Lesson 3 of 10 / Climate change, food and disease vectors
Explain changing ranges and coastal stress
Why can an ecosystem be harmed even when some organisms move?
I can explain fish and insect range shifts and climate stress on coral reefs, seagrass and mangroves.
I can explain physical climate effects, fresh-water stress, range shifts, coastal ecosystem stress and thaw feedbacks.Syllabus
Syllabus 8876, Extension A(b). Explain physical climate effects, fresh-water stress, range shifts, coastal ecosystem stress and thaw feedbacks.
About 6 min
Make a guess. You are not marked.
Sea level rises along a coast backed by a seawall. Can the mangroves simply move inland?
Show the answer
The wall blocks their landward retreat.
Mangroves need a suitable zone to shift into. A seawall removes that space, so the stand is squeezed.
The key idea
Organisms may shift towards suitable conditions, but movement is limited by habitat and life-cycle needs. Heat, altered water conditions and rising seas can stress entire coastal ecosystems.
Explore the idea
Match each habitat to a mechanism
Some fish move towards cooler waters and some insects extend into formerly cooler areas. Food, habitat, breeding sites and dispersal limit the response.
Explanation
Temperature affects metabolism, survival and reproduction. As conditions change, some fish distributions shift towards cooler waters and some insects expand polewards or to higher elevations. These are changes in distribution across time, not a claim that every individual senses a map and migrates successfully. Habitat barriers, food, breeding sites and the rate of warming can limit the response.
Corals live with zooxanthellae, photosynthetic algae in their tissue that supply most of their sugars (see the coral reefs lesson). Heat stress can disrupt this association and cause bleaching as the coral loses its partners or their pigments. A bleached coral is not necessarily already dead, but prolonged stress can reduce growth and reproduction and increase mortality, affecting other reef organisms.
Seagrasses need light for photosynthesis. Heat stress can disrupt growth, while storms, sediment disturbance and deeper water can reduce light reaching leaves. Changes in salinity or oxygen conditions can add stress. Loss of seagrass also removes shelter and feeding habitat, so an effect on one producer can spread through the community.
Mangroves tolerate coastal conditions, but they still have limits. Rapid sea-level rise, erosion, altered salinity and severe storm damage can exceed their capacity to persist. Some stands can establish further inland or accumulate sediment, but development barriers or insufficient sediment can prevent that adjustment.
Extra atmospheric CO2 also causes ocean acidification when it dissolves and changes carbonate chemistry, adding stress for reef builders. This is a related CO2 effect, not a direct consequence of warmer water alone. Avoid combining distinct mechanisms into the unsupported statement that heat itself turns the sea acidic.
Step by step
- 1
Identify the organism or habitat
Fish, insects, coral, seagrass and mangroves have different requirements.
- 2
Name the changed condition
Heat, water depth, sediment, salinity or habitat availability.
- 3
Connect to function and community
Explain effects on metabolism, photosynthesis, reproduction or habitat provision.
Worked example
Why a seagrass meadow declines
After repeated storms, water over a seagrass meadow remains more turbid. Explain a route from this change to lower seagrass growth.
One way to explain it
Suspended sediment reduces the light reaching the leaves. This can limit photosynthesis and the organic material available for growth. Reduced meadow cover can then affect animals that use it for food or shelter.
Why this answer works
- Name the limiting input: light.
- Connect a producer response to wider habitat consequences.
Watch out for this
A student says: "Species can always move to escape warming, so ecosystems do not lose organisms." What is wrong with this?
Show the answer
Suitable habitat may be inaccessible or absent, and species differ in dispersal and requirements. A range shift is a possible response, not a guarantee of persistence.
Check your understanding
Why can a seawall worsen the risk to a mangrove stand under rising sea level?
Show the answer
It may block landward establishment as the suitable coastal zone shifts.
A physical barrier can prevent adjustment even where inland habitat could otherwise become suitable.
Quick recall
Why can an ecosystem be harmed even when some organisms move?