Why Do High Tide Cockles

Figure 1 shows that high tide cockles have the fastest feeding rate, followed by mid then low tide. Cockles are opportunistic filter feeders, meaning they allow the water to pass through them for filtration. Since cockles can only feed when they are submerged under water, in the higher tidal areas they have to adapt to being submerged for a short period of time. They do this through the behavioural adaption of having to feed fast when the tide comes in. This is so they can receive enough phytoplankton before the tidal zone recedes again. Cockles in the mid tidal zone do not need to feed quite as fast, as they have more time to receive nutrients. Cockles in the low tidal zones are covered the majority of the time, so phytoplankton is available
To do this many precautions were put in place. When collecting cockles, a random number generator was used. This was to ensure no bias occurred which would have changed the results. It also meant different distances from the high tide line could be used for each quadrat. When picking the 20 cockles from each quadrat, they were picked randomly. This is because some cockles were bigger than others and if they were hand picked it is possible only big ones would have been picked, making our results inaccurate and unrepresentative of the population. In hindsight a random number generator should have also been used for this collection, because some bias may still have occurred despite trying to pick randomly. This is also relevant for experimenting on cockle feeding rates. Once again it was important to ensure that cockles were randomly picked because the smaller, younger ones may feed at a different rate to older, larger ones. While conducting the feeding experiment a control was used. This is because a change in absorption may have occurred naturally. While measuring phytoplankton levels the same spectrometer was used. This was to ensure further accuracy in case there was slight variance between machines. The cockles were observed every 2 minutes for the duration of 20 minutes. This is because if the cockles were measured less often, the results would not be as accurate. For example, if the cockles were to be measured once after the 20 minutes, their feeding activities would not be shown in the results because they may have been feeding throughout the first 10 minutes and not throughout the second 10 minutes. While feeding the cockles, caution had to be taken to not bump the containers. This is because when bumped or moved around, their siphons recede into their shells. This is a behavioural adaptation to protect their siphons by using their