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A coral reef is an underwater ecosystem formed as a ridge of mainly calcium carbonate deposits - AQA - A-Level Biology - Question 9 - 2021 - Paper 2
Question 9
A coral reef is an underwater ecosystem formed as a ridge of mainly calcium carbonate deposits. Algae are photosynthesising organisms. Some algae grow on coral reefs... show full transcript
Worked Solution & Example Answer:A coral reef is an underwater ecosystem formed as a ridge of mainly calcium carbonate deposits - AQA - A-Level Biology - Question 9 - 2021 - Paper 2
Step 1
Describe a method that could be used to determine the mean percentage cover of algae on a coral reef.
Answer
One effective method to determine the mean percentage cover of algae on a coral reef is to use a quadrat sampling technique. This involves the following steps:
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Select Random Locations: Randomly select several locations on the coral reef to ensure that the sample is representative of the area.
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Use Quadrats: At each selected location, place a quadrat of known dimensions (for example, 1m x 1m).
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Estimate Algal Cover: Within each quadrat, estimate the percentage cover of algae based on visual observation or photo-documentation. This can help quantify the algal distribution.
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Repeat: Perform this process at multiple locations to gather a large sample size of quadrat data.
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Calculate Mean: Finally, calculate the mean percentage cover of algae across all quadrat samples to obtain a comprehensive estimate.
Step 2
Explain how succession results in a wide variety of fish living on coral reefs.
Answer
Succession contributes to a wide variety of fish living on coral reefs through several mechanisms:
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Increase in Biodiversity: As the coral reef environment changes over time, it creates different habitats that can support a variety of species. Early colonizers of the reef prepare the area for subsequent species, enhancing biodiversity.
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Varied Niches: The progression of succession leads to the development of complex structures within the reef, providing a range of ecological niches. These niches offer shelter and food sources for different fish species, encouraging a diverse fish population.
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Resource Availability: With each stage of succession, the availability of resources fluctuates, leading to the establishment of various feeding relationships. Different species can exploit these resources, leading to an increase in the number of fish species supported by the reef.
Step 3
Using all the information, evaluate the effect of the two fish species on algal growth on coral reefs.
Answer
The investigation into the effect of redband parrotfish and ocean surgeonfish on algal growth reveals several significant findings:
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Significant Effect with C: The presence of the two ocean surgeonfish (C) shows a significantly lower mean percentage of algae compared to set A, suggesting that these fish are effective grazers and help reduce algal growth.
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No Significant Effect with B: In contrast, the results for the two redband parrotfish (B) show no significant decrease in algal cover, indicating that they might not have the same grazing impact as the ocean surgeonfish.
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Mixed Results with D: The combination of one redband parrotfish and one ocean surgeonfish (D) shows a P value suggesting no significant difference from the control (set A), which may indicate that the effects are not cumulative or that the presence of different species interacts in a way that mitigates the overall impact on algal growth.
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Ecological Implications: Overall, it appears that the presence of the ocean surgeonfish significantly influences algal cover, and this could have consequences for coral reef health by allowing for coral dominance over algae, which is vital for reef sustainability. Given that certain fish species play crucial roles in maintaining the balance of the reef ecosystem, understanding these dynamics is essential for conservation efforts.