Dive Pacific 175 Dec2020 Jan 2021

animals ever to exist, blue whales.
Blue whales filter their favorite food,
krill (euphausiids) and copepods
through their large baleen plates.
During the peak of their feeding
summer months, one blue whale can
eat over 3,000 kg of krill per day.
Whales not only eat these small prey
animals, they also keep them alive…
Trophic cascades
Here is where it gets really interesting.
One of the more exciting
scientific findings in the past
half century is the discovery of
wide-spread trophic cascades. A
trophic cascade is an ecological
process starting at the top at the food
chain and tumbling all the way to the
bottom and it can involve powerful,
indirect interactions that actually
change entire ecosystems for the
good or bad, depending on what is
removed or brought back into the
system.
Wolves, for example
A famous example of a trophic
cascade is what has been
documented in Yellowstone when
wolves were reintroduced in 1995
after being locally extinct for over
70 years. Wolves not only helped
control their prey population, deer
and elk, from over populating and
overgrazing, but by keeping their
prey populations in check, the
presence helped benefit all levels of
the complex web of
life in Yellowstone.
Since wild wolves
have returned to
Yellowstone, the elk
and deer are stronger, the aspens and
willows are healthier, the grasses
taller and the beaver population is
thriving.
The same trophic cascade effects
have also been well documented in
the ocean with the comeback of the
great whales, including humpback
…Some of the large baleen whales.. release vast plumes…
rich in iron and nitrogen, nutrients that fertilize the plant
plankton at the sunlit surface…
whales, fin whales and blue whales.
Some countries have argued that
killing whales is good for us; fewer
whales mean more seafood for us to
eat. But what scientists have actually
documented was, as whale populations
declined around the world,
so did their favorite prey, small
schooling fish and krill. What was
discovered is that whales not only eat
these small prey animals, they also
keep them alive! In fact, whales help
sustain the entire living system of
the ocean.
Spreading fertilizer
When some of the large baleen
whales, such as blue whales which
feed on krill at the darker depths,
rise to the surface, they release
vast amounts of fecal matter. These
plumes are rich in iron and nitrogen,
distributing nutrients that are generally
scarce in surface waters. These
nutrients fertilize the plant plankton
in the only place where plant
plankton can survive; in the sunlit
waters at the surface.
Fertilizing the surface waters is not
the only thing these whales do. By
Main Photo credit: Chuck Graham, @chuckgrahamphoto
18 Dive New Zealand | Dive Pacific