Module: MST2006 Semester/Year: Semester 1 & 2 2012/13
Mean Mark: 52.3% Maximum Mark: 70.5% Minimum Mark: 18%
Grade Distribution:1st 1.6% 2.1 19% 2.2 47% 3 25% Fail 7.8%
Average Attendance Across the Module: 72% class mean attendance rate ; mean attendance rate of students who failed exam = 55%
Feedback on Exam Strategies:
Part A Question 1 Number of Attempts:
Write short notes on the movement of sediment in sand dune systems
The question required you to present notes on the movement of sediment IN sand dune systems. The majority of you wrote good notes on the movement of sediment into the system with regards to accretion and movement of sediment out of the system in terms of erosion. In addition lots of answers covered succession and detailed different types of dune within the system. Unfortunately, this did not address the question, which required you to detail how sediment is moved (saltation, creeping etc). You were also expected to comment on the factors responsible for the movement of sediment in the system. The number of answers that used the term Aeolian was very disappointing. You are now at Stage 2 and should be using the scientific terms rather than generic terms.
Briefly discuss the use of abundance scores on intertidal rocky shores.
The question was asking you how abundance scores could be used on intertidal rocky shores. Most students recognised that the simplest forms of abundance scores use an indication of relative abundance such as Abundant (A), Common (C), Frequent (F), Occasional (O), Rare (R). Some answers highlighted that different levels of abundance might require different measures, such percentage cover. The key to the question was how abundance scores might be used and good answers indicated that the use of these in producing kite diagrams can show how relative abundance changes in relation to height on the shore, shore profile and substratum type (e.g. rock; rock pools, sand patches).
Write short notes on the principal algal species found in estuaries
Many answers were fairly comprehensive but some omitted to include microalgae (principally epipsammic diatoms). Students should have recognised, and many of you did that it is principally the green algae (Chlorophyta) that are represented whilst it is acceptable to use gut weed and sea lettuce a good answer should have identified Ulva intestinalis and U. lactuca respectively (it should become normal practice to use scientific names). Of the brown algae (Phaeophyceae) Fucus ceranoides is likely to be the most common representative, as this species is typically estuarine, although F. vesiculosus may be found and some answers recognised this. In a few answers, nutrient input was recognised as affecting algal abundance.
green macroaglae and some brown algae that are present in estuarues
Part C Number of Attempts:
Name three characteristics of fish stocks which are impacted by fishing, and briefly describe the ways in which they are changed. How might this affect breeding success?
On the whole, this question was answered well by most students who attempted it. The question was looking for: the (mean) biomass, (mean) size and (mean) age of stocks are impacted by fishing. In each case these characteristics are reduced as a result of fishing, and the answer should have briefly described how. Selective size fishing can change sex ratios if there is sexual dimorphism in a species with either the male or female being larger; by consistently selecting larger fish, the stock on the whole will be smaller, and smaller females produce on average fewer eggs, thus reducing fecundity and reducing egg output; by selecting a particular size over long periods of time, the genetic variability of a stock can be altered, with the genes for larger adult size at a given age being selected out – this reinforces the effect of size reduction in a stock. Marks were lost if 3 characteristics of fish stocks were not stated, if the answer did not explain how they are changed, and if the answer did not explain how they affect breeding success. Marks were lost if there was confusion or incomplete understanding demonstrated i.e. you won’t get away with waffling some terms that are ‘sort of’ relevant.
How does biodeposition affect the benthic macrofaunal community below aquaculture sites?
Again the majority of students answered this question well. Biodeposition causes accumulation of organic matter, increases nutrient loading (nitrogen and carbon build up) and biological oxygen demand. The macrofaunal community is altered, biodiversity is reduced, biomass is elevated and opportunistic species dominate. Marks were lost if the student did not give a complete answer, or if the answer displayed confusing, erroneous statements. Very good answers gave detail and specifics. Some students included some good material on the background to aquaculture, how it’s globally on the increase and other such material which cannot receive marks in a ‘tight’ short question such as this, as it is not relevant to the question set.
Write a short essay entitled ‘Predator-Prey interactions are a key component in determining the abundance and distribution of marine organisms.’ First off, I was expecting that students should recognise that the distributions of marine organisms are in the main governed by a combination of abiotic and biotic factors.
Predator-prey interactions are one of many biotic interactions, such as competition and larval supply/settlement etc all of which can contribute to the patterns of species distribution and community structure we observe in the marine environment. This question also allowed for good students to provide evidence to counter this statement if they felt that perhaps predator-prey interactions were not key in determining abundances and distributions. Can an argument be made for physiological tolerances and/or physical characteristics of the habitat being of more importance? None of you chose to take a broader approach like this which would have highlighted you deeper understanding of the topic.
Examples provided in course are based around the rocky intertidal but students should, in their wider reading, be able to provide evidence for the role of predator-prey interactions shaping community structure and species distributions in other habitats, i.e. coral reefs, estuarine sediments. Very few students provided any evidence of reading beyond their lecture notes, which was disappointing.
Those answers given low marks showed a distinct lack of understanding of the topic and provided very superficial answers, making unsupported statements and making only brief reference to case studies from the lectures often with factual inaccuracies. Several of you answered using rocky shore references that related to how predator-prey interactions can bring about morphological variation; this is not what the question asked you to discuss, so no marks were awarded even though several students spent a good deal of page length describing these relationships in detail.
Overall the marks for this question reflected an average performance on the whole with too many students still relying solely on lecture material and not providing evidence of additional study to support their arguments.
Part B – essay style questions
Write a short essay entitled ‘The role of disturbance in the regulation of marine benthic community structure.’ One excellent answer received a mark of 80% - the student defined Disturbance accurately and gave the White and Pickett reference for this. They introduced the essay well, over-viewing the ranges and types of marine disturbance. They distinguished between natural and anthropogenic disturbance.
They cited a total of relevant 17 papers, all cited accurately and some had lots of detail showing they had read that particular paper in depth. They gave the classic ‘paradigm’ papers for marine disturbance (e.g. Dayton, Sousa), but also some much more recent papers (2010-2012). Of the papers cited that I cited myself in lectures, the student gave some further detail demonstrating that they had read the paper themselves. There were also other references that I had not given in the lecture. There were no errors or inaccuracies.
The student covered much of the major consequences of disturbance: changes in biomass, abundance, species richness, changes in mean size within a population, the significance of temporal frequency of disturbance events to the resulting community, how it influences competitive interactions and outcomes, the degree to which size and location of bare space created influences subsequent re-colonisation rates and the types of colonisers possible etc., with clear examples. She brought in material from other modules (e.g. MST2004) but ensured that the case studies were linked appropriately to the question title and were not merely shoved in. The essay was well structured, and was not rambling in a disjointed way. She drew Connell’s IDH graph and gave a reference, but did not get time to describe it.
Many other students answered this adequately-to-well, with most failing to provide references for points made. Saying “ a study showed….” , “ a study in Chile demonstrated….” is not sufficient. Statements such as this one referring to benthic disturbances created by feeding dugongs and stingrays: “since they are completely natural, organisms are able to withstand them easily” shows poor understanding and loses marks. Some students gave a wholly inaccurate definition of Disturbance. You are strongly advised to read primary literature a lot more.
Part C Data Question.
Part ai) required you to compare Kinney & Valiela’s data to Turner’s. You were not required to evaluate whether or not the two data sets were comparable. Ensure you read the question and know what is required of you rather than going off-topic. Good answers presented a comparison between the low marsh and high marks from Kinney & Valiela’s data to the one data set from Turner. Better answers compared data at the different levels of fertilisation and highlighted key differences between the two studies.
Part aii) required you to comment on the significance of the data. You were presented with two ANOVA values in the heading of Table 1. You were not required to calculate any averages or variance to try and determine significance yourself. Good answers stated that there was no significant difference, while the best answers presented the outcomes of the two ANOVA analyses. Marks were lost in this question due to incorrect interpretation of the ANOVAs. You have all completed MST2015 so should now know that a P-value < 0.05 is significant, while a P-value less than 0.05 is not significant.
Part bi) required you to compare the 15N values for the fertilised treatments to the controls. Many answers only compared the fertilised treatments to each other and failed to describe the controls. Good answers did compare the fertilised treatments to the controls, while the best answers commented on the nature of the relationships and compared those between the treatments and controls.
Part bii) required you to compare fertilisation in the high marsh with the low marsh. Good answers stated which part of the marsh had the higher fertilisation level, while the best answers presented quantitative detail on how the fertilisation levels differed between the two areas. They also commented on the trend over the time period.
Part ci) required you to calculate average abundance of Spartina shoots and present with variance. You were expected to calculate median ± range as you had discontinuous count data. Many of you calculated mean and presented with range instead of standard deviation. Where this occurred marks were awarded for the correct calculation of range.
Part cii) required you to describe the effect of fertilisation on vegetation abundance in the high and low marsh. Good answers described the difference between the two areas of marsh. Better answers described the difference between the different treatment levels for both the high and low marsh. You were not expected to explain reasons for your findings, which many of you did, so again ensure you read the question so you know what is required in the answer.
Aside from part aii) you did not have any data to allow you to comment on the significance of the data. Many of you often referred to significant differences between treatments/marsh areas when describing patterns. If you have not conducted a statistical test you cannot discuss whether your data are significant or not.