FOOD DETECTION IN HERMIT CRABS IN STILL AND FLOWING WATER

Introduction

Hermit crabs (Eupagarus bernhardus), are carnivorous crabs, that will scavenge carrion as well as hunt. They mainly look for meals at night, to give them a chance to see their surroundings and taste the water to determine the best direction in which to go hunting (Young 1994). They are often found in large numbers, especially in mid- to lower- shore rock pools and intertidal zones (Gibson et al 2001). This study examines whether the flow of water affects the Hermit Crab’s ability to detect a food source.

The working hypothesis is that Hermit Crabs are more likely to detect a food source if they are downstream from the food, and will therefore move against the flow of water to reach it.

Method

Two quadrats were placed in an area of flowing water on the shore, one had bait in the centre, and one was left empty to be a control. The same was done in a rock pool. The crab’s entering the quadrat, and the direction from which they arrived (against flow, with flow, side), was recorded over a 15 minute period. This was done 5 times in different random locations on the shore. Once all the data was collected, Kruskal-Wallis tests were completed to get a Chi-square value and a p value.

Results

The mean results are summarised in Figure 1.

Figure 1. Mean Direction of Movement of Hermit Crab’s to the bait.

As you can see from Figure 1, a much greater number of Hermit Crab’s moved against the flow of water to reach the bait, and very little arrived with the flow of water. In the rock pool with bait, crabs appear to arrive from all sides with no great variation.

The results of the Kruskal-Wallis test are summarised in Table 1.

Table 1. Summary showing Chi-squared value and p value of Kruskal-Wallis test.

From these results (Table 1), we can be confident in accepting our working hypothesis that the Hermit Crabs detect a food source from downstream, and move against the flow of water to reach the food source. In the non-baited quadrats and in the rock pool, Hermit Crabs are equally likely to approach the food from any direction.

Discussion

Our working hypothesis was accepted as the results demonstrated that crabs are more likely to move against the flow of water to reach a food source (Miller et al 2005). The crab’s head and appendages are covered in chemical receptors which pick up the scent of food. As the scent travels past them, the chemical receptors detect it and therefore the crab follows the scent towards the food. This is why the crab moved against the flow of water towards the bait.

There are a number of things that could affect the crab’s ability to detect the food source such as the size of the rock pool they are in. If the rock pool is very large, it will take longer for the scent of the food to disperse and be detected, and it will then take longer for the crab to respond and move towards the food.

The rate of flow of the water could have affected the crabs ability and time to detect the food. The rate of flow could have been measured and the length of time it takes for the crab to respond recorded. This would have given us an estimate of how long it takes a food scent to reach the crab. If the water was flowing slowly, it may have taken longer for the crab’s to detect it and respond, and they may not have reached the bait in the 15 minute time limit. 

Another factor which could have been affecting the experiment was temperature. As it was a cold day the scent of the food would have taken slightly longer to disperse. If this experiment was then repeated on a warm sunny day the heat could have affected the time in which the scent of food travelled and therefore more hermit crabs may appear quicker and even from different directions, possibly changing our results.

While randomly placing our quadrats, the area in which they landed was not cleared of hermit crabs and therefore crabs were already inside some of the quadrats which could have slightly affected our results.           

References

Gibson, R., Hextall, B., Rogers, A. 2001. A Photographic Guide to the Sea & Shore Life of Britain & North-West Europe.

Miller, S., Harley, J. 2005 Zoology

Young, A. 1994 Marine Wildlife of Atlantic Europe

ABUNDANCE AND DIVERSITY OF BIRDS ON THE FORESHORE AT BOGGLE HOLE

Introduction

                During low tide, the rocky foreshore of Boggle Hole and Robin Hood’s Day exposes excellent feeding habitat for many species of wading and coastal species of birds. The exposed rocks are covered in gastropods, limpets, crab and many aquatic plants for the birds to feed on. The cliff faces and shore is also a good breeding habitat for some species, such as the Rock Pipit (Gooders 1995), however not many bird species breed over the winter months due to the harsh weather conditions. This is a study into the diversity and abundance of the birds on the foreshore of Boggle Hole in one day in October. 

              There are two working hypotheses that will be tested. The first is that if there is more foreshore available, there will be a greater abundance and diversity of birds. This will determine whether tide has an effect on the abundance of species. The second working hypothesis is that if more foreshore is available further down the beach at low tide, there will be a higher abundance and diversity of birds there.

Methods

                Observations were carried out at five minute intervals at six 150m intervals (see figure 1) down the beach in the morning, when the tide was going out, and in the afternoon, when the tide was coming back in. The species observed landing at each section of beach was recorded in 5 minute intervals, with 5 minute gaps between each observation period.

                After the observation periods, all the data was gathered together. The total number of individuals (irrespective of species) per 5 minute observation period was calculated, then average counts for the total period and each species observed during the 2 hour session. A Shannon diversity index was calculated for each 5 minute period.

                The test whether tide has an effect on abundance or Shannon diversity of birds, Mann-Whitney U Tests were done.

                To test whether observer location down the beach has an effect on abundance or Shannon diversity, Kruskal-Wallis tests were carried out.

Results

Figure 1 shows the mean numbers of birds seen along the beach. 

Figure 1 – Mean and standard deviation for numbers of birds observed on the foreshore of Boggle Hole in the morning and afternoon.

From the graph shows the mean and standard deviation, it appears that positions 6 and 7 were much more abundant with birds, and much more so in the morning when the tide was going out. There seems to be not much variance in the afternoon results, when the tide was coming in.

Figure 3 shows the Shannon diversity of the birds along the beach

Figure 3 - The average Shannon Diversity for each position along the foreshore of Boggle Hole

                Figure 3 shows the Shannon Diversity of the birds found at Boggle Hole. From this graph it appears that further down the beach there is a slightly higher diversity of species and higher diversity of species in the afternoon, but there is not a great difference from the morning.

Table 1 shows the results of the statistical tests carried out on the data.

Kruskal-Wallis Test	MEAN	SHANNON DIVSERITY	SIGNIFICANCE
X² Value	8.665	9.649	None
P Value	0.123	0.086	None
Mann-Whitney U Test
P value	0.936	0.575	None

Table 1 – Results of statistical tests

The Kruskal-Wallis test results in table 1 show there is no significance between observer location and abundance or Shannon Diversity of birds on the foreshore. The same can be said for the Mann-Whitney U Test results for whether tide has an effect on abundance and diversity.  Therefore we can accept the null hypothesis that observer location and tide direction have no affect on bird abundance and diversity for both instances and reject both of the working hypotheses stated in the introduction.

Discussion

                Both working hypotheses were rejected, so therefore tide and position along the foreshore of boggle hole have no affect on the abundance and diversity of birds found there. It also means that if there is more foreshore available the birds are just as abundant as they would be with little foreshore.

Many factors could have affected the abundance of birds on the day the observations were carried out. These include the weather on the day. If the weather was very bad out to sea, more animals may have come to the shore to feed and the sea would have been too dangerous for them. The weather on the foreshore may also have had an effect. If the wind was too strong, for example, the birds may have flown further inland where the weather was not as strong. The time of year could also have had an effect on results. As it was the beginning of winter, many species have flown south for the winter towards the warmer climates.

Only a very limited sample was collected from one portion of the beach over a relatively short period of time in one day. If the time was extended to a period of a week or so, a lot more data would have been collected. The same can be said if we used a longer section of beach. We could also have recorded the high and low tide times during the day, as we would then have a more accurate account of when the tide was going out and coming back in.

We could also have tested to see whether there was an increase or decrease of certain species during the day. This would have given us a more accurate result on total abundance of birds. One species in the morning may have been replaced by another in the afternoon. There may have been quite a few species, but half of them replaced by the other half in the afternoon, therefore there would have been an abundance reading of half that what was actually seen.

It is also possible that the same bird could have been recorded many times, in the same position or at different positions down the beach. So this would mean birds appeared to be more abundant when in fact it was just the same bird many times.

Reference

Gooders, J. 1995. Pocket Guide Birds of Britain And Ireland.

ENVIRONMENTAL CONSULT - MARWELL ZOO

Another university project ive had to do, is pretending to be an Environmental Consultant investigating Marwell Zoo and its suitability in terms of active conservation efforts.

A Brief History of Marwell:

Marwell Zoo covers 140 acres in Hampshire. It is situated in the estate of Marwell Hall, which was built around 1320 by Walter Woodlock. Ownership passed to the Seymour family in the 1500's and it is believed to be the place Henry VIII courted Jane Seymour. During WWII, an area of the estate was used as an airfield.

Marwell Hall

The zoo was founded by John Knowles and opened in 1972. It was one of the earliest zoos in Europe to place an emphasis on animal conservation. In 1977 a male giraffe tore a muscle and fell to the ground, unable to get up. Press suggested this occurred during mating. Attempts to help him to his feet failed and it became an international news story. He died of a heart attack. The publicity turned Marwell into a major tourist attraction when the female gave birth.

In 1999, Marwell lost all its penguins (22 African and 5 Macaroni) to Avian Malaria. Marwell was the only zoo to lose its entire colony. It was re-stocked with Humboldt penguins, which are endangered in the wild but common in captivity.

In 2003, after constructing a new enclosure for Amur leopards, a female escaped from its enclosure and fell from a tree to its death. The female was replaced and a cub born in 2005. The cub escaped from its enclosure into the male’s enclosure and was killed. On 18^th November 2007, a female Amur leopard cub was born as a result of a European Conservation Breeding Programme.

Amur Leopard (Panthera pardus orientalis) cub

Marwell Zoo is home to over 1200 animals and 235 species. They have the largest collection of ungulates in the UK.

A bit of conservation history at Marwell:

Marwell Preservation Trust was established in 1972 to manage Marwell Zoological Park. A complementary education service supporting wildlife conservation and environmental goals was subsequently developed and the Trust established a record of supporting a range of in-situ conservation initiatives. Recently, the Trust invested resources to establish and develop its own portfolio of international conservation projects. Its new identity of Marwell Wildlife seeks to address causes of extinction and manage vulnerable populations of threatened species to ensure their survival.



Current projects include:

BRITISH WILDLIFE - Marwell contributes to the conservation of biodiversity in Hampshire and the surrounding counties of southern England. Beginning with responsible stewardship of the land owned by Marwell, habitat and species restoration projects and biological surveys are undertaken and monitoring to evaluate the impacts of land management. Marwell works formally within protected areas.

SAHARA - Long term aim is to reintroduce Scimitar-Horned Oryx back into the Sahara. Marwell works with like-minded organisations and plays an active role in establishing and developing the Saharan Conservation Fund, which aims to conserve the wildlife within the Sahara and the surrounding grasslands.

Scimitar-Horned (Oryx dammah) Oryx

KENYA - The flagship for work in north Kenya is the Grevy’s Zebra, which is threatened by competition from livestock, habitat degradation and hunting. The aim is to help secure the future as part of a broader contribution to the conservation of its ecosystem. Marwell is supporting the national strategy for Grevy’s zebra conservation and the work is also supported by the Dutch Zoo Conservation Fund.

Grevy's (Equus grevyi) Zebra

ZIMBABWE - the Marwell Zimbabwe Trust (MZT) was established in 1977. it makes long-term contributions to the conservation of some of Zimbabwe’s most critical wildlife resources. It works with the Parks & Wildlife Management Authority on an agreed plan for the conservation of the country’s rhino populations. It also has a mandate to determine the population size and distribution of cheetah and to reduce human-predator conflict. An important function of the MZT is to provide opportunities for the training and development of local conservation professionals. MZT is based at Dambari Field Station near Bulawago.


In 2009, Marwell Zoo:

·         Did a review of national and international biodiversity conservation programmes.

·         Supported development of a new plan for MZT.

·         Did post-release monitoring of the addax and Scimitar-Horned Oryx in Tunisia.

·         Did ecological monitoring surveys and habitat restoration of Eelmoor Marsh SSSI in Hampshire.

·         Captive bred and released 65 sand lizards on heathlands in Dorset.

Sand Lizard (Lacerta agilis)

Environment: In 2009, Marwell used 3.5% less energy, including 5% efficiency in heating animal houses, reduced waste by 20% and increased recycling by 88%.

BIRD DIVERSITY AT WHISBY NATURE PARK

I have recently spent a day observing and identifying birds at Whisby Nature Park, Lincoln for the Conservation of Biodiversity module of my course. The point of the study was basically to see whether lakes with different characteristics have an effect on, 1) the average total count of birds observed, 2) the average species richness, 3) The average Simpson and 4) Shannon Diversity Indices.


Whisby Nature Park is a 150 hectare Local Nature Reserve made up of flooded gravel pits of different sizes and characteristics. The two lakes chosen for the study were Thorpe Lake and Grebe Lake, which are significantly different from each other. Thorpe Lake is very deep, with steep sloping sides and has an almost constant water level all year round. Grebe Lake is of varying depths with many islands and shallow margins.

Grebe Lake

Observations were carried out for 5 mintues, then a 5 minute rest period before the next 5 mintue observation period. This was done 5 times on each lake and all species seen on the water during the observation period recorded. All of the data was collected and analysed.


Results showed an obvious increase in numbers of birds on Grebe Lake with 1976 birds seen, and only 826 seen on Thorpe Lake (P=0.003). Species Richness was also greater in Grebe Lake (P=0.046) and the same can be said for the Simpson Diversity (P=0.042). Shannon Diversity showed no significant difference however (P=0.743). I'm not sure why this is. It could be that I calculated the Shannon Diversity indices wrong in the first instance, therefore effecting the results of the statistical analysis.

There are a number of bird species that favour flooded gravel pits as their general habitat, such as the Mallard (Anas platyrhynchos), Tufted Duck (Aythya fuligula), Pochard (Aythya farina), Gadwall (Anas strepera), Coot (Fulica atra), Moorhen (Gallinula chloropus), Grest-crested Grebe (Podiceps cristalus), Canada Goose (Branta Canadensis) and the Cormorant (Phalacrocorax aristotelis) in winter (Sterry 2004).

In general, Grebe Lake shows higher numbers and diversity of species. This could be due to its varying levels of depth. The shallows provide excellent feeding habitat for dabbling birds (birds that filter the first few centimetres of water) such as Shovelors (Anas strepera) and Wigeons (Anas penelope) (Guillmain, Martin & Fritz 2002).  The mid depth and deeper waters are great for diving birds such as the Tufted duck, Pochard, Goldeneye (Bucephala clangula) and Coot. The tufted duck feeds primarily on molluscs (Olney 1963), pochard usually feed on water plants such as Charophytes (Olney 1968), and the Goldeneye usual diet is pondweed (Jones & Drobney 1986), as is the Coots.


Male Tufted Duck

The mid depth waters are the perfect habitat for these species, and they were therefore seen in greater numbers than on Thorpe Lake. There is also a much greater number of Gulls at Grebe Lake, again due to the shallower water levels and the availability of food. Gulls also winter inland, and feed on human refuse (Horton, Brough & Rochard 1983). Whisby Nature Park has a visitor centre with a café so there will be refuse coming from the centre, as well as Lincoln and other town nearby with plenty of refuse.

Weather conditions should also be taken into account. It was very windy on the day the observations were carried out, and Thorpe Lake appeared to be a lot less sheltered and the water was slightly rough. Grebe Lake was more sheltered by surrounding foliage and the water appeared calmer. The ducks may have chosen the more sheltered of the two lakes on this particular day. Also, the time of year causes fluctuations in numbers due to influxes of birds from Europe (Sterry 2004) which would have effected the number observed.

The assessment could be made more accurate by doing observations at different times of day and maybe over a number of weeks or months. This would give a more accurate picture of the actual numbers of birds and the numbers of species that visit the lake. Doing the assessment over a number of weeks would give us an indication of which animals are more common on the lakes during the winter months. The assessment could be carried out at different times of year to give an example of species found throughout the year but at different times. This would give an overall greater picture of the diversity at the lakes. 

References:

Guillmain M., Martin G.R., Fritz H (2002) Feeding methods, visual fields and vigilance in dabbling ducks (Anatidae). Functional Ecology 16(4):522-529.

Horton N., Brough T., Rochard J.B.A. (1983) The Importance of Refuse Tips to Gulls Wintering in an Inland Area of South-East England. Journal of Applied Ecology 20(3):751-765.

Jones J.J., Drobney R.D. (1986) Winter Feeding Ecology of Scaup and Common Goldeneye in Michigan. The Journal of Wildlife Management 50(3):446-452.

Olney P.J.S (1963) The Food And Feeding Habitats of Tufted Duck, Aythya Fuligula. Ibis 105(1):55-62.

Olney P.J.S (1968) The food and feeding habits of the Pochard, Aythya farina. Biological Conservation 1(1):71-76.

Sterry P (2004) Collins Complete Guide to British Birds. HarperCollins Publishers Ltd. ISBN: 978-0-00-723686-2.

Jambo!

Well hello. Im Beccy. Will try not to bore you so much with what i post...not that anyone will read it really.
Will probably mainly post about uni work and campaigns etc, such as stuff from Sussex Wildlife Trust or National Trust etc...or jus other random crap that i fancy ssaying in my times of boredom. We'll see. Im very good at chatting bout useless crap! Then i gotta figure out the deal with this thing and how to post pictures....im sure ill manage.
Much love xx