Crayfish Predation on Corbicula under Laboratory Conditions

The University of Notre Dame

Crayfish Predation on Corbicula under Laboratory ConditionsAuthor(s): A. P. Covich, L. L. Dye and J. S. MatticeSource: American Midland Naturalist, Vol. 105, No. 1 (Jan., 1981), pp. 181-188Published by: The University of Notre DameStable URL: http://www.jstor.org/stable/2425023 .

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Crayfish Pr?dation on Corbicula under Laboratory Conditions1'2

A. P. COVICH,3 L L DYE and J. S. MATTICE Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830

Abstract: Crayfish pr?dation on the Asiatic clam Corbicula was examined in laboratory aquaria. In one study 20 Procambarus clarkii in separate 15-liter aquaria were offered intact live clams, 4-20 mm shell length (SL), at temperatures of 20C for 14 days. Only clams < 6 mm were consumed. Mean sustained feeding rate on 4-6 mm (SL) clams by P. clarkii which fed daily (n = 8) was ca. 11 clams/day (or ca. 0.3% of the mean crayfish body wet weight). In a second study, eight Cambarus bartonii in separate 75-liter aquaria were offered large Corbicula (24-35 mm SL) with naturally occurring or artificially produced shell perforations of two sizes at temperatures of 20C ? 1C for 8 days. Cambarus bartonii readily fed on clams with perforations large enough (4-6 mm for large crayfish) to permit insertion of the first walking leg. The mean sustained rate of feeding was ca. 1.5 clams/day (or about 4% of mean crayfish body wet weight). Cambarus bartonii were also observed to feed readily on intact Cor- bicula (<9 mm SL).

Our results demonstrate that small intact Corbicula and large damaged Corbicula can be eaten by crayfish in the laboratory. Consumption rates of large damaged Cor- bicula indicate they could be an important food resource. We have observed damaged Corbicula in large numbers only in the tailwaters of a hydroelectric generating station, although they may occur in other habitats such as wave-swept beaches and fast-flowing streams. Thus, the value of this food resource may be restricted. Small intact Corbicula are more widely distributed but their importance as a food for crayfish may also be restricted if our results with Procambarus clarkii are typical of crayfish in general. Never- theless, even at those consumption rates the number of small clams consumed per m2 could be high where crayfish densities are high, if Corbicula were the primary food.

Introduction Relatively little is known about the effect of introduction into the United States

of the Asiatic clam Corbicula on other members of the aquatic community. Britton and Morton (1979) recently determined that the Corbicula introduced into the United States was C. fluminea. However, previous investigators had identified it as C. manilensis (Sinclair and Isom, 1963). Since the first record of its occurrence in 1938 in the Columbia River, Washington, Corbicula has spread to most of the major, drainage basins of the United States and now forms a major component of the benthic community in many areas (for reviews, see: Sinclair, 1971; Aldridge and

McMahon, 1978; Mattice, 1979). Corbicula have been found in the gut contents of numerous fish species including American shad (Stevens, 1966a), striped bass

(Stevens, 1966b), buffalofish (Minckley et al, 1970), centrarchids (Turner, 1966b), river redhorse (Hackney et al, 1970) and blue catfish (Richardson et al., 1970). Ducks and raccoons are also known predators of Corbicula (Sinclair and Isom, 1963; Taylor and Counts, 1977). Pr?dation rates have not been determined, however, for

any of these vertebrate predators, and the potential for macroinvertebrate pr?dation has not been studied at all.

Crayfish are the most likely invertebrate to benefit from the potentially new food resource provided by Corbicula. Piesik (1974) showed that small Dreissena polymorpha, an immigrant bivalve now widely distributed in European reservoirs and lakes, are readily consumed by crayfish ; and he suggested that Dreissena may be the major food source for crayfish in reservoirs lacking a macrophytic zone. Corbicula

1 Supported in part by NSF Grant DEB 76-8286 and in part by the Office of Health and Environmental Research, U.S. Department of Energy, under contract W-7405-eng-26 with Union Carbide Corporation.

2 Publication No. 1536, Environmental Sciences Division, ORNL. 3 Zoology Department, University of Oklahoma, Norman 73019.

181



182 The American Midland Naturalist 105(1)

has a niche similar to that of Dreissena and may provide a new food resource for

crayfish in U.S. reservoirs and streams, although there is no reported research into this possibility. Our studies were stimulated by preliminary observations that both small Corbicula and large damaged Corbicula were apparently vulnerable to crayfish pr?dation and that clams of each type could be found in significant densities in some areas in which crayfish were also found. For instance, in parts of the Clinch River, Tennessee, densities of 100 small clams/m2 and 25 large damaged clams/m2 can be found. Crayfish densities are undetermined for that area. Our experiments were designed to demonstrate whether crayfish can consume live Corbicula and, if so, to determine clam size and consumption rate under laboratory conditions.

Methods Two types of laboratory studies were conducted, each with different species of

crayfish. Both types involved direct but discontinuous observation of crayfish maintained in individual aquaria to which Corbicula were added.

In the first study, small intact clams collected from Lake Thunderbird, Oklahoma, were presented to Procambarus clarkii obtained from ponds in Noble, Okla., and held individually in 15-liter aquaria at 20 C. Each crayfish was fed approximately 250 mg of a pelletized "standard" food (Covich, 1977) consisting of ground fish, soybeans and shrimp prior to beginning the experiment. Shelter in the form of

pottery fragments was provided for the crayfish. Ten male (wet weighty ? = 27.7 g ;

range = 21.0 - 34.6 g) and 10 female (wet weight, ? = 27.8 g; range = 23.5 - 32.9 g) crayfish were observed. Each crayfish was allowed unlimited access each

day to 40 clams ranging in size from 4 - 20 mm shell length (SL), of which half were 4-6 mm SL. Daily feeding rates (no. clams/day) were measured by counting the number of large (J> 6 mm)and small (^ 6 mm) clams remaining every 24 hr for 2 weeks. Consumed clams were replaced daily by clams of similar size.

In the second study, large damaged and undamaged clams collected from just below Melton Hill Dam on the Clinch River, Tennessee, were presented to Cambarus bartonii. These crayfish were trapped from a small branch of the same river and maintained individually in 76-liter aquaria at 20 C. The experimental crayfish included four males and four females, with carapace lengths ranging from 44-55 mm and weighing 25 - 50 g. Each crayfish was initially starved for 1 week, then exposed continuously for 8 days to 15 clams (x = 28 mm, 24-35 mm SL), with daily observation and replacement of eaten or dead clams. The set of live clams presented to each crayfish included five with no shell perforations, five with small (2.5 mm zh 0.5) shell perforations, and five with large (6 mm db 0.5) shell perforations. Be- cause we could not collect enough damaged clams, we found it necessary to artificially produce perforated shells for these experiments. Live, thin-shelled clams were held in a vice and the shell perforations produced by increasing pressure until a small hole was,formed in the eroded area of the umbo. This hole was then enlarged with forceps to either 2.5 or 6 mm in diam. In a follow-up experiment the small (2.5-mm) perforations were enlarged to 4-6 mm depending on the size of the first walking legs of each experimental crayfish. Feeding rates were determined by counting the number of clams fed upon and by estimating (to the nearest 25%) how much of each clam body was consumed over 24-hr for 8 days. Because the crayfish had been starved for ca. 1 week, estimation of normal feeding rates began after the 1st 2 days of feeding. Feeding observations were made during both light and dark periods. All eight crayfish were observed for 2 hr after adding clams in midmorning on 2 separate days. An additional 1.5 hr of observations were made on individual crayfish in the evenings by using a 25-w red incandescent light. Photoperiod was



1981 CoviGH et al.: Pr?dation by Crayfish 183

controlled by an outside photocell and thus simulated the normal seasonal photoperiod.

An estimation of consumption rate3 in terms of percent body weight per day, was calculated from the mean number of clams consumed, average body (tissue) wet weight of the consumed clams and average wet weight of the experimental crayfish. Average body wet weight (BWW) of clams was estimated from shell length (SL) using the relationship; BWW = 0.00007 SL2?8988. This regression equation was derived for 220 Clinch River clams (size range = 5-45 mm) collected in June 1978 Mattice and Malcaluso (Pers. comm.). Average body wet weight of Cambarus bartonii also was determined from a linear weight-length relationship established after the experiments by collecting, measuring and weighing 12 crayfish in the same size range as used in the experiments. Weights (W) can be estimated from carapace length (CL) by the equation: W = (2.26 CL) - 74.20.

Results Procambarus clarkii and Cambarus bartonii exhibited similar predatory behavior

in response to Corbicula. Both species routinely used the first set of walking legs and the third maxillipeds to manipulate shells. The mandibles were used for shell breakage. Attack was usually initiated on small clams by the crayfish forming a chip at the edge of the shell. This chip was gradually enlarged until the entire shell was broken, allowing living tissue to be removed. The original perforations in large clams were occasionally enlarged prior to extraction of body tissue. Both species used the first walking legs to remove pieces of tissue and subsequently transfer it to' the mouth. Chelae played only a minor role in this process. For example, C. bartonii used a chelar "cradle" which aided in the manipulative process involved in locating perforations in large (> 24 mm) clams. Both males and females of each species fed on clams during periods of intermolt; for several days after ecdysis P. clarkii consumed no clams. All C. bartonii observed were in intermolt. Feeding occurred during the day and at night (under red light and in total darkness).

Individuals were frequently observed carrying prey into their shelter for extended periods of shell breaking, Procambarus clarkii carried small (4-6 mm) clams using the first set of walking legs. If disturbed, crayfish retained the small clam and used' typical back-flipping of the telson to rapidly swim away. Cambarus bartonii also frequently carried large clams to shelter before feeding. During 4 hr of observation, clams were carried to shelter by the eight crayfish. All of these clams had either large or small perforations and were subsequently partially or wholly eaten.

Initiation of pr?dation under laboratory conditions was not equivalent for the two species. Only eight of 20 adult Procambarus clarkii began to feed on intact juvenile clams when they were first presented. In contrast, all Cambarus bartonii fed readily upon Corbicula with perforated shells during initial laboratory tests. Three C. bartonii were also observed to feed readily upon small intact Corbicula during additional observations. The largest C. bartonii (^ 50 mm carapace length) consumed clams up to 9 mm SL.

Overall mean daily rate of consumption for all Procambarus clarkii which fed during the 2-week experiment was 6.6 db 3.0 (95% CL.) clams per day (Table 1). This estimate includes four crayfish which fed irregularly and which were somewhat smaller than the others. A regression of overall daily mean number of clams eaten on days 1-14 vs. crayfish length for all twelve crayfish is significant (r2 = 0.73, ? < 0.001) (Fig. 1). The eight crayfish which fed daily consumed low numbers of clams for the 1st 4 days, after which they fed regularly at sustained higher levels. Mean sustained feeding rate for the eight regularly feeding crayfish (calculated from day 5 through day 14) was 10.8 dz 2.4 (95% CL.) clams per day. A regression




of the sustained feeding rates vs. the body weight of the eight crayfish feeding daily was not significant (r2 ?= 0.36, ? = 0.11), although the tendency for the smaller crayfish to eat less is indicated (Fig. 1). All live clams eaten were ^ 6 mm SL. The most small clams consumed in one day by any crayfish was 19. In a few instances, when large clams died and their valves gaped open, Procambarus clarkii consumed

parts of these recently dead clams. Live intact clams > 6 mm SL were not consumed.

Overall mean daily rate of consumption for Cambarus bartonii when large clams with large shell perforations were available was 2.2 zb 0.4 (95% CL.) adult clams. Feeding rate was high for the 1st 2 days (Table 2), then dropped to a lower but highly variable (coefficient of variation = 10%) level for the remainder of the observation period. The mean sustained feeding rate for the remaining 6 days was 1.5 zb 0.5 (95% CL.) clams per day. No significant relationship was found between crayfish size and consumption rate (r2 = 0.10, ? = 0.49). Rates for females

Table 1.- clarkii

-Number of small intact Corbicula (4-6 mm) consumed daily by Procambarus

No. Live

weight (g) Sex Daily mean

days 1-3 Daily meana

days 4-14 Overall dailyb

mean 34.6 33.0 32.4 27.1 30.3 31.2 29.0 32.9

M M M M F M F F

9.0 4.7 1.3 4.0 2.7 4.0 5.3 4.3

14.8 15.4 12.1 9.4 9.6 9.0 8.7 7.8

13.6 13.0 9.4 8.4 8.2 8.0 7.9 7.4

consumed clams daily

9 10 11 12

25.6 24.8 28.5 23.6

M M F M

0.7 0 0.3 0.7

1.5 1.4 1.3 0.5

1.2 1.1 1.0 0.5

consumed clams

intermittently

a Means of day 4-14 averaged to obtain mean sustained feeding rate for first eight individual crayfish = 10.8 ? 2.4 (95% CL.) b All 12 individual daily means averaged to obtain overall mean feeding rate = 6.6 ? 3.0 (95% CL.)

? ?J ? => ? ? ? ?

?

< _J ?

er ?J OQ ? =>

IO

r2 = 0.73 ? =0.0004

(b)

r2 = 0.36 P = 0.11

J_L 20 25 30 35 40 20 25 30 35 40

R clarkii WEIGHT (g)

Fig. 1.?A regression of mean number of clams consumed daily between days 5-14 vs. the eight Procambarus clarkii which fed at sustained high levels after day 4



1981 CoviGH et al.: Pr?dation by Crayfish 185

(1.5 clams/day) and males (1.6 clams/day) were not significantly different (t-test: 0.80 < ? < 0.85). Two individuals consumed 21 clams during the 8-day observation period. Observation of one of the males was cut short when he escaped.

When offered a choice of clams (> 24 mm SL) with large (6 mm) or small (2 mm) shell perforations or with intact shells, Cambarus bartonii consumed only those clams with large shell perforations. Clams with intact shells or with 2-mm perforations were manipulated but not eaten. During the 1st 2 days, shell perforations of all clams consumed were actively enlarged, apparently to facilitate removal of soft visceral tissue. In the following 6 days shell perforations were less frequently enlarged and the soft tissue of each clam less completely consumed. Individual crayfish differed in their handling times and in their consistency in locating shell perforations. In four instances, when C. bartonii were observed feeding, time spent feeding on a single clam ranged from 45-120 min. In some instances, C. bartonii would move from clam to clam, feeding a little on each during the observation.

In a follow-up experiment, Cambarus bartonii were offered a choice of clams (> 24 mm SL) with only 2-mm perforations or with no perforations. Only one clam was eaten during a 5-day period; this clam had died and the valves had gaped open. Shell perforations were then enlarged to accommodate the distal segment of the first walking leg (4-5 mm) and all but one of the six crayfish fed.

An estimate of percent body wet weight consumed per day was determined for each experiment (Table 3). Procambarus clarkii feeding on small intact clams consumed approximately 0.26% body weight per day, while Cambarus bartonii consumed approximately 4.2% of their body weight per day feeding on adult Corbicula with perforated shells. On average, the consumption of small, intact Corbicula pro-

Table 2.?Number of large clams with large shell perforations consumed by Cambarus bartonii. Amount of each clam body consumed estimated to nearest 25%_

Carapace No._length (mm)_Sex_Days 1-2_Days 3-8a_All days*> 1 46 M 4.6 2.1 2.7 2 47 F 4.9 1.9 2.6 3 44 M 3.8 1.7 2.2 4 53 F 2.5 2.0 2.1 . 5 47 F 4.5 1.1 2.1 6 55 M 4.4 -c -c 7 51 F 4.4 1.0 1.7 8 52 M 4.2 1.0 1.7 a Means for days 3-8 averaged to obtain mean sustained feeding rate = 1.5 ? 0.5 (95% CL.) except for crayfish No. 6 which escaped (n = 7) b Means for all days and all eight crayfish averaged to obtain overall mean feeding rate = 2.2 ? 0.4 (95% CL.) (w=7) c Crayfish #6 escaped on day 5

Table 3.?Estimated percent body weight of clams consumed by crayfish per day. _The source of the numbers in columns 1-4 is explained below_

? 2 3 4 5 (3 Crayfish Crayfish Clam Clam Consumption rate

species_wt. (g) lengths (mm) BWW (g) # clams/day g/day % BWW/day P. clarkii 31.3a 5c 0.0074e 10.8f 0.08 0.26% C. bartonii 37.4b 27.5d 1.0410e 1.5f 1.56 4.18% a Mean weight of the eight actively feeding crayfish b Mean weight estimated from length-weight regression c Median SL of small clams eaten, range = 4-6mm d Mean SL of large clams eaten, range = 24-35mm e Clam body wet weights ( BWW ) estimated based on regression of weight vs. shell length f Mean sustained feeding rates indicated in Tables 1 and 2




vided considerably less energy input to P. clarkii than consumption of adult perforated Corbicula provided to C. bartonii.

Discussion Under experimental conditions both Procambarus clarkii and Cambarus bartonii

did consume Corbicula. Three classes of clams were eaten : ( 1 ) small clams between 4 and 6 mm shell length; (2) larger clams which had perforations in the shells, and (3) clams which had recently died permitting the shell valves to gape open. Con- sumption of the former two classes required a complex set of directed behaviors. Feeding began with apparently random manipulation of clams. Only perforated or small clams were transported to shelter for further feeding activities, which suggests that this manipulation is important in prey recognition. Shell-chipping or occasional enlargement of perforations followed. Finally? pieces of clam flesh were transported to the mouth using the first walking legs. The complex behavior required for feeding on Corbicula appears to be sufficiently well-developed to suggest that crayfish could readily consume Corbicula in the field.

Our results differ from those obtained by Piesik (1974) in a study of Orconectes limosus pr?dation on another freshwater bivalve in Poland. First, the maximum size of intact clam consumed in the two studies differed slightly. Large O. limosus (^45 mm carapace length) consumed Dreissena up to 12 mm SL, although few clams greater than 8 mm were eaten; Procambarus clarkii of similar size consumed Corbicula <^ 6 mm SL, whereas Cambarus bartonii consumed clams up to 9 mm SL. Data are not available on the growth rate of each of the clam species; however, it appears that Dreissena may be exposed to pr?dation for a longer time. Secondly, and most significantly, the feeding rates of crayfish on small clams reported by Piesik were substantially higher than those we found. Mean consumption by O. limosus ranging from 47-90 mm total body length (^ 23-45 mm carapace length) was ca. 36 small (4-5 mm) Dreissena per day; one large female consumed an average of 110 clams per day for 5 days. Procambarus clarkii of similar size consumed on the average only about 10 small (4-6 mm) Corbicula per day, and maximally only 19. Data from Stanczykowska (1964) indicate that Dreissena tissue weight is somewhat less than that of Corbicula for the same shell length, but it would still appear that the feeding rates we observed at similar temperatures would result in considerably less weight consumption by P. clarkii.

Lack of familiarity with the food source may partially account for the lower rates which we found for Procambarus clarkii feeding on 4-6 mm clams. The experimental crayfish used by Piesik were collected from a habitat where Dreissena was the major food source, whereas the P. clarkii which we observed had not eaten Corbicula prior to the experiment. The increase in number of clams eaten and number of crayfish feeding over the 1st 4 days indicates a familiarization process may have occurred. The fact that P. clarkii never consumed all available small clams, together with the indication that consumption rate was affected by crayfish size, suggests consumption by P. clarkii was limited by satiation or capability. Comparable studies of Cambarus bartonii pr?dation on small Corbicula were not conducted; however, casual observation suggested that this species may be a more aggressive consumer of Corbicula than P. clarkii.

The differences in pr?dation rates and maximal sizes of vulnerable prey may also be due to differences in shell morphology or body size of Dreissena and Corbicula, or to interspecific differences in the predators. Dreissena shells are elongate and thin, whereas those of Corbicula are more globose and thicker. As Vermeij and Covich (1978) noted, Corbicula is distinctly different from other freshwater bivalves in having crenulated and interlocking hinges. All of these factors may increase struc-



1981 CoviCH et al.: Pr?dation by Crayfish 187

turai integrity and lower crayfish efficiency in breaking intact Corbicula shells. How- ever, some crayfish species may be more efficient at shell-breaking. The role of substratum preference also must be considered from the aspect of prey encounter fre- quencies and pr?dation (Tevesz and McCall, 1979). Further studies of crayfish pr?dation on clams will be required to determine the importance of predator and shell morphological differences on pr?dation rates and the size refuge of clams.

Energy flow to crayfish populations from pr?dation on Corbicula may be significant only under limited conditions, i.e., where adult clams with perforated or eroded shells are available. Our estimate of percent body weight consumed per day by Cambarus bartonii (4.2%) falls within the range of natural consumption rates (2-5%) for other crayfish of similar size (Kossakowski, 1975, Orconectes limosus; Moshiri and Goldman, 1969, Pacifastacus leniusculus). Thus crayfish could obtain most, if not all, of their normal daily food intake from adult Corbicula with perforated shells. However, the distribution of live Corbicula with perforated shells is probably very limited. We have collected significant numbers only below a dam where water flow varies greatly and the substratum consists of rocks, boulders and rubble. Other habitats such as wave-swept beaches and fast-flowing streams may have relatively high densities of eroded and damaged shells. Although intact Cor- bicula are much more widely distributed, consumption of intact Corbicula is limited to small sizes (<6 or 9 mm) depending on the species of crayfish. At the rates of consumption shown by Procambarus clarkii (^0.3% body weight), intact Corbicula would provide only a small portion of the normal daily food requirements. Given the limited distribution of perforated clams and apparent low vulnerability of intact clams3 it is doubtful that an increase in Corbicula populations would result in in- creased crayfish production.

Although consumption of Corbicula may not increase crayfish production, the interaction may have significant impact on the Corbicula populations. Reports of crayfish densities have varied from 0.6-30 adults per sq m (Abrahamson and Gold- man, 1970; Capelli and Magnuson, 1975; Momot, 1977; Stein, 1977). Even at an average consumption rate of only 10 small clams/day, a well-established crayfish population would consume a large number of clams daily. Whether crayfish would actually consume clams in large numbers under natural conditions would depend on a wide variety of factors, the most significant being the alternative food sources. Although alternative food utilization by crayfish has been only slightly studied (Covich, 1977; Magnuson et al, 1975; Seroll and Coler, 1975), the range of potential known crayfish food resources is broad (Budd et al3 1978; Caine, 1975; Momot et al, 1978). Evaluation of crayfish pr?dation on Corbicula with alternative food available is necessary before the impact on Corbicula population can be predicted.

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https://www.researchgate.net/publication/249579652_Demonstrated_Food_Preferences_of_Orconectes_Immunis_Hagen_Decapoda_Astacidea?el=1_x_8&enrichId=rgreq-28e38820-34fa-42ad-94cd-ff9fc77e4948&enrichSource=Y292ZXJQYWdlOzI0NTgxMzE3NDtBUzoxNzI4NjU3NzczMTU4NDBAMTQxODIyNTgyMTY1MQ==


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-. 1966b. Food habits of striped bass, Roccus saxatilis in the Sacramento-San Joaqu?n Delta. Ibid., 136:68-96.

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Tevesz, M. J. S. and P. L. McCall. 1979. Evolution of substratum preference in bivalves (Mollusca). /. PaleontoL, 53:112-120.

Turner, J. L. 1966. Distribution and food habits of Gentrarchid fishes in the Sacramento-San Joaqu?n Delta. Calif. Fish Game Fish Bull, 136:144-153.

Vermeij, G. J. and A. P. Covich. 1978. Co-evolution of freshwater gastropods and their predators. Am. Nat., 112:833-843.

Submitted 2 January 1980 Accepted 4 June 1980



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Crayfish Predation on Corbicula under Laboratory Conditions