Oceanography 10, T. James Noyes, El Camino College
10E-1
Kelp Forests
The Biology of Kelp
Kelp are one example of the many varieties of macroalgae (“large
algae”), better known as seaweeds. Species of kelp grow larger than
any other macroalgae, creating huge undersea “forests” close to
the shoreline. They stretch up towards the sunlit surface using
pneumatocysts, carbon-dioxide-filled bladders, helping their blades
to carry out photosynthesis. Kelp keep themselves from being
pushed onto beaches or drifting off into the ocean where there are
few nutrients by anchoring themselves to the bottom with large rocks
using a structure called a holdfast. As with all algae, kelp need
nutrients for photosynthesis. Kelp absorb nutrients directly out of the
ocean water. The blades, pneumatocysts, and holdfast are connected
by a long, flexible stipe which can reach lengths of 100 feet (30
meters) or more.
Blades
Pneumatocysts
Stipe
Holdfast
Rocks
Pneumatocysts
Kelp Forest. Courtesy of Kip Evans, Channel Islands National
Marine Sanctuary, National Oceanic and Atmospheric Administration
Pneumatocysts
Pneumatocysts. NOAA.
Oceanography 10, T. James Noyes, El Camino College
As with all algae, kelp need sunlight and nutrients to make
their own food via photosynthesis. In addition, kelp prefer
living in cold water. Their spores (reproductive cells)
cannot survive in warm water, perhaps because there tends
to be fewer nutrients since waves have difficulty bringing
nutrients up from below if the surface water is too warm
(the deeper, colder water resists coming up and sinks back
down later due to its higher density). As noted above, kelp
need a rocky bottom to hold themselves in place. Waves
and currents are desirable for bringing nutrients into the
kelp forest, but if they are too strong, they may break the
stipe of the kelp or tear it loose from the bottom. Even if
this happens, kelp can grow back amazingly fast. Under
good conditions kelp can grow over 2 feet per day!
10E-2
Kelp Holdfast. Courtesy of Shane
Anderson. Channel Islands National
Marine Sanctuary, NOAA.
Pneumatocysts
Holdfast
The kelp’s holdfast (which grabs onto the rocks) is not “roots,” because it does not absorb
nutrients from the rocks or the water. However, the holdfast does host special blades
which produce spores (for reproduction).
Kelp have a fascinating and complicated method of reproduction. Kelp produce male and
female spores which grow into small male and female “gametophytes” on the ocean
bottom. The male gametophytes release “antherozoids” (like sperm) that fertilize the
eggs of the female gametophytes. The eggs are then released as plankton. If an egg
settles in a good spot, it can grow into a huge algae.
Oceanography 10, T. James Noyes, El Camino College
10E-3
Benefits of Kelp and Kelp Forests
Kelp is used for a variety of purposes. Of course, people eat
kelp (e.g., sushi). Kelp is also used as fertilizer for crops on
land (It is rich in nutrients absorbed from the ocean water.)
and to make feed for livestock like cows, chickens, and
pigs. In addition, kelp byproducts like algin are found in ice
cream (makes it smooth by keeping ice crystals from
forming), cosmetics (it keeps moisturizers moist and creamy
and keeps them from becoming solid over time), and beer
Yummy kelp.
(keeps it foamy). Algin from kelp helps keep toothpaste
thick (not too “runny”) and yogurt creamy
(not too solid). Moreover, kelp is
particularly good at absorbing iodine from
ocean water 1, an element which we need in
small amounts (to avoid growing a goiter,
an enlargement of the thyroid found in your
neck, and prevent mental retardation in
growing children) and is used in antiseptics
and other pharmaceuticals. To harvest kelp
for all these uses and more, the top few feet
of kelp forests are “mowed” periodically.
In the past, large amounts of kelp were
burned, because the resulting ash is rich in
soda (sodium carbonate) and potash
(potassium carbonate). These ingredients
were needed to make glass and soap.
1
Most of the world’s iodine is dissolved in ocean water. All organisms, not just us, need a little bit of iodine, and
kelp help iodine to get into the marine food chain.
Oceanography 10, T. James Noyes, El Camino College
10E-4
Fish of the Kelp Forest. National Oceanic and Atmospheric Administration.
Right: Garibaldi. Channel Islands National Marine Sanctuary, NOAA.
Kelp forests are home to a wide variety of algae and animals, many of which we catch for food
and other uses. However, few animals eat living kelp. Some simply use the forest as a place to
hide, but many are there because of another food source. Kelp like to live in cold, nutrient-rich
upwelling zones, the same environment preferred by phytoplankton. Many animals live on the
kelp, using it as a way to stay close to shore in the nutrient-rich waters where phytoplankton (and
small zooplankton attracted to them) are most abundant. The classic example is bryozoans, tiny
“moss animals” that resemble sea anemones and form the white “splotches” that you often find
on kelp that has washed ashore. Presumably many small animals find it easier to dine on small
plankton than chew through thick, tough kelp. However, once waves break kelp free from the
bottom and the kelp begins to decompose (“break down”), many organisms find it a bit tastier.
Just think of all the “sand fleas” that one can see hopping around dead kelp washed up on the
beach. Kelp detritus (dead, decaying kelp) is an important food source for many ocean
organisms.
bryozoans
on a
kelp
blade
Bryozoans on a Kelp Blade. USGS.
Ghost Forests
Bryozoan. Courtesy of
The Alpha Wolf (CC BY-SA 3.0).
If you look at old pictures of ocean life from California’s kelp forests, they show a variety of
organisms (particularly large fish or tasty shellfish) that are rarely, if ever, seen anymore. Kelp
forests host a lot of life now, but they use to have a lot more life. Given that regular monitoring
only started within the last few decades, we probably do not even know what “normal”
conditions are. Sadly, the latest generation of scuba divers and marine biologists may not even
realize what they are missing. For this reason, many environmentalists have taken to calling our
kelp forests “ghost forests,” ecosystems where some parts of the food web are only occupied by
“ghosts” – for those who can see.
Oceanography 10, T. James Noyes, El Camino College
10E-5
“The damage is so pervasive that it may be impossible ever to know or reconstruct the ecosystem. In fact,
each succeeding generation of biologists has markedly different expectations of what is natural, because
they study increasingly altered systems that bear less and less resemblance to the former, pre-exploitation
version. This loss of perspective is accompanied by fewer direct human experiences (or even memories)
of once undisturbed systems.”
− Dr. Paul Dayton, Marine Ecologist (1998)
(Dr. Dayton has monitored California’s kelp forests for over 25 years.)
Urchin Barrens
Sea urchins are one of the few animals that eat live kelp. Typically, they are happy to catch and
eat kelp detritus (dead, decaying kelp that waves have broken loose), but if there is not enough
food drifting in the water, they will search out live kelp to dine on. Since sea urchins are benthic
animals (bottom dwellers), they attack the kelp holdfast first, which causes the entire kelp to
break free and die. Under certain circumstances, sea urchins can eat nearly all the kelp in a kelp
forest, thus destroying it: the resulting empty spot on ocean bottom where a kelp forest once
stood is called an urchin barren. Little life remains afterwards, because all the animals that
depend on the kelp leave or die. The sea urchin population also collapses, because they are left
with little kelp to eat. The few remaining sea urchins will keep the kelp forest from growing back
again until they are eliminated from the area, typically by disease. Fortunately, kelp can grow
back relatively quickly once the urchins are eliminated and the forest can be restored.
Sea urchins can eat up a kelp forest if they can eat the kelp faster than it can grow. This can
happen if the water becomes too warm (kelp cannot reproduce) or if the sea urchin population
grows too large (which can happen if the animals that eat the sea urchins are removed).
Sea Urchins. Right: Courtesy of Greg Burton.
Animals that Eat Sea Urchins: Sheephead and Sea Otter. Notice the sea urchin in the sea otter’s paws.
Left: Channel Islands National Marine Sanctuary, NOAA. Right: NOAA
Oceanography 10, T. James Noyes, El Camino College
10E-6
Marine Reserves
A solution to the overfishing problem that is growing in popularity is marine reserves. For
example, inspired by a nature film, President George W. Bush created a huge marine reserve
north of the Hawaiian Islands (2006). The essential idea behind marine reserves is that no
animals can be harvested from the reserve (they are “no fishing” zones). Free from fishing, the
populations of the animals inside the reserve will grow, and when they outgrow the reserve,
fish and other animals will have to leave the reserve to find food and other resources. Once
they are outside the reserve, fishermen can catch as many as they like. The beauty of the idea
is that no matter how many animals fishermen take outside the reserve, there will always be a
population inside the reserve to reproduce the next generation. Therefore, fishermen can never
accidentally “overfish.” If natural changes in the environment cause the population to go
down, then the fishermen will catch fewer fish, but the population will rebound inside the
reserve once the environment improves and so will the fishermen’s catch outside the reserve.
Thus, fishermen’s catch will go up and down with natural cycles. Marine reserves may seem
like a good idea, but there are problems. Often the best places for reserves are the best fishing
spots, so immediately after the reserves are put in place, fishermen will catch few fish and their
incomes drop until the population inside the reserves grows large enough for fish to “spill”
over the boundaries. Dozens of studies of marine reserves have shown that this can happen
remarkably quickly (within a few years in some cases, but this is still a long time for fishermen
to be out of work). Since 1999, California has been trying to institute a system of marine
reserves called “marine protected areas” (MPAs). Talks were stalled for many years, but
thanks in part to leadership by then-Governor Schwarzenegger, no fishing is allowed along
10% of the central coast 2 of California (from Santa Barbara to Santa Cruz), and fishing is
restricted along another 10% of the central coast. California’s recreational fishermen tend to
be in favor of the reserves, hoping that they will bring back some rare species, but commercial
fishermen remain skeptical for the most part, claiming that pollution from coastal cities and
agriculture are the real reason for fish declines, not overfishing. In December 2010, the MPAs
for Southern California were finalized; they restrict fishing along about 16.5% of our coast.
Stay tuned, because the next decade should help us determine if marine protected areas could
be an important part of the solution to California’s overfishing problem.
At First:
No g
in
F is h
2
Later:
No g
in
F is h
This is the easiest place to agree on, because it is the part of California where the fewest people live and fish.
The system consists of 29 reserves, only half of which ban all fishing.