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An optimization study on the feeding behavior of Luldiaclathrata say (Echinodermata: Asteroidea)J. B. McClintock a & J. M. Lawrence aa Department of Biology, University of South Florida, Tampa, Florida, 33620Published online: 22 Jan 2009.

To cite this article: J. B. McClintock & J. M. Lawrence (1981): An optimization study on the feeding behavior of Luldia clathratasay (Echinodermata: Asteroidea), Marine Behaviour and Physiology, 7:4, 263-275

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Mar. Behav. Physiol. 1981, Vol. 7, pp. 263-2750091-181X/81/0704-0263 $06.50/0© 1981 Gordon and Breach Science Publishers, Inc.Printed in Great Britain

An Optimization Study on theFeeding Behavior of Luldiaclathrata Say (Echinodermata:Asteroidea)J . B. McCLINTOCK AND J . M. LAWRENCE

Department of Biology, University of South Florida, Tampa, Florida 33620

(Received June 24, 1980)

The rates of feeding, behavioral responses to changes in prey density, selection for differentsizes of prey, and field activity patterns of the starfish Luidia clathrata lend support to the pre-dictions of optimal feeding theory. Rates of location, ingestion, and digestion of prey were high.Individuals offered different densities of prey showed a strong functional response. Individualspresented with different sizes of prey chose the smaller sizes. This selective behavior may berelated to ease of manipulation, available stomach area, or maximal food intake per unit time.In the field Luidia clathrata exhibited one peak of activity at dusk, although there was never onehundred percent activity or inactivity at any time. It is not known if this diurnal pattern is causedby patterns in prey or predator, although the former is unlikely as L. clathrata feeds on infauna.The "time buried" during the inactive period in L. clathrata may be related to the period ofdigestion.

INTRODUCTION

Many studies have attempted to explain feeding behavior in animals interms of optimizational strategy (for reviews see Pyke et al., 1977 ; Krebs andDavies, 1978). Emlen (1973) suggested that selection for efficiency in feeding,which would lead to optimization, may act in the following ways : increasedability to locate, acquire, and ingest foods; increased ability to choose thebest (with respect to fitness) foods; and increased ability to recognize foodneeds and to feed in response to some optimal (again with respect to fitness)schedule. Asteroids are important predators (Paine 1966, 1971,1974, 1976;Menge, in press) whose rates of feeding, selectivity for food items, and forag-ing periodicity may be important in understanding trophic structure withinmarine benthic communities (Thorson, 1952; Christensen, 1970).

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2 6 4 J. B. MCCLINTOCK AND J. M. LAWRENCE

Luidia clathrata is distributed widely along the Atlantic Coast, from NewJersey to Brazil in 0-75 m depth (Downey, 1973) and is found in abundancein Tampa Bay (Bloom et al, 1972; Lawrence and Dehn, 1979). Luidiaclathrata is a non-selective feeder which ingests bottom material and extractsinfauna (Hulings and Hemlay, 1963). In Tampa Bay, L. clathrata feedsprimarily on the lamellibranch mollusk Tellina versicolor as well as brittlestars, ostracods, and cumaceans (Lawrence et al, 1974). Investigation of thefeeding biology of Luidia clathrata may provide insight into the role of thisasteroid in influencing the distribution and abundance of infaunal organisms.

The purpose of this study was to investigate whether the feeding behaviorof Luidia clathrata conforms to predictions of optimizational theory. Thefollowing questions were asked : What is the rate at which L. clathrata locates,ingests, and digests prey ? Is there a "functional response" to varying densitiesof prey items? Does L. clathrata show preference for certain sizes of prey? Isthe buried period associated with the digestive period? Does Luidia clathrataexhibit periods of daily activity in the field?

METHODS

Specimens of Luidia clathrata (arm length = 5-6 cm) were collected inOctober and November 1979, from Old Tampa Bay, Florida (approximately27°55' N, 83°35' W) in 2-4 m water. Ten specimens were placed individuallyinto 40-liter aquaria with artificial sea water (25°C and 22 ppt respectively)for at least one week prior to experimentation. Starfish were fed a main-tenance diet (1.88 g/starfish/week) of Doriax variabilis (Diehl and Lawrence,1979) which is a suitable prey item (Dehn, 1974; Klinger, 1978).

Feeding by Luidia clathrata was divided into search time, ingestion time,and digestion time. These times were measured by placing one Donaxvariabilis (1.0-1.5 cm length) 20 cm away from individual L. clathrata( 10-12 cm diameter). Luidia clathrata is reported to be 100 % accurate at foodlocation at this distance (Dehn, 1974). Search time was defined as startingfrom introduction of prey into the aquaria and terminating with predator-prey contact: Ingestion time was defined as the time from predator-preycontact until the disappearance of prey through the oral opening. Digestiontime began immediately following ingestion and terminated with extrusionof the bivalve shell from the oral opening. The use of glass bottom aquariacovered with a thin layer of sand permitted observations of shell extrusion.

The effect of prey number on the activity period (search and ingestiontimes) was measured by offering individual Luidia clathrata 1,5, or 10 Donaxvariabilis at a time. All prey were placed 10 cm from starfish. The groups of5 and 10 D. variabilis were placed close together to standardize the experiment.Responses to changes in prey density were monitored by observing both

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FEEDING OF LUIDIA CLATHRATA 265

number of prey consumed and measuring the length of the search period.Selectivity for different sizes of prey was examined by a variation of the

methods of Christensen (1970). Three size classes of flat, circular bivalvemodels were made of plaster of Paris homogenized with Donax variabilis(without the shell), similar to the procedure of Collins (1974). The preymodels contained a 1 to 15 (weight/weight) ratio of D. variabilis and plasterof Paris, and were all 0.2 cm in depth with diameters of 0.5, 1.0, or 2.0 cm.These were placed in glass petri dishes (10 cm diameter). Individual Luidiaclathrata were placed directly over each dish in approximately equal contactwith all prey models supplied. In one experiment, individual L. clathratawere simultaneously offered five prey models from each of the three sizeclasses. In a second experiment, individual L. clathrata were offered equalamounts (by weight) of the different sized prey models. Each individualstarfish received a combination of 5 large, 10 medium, and 20 small sizedprey models. In both experiments the time spent actively feeding, and thenumber and sizes of prey models eaten were recorded.

The ability oí Luidia clathrata to ingest the large sized (2.0 cm) prey modelswas observed by presenting individuals with 3 of these prey models. Thetime spent manipulating the models and the number ingested was recorded.

To correlate the amount of food ingested with digestion time, two groupsof Luidia clathrata were placed in a sea water table (1.7 m x 1.1 m) with arecirculating sea water system and offered different numbers of Donaxvariabilis. The sea water table was divided into two equal sections. In onegroup each individual L. clathrata was offered one D. variabilis. In the othergroup each individual L. clathrata was offered five D. variabilis. The numberof active starfish was recorded over a sixteen hour period for both groups.

The field activity patterns of Luidia clathrata were investigated in OldTampa Bay using a modification of the methods of Ferlin-Lubini and Ribi(1978). A 30 m transect line was placed 3-4 m in depth approximately 300 mfrom shore. Thirty starfish were collected and immediately placed within anenclosure (1.5 m x 1.5 m). The number of active L. clathrata within 1 m oneither side of the transect line and within the enclosure was recorded every3 hours for a 24 hour period. Individual starfish moving about the sea floor,and thus exposed to view were considered "active".

Where necessary, confidence limits were calculated to indicate statisticalsignificance. In order to comply with the assumptions of parametric statisticsthe angular transformation was performed on data presented in percentageform.

RESULTS

The search, ingestion, and digestion times for Luidia clathrata presentedsingle prey varied greatly (Figure 1). The mean search time was 320 sec

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266 J. B. MCCLINTOCK AND J. M. LAWRENCE

600-(s

ec

)

CD

E•= 4 0 0 •co

Ing

es

« 200 -

rch 1

Sea

iI

600

400

IQCD

o

200 ICD

"i5'

SEARCH INGESTION DIGESTION

FIGURE I Search, ingestion, and digestion times of Luidia clathrata. Individual Donaxvariabilis (mean size 1.02 ±0.04 cm) were introduced 20 cm distant from quiescent L. clathrata(mean size 10.58 ±0.21 cm). Means ±1 S.E. are given, (n = 10.)

60 n

5 0 -

40 -

30-

2 20 H

10-

10

NUMBER OF AVAILABLE PREY

FIGURE 1 Length of active periods of Luidia clathrata (mean size 10.95 ±0.21 cm) withdifferent numbers of Donax variabilis available for ingestion. Means ±95% confidence limitsare given, (n = 10.)

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FEEDING OF LUIDIA CLATHRATA 267100

QUJ 9 0l -wUJC5Z>. 80UJ

cra.UJm 70

I60-

501 5

NUMBER OF AVAILABLE PREY

10

FIGURE 3 Percent of available prey ingested by Luidia clathrata (mean size 10.95 ±0.21 cm)with different densities of Donax variabilis available for ingestion. Means ±95% confidencelimits are given, (n = 10.) Confidence limits were based on the angular transformation.

(±80.31 sec S.E.). The mean ingestion time was 72 sec (±17.46 sec S.E.).The mean time of digestion was 582 min (±31.74 min S.E.). In most casesstarfish immediately became active when prey were introduced into theaquaria, and showed a strong feeding response at a distance of 20 cm. In nocase did L. clathrata fail to locate the prey. The length of this activity period(search and ingestion times) of L. clathrata demonstrated a marked functionalresponse to changes in prey density, responding significantly (P < 0.05) toeach increase in density with increased periods of activity (Figure 2). Meanvalues of activity period for L. clathrata with prey densities of one, five, andten were 12.7, 21.7, and 48.2 min respectively.

The percent of available prey ingested varied significantly (P ^ 0.05)when individual starfish were offered different densities of prey (Figure 3).Starfish ingested 100 % of available prey when offered only one prey. Whenprey density was increased to five and ten prey per aquaria the percentage ofprey ingested decreased to 92 % and 62 % respectively.

Typically, Luidia clathrata offered Donax variabilis responded with analmost immediate search response,, followed by ingestion, and then a randomsearch of the aquarium. This post-ingestion searching behavior involved a

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268 J. B. MCCLINTOCK AND J. M. LAWRENCE

high degree of activity. Frequently, the entire bottom surface of the aquariumwas covered.

Luidia clathrata showed no significant preference-between the small andmedium sized prey models. However, there was no ingestion of the largeprey (2.0 cm) by any individual presented with three prey sizes. When L.clathrata was simultaneously offered equal amounts by weight of the threeprey sizes, the smallest of the available prey model sizes were usually ingested.When L. clathrata was simultaneously offered equal numbers of the threeprey sizes, the middle size class (1.0 cm) was ingested more frequently thanthe smaller size class (0.5 cm) (Figure 4).

Luidia clathrata offered the three sizes of prey would locate one of thesmaller prey models and then place their oral disc directly over the prey.Coordinated movement of arms and tube feet were used to hump up overthe prey model. The mouth would expand and the prey model was forcedinto the stomach by the tube feet. Feeding then proceeded with activemanipulation of other prey models by coordinated tube foot movements.Luidia clathrata offered only large prey models showed a strong feeding

50 i

0.5 1.0SIZE OF PREY (cm)

FIGURE 4 Percent of available prey ingested by Luidia clathrata (mean size 11.21 ±0.21 cm)simultaneously offered equal amounts (7.0 g) (solid circles) and equal numbers (open circles) ofthree sizes of prey (0.5,1.0 and 2.0 cm). Means ±95 % confidence limits are given, (n = 10.)Confidence limits were based on the angular transformation.

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FEEDING OF LUIDIA CLATHRATA 269

response. Mean time spent manipulating the large prey models, even if theywere not ingested, was 18.6 min (Table 1).

The amount of prey consumed affects the length of the period of activity(Figure 5). Luidia clathrata offered only 1 prey were significantly moreactive than those which ingested 5 prey (Wilcoxin paired-sign test, P ^ 0.05).Activity dropped to a minimum level after 3 hours for both groups tested.This was most pronounced after 12 hours when only 10 % of the individualswhich ingested 5 prey were active while 50 % of those which ingested onlyone prey were active.

TABLE I Number of prey ingested ( ± 1 S. E.) and time spent manipulating prey ( ± 1 S. E.)by individual Luidia clathrata simultaneously offered three large (2.0 cm diameter) prey models.

(i> = 10.)

Size (arm length, cm) Number of preyingested

Time spent manipulatingprey (min)

11.10±0.19 0.67 ±0.17 18.60 ±2.30

12 16

HOURS

FIGURE 5 Percent of active individuals of Luidia clathrata offered different numbers ofDonax variabilis. Circles represent individuals offered 1 prey; triangles represent individualsoffered 5 prey, (n = .10.)

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270 J. B. MCCLINTOCK AND J. M. LAWRENCE

Luidia clathrata exhibited one peak of activity occuring at dusk. Numbersof active individuals counted along the 30 m transect ranged from a high of22 at 2200 hours to a low of 2 at 1000 hours (Figure 6). The results of thecaging experiment indicated that although some individuals were active orinactive at any time, a sharp increase in number of active individuals occuredat 1900 hours followed by a general decline to minimal levels of activity by0400 hours (Figure 7).

DISCUSSION

Both Luidia sarsi and L. foliota complete digestion of a single prey item within16 to 24 hours (Fenchel, 1965; Mauzey et al., 1968). The digestive period ofL. clathrata is considerably lower with an average value of approximately10 hours. Most asteroids are considered relatively sluggish with corre-spondingly slow feeding rates, but species of Luidia are efficient at locating,capturing, and ingesting prey. High feeding rates in L. clathrata, L. sarsi(Fenchel, 1965), and L. ciliaris (Brun, 1972) are related to the high degree ofmobility noted within the genus. Luidia clathrata ingested smaller prey atrelatively higher rates. The immediate search response when prey wereintroduced into aquaria suggest that L. clathrata respond to chemical stimulias has been proposed by Dehn (1974) and Klinger (1978). Chemosensitivityhas been noted in Asterias rubens and Marthasterias glacialis (Castilla andCrisp, 1970; Valentincic, 1973).

The ability to use feeding time efficiently may be enhanced by an organism'sability to respond to changes in prey availability. Menge (1972) stated thatthe functional response of asteroids is great as a result of their ability to eatmany prey simultaneously. The results of this study indicate that Luidiaclathrata exhibits a "functional response" to changes in prey density. Bothnumber of prey ingested as well as time spent active immediately followingprey ingestion were significantly increased when prey density increased. Dehn(1974) and Fenchel (1965) both noted increased activity in Luidia spp. in thepresence of prey. Mauzey et al., (1968) noted that L. foliota, as well as anumber of other asteroids, will feed on a variety of prey species in accordancewith relative densities of prey in a particular habitat. Although feedingpreferences were not investigated in this study, the functional response ofL. clathrata to changes in prey density of one prey species suggests indirectlyan ability to respond to changes in prey availability in the natural environ-ment. This ability to increase feeding rate as a function of prey density mayallow L. clathrata to more efficiently exploit prey within the marine benthiccommunity.

Luidia clathrata shows a distinct preference for certain sizes of prey. Whensimultaneously offered différent sizes of prey they consistently chose prey

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FEEDING OF LUIDIA CLATHRATA 27125

20

Q

Q? 15LU

< 10u.Ooc

m 5 -

1000 1300 16O0 1900 2200 01O0 0400 0700

TIME OF DAY (h)

FIGURE 6 Percent of active individuals oiLuidia clathrata along a 30 m transect followed overa 24 h period in Tampa Bay at a depth of 3-4 m in October, 1979.

100 -i

80-

o> 60azm

a«20-

1000 1300 1600 1900 22OO 0100 0400 0700

TIME OF DAY (h)

FIGURE 7 NumberofactiveindividualsofLuW/ac/a/Ara<awithinanenclosure(2.5m x 1.5m)in Tampa Bay followed over a 24 h period at a depth of 3 m in October, 1979. (n — 30.)

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2 7 2 J. B. MCCLINTOCK AND J. M. LAWRENCE

of the smaller size classes. Prey of the larger size class were avoided as long assmaller prey were available. Krebs and Davies (1978) stated that choice of aprey item by a predator has a cost in terms of the time taken to handle anddigest the prey and a benefit in terms of its net food value (net food valuemeans the gross value minus the energy costs of handling and digesting prey).lîLuidia is accepting the optimal prey, the cost-benefit ratio of manipulatingand ingesting large prey items is high relative to the cost-benefit ratio ofingesting the smaller prey. The avoidance of large prey by L. clathrata mayindicate an ability to more efficiently pack the stomach with small prey.Fenchel (1965) noted that L. sarsi select smaller specimens when offered preyof various sizes. He proposed that L. sarsi may fill the stomach more effici-ently with small prey. The results of this study support Fenchel's hypothesisas L. clathrata always consumed the greatest amount of prey when ingestingsmall prey. Christensen (1970) noted that Astropecten irregularis displays adistinct preference for smaller specimens of Spisula subtruncata. The stomachof A. irregularis was frequently found to be packed with prey of meiofaunalsize (i.e. 2 mm) and Christensen attributed this to ease of handling andingesting small prey. He also suggested that adult S. subtruncata succeed inescaping from predatory starfish more often than younger specimens.Astropecten latespinous also selects small prey (Doi, 1976). Doi suggestedthat selection for smaller prey within a mixed size prey population is morebeneficial as food intake may be maximal within limited feeding time. Luidiaclathrata may select small prey due to one or more of the following: ease ofmanipulation; maximal prey intake as related to stomach space; maximalprey intake related to limited feeding time.

Luidia clathrata is capable of ingesting relatively large prey items. Severalasteroids select large prey. One of the most extreme examples is that ofOdontaster validus which successfully attacks the gargantuan Acondontasterconspicuus, an asteroid many times the diameter of Odontaster (Dayton et al.,1974). Pisaster ochraceus found on the San Juan Islands choose large chitonsmost frequently, while the small Balanus balanoides and Mytilus edulis arethought to be of secondary importance (Mauzey, 1966). Young P. ochraceususually feed on young specimens of the same prey taken by older individuals,but ingest several small prey species that the larger individuals seldom take(Feder, 1959). Pisaster ochraceus does not consume small M. edulis inproportion to their abundance (Paine, 1976), but whether this is becausesmaller prey are less appealing to a large predator is unknown. The tendencyof some asteroids to select large prey may be related to their extraoraldigestive capacity. Luidia clathrata is incapable of digesting any prey itemthat cannot be ingested. Thus it may be that selection for smaller prey is dueto mechanical limitations.

Activity ofLuidia clathrata varied inversely with the amount of prey. Thus

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FEEDING OF LUIDIA CLATHRATA 273

the buried period in L. clathrata may be related to the digestive period assuggested by Dehn (1974) and Brun (1972).

Field populations oîLuidia clathrata found in Tampa Bay exhibit a diurnalactivity pattern, with maximum levels of activity at dusk. Similar diurnalrhythms have been noted in other asteroids (Mori and Matsutani, 1952;Fenchel, 1965; Ebling et al, 1966; Ferlin-Lubini and Ribi, 1978). Emlen(1973) suggested that selection may favor an increased ability to respond tosome optimal schedule. Cloudsley-Thompson (1960) cites reproduction,prey capture, avoidance of competition, and avoidance of prédation asadaptive functions of cyclic activity.

Reproduction in Luidia clathrata occurs on an annual cycle (Lawrence,1973) and would consequently appear an unlikely determinant of diurnalactivity. Some asteroids become active as a function of prey availability.Marthasterias glacialis which preys upon the sea urchin Paracentrotuslividus is active only during daylight hours. This system of diurnal migrationsseparates prey from predator, so that populations may survive (Ebling et al.,1966). It is unlikely that the availability of infaunal prey varies on a dailybasis and determines the diurnal activity patterns oí Luidia clathrata. Inter-or intraspecific competition seem unlikely to affect patterns of activity ofL. clathrata. However diurnal activity patterns observed may be related toprédation. The activity pattern of Astropecten bispinosis may decreasecontact with its predator A. aranciacus (Ferlin-Lubini and Ribi, 1978). Thenocturnal activity of the echinoids Diadema setosum and Centrostephanouscoronatus and the crinoid Heterometra savigny have been suggested to be anavoidance to the day time predatory habits offish (Thornton, 1956; Nelsonand Vance, 1979; Magnus, 1963, respectively).

Acknowledgements

We thank Thomas Klinger and Stephen Watts for their assistance in the laboratory and thefield.

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