Hunting behavior in the carnivore marine snail, nitidus

Andrea Kilströmer

Degree project for Bachelor of Science in Biology 15 hec

Department of Marine Ecology University of Gothenburg

Contribution number 540

Supervisor: Prof. Kerstin Johannesson

Hunting behavior in the carnivore marine snail, Nassarius nitidus Andrea Kilströmer Department of Marine Ecology-Tjärnö, University of Gothenburg

ABSTRACT Little is known about the mechanisms involved in food localization within the of Nassarius nitidus. In the present paper I shall perform experimental tests of hypotheses based on chemical cues and group behavior. Studies presented on sibling species have confirmed the involvement of olfactory signals in the water; hitherto this has not been studied in N. nitidus. Two main experiments were conducted in which the existence of a food-seeking response, activated by the presence of an extract in the nearby surroundings, was verified. Confirmation was attained when food-extract penetrated the water surface and the individuals affected (97 %) quickly unburied themselves and descended down the food gradient with the intention of stumbling across the food source. An alternative option might also have been the occurrence of a rheotaxis response triggered by the mere exposure of a food stimulus; ergo move against the current when detection of the odor has been confirmed and regardless of a food gradient. However, this theory was later discarded; since the current itself proved to have no- or even a discouraging effect on the whelks’ food-seeking response (70 % moved downstream; 30 % moved upstream). As it happened the key turned out to be the establishment of the food gradient in the water, which guided the specimens (44 out of 45) in the right direction.

INTRODUCTION Chemical compounds are of a current when first activated by food widely recognized as being involved in the extract from above? interactions in marine communities, although the mechanisms by which they Earlier work has described a positive mediate are still unidentified (Kohn 1961). food-seeking response in Nassariid species, In 1971, Gurin and Carr conducted an due to the establishment of a gradient of experiment in which they discovered a chemical stimuli (Crisp 1978; Morton and protein, derived from oyster fluid, with the Yuen 2000; Bachelet et al. 2004). The capacity of stimulating Nassarius obsoletus authors discovered the existence of a in its search for food. This was one of the behavior guiding the whelks to move earliest discoveries in which a food-seeking upstream in the direction of the food source. response, in a marine , was allocated The whelks moved with determination entirely due to the presence of a chemical against the current and pinpointed the entity. Thus the implication of chemical location of the food item. Similar studies on cues in food localization is yet to be the species of our interest however, are discovered and more research is required on scarce and not much has been investigated the subject. or presented. The present paper was undertaken in order to address the issue of chemical Two additional questions was also stimuli and acquire an insight in the hunting undertaken thus to standardize the methods; behavior of N. nitidus. The following (III) could a time-lag in the food-seeking questions were included: (I) How does the response be expected between fresh and marine snail N. nitidus locate food? (II) Do decaying carrion? (IV) How long time is to the whelks exhibit a rheotaxis response? be expected between newly saturated snails And if so, can it be triggered by either; (i) a and their next search for food? food gradient or, (ii) by the mere exposure

1 The whelk lingers in the deep water, The taxonomic identifications and partly buried in the sediment with only its distributions of the group nassariids siphon protruding, until it has reached (, Prosobranchia) has for a long sexual maturity. Sexual maturity occurs time been tainted with confusion and when the snail is about four years old and uncertainty. Sibling species has been has reached an average length of 15 mm. At confounded or even wrongly considered the this stage in life it begins for the first time to same species. The nassariid used in the go on seasonal migrations. Moving from the present paper, Nassarius nitidus (Jeffreys deep water early in the spring with water 1867), was for a long time confused with its temperatures around 7°C, and reaching the sibling species Nassarius reticulatus shallow waters in June. During the summer (Linnaeus 1758). This was due to their months it then remains stationary within the similarity in both appearance and shallow waters. The return towards deeper distribution. water begins in September, to avoid the risk Rolán and Luque (1994) were the first of freezing during the colder month, and is to demonstrate that the two nassariids in fully completed in December. fact were different species; with both morphological and behavioral differences. Moving over surfaces most snails and slugs Their findings also provided evidence for a leave behind a silvery mucus trail, which differentiated preference in habitat; where eases locomotion (Hosokawa et al. 2009). the more sheltered bay was preferred by N. Besides locomotion the trail is also thought nitidus, and a more exposed open shore was to be a sort of communication between preferred by N. reticulatus. Later Sanjuan et conspecifics, enabling them to congregate al (1997) conducted a genetic data analyze and find a suitable partner by trail following and investigated the biological (Stafford and Davies 2005; Johannesson et characteristics for the two species. Their al. 2008). A pre-existing trail also reduces results were corresponding with the the energy costs associated with the previously presented data, and showed a production of mucus, since it now can strong indication towards two valid taxa at benefit from locomoting over the old one the specific level for N. nitidus and N. (Davies and Black well 2007). reticulatus. Since the history is surrounded with As mentioned above, N. nitidus is a uncertainty, only a few papers have been scavenger and rely on the unpredicted presented in which N. nitidus is the supply of carrion presented in the nearby employed name. Therefore, some sources surroundings. The abundant blue mussel used in the present paper refer to papers on Mytilus edulis is a favored sustenance which N. reticulatus instead. it can devour when found damaged (Morton 2000). Injured individuals of this species Ecology cause the snails to peer out of the sediment The netted dog whelk N. nitidus is a marine and proceed towards the mussel. They then scavenging snail, frequently found in quickly start to feed by extending their shallow waters with sandy bottoms along proboscis and take big chunks of the item. the Swedish west coast (Tallmark 1980). As The proboscis originates from the early seen in many other marine snails, N. nitidus larval stage and by which it can quickly spends its first few days as plankton drifting process a meal (Page 2005). The amount in the pelagic before settling in the sediment consumed can reach up to an astonishing at a depth of 20 meters. In the deep water 50% of their bodyweight per day (Morton the larva undergoes metamorphosis and 1990). transforms into a fully developed whelk. Feeding snails contribute to an increase of compounds in the water mass

2 (personal observation), which in turn can During the foregoing trails the whelks were lure larger predators to the area; such as allowed access to sediment, which also had hermit crabs (Pagurus), shore crabs been collected from the nearby (Carcinus maenas), etc. For this reason they surroundings of the Sven Lovén Center. need to eat fast, or they will lose the Before introducing the whelks to the opportunity to feed or even end up being the sediment, it was filtered in a 500 µm mesh. prey along with the blue mussel. Filtering was necessary due to the high risk Eggs from the common sand goby, of any uncounted individuals or any larger Pomatoschistus minutus, has also been seen organisms to enter and taint the outcome of eaten by N. nitidus (Jarvi et al. the results. To avoid creating homogeny unpublished); since the breeding season of sediment consisting of only fine particles, the sand goby peaks at the same time as the gravel was sorted and blended in with the snail begins their inshore migration, it rest. provides an appreciated meal. This results in a “predator-prey relationship” between Experimental design the two species; the goby trying to defend All experiments were conducted in a larger its nest and avoid a decrease in clutch size, aquarium (100 x 41 x 6.5 cm) divided in and contrary the snail trying to acquire food three long straight channels and placed by sneaking past the guarding male. outside under natural lighting (see picture 1). A ~2.5 cm thick layer of sediment were MATERIAL AND METHODS The research placed inside each channel and then filled was carried out at the Sven Lovén Center with seawater of an additional depth of ~2 for Marine sciences at Tjärnö on the cm. Surface seawater was allowed to run Swedish west coast during April to May of thru the channels in a constant direction and 2010. Experiments were designed to speed of ~1.7 cm/s. investigate the feeding behavior of N. No attempt was made to control nitidus. environmental parameters; however, the experiments were performed during the day Similar-sized adults (shell height 16.3 -23.6 under a short period of time (April-May mm) of N. nitidus was collected from the 2010). direct surroundings of the Sven Lovén Center, using either a sink net baited with flesh from the fish Molva molva or by hand after a crushed M. edulis had been introduced in the water. All whelks were then maintained indoors in aquaria with running seawater and without sediment. During the experiments, water temperature and salinity ranges were 5.4 to 15.8 °C and 23.1 to 31.2 ‰, respectively. The whelks were held under two different feeding conditions based on their purpose, due to the differences in the experiments; (I) in the series the whelks were initially feed until satiated, and then kept starved during the foregoing trails Picture 1: Showing the experimental set- up, in which all experiments took place. (II) the whelks were maintained in aquaria without food for two weeks prior to Experimentally-naïve whelks were allowed the experiments. to completely bury themselves before any

experiments were initiated. The unburying

3 response in the subsequent experiments that was the case. The procedure was entailed the entire shell to emerge from the repeated three times for each extract, using sediment, and the exposure of the soft body. 10 whelks in each replicate i.e. a total The channels were flushed for thirty number of 60 individuals. minutes in between every replicate to ensure no contamination. The sediment was also Water flow response disrupted in order to remove previous trails To investigate if the specimens choose to or burrows in which chemical cues still move against the water flow when triggered might remain. by a food stimuli but without having the presence of a food gradient in the water, a Extract preparation second experiment was conducted. Two different extracts was used during the Whelks were placed in a straight line experiments; (I) surface seawater, to across the middle of the channel. Extract stimulate the spontaneous behavior of N. was then sprayed directly on top of them, nitidus when activated by a new fresh using the same amount and technique as in release of seawater or when distracted by a the previous experiments. This caused the foreign object (the pipette), and (II) “food extract to quickly descend down the current extract”, used to reveal the response and leave the system and offer the preferred triggered by the presence of food. This “no gradient”. The response to the treatment potion was in addition divided into two was observed for five minutes and a goal subcategories; (i) “old”, and (ii) “fresh”. bar was set to a distance of ten centimeters To prepare the food extract, three upstream and thus consequently freshly crushed M. edulis were blended in 3 downstream. The test was then repeated dl pure seawater and then filtered in a 30 twelve times for both extracts using five µm mesh. whelks in each trail i.e. a total number of The fresh extract was made daily to 120 individuals. avoid deterioration or loss of essential compounds. Food gradient response The “old” extract was stored in a To analyze if the food seeking response was canister throughout the study along with the activated by the assembly of a food same amount of seawater, stored in an exact gradient; olfactory substances were added replica of the canister. They were then repeatedly for one minute’s time in the placed in a cooling room with temperatures water mass. close to zero. The experimental set-up was designed in the same way as in the “water flow Unburying response response” assay, apart from the distance to The first experiment was merely to reveal which the extracts were added. To ensure whether or not the whelks were responsive the creation of a gradient, the same to an olfactory signal derived from technique as in the first experiment was nonconspecific carrion in an artificial practiced. The test was repeated eight times environment. for both extracts i.e. a total number of 80 A gradient was created, using their individuals. preferred food item M. edulis, by adding 20 ml extract close to the inflow of the Series, unburying response channel. This was done with the use of a A series was conducted to observe whether small pipette. To ensure the assembly of a or not the unburying response was affected gradient upstream, extract was added three by hunger and if they chose to seek out food times under a minute’s time. The unburying more quickly when hungry. response was then observed for five The whelks were feed until satiated minutes, or until all whelks had emerged if and then starved for a controlled number of

4 days in order to investigate their willingness to unbury themselves. Three replicates, using five whelks in each, were repeated with both extracts for each day during one week’s time i.e. a total number of 240 individuals. The unburying response was observed in the same way as in the previous experiments.

Food preference A one-choice assay was conducted to determine if a feeding preference towards Figure 1: Illustrating the number of fresh or decaying carrion exists. individuals displaying the unburying Five whelks were placed in a line response in N. nitidus when exposed to across the channel and treated with either treatment of either I) fresh seawater or, II) old or fresh extracts; also a control group seawater containing extracts from M. was tested. The extracts were added using edulis. the same technique as in the previous experiment and also the fixed five minutes The displayed reactions was analyzed in a bar was exercised. The time it took for all 2x2 contingency table and assumed a value whelks to emerged, if that was the case, was larger than the critical of 3.84, which means observed and noted. The experiment was that the correlations were significant at the repeated five times for both extract i.e. a 0.05-level. The null hypothesis could total number of 50 individuals. therefore be rejected.

STATISTICAL ANALYSIS The results from Water flow response the experiments were statistically analyzed Table 1 describes, as before, how N. nitidus with a Chi square 2x2 contingency table, is nonresponsive towards control treatment and the probability level was found in the but on the contrary show a significant Chi square distribution table. response towards the mussel treatment 2 (df=1; chi =120; P<0.01) RESULTS When activated by mussel extract Unburying response from above; 70 % of the subjects moved Control displayed no response down the current and passed the goal bar of (0/30) towards the exposure of additional 10 centimeters, whereas 30 % chose to seawater nor to the intruding pipette (see move against the current. figure 1). They remained buried in the sediment with only the siphon protruding Table 1: Stimulated by either clean with which they on occasion waved in the seawater or seawater containing extract direction of the current. On the other hand, a from M. edulis directly from overhead, the significant difference was displayed when direction of movement was investigated. the whelks were exposed to mussel Upstream Downstream treatment and responded by quickly unbury Clean and start moving around the channel (df=1; seawater 0 0 Extract of chi2=56.13). M. edulis 11 26

The obtained results showed no statistical difference between upstream- and downstream movement, hence the whelks had a randomized movement pattern. The

5 null hypothesis could therefore not be On day five, 4/15 whelks unburied rejected, and no confirmation was obtained themselves when presented to the chemical towards the rheotaxis model. stimuli. On day six, 6/15 whelks reacted by Food gradient response unbury themselves. Streams containing extract from M. edulis On day seven, 8/15 whelks emerged stimulated N. nitidus to move upstream i.e. more than 50% of the total number. towards higher concentrations, as seen in table 2. 44 out of 45 responded to the mussel treatment and displayed a significant rheotaxis by crossing the fixed goal bar of 10 centimeters upstream. As demonstrated earlier, no response was reported in the control treatment.

Table 2: By the establishment of a food Figure 2: Unburying responses of recently gradient, consisting of extract from the (within 10 min) satiated N. nitidus and a bivalve M. edulis placed in the incoming follow-up over the next seven days. stream, the rheotaxis response was investigated. Food preference

The response time towards decaying carrion Upstream Still buried in the one-choice assay was significantly Clean seawater 0 45 longer (p-value 0.003) than for fresh Extract of carrion; 253.4 versus 44.6 s (see table 3). M. edulis 44 1 Table 3: Activated by the presence of The chi2 value (86.09) was larger than the extract from either fresh or decaying food, critical value; which means that the the total time for all whelks to react by unburying, or until the fixed 5 minutes bar correlations were significant at the 0.05- was exceeded if that was the case, was level; suggesting that this behavior is in scrutinized. concordance with the unburying response.

Fresh M. edulis Old M. edulis Series, unburying response The whelks ignored the presented food Time (s) Time (s) initially, but became more responsive over 27 210 time after last meal (see figure 2). 34 300 On day zero and one, no whelks 68 157 emerged (0/15). All remained stationary in 42 300 the sediment with only the siphon 52 300 protruding seeming unaffected by the induced odor in the water mass. In three replicates in which old extract was On day two and three respectively, used; the time limit was exceeded and noted 3/15 whelks unburied themselves and began as 300. to investigate the vicinity by moving around. DISCUSSION Several interesting patterns On day four, 5/15 whelks responded was revealed in the present study; namely positive towards the treatment and unburied (I) the response towards a food stimuli was themselves immediately when they sensed to quickly unbury and seek out the food, (II) the odor in the water. starved individuals displayed a more eager food-seeking behavior, (III) a preference

6 towards fresh food was found, and (IV) the sp) and bivalve (Tapes philippinarum); unburying response was triggered by the which underlie our choice of experimental presence of a food gradient in the water food extract. mass. The unburying response, to begin The feeding behavior of N. reticulatus with, was performed in a quick and resolute was investigated by Davenport et al. (2002) way, indicating that the behavior has arisen in Scotland, UK; where they examined the due to the scarce distribution of food in the hunting behavior both with and without ocean. The whelks need to seek out food substratum. Their experiments showed that when the possibility is presented; or else cod- and crab extract provoked the most they won’t succeed in having a high fitness. impressive display. It became evident when An individual which has starved in the all animals were showing activity towards absence of available food react therefore the stimulus within minutes; by waving of more swiftly since it is in a great need of the siphon, shell rocking, eversion of the nourishment. The same is true for the proboscis and rapid movements around the preference towards fresh food, indicating aquaria. These results corroborate what that they are in agreement. Fresh food Mary Crisp saw in her experiments in 1978. supply more nutrition and a lowered risk of The activity- and unburying response competitors; since the food item has been in from the above mentioned studies are in the water for a shorter time and hence fewer agreement with the findings in the present organisms had had time to be attracted. paper. Where the majorities of the When creating a food gradient, it specimens reacted towards the M. edulis became clear that the whelks needed a treatment, none on the contrary reacted concentration to follow in order to find the towards the control treatment. M. edulis food source. This discovery came as a extract triggered the specimens to emerge surprise, since we first thought the whelks out of the sediment and quickly start to should be satisfied by simply sense the odor move around the aquarium waving their in the water and then strictly starts to move siphon in the direction of the food source. against the current; instead they became The foreign object, saturated as the pipette, confused and unfocused. No significant induced no reaction nor did the introduction results were obtained in the experiment of a new fresh release of sea water. using only water flow; but the rheotaxis response was significant at the 0.05-level in Extract was prepared in a canteen during the the food gradient experiment. length of the series and from which the whelks was treated in order to reveal a Morton and Yuen (2000) performed an hypothetical behavior. In the food experiment with the sibling species, preference experiment this was proved to be Nassarius festivus, in which they looked at a bad choice of sustenance; since it was (1) food preferences, and (2) food detection evident that they preferred fresh food before distance. For bait they used; fish old. The obtained results might therefore (Lateolabrax sp), bivalve (Tapes have been more evident if extract had been philippinarum), soldier crab (Mictyris made daily, which is something that should longicarpus) and mud-shrimp (Upogebia be made different if the experiment was to major). Their results showed that N. festivus be tested again. The length of the series was was able to detect a food item from a also cut short due to lack of time and a distance of 80 cm (it should be noted that clear-cut result could therefore not be this was the maximum length used in this obtained. This parameter should be more experiment which indicate that N. festivus carefully maintained in a follow-up, in order might be able to detect food from a greater to exhibit a more interesting result. distance). The study also revealed that the preferred food item was fish (Lateolabrax

7 LITERATURE CITED males trade off between defenses against egg Bachelet, G., Simon-Bouhet, B., Desclaux, C., predators and sneak intrusions. Garcia-Meunier, P., Mairesse, G., Kohn, A. J. 1961 Chemoreception in gastropod Montaudouin, X., Raigné, H., Randriambao molluscs. Am. Zool. 1: 292-308 K., Sauriau, P. G. and Viard F. 2004 Morton, B. 1990 The physiology and feeding Invasion of the eastern Bay of Biscay by the behavior of two scavenging gastropods in nassariid gastropod Cyclope neritea: origin Hong Kong the subtidal Babylonia lutosa and effects on the resident fauna. Mar. Ecol. (Lamarck) and the intertidal Nassarius Prog. Ser. 276: 147-159 festivus (Powys). J. Moll. Stud. 56, 275-288 Crisp, M. 1978 Effects of feeding on the Morton, B and Yuen, W. Y. 2000 The feeding behaviour of Nassarius-species (Gastropoda, behavior and competition for carrion Prosobranchia). J. Mar. Biol. Ass. U. K. 58: between two sympatric scavengers on a 659-669 sandy shore in Hong Kong: the gastropod, Davenport, J. and Moore, P. G. 2002 Nassarius festivus (Powys) and the hermit Behavioural responses of the netted crab, Diogenes edwardsii (De Haan). J. Exp. dogwhelk Nassarius reticulatus to olfactory Mar. Biol. Ecol. 246:1–29 signals derived from conspecific and Page, L. R. 2005 Development of foregut and nonspecific carrion. J. Mar. Biol. Ass. U.K. proboscis in the buccinid neogastropod 82: 967-969 Nassarius mendicus: evolutionary Davies, M. S., and Blackwell J. 2007 Energy opportunity exploited by a developmental saving through trail following in a marine module. J. Morphol. 264: 327-338 snail. Proc. R. Soc. B. 274: 1233-1236 Rolán, E. and Luque, A. A. 1994 Nassarius Gurin, S., Carr, W. E. 1971 Chemoreception in reticulatus (Linnaeus, 1758) y Nassarius Nassarius obsoletus: the role of specific nitidus (Jeffreys, 1867) (Gastropoda, stimulatory proteins. Science, 174: 293-295 Nassaridae), dos especies válidas de los Hosokawa, D., Ishikawa, T., Morikawa, H., mares de Europa. Iberus, 12: 59-76. Imai, Y. and Yamaguchi, T. 2009 Sanjuan, A., Perez-Losada, M. and Rolán, E. Development of a biologically inspired 1997 Allozyme evidence for cryptic locomotion system for a capsule endoscope. speciation in sympatric populations of Int. J. Med. Robotics. Comput. Assist. Surg. Nassarius spp. (: Gastropoda). J. 5: 471-478 Mar. Biol. Ass. U.K. 77: 773-784. Johannesson, K., Havenhand, J. N., Jonsson, P. Stafford, R. and Davies, M. S. 2005 Examining R., Lindegarth, M., Sundin, A. and refuge locomotion mechanisms in intertidal Hollander, J. 2008 Male discrimination of snails using artificial life simulation the female mucous trails permits assortative techniques. Lect. Notes. Artif. Intell. 3630: mating in a marine snail species. Evolution 520-529 62-12: 3178-3184 Tallmark, B. 1980 Population dynamics of Järvi-Laturi, M., Lindström, K., Kvarnemo, C. Nassarius reticulatus (Gastropoda, and Svensson, O. “Manuscript” Sand goby Prosobranchia) in Gullmar Fjord. Mar. Ecol. Prog. Ser. 3: 51-62

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