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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 1
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 1
Step 1
Describe a method that could be used to determine the mean percentage cover of algae on a coral reef.
Answer
A suitable method to determine the mean percentage cover of algae on a coral reef would be to use a random sampling technique. This involves the following steps:
- Determine Sampling Locations: Use a random number generator to select various grid positions on a map of the coral reef.
- Collect Data: At each random position, establish quadrats of a fixed size (e.g., 0.25 m²) to assess the algae cover.
- Calculate Percentage Cover: For each quadrat, visually estimate the percentage of the area covered by algae. Then, calculate the mean percentage cover by summing the individual percentage covers from all quadrats and dividing by the total number of quadrats sampled.
Step 2
Explain how succession results in a wide variety of fish living on coral reefs.
Answer
Succession on coral reefs leads to a wide variety of fish living there due to several interrelated factors:
- Increase in Biodiversity: The process of succession increases the diversity of species and habitats available. As different algal species occupy the reef, they create niches that various fish species can exploit.
- Habitat Complexity: The structural complexity provided by the growing algae and other organisms offers more shelter and food sources. This variety supports different feeding strategies and lifestyles among fish.
- Resource Availability: As the algal cover evolves, it can support different groups of herbivores, which in turn attracts higher trophic levels, leading to a rich and diverse fish community.
Step 3
Evaluate the effect of the two fish species on algal growth on coral reefs.
Answer
The evaluation of the effect of the two fish species on algal growth reveals a complex interaction:
- Statistical Evidence: The P values from the study indicate that the presence of the ocean surgeonfish (set C) significantly decreases algal growth, as shown by the P value of <0.001. This suggests that the reduction in algal cover is unlikely to be due to chance.
- Comparative Analysis: Although the redband parrotfish (set D) did not show significant differences compared with control set A (P = 0.634), there is no strong evidence to conclude that this species has a notable effect on algal levels. Set B with two redband parrotfish also shows a P value of 0.841, indicating no significant impact.
- Broad Assessment: Overall, the data suggest that while the ocean surgeonfish plays a crucial role in controlling algal growth through grazing, the other species do not similarly affect the algal cover. This indicates a complex dynamic in marine ecosystems where specific species have more pronounced effects on community composition.