Listening Section 4: Note & Table Completion: Question 1

Transcript-based practice (no audio).

Lecturer: Good morning, everyone. Today I want to take you beneath the waves to look at one of the ocean's most productive ecosystems: the kelp forest. Kelp forests grow in cool, nutrient-rich coastal waters, in water shallow enough for sunlight to reach the seabed. The dominant species along much of the Pacific coast is giant kelp, or Macrocystis pyrifera, and it's one of the fastest-growing organisms on the planet. Under good conditions it can grow as much as fifty centimetres a day.

Structurally, a kelp forest has three distinct layers. At the surface sits the canopy, made up of broad blades that float because each one carries small, gas-filled structures called pneumatocysts. Below that is the midwater layer, formed by long, flexible stalks called stipes. And at the base, kelp doesn't have roots the way a land plant does; instead it has a holdfast, a tangled, root-like structure that anchors the organism to rock on the seafloor.

A key relationship in this ecosystem is between kelp and sea urchins. Urchins graze on kelp, and their favourite target is the holdfast, chew through enough holdfasts and an entire kelp plant simply detaches and drifts away. Left unchecked, urchin populations can strip a rocky reef completely bare, creating what ecologists call an urchin barren.

What normally keeps urchin numbers in check is a keystone predator: the sea otter. Otters eat urchins voraciously, keeping numbers low enough for kelp forests to flourish. Historically, though, otters were hunted almost to extinction along the Pacific coast because of the fur trade during the eighteenth and nineteenth centuries, and without otters, urchin barrens spread across huge stretches of coastline.

Even after otter numbers partly recovered through legal protection, kelp forests remained vulnerable to sudden shocks. A striking example occurred in 2013, when sea star populations were struck by a wasting disease that devastated another major urchin predator, the sunflower sea star. With that predator gone, urchin numbers exploded, and vast stretches of kelp forest in California and Oregon were converted to barren rock within a few years.

To reverse this, marine biologists have turned to active restoration. Teams of divers now carry out manual culling, physically removing urchins from degraded reefs to give kelp spores a chance to re-establish. It's slow work, but kelp can recover quickly once grazing pressure eases.

Finally, this matters beyond the reef itself: kelp forests are exceptionally efficient at capturing atmospheric carbon dioxide and locking it away in ocean sediments, a process researchers now call blue carbon. Protecting kelp isn't just about biodiversity. It may also help mitigate climate change.

Complete the notes below. Write NO MORE THAN TWO WORDS AND/OR A NUMBER for each answer.

Kelp Forest Ecology. Lecture Notes

Species and growth

• Dominant species: giant kelp (Macrocystis pyrifera)
• Growth rate: up to (1) ______________ per day

Structure

• Buoyant structures on the canopy blades: (2) ______________
• Anchoring structure (not a true root): (3) ______________

Grazing pressure

• Bare reef caused by unchecked grazing: an (4) ______________
• Keystone predator that controls urchins: the (5) ______________
• Historical cause of that predator's decline: the (6) ______________
• 2013 event: sea stars struck by a (7) ______________

Restoration and value

• Diver-led restoration technique: (8) ______________
• Carbon captured and stored by kelp forests: known as "(9) ______________ carbon"