents reveal species. A start in this direction has been made on the major types of food eaten by a fish but do not a limited number offish. Hynes (1950), Tugendhat add substantially to our understanding ofthe in­ (1960), and Beukema (1968) examined some ofthe teractions between predator and prey. behavioral feeding patterns of the threespine Ivlev (1961), discussing selective feeding by stickleback, Gasterosteus aculeatus. They found fishes, included the role of "constitutional de­ that selective feeding of the stickleback is fenses" of potential prey species as a mechanism influenced by degree of satiation and palatability which may contribute to predatory selectivity. offood. This may have implications extendinginto Selectivity in food thus entails not only "prefer­ the natural environment with regard to seasonal, ence" but avoidance ofspecific potential food items predatory, or man-induced changes in community (Berg 1979). Bakus (1966) considered the possible structure. In food-limited situations "selectivity" role of antipredatory responses by some tropical may decrease. The presence of a predatory deter­ reef inhabitants. He noted that several members rent in an organism may thus be functionally of a reef community that are not readily able to operative only in a nonstressed community with retreat into the security of a coral crevice or not nonstarved predators. naturally protected by skeletal armor are either Polychaetes often dominate marine benthic poisonous, venomous, or distasteful to predators. communities (Sanders et al. 1965) and many bot­ Acidic secretions from epidermal glands of some tom feeding fish eatsubstantial quantities ofthese opisthobranch gastropods (Graham 1957; worms (Qasim 1957; Nikolsky 1963; Kislalioglu Thompson 1960, 1969) and some nemerteans and Gibson 1977). Obscurance of taxonomic (Gibson 1972) function as predatory deterrents. In characters due to digestion often prevents iden­ view ofthe fact that predation is a well established tification ofprey to species, so food items tend to be cause of quantitative changes in a population of listed in terms ofhigher taxonomic levels (Hynes prey species, the ability of some members of a 1950; Kneib and Stiven 1978). This is especially true for soft bodied preyorganismsand meansthat 'University ofDelaware, College ofMarine Studies Contribu­ accurate feeding records are often nonspecific and tion No. 130. 'University of Delaware, College of Marine Studies, Lewes, possibly biased relative to the researcher's DE 19958. taxonomic expertise.

Manuscript accepted April 1979. FISHERY BULLETIN: VOL. 77, NO.3, 1980. 605 FISHERY BULLETIN: VOL. 77, NO.3 Phyllodocid polychaetes secrete copious ally from Henlopen Flat, Lewes, Del., in early amounts of mucus when irritated (Fauchald September 1978. Seoloplos fragilis was used as a 1977). Pettibone (1963) briefly noted that the control in the behavioral experiments because, de­ mucoid secretion of Phyllodoce maculata may be spite its overall gross similarity to phyllodocids offensive to predators. Preliminary observations (i.e., long, thin worms of similar proportions), S. of P. maculata and P. mucosa (Prezant 1975, un­ fragilis produces considerably less external mucus publ. data) have confirmed that an epithelial, than P. mucosa. Worms were maintained in sepa­ mucoid secretion acts as an antipredatory rate finger bowls on a running seawater table at mechanism against at least one species offish, the 17° C and 32%0 salinity. rock gunnel, Pholis gunnellus. Fish used in behavioral experiments (Table 1) The presentstudy extends these observationsby were collected in July 1978 and allowed to quantitative experiments on behavioral interac­ acclimatize for 30-60 days in separate compart­ tions ofPhyllodoce mucosa with several species of ments on the seawater table. During acclimatiza­ small or juvenile fish, and examines the possible tion, the fish were fed a variety of foods from a defensive mechanism of this polychaete. Initial widemouthed glass pipette. Foods included bits of observations concerning antipredatory fresh blue mussel, Mytilus edulis; and American mechanisms in the phyllodocids Eumida san­ oyster, Crassostrea uirginica; live tubificid guinea and P. maculata, the large flatworm oligochaetes, Tubifex spp.; brine shrimp, Artemia Stylochus zebra, the sipunculid Phaseoleopsis marina; and, infrequently, frozen brine shrimp. gouldi, and the nemertean Lineus ruber are also Phyllodoce mucosa, typically found on fine sand reported. substrata from low water to depths over 500 m, ranges from Labrador to Mexico (Pettibone 1963) METHODS thus geographically overlapping with all fish species used in this study (Table 1). Phyllodoee mucosa (Phyllodocidae) was col­ Since this research dealt principally with the lected in late August 1978 in Nahant Bay, Mass., inability of certain predators to eat P. mucosa, it by epibenthic sled from a fine sand substratum at a was important to insure that the fish used would depth of about 17 m. Eumida sanguinea and the actively feed throughout the experimental period. orbiniid Scoloplos fragilis were collected intertid- Accordingly, several other species of polychaetes

TABLE I.-The range, habitat, food habits, and collection sites ofthe species offish used in the feeding experiments. The last column lists thetestorganismsoffered tofish. Quantitativeresults are available only for Phyllodoce mucosa. Range, habitat, and feeding habit data for the fish are from Hildebrand and Schroeder (1928), Bigelow and Schroeder (1953), Chao and Musick (1977), and Kneib and Stiven (1978).

Fish species Range and habitat Feeding habits Fish collection site Test organism Atlantic silverside, Nova Scotia to northern Small crustaceans and Lewes Beach, Lewes, Phyllodoce mucosa Menldla menldla Florida; often over mollUSCS, annelids, Del. Scoloplos Iragl/ls sandy or gravelly shores small fish, eggs, and plant material Weakfish, Nova Scotia to Florida; Fish, crabs, amphipods, Lewes Beach P. mucosa Cynosclon regalls shallow coastal waters mysids, shrimp, mol· Phasco/oopsls gouldi in summer luscs, annelids S.lragl/is Windowpane flounder. Gulf of SI. Lawrence to Mobile prey such as Lewes Beach and Phyllodoce mucosa Lophopsetta macu/a/a South Carolina; sand bot· myslds, fish, shrimp, near Delaware Bay Eumlda sangulnea toms from low water to 50 m errant polychaetes mouth at 1S m S. tragI/is Sheepshead minnow, Cape Cod to Mexico; Mobile epifauna Lewes Beach P. mucosa Cyprinodon varlegatus shallow waters of inlets inclueing annelids S. tragilis 'and bays; salt marshes Mummichog, Labrador to Mexico; Omnivorous (at least Canary Creek. P. mucosa Fundu/us he/erocll/us shallow coastal waters when >30 mm) including Lewes, Del. Phasco/eopsis gould; especially salt marshes small crustaceans, S.lragiiis annelids, and carrion Threespine stickleback, Labrador to Virginia; Small invertebrates, East Point, Nahant, Phylfodoce mucosa Gas/eros/eus acu/eatus salt and fresh waters fish fry, eggs Mass., tide pool S.lrag/lis Striped sea robin, Gulf of Maine to Soulh Crustaceans, molluscs, Near Delaware Bay Sty/ochus zebra Prlonotus evo/ans ,Carolina; coastal bottom annelids, small fish mouth at 18 "' Phasco/eopsls gould; dweller Uneus ruber Rock gunnel, Hudson Strait to Delaware; Molluscs, crustaceans, East Point, Nahant Phylfodoce mucosa Pholis gunnelus generally on rocky OOt- annelids tide pool P. macu/ara toms from low vlater to Nephtys Inclsa over 200 m

606 PREZANT: ANTIPREDATION MECHANISM OF PHYLLODOCE MUCOSA were fed to the fish before and following be­ itative tests subjecting various other test or­ havioral experiments. These worms, which were ganisms found on Henlopen Flats to potential from various size classes, included: Spio filicornis predation are also noted on Table 1. (SpionidaeJ and Nephtys incisa (Nephtyidae) col­ To test whether the mucoid secretion truly acts lected from Nahant Bay; and Glycera americana as the predatory inhibitor in P. mucosa, two (Glyceridae), Nereis virens (Nereidae), further tests were carried out. First, mucus was Scolecolepides viridis (Orbiniidae), and Hydroides removed from the surface of P. mucosa by re­ dianthus (Serpulidae) collected from Henlopen peatedly sucking the worm in and out of a Flats. narrow-mouthed glass pipette and then gently The feeding behavior of each species of fish, dabbing it with a clean, lintless cloth. The worm excludingPrionotus evolans and Pholis gunnellus, was then fed to a rock gunnel. Second, mucus from was tested quantitatively withPhyllodoce mucosa P. mucosa was collected by placing several of the and Scoloplos fragilis. Fish were starved for 24-48 worms in a small, dry stendor dish, allowing the h prior to testing. An individual fish was then worms to physically irritate each other and thus placed in a separate 4 I glass aquarium or in a produce a copious supply ofmucus. After the phyl­ small compartment on the seawater table and al­ lodocids were removed from the dish, a small lowed to acclimate for 60 min prior to experimen­ Nephtys incisa, which secretes very little external tation. Each test session was composed of two sets mucus, was placed in itand allowed to accumulate of observations separated by a 5-min interval. A a thick mucoid coat. The nephtyd was then fed to set consisted offive I-min trials each separated by the rock gunnel. a 2-min interval. The trials entailed repeated ex­ For histological study of the mucus-producing posure of randomly chosen worms to potential organs of P. mucosa, entire worms were fixed in predation by each fish by dropping the worm from Zenker's or Hollande's fixatives and embedded in a widemouthed glass pipette in close proximity to polyester wax. Blocks were cut at 5 p..m and sec­ the head ofthe fish. Since the fish were previously tions stained with Mallory's "Azan" or toluidine fed from a pipette, they showed no hesitation in blue in 1.0% borax. accepting potential food items delivered in this To examine the ultrastructure ofthe parapodial manner. Following release from the pipette, sev­ cirri of P. mucosa, small worms were fixed for 1 h eral possible combinationsofbehavioral responses in cold Anderson's fixative, cut into 2 mm sections of the fish were noted: 1) ingestion ofthe worm, 2) with a razor blade, thoroughly rinsed with phos­ rejection of the worm following an active attempt phate buffer (pH 7.2), and postfixed for 1 h in 2.0% at ingestion, 3) presence or absence of investiga­ osmium tetroxide in a phosphate buffer. Following tions of the worm by the fish (investigation is dehydration in a graded acetone series, the speci­ defined here as an obvious "enticement" of the fish mens were embedded in Spurr's low viscosity to the worm without an attempt at ingestion), and medium and polymerized at 60° C for 48 h. Thin 4) avoidance ofthe fish to the worm. The behavior sections, cut on a Porter-Blum3 MTI ultramicro­ ofP. mucosa was also noted following release from tome using glass knives, were stainedwith uranyl the pipette and after rejection or avoidance by the acetate and Sato lead citrate. Sections were fish. examined with a Philips EM201 transmission If the worm sank to the floor of the aquarium, electron microscope at an accelerating voltage of either after rejection or without any contact with 80 kV. the fish, it was taken off the bottom and again dropped in front of the fish. This process was re­ RESULTS peated as often as a I-min trial would allow. Dis­ counting delays due to behavioral interactions, Response of Fish this averaged one exposure every 6 s. Prior to the start of the first set of each test session and 1 min Results of the feeding experiments for the vari­ after each trial ended, the fish was fed a small ous species of fish being fed P. mucosa along with portion of frozen brine shrimp to ensure active the length ofeach are summarized in Tables 2 and feeding. If at any time during a test the fish re­ fused to eat the brine shrimp, the experiment was terminated. Because ofterminations, the number "Reference to trade names does not imply endorsement by the University of Delaware, College of Marine Studies or by the of sessions per species offish varied. Initial qual- National Marine Fisheries Service, NOAA.

607 FISHERY BULLETIN: VOL, 77. NO.3

TABLE 2.-Number ofattempts to ingest Phyllodoce mucosa by TABLE 3 .-Number ofinvestigations undertaken byfour species several species of fish. An attempt is defined as a single intake of fish when exposed to Phyllodoce mucosa. This table excludes and expulsion of the worm. The number following the ab- Fundulus heteroclitus and Cyprinodon variegatus because these breviated fish binomial stands for an individual fish and the species showed no or insignificant investigatory behavior with· small letter that follows stands for an individual worm. The two out attempts at ingestion. Abbreviations and notations as in numbers in parenthesis in the first column are the standard Table 2. lengths of the fish and maximum length of the worm, in mil· Set A, trial Set B, trial limeters, respectively. Fh = Fundulus heteroclitus, Ga = Gas- Session 1 2 3 4 5 2 3 4 5 Total terosteus aculeatus, Mm = Menidia menidia, Cv = Cyprinodon Gala (18,9) 0 0 0 0 4 0 0 4 3 3 14 variegatus, Lm = Lophopsetta maculata, Cr = Cynoscion reo Ga2a (18,15) 0 0 0 0 2 0 2 galis, t =experiment terminated, * = worm eaten. Ga2b (18,12) 0 0 0 0 3 2 5 Ga3c (18,13) 0 0 Set A, trial Set B, trial Ga3d (18,24) 3 0 2 1 1 0 0 0 9 Session 2 3 4 5 2 3 4 5 Total Ga4e (18,12) 0 0 5 1 t 6 Ga5e (18,12) 0 2 2 1 5 Fhla (63.22) 3 5' 8 t Fhlb (63.29) 9 4' 13 Mmla (44,24) 0 0 0 2 0 2 0 1 0 1 6 Fh2c (66,18) 4 2' 6 Mm2b (37,22) 4 0 0 1 0 0 0 0 0 0 5 Fh3d (52,19) 13' 13 Mm3c (51,14) 0 1 3 1 t 5 Fh4e (61.19) 10' 10 Mm4d (54,14) 0 0 0 Mm5e (64,18) 0 Gala (18,9) 1 0 0 4 7 3 0 6 5 0 26 Mm5f (64,23) 0 Ga2a (18,15) 21 4 0 2 1 20 5' 53 Mm6g (67,13) 0 Ga2b (18,12) 2 4 0 2 1 20 5' 34 Ga3c (18,13) 29 5' 34 Lml a (69,29) 0 0 0 0 0 0 0 0 0 1 1 Ga3d (18,24) 0 0 0 0 0 0 0 0 0 1 Lmlb (69,21) 0 2 0 3 3 2 2 1 2 3 18 Ga4e (18,12) 14 5 0 0 Ot 19 Lm2a (91,29) 0 0 0 0 2 0 0 0 1 0 3 Ga5e (18,12) 8 0 0 0 Ot 8 Lm2c (91,17) 0 0 0 0 0 0 0 0 0 0 0 Lm2d (91,21) 0 0 0 3 2 1 2 2 0 2 12 Mmla (44,24) 5 2 1 3 1 0 0 0 0 0 12 Mm2b (37.22) 4 3 1 1 0 1 1 0 0 0 11 Crla (42,24) 3 0 1 6 2 3 4 0 3 1 23 Mm3c(51,17) 10 4 4 0 Ot 18 Crlb (42,16) 2 1 1 3 1 3 2 4 2 4 23 Mm4d (54.14) 3 2 2' 7 Crl c (42,26) t 0 Mm5e (64,18) l' 1 Cr2d (46,14) 2 0 3 2 3 2 3 4 3 23 Mm5f (64.23) 2' 2 Cr2e (46,22) t 0 Mm6g (67,13) 4' 4 Cr2t (46,17) 1 2 2 2 2 3 4 19 Cvl a (46,24) 2 2 1 1 1 1 1 3 1 2 15 Cvlb (46,24) 1 1 1 1 2 2 3 4 1 0 16 Cv2c (46,14) 3 1 1 1 0 1 1 0 0 0 8 Cv2d (46,12) 2 3 3 1 2 2 3 3 3 2 24 TABLE 4.-Number ofattempts to ingest the control polychaete Lmla (69,29) 3 1 1 2 1 2 0 0 1 0 11 Scoloplos tragi/is and size offish and worm used, Abbreviations Lmlb (69,21) 6 4 3 1 3 5 5 3 0 1 31 Lm2a (91,29) 2 1 2 2 2 2 0 0 1 1 13 and notations as in Table 2. Lm2c (91,17) 2 5 5 1 3 3 3 0 0 0 22 Trial Trial Lm2d (91,21) 7 3 3 4 3 3 3 0 0 1 27 Session 2 Session 1 2 Crl a (42,24) 1 2 1 1 0 0 1 0 0 0 6 I Crlb (42,16) 2 2 4 2 2 2 2 3 2 2 23 Fhlx (48,15) Lmlw (69,16) 4 Crlc (42,26) Ot 0 Fhly (48,20) Lmlx( 69,25) 1 Cr2d (46,14) 2 6 6 5 4 5 6 4 5 44 Galx (18,11) Lm2y (91,17) 12 9 Cr2e (46,22) Ot 0 Ga2y (18, 9) Lm2z (91,23) llt Cr2f (46,17) 2 4 5 5 3 4 5 3 5 4 40 Mmlx (37,14) Crlx (42,14) 1 Mm2y (64,13) Crly (42,17) 5 Cvlx (46,13) 3. The large number of ingestive attempts in a Cv2y (46,26) given trial (Table 2) resulted from the rapid, re­ petitive actions ofa fish not allowing the worm to (rapid protraction and retraction of jaws and in­ settle to the floor ofthe aquarium following initial take and expulsion ofwater). In session Fhla, the attempts. Results of the control series using S. worm was held in the mouth and only partially fragilis and sizes of fish and worms are given in ejected ~any times prior to ingestion. During Table 4. trial 2 of set A in session Fhlb, the fish, on the Of the six species of fish quantitatively tested, fourth attempt, took in the worm and exhibited a only the mummichog, Fundulus heteroclitus, con­ choking response which lasted 15 s before spitting sistently ingested P. mucosa early in set A (Table ­ out the posterior portion ofthe worm. The remain­ 2). This species of fish showed no investigative ing portion of the polychaete was eaten after two behavior before taking the worm into its mouth. further attempts. The maximal number of at­ Nevertheless, F. heteroclitus did show some dis­ tempts prior to ingestion by F. heteroclitus was taste for this polychaete; in two cases the mum­ demonstrated by the smallest mummichog (Fh3d) michog sucked the worm in and out 13 times prior and in trials involving the largest phyllodocid to ingestion. When F. heteroclitus did eat the Whlb) (Table 2). Scalaplas fragilis was consumed worm, ingestion was immediately followed by a on the first attempt by F. heteraclitus in each con­ variable period (10-45 s) of choking or "coughing" trol test (Table 4). 608 PREZANT: ANTIPREDATION MECHANISM OF PHYLLODOCE MUCOSA While only one size class of Gasterosteus though alive, lost several parapodia and cirri and aculeatus was used, there was no trend between appeared sluggish. This same worm was again size ofthe worm and ingestionby the fish (Table 2). placed in the aquarium with the fish and was The largest as well as some of the smaller worms again set upon, producing a coughing response were not consumed. Sessions Gala, 2b, and 3a all lasting 30 s but was not rejected. This fish did resulted in ultimate ingestion of P. mucosa but postfeed on A. marina and M. menidia showed no involved 34-53 prior ingestive attempts. Of the hesitation in consuming S. fragilis. seven sessions observed with G. aculeatus, these Only a single size class of sheepshead minnow, three sessions showed the highest number of at­ Cyprinodon variegatus, was available. This tempted ingestions prior to consumption. In ses­ species was exposed to P. mucosa ranging in size sion Ga2a, there was a renewed expression of the from 12 to 24 mm and showed a consistent rejec­ antipredation mechanism at the start ofset B (Ta­ tion of each size class (Table 2). In no case was a ble 2). Thus, sets A and B start with 21 and 20 coughing reaction noted. Cyprinodon variegatus attempts, respectively, followed by a decrease in appeared able to distinguish between P. mucosa the number of attempts in set A and consumption and A. marina from short distances (up to 15 em). in trial 2 of set B. The fish showed almost no investigatory behavior In most ofthe sessions between G. aculeatus and after initial ingestive attempts in a given trial but P. mucosa, lack of ingestive attempts seemed to did quickly swim over to feed on A. marina in correspond with the presence of investigative re­ every case of exposure. Scoloplos fragilis was sponses (Tables 2, 3). These investigations in­ eaten on the first attempt in each control test with volved a close approach to the worm as it sank C. variegatus (Table 4). through the water column, and in some cases a The windowpane flounder, Lophopsetta recoil from the worm without evidence of direct maculata, was the largest fish used in this study. contact. In cases where the worm was consumed, This species rejected the phyllodocids without fail, the fish exhibited a coughing response which showing 11-31 attempts at ingestion (Table 2) and lasted several seconds. Gasterosteus aculeatus also exhibited coughing responses following in­ readily consumed S. fragilis (Table 4). gestive attempts. The two sessions with L. A correlation between the size of the Atlantic maculata, making the greatest number of at­ silverside, Menidia menidia, and its ability to con­ tempts to ingest (Lmlb and 2d) (Table 2), also sume P. mucosa is suggested (Table 2). Smaller registered the greatest degree of inquisitiveness fish showed little interest in the worms following (Table 3). There was no relation between size of initial experiences in set A, while the larger fish fish and size of worm in these interactions. As often consumed the worm very early in the first Table 4 shows, there was some hesitation by the set. During set A, fish <50 mm initiated several larger L. maculata in the control series when of­ attacks on the phyllodocids, and the worm was fered S. fragilis. In all ofthese control tests butone easily taken into the buccal cavity before rejec­ (Lm2z was terminated), the fish eventually ate the tion. A rejected worm was often so densely covered worm, but in Lm2y the fish made 21 attempts and with mucus that it would cling to the lower lip of ran into the second trial ofset A prior to ingestion. the fish by a mucus thread for several seconds. Less than 1 h later, this same fish actively and Menidia menidia also exhibited coughing reac­ quickly fed on 12 mm Scolecolepides viridis and 31 tions following attempted and successful inges­ mm Nereis virens. tions. Larger silversides were quick to respond to Juvenile weakfish, Cynoscion regalis, also re­ potential food items released into the aquarium fused to eat P. mucosa (Table 2). There may be a and swiftly sucked them in. In set Mm5f, a 64 mm relationship between the number of attempts to fish was fed a 23 mm worm. On the first attempt at ingest and the size of the worm in these cases ingestion by the fish, the worm was quickly taken, (Table 2). In CrIc and 2e, the worms used were whereupon the fish reacted with a coughing re­ . among the three largest (26 and 22 mm, respec­ sponse lasting 45 s. The fish also exhibited a vio­ tively), and in both cases the fish showed a violent lent lateral head shaking during this time. Fol­ headshaking response to void its buccal chamber. lowing this, the worm was totally ejected but the It thereafter became "nervous" and would not feed fish continued reacting as described for several on A. marina. In Crla a 24 mm worm was used, seconds. This was the only case where an entire and in the entire session only six attempts at in­ worm was injured prior to ejection. The worm, gestion were made. All the remaining P. mucosa 609 FISHERY BULLETIN: VOL. 77, NO.3 tested with C. regalis were <20 mm long, and in­ Behavior of Phyllodoce mucosa gestive attempts ranged from 23 to 44/session. Cynoscion regalis exhibited frequent investiga­ Phyllodoce mucosa showed relatively consistent tive responses (Table 3) which, unlike those of reactions upon release into the aquarium and fol­ most ofthe other fish, usually involved direct con­ lowing rejection. When first released, the worm tact with the wormby bumpingit with its snout. In fell slowly through the water in a semicurl posi­ some cases following this contact, the fish would tion, or curled in a tight ball and fell at a slightly show a headshaking reaction similar to that pro­ faster rate. After a worm was taken and rejected duced by attempted ingestion. Cynoscion regalis by a fish, it was covered with a thick layer of consumed Scoloptos tragilis during the first trials viscous mucus. Immediately after rejection, the of the control series (Table 4). worm coiled into the tight, spheroid position. In During the course of these experiments, indi­ this position, it was either retaken by the fish and viduals of each species of fish were given the op­ the process repeated until the worm was eaten, or portunity to feed on several other species of the worm was dropped, after initial attempts, to polychaetes. These included Spio filicornis, Neph­ the floor ofthe tank. Ifthe worm drifted unharmed tys incisa, Nereis virens, Glycera americana, to the floor of the aquarium, it usually started Scolecolepides viridis, and Hydroides dianthus. what appeared to be an exploratory phase which Each fish readily consumed each of these species consisted of several short excursions in various from several size classes, in almost every case on directions before setting out on a single, straight the first attempt. path toward one of the corners of the aquarium. Preliminary data has also been collected on During this exploratory period, the worm held its dorsal parapodial cirri folded against its dorsum. Eumida sanguinea tested with L. maculata. Test worms ranged from 9 to 13 mm long and were consistently rejected. A 69 mm L. maculata re­ Histology and Ultrastructure of jected a 13 mm long E. sanguinea 20 times over a Phyllodoce mucosa Parapodial Cirri single session, while a 91 mm flounder rejected a The glandular and sensitive dorsal and ventral 12 mm long worm 38 times in a session. Investiga­ tions ranged from 6 to 10/session and showed no parapodial cirri of P. mucosa are the primary obvious relationship with ingestive attempts. In sources of externally released mucoid secretion. qualitative observations, it was also noted thatthe The dorsal cirrus possesses a large nerve which runs along the cirral axis and then radiates cen­ rock gunnel rejected both P. mucosa and P. maculata. trally into several smaller nerves which wind be­ tween the large cirral mucocytes (Figure 1). Removal of the mucus coat from P. mucosa re­ Numerous free neural extensions penetrate the sulted in quick consumption by Phalis gunnellus. cirral epithelium. Large, ovoid mucocytes, which Emplacement ofthe phyllodocid mucus on a small stain beta-metachromatically with toluidine blue Nephyts incisa, which were previously a quick (Figure 1, lower), fill most of the cirrus. These meal for P. gunneilus, resulted in rejection ofthe broad and elongated cells have small basal nuclei. nephtyd polychaete by the rock gunnel many In worms thathave been irritated prior to fixation, times prior to ingestion. the previously metachromatic mucocytes appear Initial observations were also made on the sea as large, empty vacuoles surrounded by many robin, Prionotus euolans, fed Stylochus zebra, immature mucus cells (Figure 1, upper). The lat­ Lineus ruber, and Phascoleopsis gouldi. Fundulus ter are usually small, irregularly shaped cells heteroclitus and C. regalis were also tested withP. which are densely packed with basophilic but or­ gouldi. In each case the fish showed adverse reac­ thochromatic secretory granules. The outer, cen­ tions (coughing, headshaking, and rejection) after tral portion ofthe dorsal cirrus has a narrow bank ingestive attempts. The sea robin rejected S. zebra of melanic pigment cells. There are also thin mus­ 75 times over eight trials before consuming the cle bands which enter the cirrus along the dorsal flatworm. In many cases, the turbellarian was region of the cirral peduncle. held in the buccal chamber for as long as 21 s Electron microscopy reveals a dense microvillar before ejection. Both the nemertean and the flat­ and ciliary border lining the short, columnar worm produced copius quantities of mucus when epithelium of the dorsal cirrus (Figure 2). The irritated, whereas the sipunculid did not. epithelial cells have large, irregular nuclei with 610 PREZANT: ANTIPREDATION MECHANISM OF PHYLLODOGE MUG(' I DISCUSSION AND CONCLUSIONS

Many factors influence successful predation. Griffiths (1975) believed that prey abundance and prey size are two of the prime variables affecting predation success but that situations do occur in which predators reactto prey characteristicsother thanbody size. These characteristics include phys­ ical avoidance by potential prey (Fagade and Olaniyan 1973) which may be chemically mediated by a secretion released by the predator (Mackie et al. 1968; Doering 1976; Mayo and Mac­ kie 1976), physical deterrents ofthe potential prey species such as spines (Hoogland et al. 1956; Bakus 1966), or innate defense mechanisms ofthe potential prey such as toxicity or unpalatability (Thompson 1960; Bakus 1966, 1968; Gibson 1972; Rahemtulla and Ll'lvtrup 1974). An epidermal, mucoid secretion is responsible for the protection of at least some phyllodocid polychaetes from ac­ tive predation by some small orjuvenilefish. Since FIGURE L-Upper: An oblique-frontal section of the dorsal phyllodocids are relatively small benthic worms, parapoidial cirrus of the polychaete Phyllodoce mucosa. This it is unlikely that many large fish would expend specimen was irritated prior to fixation resulting in the loss of the energy needed to use them as a primary food the mucoid secretion produced by mature cirral mucocytes. The vacuolated regions mark the remnants of the mature muco­ source; thus only smaller fish would potentially cytes. The large cirral nerve is also evident. Zenker's fixative, make any notable impacton the phyllodocid popu­ "Azan" stain. m = immature mucocyte; n = neural extension; lations. N = cirral nerve; V = vacuolated mucocyte. Lower: The dorsal Russell (1966) tested the palatability of tissues parapodial cirrus of a relaxed specimen of P. mucosa in trans­ from 48 species of marine organisms with two verse section, fixed without excessive mucus loss. The cirral mucocytes show a beta-metachromatic reaction with toluidine marine (Pelatus quadrilineatus and Torquigener blue. Hollande's fixative, toluidine blue stain. M = meta­ hamiltoni) and two freshwater (Gambusia affinis chromatic mucocyte. and Carassius auratus) species of fish ranging from 25 to 90 mm. This involved choice experi­ ments with the fish simultaneously offered a abundant heterochromatin material. Many im­ known palatable organism and a test organism of mature secretory inclusions are present near the unknown palatability. The results revealed many epithelial surface as well as subepithelially. The unpalatable species which were rejected by the immature secretory droplets occur in a loose for­ fish. The majority of these tests involved only mation and are surrounded by a dense array of three or fewer trials and there is little note con­ smooth endoplasmic reticulum. The larger, less cerning specific reaction of fish to potential prey electron dense, mature secretory droplets occur in items. Among the palatable items found by Rus­ tighter, membrane bound accumulations. Figure sell was Phyllodoce malgremi. Phyllodocids, as all 2 shows a portion of a vacuolated mucous cell other test organisms, were cut to acceptable sizes bounding a central nucleus. Both the mature and based on preliminary trials which noted size limits vacuolated secretory cells have numerous, small of prey for each fish. Phyllodoce malgremi might mitochondria associated with them. indeed be consumed by these particular fish but The smaller, ventral cirrus is histologically and the limited number oftrials (two per fish) and lack cytologically similar to the dorsal cirrus, and is of corresponding worm size data plus the previous equipped with oblong mucocytes in both mature treatment of the worms (i.e., sectioned into frag­ and immature stages. Also presentis a large cirral ments) may have led to misleading data concern­ nerve and thin longitudinal muscle bands. ing palatability. Melanic pigmentation is not obvious in sections of Few reports list phyllodocids as a major portion the ventral cirri. ofa fish's diet; however, Wigley (1956) did list four 611 FISHERY BULLETIN: VOL. 77, NO.3

FIGURE 2.-The ultrastructure ofthe dorsal parapodial cirrus ofthe polychaetePhyllodoce mucosa. The micrograph shows the dense array of cilia and microvilli which line the cirral epithelium as well as mature and immature secretory droplets and associated organelles. Anderson's and osmium tetroxide fixation, uranyl acetate, and Sato lead stain. S = mature secretory droplets; A = mitochondria; E = smooth endoplasmic reticulum. Other abbreviations as in Figure 1. species of phyllodocids in the food of the haddock, sufficient time to retreat from harm. Chiszar and Melanogrammus aeglefinis. No phyllodocid!l were Windell (1973) f~und that satiated bluegill, among the 11 dominant prey species of the larger Lepomis macrochirus, have more selective feeding fish examined. Wigley noted, however, that be­ habits than starved fish. This may imply that in cause ofthe small, subterminal mouth, most ofthe natural conditions a normally feeding fish may not haddocks' prey were small and thin. Small inver­ persist in an attack on an unpalatable prey or­ tebrates, including phyllodocids, were listed as ganism. dominant foods ofthe few smaller (14-30 cm) had­ Murdoch et al. (1975) suggested that predators dock examined. Annelids composed only 1.9% of distribute attacks among prey species in response the prey items found in the haddock study and no to the prey's relative densities. These authors note was made ofthe diet offish <14 cm. Data for broke down events leading to final ingestion of small juveniles is found in only a few studies in­ prey into a series of predatory behaviors, includ­ volving bulk analysis of fish stomach contents ing "choosing" to attack the prey species. Once a (Stickney et al. 1975; Chao and Musick 1977). potential prey is perceived and located, the In nature, initial rejection and adverse reaction "choice" is up to the predator whether to attack or ofa fish to P. mucosa may give the potential prey not. If the organism is attacked and successfully 612 PREZANT: ANTIPREDATION MECHANISM OF PHYLLODOCE MUCOSA consumed, the predator may set up a "specific instead indicate that the mucus contains some searching image" (Tinbergen 1960), which would irritating or obnoxious substance which repels the increase its chance of locating additional speci­ fish. mens provided more of the same prey species can The high sensitivity and secretory nature of the be found while reinforcement is still fresh. Thus, parapodial cirri is reflected in the complex ultra­ this 'pattern is only relevant when prey species structure shown in Figure 2, however, P. mucosa occur in relatively high densities. Phyllodoce mu­ does not seem able to continually produce an cosa is found in moderately high densities in Na­ adequate supply of protective mucus. This is indi­ hant Bay with many other polychaetes such as cated by ingestion of the worm by G. aculeatus Prionospio malmgreni, Scoloplos armiger, and following numerous rejections from this fish's Nephtys spp. If a small fish encounters and at- small, sharply toothed buccal cavity which may . tempts to eat a Phyllodoce mucosa but is repulsed have removed the protective cover. Similarresults by the worm's defenses several times, the fish may are obtainable with a smallmouthed pipette, eventually set up a negative searching image and which simulates this. The large, empty vacuoles in thus avoid further "discomfort" caused by at­ the dorsal cirri surrounded by immature muco­ tempted ingestion. While simultaneous choices of cytes indicate a lag between total loss ofavailable food may be a rare event in nature (Beukema secretion and maturation of additional, functional 1968), when it does occur between a phyllodocid lllucocytes. and another type ofprey ofsimilar size, a fish with Beukema (1968) suggested that G. aculeatus a negative image may "select" the nonphyllodocid hunts by sight only and its sense of smell plays prey. This is indicated in the present data by the little if any role in finding food. This is supported relationship between ingestive attempts and in­ in the data presented here by the correlation be­ vestigations of Gasterosteus aculeatus and the tween investigations and ingestive attempts. In­ "loss of interest" shown by the smaller Menidia vestigations involved no direct contact but only menidia. close observation of the worm by the fish. Kneib and Stiven (1978) recently found that the Ejectory behavior by G. aculeatus feeding on diet of F. heteroclitus in a North Carolina salt clumps of Tubifex spp. oligochaetes was discussed marsh varied with the size of the fish (smaller fish by Tugendhat (1960) who found that this action were carnivorous while larger individuals were caused a breakdown ofthe clumps into individual omnivorous). In this case, alteration in diet worms which were easily ingested. Hynes (1950) seemed to reflect a physiological and morphologi­ noted that young G. aculeatus feed on proportion­ cal change in the fish with growth. This conversion ally smaller prey items and that the diet changed offood habits may be based upon the ability ofthe to larger prey as the fish grew. The largest phyl­ fish to eat different food items because of its pro­ lodocid fed to a G. aculeatus in the present study portionally larger size oritmight indicate a change was 24 mm long, and it was investigated but only in the "ability" ofthe fish to consume less appeal­ one attempt at ingestion was made. In this case, ing food items ifthe "need" arises. Data presented the worm probably was too large for the fish to here indicate that larger M. menidia might be deal with. more effective in consuming phyllodocids than The only species of fish tested which consis­ smaller M. menidia. Smaller fish may not be able tently ateP. mucosa wasF. heteroclitus. Fundulus to "handle" a phyllodocid ofa size thata largerfish heteroclitus, a well-known inhabitant of salt might readily consume. This is based solely upon marshes, is only rarely found in strictly saline the reaction of the fish to the mucoid secretion environments (Hildebrand and Schroeder 1928). since smaller fish were able to consume compara­ Vince et al. (1976) showed thatF. heteroclitus may tively large nonphyllodocid polychaetes. cause an impact on the abundance and distribu­ The largest fish used in the present study, a tion ofsome prey species, and Fraser (1973) found juvenile Lophopsetta maculata, about 9 cm long, that Fundulus spp. would consume prey items in consistently rejected P. mucosa. Lophopsetta proportion to prey densities. Since P. mucosa is not maculata is an active predator ofmobile prey (Ta­ a normal resident of salt marshes the question ble 1). The large buccal chamberand distensibility must be asked: does the fact that these two or­ ofthe esophagus ofthis flounder preclude the pos­ ganisms occur in different environments influence sibility that the phyllodocid mucus acts as a physi­ the predator-prey interactions between these cal barrierto ingestion (i.e., an occlusive plug) but species when brought together? According to Tin- 613 FISHERY BULLETIN: VOL. 77, NO.3 bergen (1960), there may be an obvious delay in munities? How does effectiveness of antipredation the attack on a potential prey if it is new to the mechanisms vary with size ofpredators or degree predator. No such delay was seen in these experi­ of predator satiation? In similar-sized predators, ments using semistarved fish. Itis unlikely thatP. what differences allow one species to prey on a mucosa has developed a defense mechanism which given organism and not on the other? What is specific in its action only to marine fish. The changes in diet would be found if feeding studies ability of F. heteroclitus to consistently consume involving analyses of stomach contents typically P. mucosa probably reflects the predaceous mum­ were extended to include all size classes of fish? michog's lack of sensitivity or its ability to over­ Does previous exposure to an antipredation come the irritation or unpalatability of this worm. mechanism produce "learning" in potential Cyprinodon variegatus always rejected the phyl­ marine predators? lodocids and rarely investigated the worm without In responding to slow-moving predators many attempted ingestion. The small, terminal mouth potential prey species have evolved escape reac­ ofthis fish, with its large tricuspid teeth and pro­ tions (Doering 1976). In dealing with highly tractile premaxillaries, was quite efficient at mobile fish predators, many species of potential quickly devouring all nonphyllodocid polychaetes prey have developed such defense mechanisms as offered to the fish during these experiments. protective secretions. Lagler et al. (1977:142) Cynoscion regalis is primarily an active pelagic stated, "In general the esophagus [of fish] is so predator (Table 1). There has been some research distensible that it can accommodate anything that concerning the feeding habits ofjuvenilesciaenids the fish can get into its mouth .... " With the dis­ (Thomas 1977; Chao and Musick 1977) which covery of the repulsive characteristics of certain found that small C. regalis feed mainly on mysids, phyllodocids, the indications of antipredation copepods, and small fish. Annelids do form, how­ mechanisms in a sipunculid and turbellarian re­ ever, a portion of the weakfish's diet (Table 1). ported here, added to what is known ofnemerteans Bigelow and Schroeder (1953) noted that the diet and opisthobranchs, it is clear that a closer exami­ ofC. regalis varies with locality and availability of nation must be made of interspecific molecular prey. Small weakfish reject P. mucosa as a food interactions which occur within marine com­ item. Cynoscion regalis showed active investiga­ munities. tory behavior which usually consisted of tapping or bumping the sinking worm with its snout. Di­ ACKNOWLEDGMENTS rect contact often resulted in a rapid shunning of the worm by the fish. This may indicate the pres­ I gratefully acknowledge the many helpful ence of sensitive nares chemoreceptors. The suggestions concerning this manuscript which juvenile fish would not be a major threat to these were received from M. R. Carriker, F. C. Daiber, B. worms even were they readily available. Brown, R. Palmer, and L. Williams. I also thank L. Preliminary work indicates that antipredation Watling and G. Entrot for constructive criticisms responses are active in P. maculata, E. sanguinea, of an earlier draft of this paper. Harlan Dean, G. Phascoleopsis gouldi, Stylochus zebra, and Lineus Entrot, S. Howe, P. Nimeskern, F. Prezant, J. ruber. All these organisms, except the sipunculid, Vargas, and W. Wehling helped in the collection of secrete large quantities of mucus. The epidermis animals used in this study, and I thank them for of many sipunculids is densely packed with gland their efforts. The use of the RV Clione and cells (Tetry 1959) and some secretion from these facilities atthe Marine Science Institute, Nahant, glands may serve to protect the animal from pre­ Mass., were kindly supplied by N. W. Riser. dation. Stylochus zebra, is a commensal ofpagurid Thanks also to P. Savage for typing the manus­ crabs; abundant production ofmucus by this worm cript. may tend to keep this relationship commensal. The role ofsecretory defense mechanisms is well LITERATURE CITED established in many species of marine animals (Graham 1957; Thompson 1960, 1969; Bakus 1968), butmany questions concerning the broader BAKUS, G. J. 1966. Some relationships offishes to benthic organisms on aspects of antipredational responses remain un­ coral reefs. Nature (Lond.) 210:280-284. answered. Are antipredation responses reflected 1968. Defensive mechanisms and ecology ofsome tropical in the composition of marine benthic com- holothurians. Mar. BioI. (Berl.) 2:23-32. 614 PREZANT: ANTIPREDATION MECHANISM OF PHYLWDOCE MUCOSA

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