Hunting Behavior in the Carnivore Marine Snail, Nassarius Nitidus
Total Page：16
File Type：pdf, Size：1020Kb
Hunting behavior in the carnivore marine snail, Nassarius 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 species 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 animal, 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 Taxonomy 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 (Gastropoda, 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.