Feeding Habits of the Sand Shrimp Crangon Septemspinosa
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FAU Institutional Repository http://purl.fcla.edu/fau/fauir This paper was submitted by the faculty of FAU’s Harbor Branch Oceanographic Institute. Notice: ©1974 Marine Biological Laboratory. The final published version of this manuscript is available at http://www.biolbull.org/. This article may be cited as: Wilcox, J. R., & Jeffries, H. P. (1974). Feeding habits of the sand shrimp Crangon septemspinosa. The Biological Bulletin, 146(3), 424‐ 434. Reference: Bioi Bull., 146: 424-434. (June, 1974) FEEDING HABITS OF THE S~~ND SHRI~vlP CRANGON SEPTEM5;P/NOSA4 1 ]. ROSS WILCOX 2 AND H. PERRY JEFFRIES Graduate School of Occo"ography, Ulli'('crsity of Rhode Isla"d. K;'llIS/Oll, Rhode Island 02881 The sand shrinlp Crangon septetllspinosa Say is a common estuarine decapod distributed along the northwestern Atlantic from Newfoundland to eastern Florida (Squires, 1965; Williams, 1955, 1965; Price, 1962). Although C. septemspinosa is .carnivorous (Price, 1962; Regnault, 1970), it also may ingest organic nlatter in various forms. Crangon spp. has diverse feeding habits. Lloyd and Yonge (1947) classified Crangon vulgaris (== Crangon crangon) , an European species, as an omnivore after finding algae, polychaetes, gastropods, bivalves, amphipods, fish eggs and fish larvae in the digestive tract. Ho\\Oever, they felt that C. vulgaris preferred animal tissues. Allen (1960) categorized Crallgon all1nani, another European species, as a carnivore, but noted that sand and mud particles were always found in the stomach. Tiews (1968), in reviewing the literature on C. crangon, con sidered that the species was an onlnivore, but animal tissues did comprise the main food items. Kosaka (1970) classified a Japanese species Crangon affinis as a carnivore, but sand and mud were always present with the food. Willianls (1955, 1958) found a variety of recognizable and unrecognizable material in the alimentary canal of three species of penaeid shrinlp and believed that "softer and more easily digested materials could easily form the bulk of the diet" [1955, page 143]. Dahl (1968) noted that the food of several Australian prawns was small animals and a large amount of unrecognizable material, which might form the main component of the diet. To derive this nlaterial, shrimp browse on the microorganisms (bacteria, algae, and microfauna), which grow on the sub stratum. Frankenberg and Smith (1967) found seven crustaceans that ate fecal material. Also Johannes and Satomi (1966) observed that the grass shrimp Palaemonetes pugio assimilated the organic nlaterial in and on fecal pellets. An ability to utilize diverse foods has survival value in a seasonally changing environment. Thus, when preferred food is scarce, organic debris is usually avail able to estuarine animals (Darnell, 1967, 1968; Odum and de la Cruz, 1967; Odum, 1971). The objective of this study was to determine the kinds of food utilized by C. septemspinosa. Stomach contents and time of feeding were observed in a natural population; rate of digestion and growth performance on prepared diets were evaluated in the laboratory. 1 Based on a Ph.D. dissertation by J. Ross Wilcox submitted to the University of Rhode Island. Parts of this work were supported by a Grant (18050-DTX) from the Environmental Protection Administration to H. Perry Jeffries. The Harbor Branch Foundation provided support to JRW while preparing the final manuscript. 2 Present address: Harbor Branch Foundation Laboratory, RFD 1, Box 196, Fort Pierce, Florida 33450. 424 FEEDING HABITS OF CRANGON 425 MATERIALS AND METHODS Collecting area Shrimp were seined (2 X 1 m; 2 111111 nlesh) fronl sand flats in the Pettaquanls 0 cutt River, Rhode Island, near Sprague Bridge (41 0 26' 55" N, 71 27' OS" W). This river enlpties into Rhode Island Sou'nd near the mouth of Narragansett Bay. The station had the following characteristics: \vater depths of 0.5-1.0 m, average salinity of 27%0, fine to coarse sand, and current velocities of approximately 20 30 cm/sec at full tidal flow. Stomach analyses From May to October, 1971, a total of 225 stomachs were examined. Shrimp \vere collected during the day; those selected had the anterior chamber of the proventriculus expanded \vith material, \vhich could be seen through the carapace. The shrimp were frozen immediately; after thawing the carapace was lifted and the internal organs exposed. The stomach was removed and opened on a microscope slide. The contents were examined with a dissecting microscope (9-75 x) and identified. Frequency of occurrence was expressed as the nutTlber of stomachs in which each food item occurred as a percentage of the total number of individuals examined. Volumetric importance of each food type was made by visual estinlate. Time of feeding Sanlpling was conducted over a 24-hour period on July i and 8, 1971. Each hour, 30 shrimp were selected randomly fronl seining and frozen immediately. Later estimates of stomach fullness were nlade (full, half-full, and empty). The contents of full and half-full stomachs were examined for trituration. Rate of digestion studies Shrimp, 15 to 54 mm in length, \vere collected on July 20, 1971 and \vere separated into 5 mnl size groups. Three shrimp frotn each group were placed in a plastic container (20 X 20 X 40 cm) with holes drilled in the sides for water circulation. The vessels, \vhich contained 1-2 cm of clean sand, were covered and submerged in a \vater table (15 cm water depth). Seawater was filtered through a sand bed (30 X 50 X 30 cm) to remove par ticulate material before flowing through the water table. The filter retained ap proximately 93% of the chlorophyll a in the entering \vater (chlorophyll determined by a method of Strickland and Parsons, 1965). The flow rate through each filter was approximately 550 mIlmine Each water table had two filters. Three diets of varying texture were tried: tissues of Crangon, fish meal (Point Judith Fisherman's Cooperative, Point Judith, Rhode Island), and the clam M ercenaria mercenaria. All tissues were dehydrated, and 6 g of each diet \vere nlixed with 0.5 g of carnline and 30 ml of 2.2% agar (Bacto-agar, Difco Labora tories, Detroit, Michigan). Before each trial, shrinlp were starved for two days. Blocks of food were then placed in each conlparttnent; and upon ingestion, the dyed food was easily seen 426 J. R. WILCOX AND H. P. JEFFRIES through the carapace. During the first 6 hours, the shrimp were observed hourly for reduction of coloration in the stomach and for its appearance in the intestine. One shrimp from each of the three feeding groups was sacrificed each hour over the 6-hour observational period, and estimates of the' rate and degree of physical digestion of its stomach contents were made. Inspections were also made at 12 and 24 hours after feeding. Feeding studies All procedures were as described previously, except that the experiments were 8-weeks long. Growth was estimated fronl successive measurements (to the nearest nun) on the sanle individual every 2 weeks. The follo\ving diets were tested : Candida sake, a marine yeast isolated from macrovegetation taken fronl tide pools at Narragansett, Rhode Island and grown in malt extract broth (25 gil of seawater); Baker's yeast (Fleishmann's Yeast, Standard Brands, Inc., New York); brine shrimp (Metaframe Co., San Fran cisco, California) ; an unknown bacterium, probably a met11ber of the Pseudomonas group isolated from Narragansett Bay seawater and grown in an "OZR" medium (1.0 g yeast extract and 1.0 g trypticasell of seawater) ; calanoid copepods taken over a year's period in ~arragansett Bay; Spartina alterifiora detritus and attached nlicroflora collected at Bissels Cove in North Kingston, Rhode Island (the size fraction between 0.500 and 0.017 nlt11) ; TetraMin, a tropical fish food (TetraKrafte\Verke, \\lest Gernlany); finely chopped hard-boiled egg; and glycogen obtained from Nutritional Biochenlical Co., Cleveland, Ohio. All other foods were as described previously. Foods were dehydrated by heat or freeze-drying. Six gram portions were mixed with 30 ml of 2.2j1r agar; the gel \vas cut into 2 g blocks, which were fed to the shrimp daily. Experiments were run during spring, sunlmer, late summer, and fall; mean water temperatures were 15, 20, 20, and 17° C respectively. Controls were given fresh clanl tissue. A second control was nlaintained without food during the sunlnler and late sunlnler experinlents. The gro\\i·th rates were calculated according to the follo\ving equation \\rhich permits comparisons among groups of gro\vth curves but makes no assunlptions about the gro\vth nlodel (Rao, 1958) : where B = growth rate in arbitary units; gi = the sunl of the growth inc-renlents in mnl atllong all treatnlents for each growth period; Xl = the size increment,for each shrimp during each growth period; and i == the number of incremental periods. To equalize the variances, the gro\\rth rates were transfornlecl by square root. Treatments within each season were compared by one-way analysis of variance (astle, 1963). Fisher's Least Significant Difference (LSD) was used for pair wise conlparison of groups with 111ltltiple nleans (Fryer, 1966). If two means differed by the LSD calculated at a preselected probability, they were statistically different. FEEDING HABITS OF CRAftlCON 427 100-----------------------------. o FULL STOMACH • EMPTY STOMACH I Z ~ 50 0:: W a. 3 579 :3 5 7 9 TI ME in FIGlTRE 1. Stomach fullness compared \vith time of day for a field population of C. seplclnspinosa. The arro\vs indicate the time of sunset and sunrise. RESULTS Stol1uJ.ch analyses In ternlS of volulne and frequency of occurrence, organic debris, sand, and crustacean parts were the nlajor conlponents of 225 stonlachs exanlined. Organic debris conlprised 85 % of the volunle and occurred in all the stonlachs exatnined.