Mud Whelk
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Introduction to the ecological niche of the mud whelk, Cominella Glandiformis
Mud whelks that are being investigated belong to the Gastropoda class and Buccinidae family. This means that they are similar to snails, having muscular foot and a spiraled shell. Cominella Glandiformis is most widely distributed among the many Cominella spp. found in New Zealand. They live exclusively on moderately sheltered beaches, principally on shores of mud. These mud whelks are ubiquitous on enclosed mudflats, creeping about actively on the surface, which is subjected greatly to fluctuating salinity and humidity.
Intensity of individuals is greatest where the beds of Austrovenus Stutchburyi and pipi are densest as these are its primary food source. Apart from this, they are quite randomly spread and only gather while feeding. Wherever Cominella Adspersa and Cominella Glandiformis are found in the same area, Cominella Glandiformis is abundant in the upper regions and adspersa in the lower regions. This illustrates the Gauzes Competitive Exclusion Principle , as both species have similar niches.
Behaviour patterns of these mud whelks are quite straightforward: random locomotory movements, burrowing and feeding. There is not much evidence as to its activity period. However, the prospect of a “biological clock” controlling daily rhythms has been investigated recently (Kennedy, 1970), but with inconclusive and indecisive results.
An active carnivore, Cominella Glandiformis, scavenges the intertidal shores, feeding on dead and moribund animal matter. For this reason, it is considered an important Ðcommercial cleaner of our seashores. Temperature fluctuations in this habitat are habitual to the whelks. In my initial research, I found out that there isnt any evidence of a type of feeding activity rhythm shown by the whelks and then I thought to investigate if temperature affected what time they fed and hence their feeding activity period.
Adaptations:
Organisms best suited for mudflats are burrowers. These mud whelks have some adaptations for movement and feeding that enable it to move through and survive the mudflat sediment, which comprises of sand, silt, mud and organic content. These adaptations are substantial as my investigation is based on the feeding response time in different temperatures.
They have a very long trunk-like siphon at the end of their pointed shell. This allows them to draw in their water current with precision and accurately locate the smells of decaying food. (Structural)
The mud whelk has a long proboscis, which it thrusts out to get its share of food. This structural adaptation allows several numbers of whelks to feed on one cockle.
The pallial siphon (merely an extension of the edge of the mantle) works in conjunction with the osphradium , a chemosensory organ for testing the environment in which animal lives. Water is drawn into the mantle cavity and passes over the osphradium as the siphon makes sweeping arcs; course is then set and taken along the gradient of food particles. The siphon also aids them to respire by constantly drawing in water and this respiration process takes place across the gill behind its head.
Cominella Glandiformis exhibits a unique pose among its class with its “standing behaviour”. Individuals extend their foot from the shell and raise the shell high off the substrate. It is possibly preparatory to the incoming tide, which acts as a means of dispersal. This behaviour aids them in survival by stopping their feeding activity and seeking the burrows before the harsh tide is in.
These mud whelks have a keen sense of smell and can respond to food up to fifteen metres away (Chemotaxic response triggered by the chemosensory organ, osphradium). These adaptations are what enable them to feed and survive, but the question is do these adaptations work better in higher temperatures resulting the feeding activity period to be when the temperatures are high.
The purpose of this investigation is to determine whether variations in seawater temperatures affect the time taken for the cockle to reach the food source, i.e. feeding response time and hence establish the feeding activity period of the whelks by seeing if there is an optimum temperature at which they can sense and feed faster.
Hypothesis:
Higher temperatures should mean that the whelks react more rapidly and reach the food source sooner because the smell of the cockle is sensed faster by its osphradium in high temperatures. This means that whelks should probably be active at the time of the day that has the highest temperature, i.e. the noon as it will take them less time to feed.
Equipment:
25 Mud whelks
Water bath
Stopwatch
Water and ice Ð- to get below ambient and 20 degrees temperatures.
Seawater collected that same day to get the ambient temperature.
Electronic thermometer
Five 30 cm rulers
10 cockles of the same species Austrovenus Stutchburyi
5 salt water tanks to generate water baths.
Method:
The equipment was set-up in the same room, so the factors such as light intensity and so on wouldnt have any slightest effect on the investigation.
Five seawater tanks were utilized to generate water baths with varying temperatures (independent variable) of the following rangeЖ below ambient, ambient, 20ÐÑ”, 25ÐÑ” and 30ÐÑ”. This range was appropriate and ensured sufficient data for investigation and analysis.
Firstly, seawater was collected on that day and the ambient temperature of it was measured using an electronic thermometer and was stored in lab conditions. The ambient temperature that day was around 18.9ÐÑ” at midday and 17.3ÐÑ” at 9:00 am.
Large number of small blocks of ice were used to generate the below ambient temperature, while heating the seawater generated 20ÐÑ”, 25ÐÑ” and 30ÐÑ” temperatures. A water bath with no lid was used so as to keep the humidity of the water baths fixed and therefore induce no other varying independent variable affecting the experiment.