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Introduction
O. R. Chaparro, C. J. Segura, J. M. Navaro, and R. J. Thompson research on the feeding strategies of female gastropods (snails/slugs), scientifically classified as Credipula fecunda. The study focuses on the effect of food supply on the feeding strategy of C. fecunda. It is interesting to note that most gastropods can change sexes at some point in life (protandric hermaphrodites). Young and mature males can move from one place to another, but mature females lack locomotory senses (Chaparro et al. 79). Changing sexes from male to female takes away the mobility, and shifts feeding patterns from a combination of using the radula (tongue) and gills (suspension-feeding), to exclusively using gills to feed (Chaparro et al. 80).
Hypothesis
The hypothesis is that snails and other mollusks alter the feeding mechanisms based on the amount of food available in the water habitat. The hypothesis is the basis of establishing mechanical, physical, and biochemical responses of the limpets (snails) to food concentration and quality. The research focuses on the control of feeding through the food canal and food pouch and the excretion of pseudofaeces from the digestive tracts when food supply levels are high (Chaparro et al. 80).
Discussion
Sampling and Variables
The study samples were immobile female gastropods of the C. fecunda classification with shell length of 35-45 mm. The samples were collected from the intertidal ecosystem (an area of varying tides) of Yaldad Bay, located on Chiloe Island, southern Chile (43 ˚08́ S, 73 ˚44́ W). The variables used were shell length (35-45 mm), sea water temperature (16.5-17.5˚) and algae volume (15000-200,000 cells ml-1) (Chaparro et al. 80).
Experimental Procedures
The gastropods were sampled from the pebble substrate and reattached to a clear glass plate. All the reattached limpet (snail) samples were placed at in 20-1 tanks containing filtered (0.45µm) sea water for 48 hours at 16.5-17.5˚ C and 30 psu. The C. fecunda were fed on algae that had been cultured (reproduced) in the lab at concentration levels of 15000-200,000 cells ml-1. The maximum concentration levels depicted a chlorophyll-a value of 100 µg 1-1. The maximum levels of concentration at the natural habitat in Yaldad bay were 40 µg 1-1 (80). Each sample was acclimated in a separate 1.3-1 container with a continuous flow of filtered sea water at the optimum concentration levels. The C. fecunda were observed at intervals for two hours each (Chaparro et al. 80).
The observation involved inverting the limpet on a supporting frame to study the abdomen through the transparent glass plate, mounted on a dissecting microscope lens. A Pulnix TMC7 video camera fitted to the microscope eased recording of the movement of food through the food canal and food pouch, and the excretion of pseudofaeces from the digestive tract. The two hours of observation per limpet enabled observation of normal feeding strategies. The C. fecunda fed, deposited eggs and cleaned the egg mass normally (Chaparro et al. 80).
The feeding activity was captured as follows:
Mucous Ball
The volume of the mucous ball was calculated as 4/3πr3. The total volume of the balls was summed up, distinguishing between the balls that had been ingested and those that were rejected. The rejected mucous balls were labeled “type-I” pseudofaeces (Chaparro et al. 80).
Mucous Cord
The researchers recorded the volume of mucous cords produced in the neck canal and computed the volumetric data indirectly using the formula πr2 l. The rejected mucous cords were labeled “type-II” pseudofaeces (Chaparro et al. 81).
Direct Rejection Tract
There are instances when food is transferred to the mantle margin by a ciliary tract without going through the food pouch. The researchers labeled the rejected material “type-III” pseudofaeces. The scientists recorded “type-III pseudofaeces’ frequency and volume produced (Chaparro et al. 81).
Evidence
Mucous Balls
The volume of the mucous balls increased as the concentration of algae cells in the sea water increased. The frequency of radula (tongue) outthrusts also increased as the food particle concentration increased. The rate of mucous ball ingestion was low or remained constant at 90,000 Isochrysis galbana cells ml-1, but increased at 140,000 cells ml-1 before reducing at higher levels of I. galbana concentration. The frequency of mucous ball production fluctuated at different concentration level, similar to the rate of mucous ball ingestion. The difference between the rate of production and the rate of ingestion provided an estimate of the excretion rate, which increased rapidly with cell concentration. The limpets ingested 90% of the mucous balls produced at 150,000 cells ml-1. However, as the cell concentration increased, the volume of mucous balls ingested decreased (Chaparro et al. 81).
Mucous Cords
The volume of the mucous cords increased as cell concentration increased (Chaparro et al. 81). The rate of ingestion remained unaffected by cell concentration. The width of the mucous cord increased in as the concentration increased. However, the length (9 mm) remained fairly constant. The frequency of mucous cord production increased with cell concentration. The volume of mucous balls ingested increased as cell concentration increased up to 150,000 cells ml-1. The production of pseudofaeces was minimal at cell concentrations below 100,000 cells ml-1 but increased rapidly with cell concentration. The limpets ingested 93% of the mucous cords produced below 150,000 cells ml-1 but decreased with an increase in cell concentration (Chaparro et al. 82).
Direct Rejection Tract
The concentration of I. galbana cells did not affect the rate of excretion of type-III pseudofaeces and. There was no activity in the rejection tract below 60,000 cells ml-1. However, the activity increased to 65% at maximum concentration levels (Chaparro et al. 83).
Conclusion
The analysis shows that snails and other mollusks alter the feeding mechanisms based on the amount of food available in the water habitat. The feeding mechanism of the C. fecunda adapts to the availability of food in the natural habitat (Chaparro et al. 86). Changes in physiological processes enable it to maximize and utilize food at different levels of concentration.
Works Cited
Chaparro, O. R., C. J. Segura, J. M. Navarro and R. J. Thompson. “The effect of food supply on feeding strategy in sessile female gastropods Crepidula fecunda.” Marine Biology 144.1 (2004): 79-87. Print.
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