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Marine Food Webs Worksheet

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Marine Food Webs Worksheet

A marine reserve team is investigating changes in a New Zealand coastal food web. Use the evidence below to trace energy, predict impacts and recommend a kaitiakitanga response. In food-web arrows, the arrow points from the food organism to the organism that eats it.

Evidence: the Ōtākou coastal food web

The organisms in this simplified South Island rocky-reef web are linked by feeding relationships. Kelp and microscopic phytoplankton use sunlight to make food. Sea urchins graze kelp; zooplankton eat phytoplankton; small fish eat zooplankton; crayfish eat smaller animals and algae; snapper eat small fish, crayfish and sea urchins; seals eat fish; and orca can prey on seals. Decomposers break down dead organisms and wastes, returning nutrients to the ecosystem. These links are simplified: diets can vary with place, age and season.

Kelp → sea urchin

Phytoplankton → zooplankton

Zooplankton → small fish

Sea urchin → snapper

Crayfish → snapper

Small fish → snapper; small fish → seal

Snapper → seal; seal → orca

Dead organisms and waste → decomposers

Investigate the web

Answer using the briefing and food-web links. Give evidence from the web where asked.

1.Which statement best describes a food web?

A single sequence showing one feeding pathway
A network of connected feeding relationships among organisms
A list of organisms that live in one habitat
A diagram of where organisms are found

2.Identify the two producers in this coastal web and explain what makes an organism a producer.

3.In the link phytoplankton → zooplankton, what does the arrow show?

Zooplankton provides energy to phytoplankton
Energy and matter move from phytoplankton to zooplankton when it is eaten
Phytoplankton hunts zooplankton
Both organisms eat each other

4.Complete this pathway from producer to top predator using organisms in the web: phytoplankton → → → → orca.

5.Snapper eats both crayfish and sea urchins. What feeding role does snapper have in relation to these organisms? Give one other organism that eats snapper.

6.A warm-water event reduces the phytoplankton population. Predict one possible effect on zooplankton and one knock-on effect further along the web. Explain the links in your reasoning.

7.Sea urchin numbers rise sharply after a predator declines. Use the web to predict a possible impact on kelp, then describe one wider consequence for the reef.

8.Match each term to its definition.

Producer
Primary consumer
Decomposer
Biodiversity

Organism that eats a producer
Organism that makes its own food
Organism that breaks down dead material and waste
Variety of living species in an area

9.A rāhui temporarily restricts gathering in part of a local coast. Explain how this could support kaitiakitanga and help a marine food web, while recognising that ecosystems are complex.

10.A survey records fewer snapper but more sea urchins. Suggest one explanation consistent with the food web and one piece of further evidence scientists should collect before concluding what caused the change.