Dredging in Dorset – beach, river and pond life on Y13 biology trip

News from the Biology Department: 

“Our twelve Upper Sixth Biologists had an enjoyable and educational day studying ecology at three different sites and learning about a range of approaches that can be useful to estimate population sizes of various organisms. To provide more detailed feedback about the techniques they encountered each pupil chose a specific aspect of the day to prepare a handout and give a presentation to the rest of the group; their comments about the various activities they participated in during the day have been collated.

On arrival at Leeson House Field Studies Centre, in Langton Matravers near Swanage, we met the Senior Field Studies Tutor, Mike Gould. Our first activity was investigating the contents of several Longworth small mammal traps that had been left out the previous night. Mike showed us how to open the traps and let the mammals out safely and then allowed volunteers to release the animals that had been caught in the traps into a large plastic bag. The traps contained two Wood Mice and a Vole and, having identified them, we gently released them back into their natural habitat. We learnt how to humanely capture mammals, the conditions needed to keep them alive whilst in captivity in the traps and how recording data about these individuals can help with conservation. 

A Robinson-style moth trap had also been left out overnight and as Mike removed the egg cartons from inside and we passed these around, he was able to name and often explain the common names for the variety of moths that had been attracted in during the night by the light. We learnt that there are about 2,500 species of Lepidoptera (insects with a coiled proboscis for feeding and wings covered with tiny scales) found in the British Isles but only approximately 70 species of butterflies so the majority are moths but most of us are less familiar with them because they are active at night.

Woodlice had been collected by Mike the day before our visit and marked with a small spot of paint, which would not harm them or make them more visible to predators. He recorded the numbers marked and then released them back in the same location. To estimate the population size of woodlice in the area we hunted for the same length of time and collected as many woodlice as possible then counted the total number and recorded how many were recaptured (individuals with a small dot of non-toxic paint on their backs). Using the results from our ‘mark, release, recapture’ technique we used the Lincoln index to estimate the population, based on some important assumptions e.g. that the marked organisms are not harmed, they have mixed randomly with unmarked individuals & dispersed evenly and that there have not been any changes to the population due to birth, death, emigration or immigration of woodlice.

While we were counting woodlice Mike set up a mist net to capture some small birds, which he placed into bags to keep them calm until he showed them to us. It was really interesting to see the way in which birds could be monitored using a simple unique identification ring, which allows the Natural History Museum to be able to track their migration patterns.  Our guide was clearly an enthusiastic expert and showed us how to tell the gender and age of a bird by looking at physical characteristics. Once the two female Goldcrests and ChiffChaff had been weighed and their wing-span measured Mike chose the appropriate size of ring to place on them and recorded their details in his log book before they were released.

Using appropriate nets we collected and tried to identify some of the invertebrates dislodged by shaking trees (described as ‘tree beating’) and used sweep nets moving in a figure-of-eight pattern to collect some of the organisms living in the long grass, nettles and shrubs (but not brambles).

During pond dipping we reached the net into the pond and gently moved it across the bottom of the pond. After depositing the contents of the net in the tray (containing water) we set about identifying the organisms caught.  This gave us a greater understanding of using this technique to sample populations and it was intriguing to explore some pond organisms up close. We were particularly excited to catch some great crested newts and it was interesting to watch how aquatic invertebrate species such as water boatmen and diving beetles move through the water. 

Mike gave us a short explanation of the lichen distribution on a wall outside Leeson house. We learnt that lichens involved two different organisms living symbiotically; an algal species which photosynthesises and a fungal species which protects the algae from dessication. He spoke about the factors affecting the distribution of Lichen especially the abiotic factors, such as temperature and substrate. We looked at the differences between species of lichen on the north facing side of the wall and the south facing side and concluded that there is a higher diversity on the south facing side as there is more sunlight falling on this side of the wall and it is warmer. It was explained to us how substrate can affect the distribution of lichen, for example on the top of the wall there was less lichen growing because of other debris inhibiting growth. Observation of the lichen helped us to understand and apply our knowledge of abiotic factors which can affect distribution and we learnt how lichens can be used as indicators of pollution.

Arriving at Kimmeridge Bay for low tide provided us with the perfect opportunity to learn about zonation and see how the different species are separated into horizontals bands depending on the abiotic and biotic factors. We looked specifically at the distribution of the four species of periwinkle (Littorina sp.) that are found in distinct zones on the shore, where they will experience an enormous variation in abiotic factors such as temperature and salinity at different times of the day and night, depending on the state of the tide.

Starting at the sea, when the tide was at its lowest, we worked in groups to collect data for Mrs. Newland’s required practical investigating the distribution of the rough periwinkle, using an interrupted belt transect. We used a spirit level attached to a piece of wood and two metre rulers to determine the height change between the locations where we placed our quadrats to count the numbers of rough periwinkles. Many of the rough periwinkles were found in cracks in the rock and they can survive out of water for a reasonable period of time. Their distribution is affected by a range of abiotic factors including dessication, salinity, temperature and substrate.

One highlight of the day was finding cushion stars in the low tide pools at Kimmeridge, and seeing Dr Jancis completely in her element! As John Steinbeck wrote “it is advisable to look from the tide pool to the stars and then back to the tide pool”. Rock pools exist in intertidal zones, which are submerged by the sea during high tides and storms. Try as we might, all most of us found was lots of bare rocks but Mike knew just where and how to look and easily found a whole treasure trove of marine life to show us including fish, sea anemones, brittlestars and a very large and angry swimming crab. Some of us did some fossil hunting, finding interesting specimens in the rocks on the beach and a few in the debris that had fallen from the cliffs.

In the afternoon we visited the River Piddle (a name which did not amuse Queen Victoria) to do some kick sampling, look at freshwater indicator species used to assess water pollution, and calculate the species diversity and species richness of the river in samples taken from two different sites where the flow rate varied. This involved putting on chest waders, wading into the river and kicking up the bottom of the river for 20 seconds while holding the net in position to collect any animals dislodged from the bed of the river. When we brought the samples back to the river bank we separated the different species we had collected in the trays and tallied the quantities. There was a significant difference between the organisms we collected in the two different areas with one site having many Daphnia (water fleas) and shrimps and at the other site there was a competitive element introduced to see who caught most fish in their nets. In addition to recording the living organisms present we assessed differences in the abiotic factors at the two sites by recording factors such as flow rate, temperature, pH, phosphate and nitrate concentrations.

The vibrant colours of a beautiful Kingfisher flying along the river and perching on a tree overlooking the river provided a beautiful end to a most interesting day.”