Behaviour
Introduction
Bivalves of the family Lucinidae are remarkable for their obligate symbiosis with sulphide-oxidising Proteobacteria, housed in the ctenidia, from which they gain much of their nutrition. Lucinidae are by far the most diverse (Taylor & Glover, 2010). They are particularly varied and abundant in the tropics, with a depth range from the intertidal zone to around 2500 m, and occupying a wide range of habitats, including mangrove muds, intertidal sands, seagrass beds, subtidal sites of organic enrichment, oxygen minimum zones, cold seeps, mud volcanoes, and hydrothermal vents.
Codakia paytenorum in particular is one such species part of the Lucinidae family and (Iredale, 1937)] are abundant in Thalassia-dominated habitats of the western Atlantic and Indo-West Pacific (Moore et al., 1968; Taylor & Lewis, 1970; Jackson, 1972).
Climate change being a very prominent problem in our era affecting all marine life due to increased temperature effects, a study is done to determine if rise in temperatures especially in seawater will make any changes to all marine life or only specific marine animals. It is found that climate change can result in sea level rise, which may lead to loss of available beaches and coasts, storms and cyclones can be highly destructive and cause rapid erosion of dune systems. Temperatures are projected to rise in the coming years (Hawkes et al. 2009).
Materials and Methods
A total of 45 clams were sifted from the sandy sediments when the tide was low on the reefs off the beach of Shark Bay at Heron Island. The clams were then separated into 3 experimental setups of 3 different temperatures with 15 clams each to determine if temperature affected the rate at which the clams require to burrow and also to see if temperatures would affect the rate of filtration of the clams.
2.5 ml of shellfish diet 1800 was used to determine the filtration rate. Water samples were collected every 2 hours for a period of 8 hours and then ran through a photo spectrometry machine to determine the absorption rate and calculate the difference between each 2 hour interval.
Results
Each experimental set up had 15 clams. The clams were subjected to different temperatures to first test for the rate of burrowing. Clams were found to burrow slower in colder temperatures than in warmer temperatures. The optimum temperature from this experiment appears to be 22.4 degrees Celsius, with most number of clams completely burrowed at the 8th hour. All clams completed burrowing by the 10th hour allowing the next step of the experiment to begin as depicted in Table 1. Testing the filtration rate.
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Time
|
Control (19.6 degrees C)
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Warmer (22.4 degrees C)
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Warmest (25.5 degrees C)
|
|
After 2 hours
|
0
|
0
|
0
|
|
After 4 hours
|
0
|
2
|
0
|
|
After 6 hours
|
3
|
7
|
4
|
|
After 8 hours
|
8
|
14
|
10
|
|
After 10 hours
|
15
|
15
|
15
|
Table 1. Time taken for all clams in the experimental set up to complete burrowing.
Filtration rate was observed to also be most effective at 22.4 degrees Celsius. Control showed a constant increase but the increases were not as much as that of the warmer temperatures.
|
Time
|
Control (19.6 degrees C)
|
Warmer (22.4 degrees C)
|
Warmest (25.5 degrees C)
|
|
Prior to feed added
|
100%
|
100%
|
100%
|
|
Feed added
|
86.2%
|
91.6%
|
80.6%
|
|
After 2 hours
|
86.3%
|
96.7%
|
86.5%
|
|
After 4 hours
|
88.0%
|
94.1%
|
92.8%
|
|
After 6 hours
|
89.8%
|
98.0%
|
93.1%
|
|
After 8 hours
|
91.5%
|
95.0%
|
93.0%
|
Table 2. Filtration rate measured with a spectrophotometer to determine the efficacy of filtration under different temperatures.
Discussion
Temperature was the main factor considered in this experiment however, light was not factored in until an accidental observation of increased activity under low light levels or completely no light present was noted. Clams in the control tanks and the warmest tanks were slightly exposed to ambient light due to being positioned closer to the edge; however the clams at 22.4 degrees Celsius were exposed to the least amount of light. A piece of fabric was used at the 6th hour to simulate cover and darkness to determine if light was a factor to be considered. A relatively significant increase in number clams completing its burrowing process was noted in the following two hours, making light a possible factor. This could mean that clams are possibly nocturnal or have preference for low light areas.
Temperature was also found to affect filtration rate. Most effective temperature being 22.4 degrees Celsius, with a slight discrepancy in the results wherein the absorption rate went up and back down from 98% to 95% as seen in Table 2. A possible explanation for this is that there were wastes generated by the clams which contributed to the additional turbidity of the water thus the results.
Clams shut tight when slight water movement was detected. This was observed when slight movement of the tanks caused the clams to immediately retract its foot and shut its valves tight. The foot was observed to be extended even when there is little sediment present around, giving rise to the possibility that these bivalves do not necessarily need to be completely burrowed to be able to feed.
Future research can be done with regards to light by exposing one batch of clams to varying brightness in environments and also to determine if clams can filter even without burrowing by having little sediment in the tanks.
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