Time To Read
Date Last Modified
Place 02 · Monterey Bay · Chapter 3 of 7
A Forest Underwater
The tallest forest in Monterey Bay has no wood, no roots and no flowers, and it can grow two feet in a day.
About 15 minutes · 1 video · 1 live kelp cam · 3 quick activities
Start here
Everything here runs on sunlight
On land, the food starts with trees and grass. In Monterey Bay, the job is split between a giant and a crowd: giant kelp, which can grow two feet in a day, and trillions of phytoplankton too small to see. Last chapter’s cold, upwelled water is their fertilizer. Every otter, sardine and humpback whale in the bay is, one bite removed or five, eating their sunlight.
Watch this
See it move
TED-Ed — The Secret Life of Plankton. Six minutes of things you have swallowed at the beach, lit and filmed like movie stars.
While you watch, look for
- What makes something plankton (it is about how it travels, not how big it is)
- Which plankton make their own food from sunlight, and which ones eat the others
- Something you did not expect. Hold onto it.
The short version
Three things going on here
The giant
Kelp is not a plant
Giant kelp is a brown alga. It grips the rock with a holdfast instead of roots, floats its fronds up to the light on little gas-filled bulbs, and can grow about 60 centimeters (two feet) in a single day. A full-grown forest can top 30 meters, taller than a ten-story building.
The crowd
Small, green and everywhere
Phytoplankton are single-celled drifters, like diatoms, that photosynthesize in the sunlit top layer. One at a time they are invisible; together they do about half of all the photosynthesis on Earth. After a week of upwelling, there are enough of them to tint the bay green.
The catch
Ten percent per step
Each time something gets eaten, only about 10% of the energy moves up a level; the rest is burned on swimming, staying warm and simply being alive. That is why the bay needs mountains of plankton to feed a few great white sharks. It is also why the biggest animal that visits the bay, the blue whale, eats near the bottom of the chain: tiny krill.
Photos: isaac mijangos, turek, Adam Ernster / Pexels
Play with it
Watch a kelp forest right now
This is a live camera inside the Monterey Bay Aquarium’s Kelp Forest exhibit: real giant kelp, 28 feet deep, growing in seawater pumped in from the bay. Watch for a few minutes and sort everything you see into producers (anything growing) and consumers (anything swimming).
Live cam: Monterey Bay Aquarium, Live Kelp Forest Cam (YouTube). If it is dark in California, you may see a replay.
Two questions to answer while you are in there
- Find one producer and one consumer. Which trophic level is each on?
- Kelp has no roots and no trunk, so what is holding those fronds up toward the light?
Try it yourself
Check yourself
Try it
Build the Summary
Pick the one true statement in each set, and the chapter summary builds itself as you go.
Try it · interactive
Energy Pyramid
Pour a million units of captured sunlight into the bottom of the bay’s food pyramid, climb it one bite at a time, then change the efficiency and see how little is left for a sea otter or a great white shark.
Open the Energy Pyramid in its own window (opens in a new tab).
Words you will hear
Four terms, that is all
Primary production
Living things making food from sunlight
Phytoplankton
Tiny drifting producers, mostly single cells
Trophic level
A step on the food chain
The 10% rule
About a tenth of energy passes up
Check your understanding
Practice the whole chapter
Everything in this chapter, in eight quick questions. Retry as often as you like. Read the feedback on every answer, right or wrong, because that is where the learning is.
Practice
Practice: A Forest Underwater
Eight questions covering the video, the three cards, the four terms and the interactive above.
If you want more
Go deeper
- Webb 7.1 and 7.2 — Primary Production, The Producers — LibreTexts · 10 minutes
- MiraCosta 13.2 — Trophic Pyramids — LibreTexts · the food pyramid and food webs · 5 minutes
- MiraCosta 15.14 — Kelp and Kelp Forests — LibreTexts · photos, very little reading · 5 minutes
Photo credits (Pexels): isaac mijangos, James Collington, turek, Adam Ernster.