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Marine Environment Impacts Worksheet

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Marine Environment Impacts Worksheet

Explore how human activities and changing conditions affect marine ecosystems. Read the field briefing, then answer each question. For written answers, use evidence from the briefing or your science knowledge.

Coastal Field Briefing

A marine team is monitoring a bay in Aotearoa New Zealand. After heavy rain, fertiliser and animal waste wash from land into streams and then the sea. Extra nutrients can fuel algal blooms. When algae die, decomposers use oxygen as they break them down; oxygen may fall so low that fish and shellfish struggle to survive. Plastic rubbish can entangle animals or be mistaken for food. At the same time, carbon dioxide from human activities dissolves into seawater and lowers its pH, making the water more acidic. This can make it harder for some shell-forming organisms to build and maintain shells. Sunlight becomes weaker with depth, so most photosynthesis by marine plants happens near the surface. Currents move water, heat and nutrients, and can help animals travel between feeding and breeding areas.

Investigate the Impacts

1.Which chain of events best explains how runoff can create a low-oxygen area in the bay?

Runoff adds nutrients → algae grow rapidly → decomposers break down dead algae and use oxygen
Runoff adds plastic → sunlight increases → oxygen disappears
Runoff adds nutrients → currents stop → fish use all the oxygen

2.The team measures seawater pH before and after a rise in dissolved carbon dioxide. Predict the direction of the pH change and explain what it means for shell-forming organisms.

3.Select every marine condition from this list that can affect where organisms live: light availability, salinity, oxygen level, pH, water temperature.

Light availability
Salinity
Oxygen level
pH
Water temperature

4.Plastic pollution can harm marine animals in more than one way. Name two different ways and briefly explain each.

5.Complete the statement: As depth increases, light generally .

6.Complete the statement: Most marine plant photosynthesis occurs nearer the .

7.Complete the statement: Currents can transport heat and .

8.A fishing fleet catches many large predatory fish. Describe one possible change this could cause elsewhere in the food web.

9.An algal bloom is followed by dead fish. Give the most likely connection between these observations, and suggest one practical action that could reduce the chance of future blooms.

10.A class wants to test how salinity affects a small marine organism in a safe, supervised investigation. State a testable hypothesis, one factor to change, two conditions to keep the same, and one measurement to record. Do not suggest releasing organisms or changing their habitat.