Total Pageviews

Tuesday, September 20, 2011

Whale Poo

It turns out that Whale Poo# is vital to the ecology of the oceans.  Or at least it was when we had plenty of whales.  The lack thereof may explain part of the decline of our world fisheries.  I am not arguing against the devastating effect of our overfishing.  I'm not arguing against the destructiveness of our fishing methods.  They too are clearly trashing our fish resources but, with lots of whales, the amount of fish we could take sustainably would increase.

#Also see New Scientist, 9 July 2011,p36

It turns out that whales pump nutrients from deep water and urinate and defecate them into surface waters.  Even better, whale defecation is floculant and tends to float in surface waters where it powers the surface ecology.  You probably immediately thought of Sperm Whales who eat giant squid from great depths but some of the baleen whales also pump nutrients.  For instance Gray Whales skim the sea bottom collecting bottom organisms and mud.  They filter out the mud through their coarse baleen.  Humpbacks herd shoals of fish and Krill to the surface where they can trap them against the surface to feed on them.  It has been found that Krill, in contrast to what was once thought, often are also found at great depths feeding on the bottom.  Undoubtedly, as we learn more about these animals we will find more about how they bring nutrients to the photic zone.

Moreover, whales are part of the trapping of nutrients in surface layers.  Let me digress for a moment.

There is often confusion between the observed biomass and the biodiversity of an environment on the one hand and the amount of  sustainable harvesting which is possible on the other.  The first people who looked at tropical forests and tropical coral reefs saw a huge biomass of animals and an astonishing diversity of animals and plants. It was fairly natural to assume that one could harvest huge quantities of food and other valuable resources from both.  Unfortunately, the large biomass relates more to the ability of these environments to hold and recycle nutrients within their ecological system.  The incredible diversity of species is partially related to how long they have been stable ecological regimes with huge spans of time for diversity to occur.    In the Amazon jungles, for instance, the huge area covered by jungle obtains its nutrients from the weathering of the Andes mountains to the West and from dust blown from the Sahara desert.  When parts of the jungle are cleared and farmed, it has been found that after a couple of crops, the soil is exhausted.  Similarly, coral reefs when heavily fished are soon exhausted.  Coral reefs exist in very nutrient poor water.  In fact, they can only live in very clear and hence nutrient poor water.    Coral polyps contain zoozanthellae, a type of algae, and they need sunshine to live.  Corals polyps have evolved to grow in very poor waters by evolving a symbiotic relationship with internally contained algae and  now can not grow in rich, algae filled water as their symbiotic algae will not get enough light.  Not a lot of nutrient enters the coral environments and so not much food can be sustainably removed.

Compare this with any of the upwelling environments off desert coasts such as the coast of Peru or the coast of South West Africa.  There, nutrient rich water wells up from below and the productivity and harvestability is astounding.  Much of the fish meal for the world, for instance, comes from the anchovy off the coast of Peru.  The species diversity is nowhere as great as on a coral reef or in a jungle but the productivity and hence the amount that can be sustainably harvested is huge. 

So back to the whales.  There are two factors that lead to huge biomass in an environment.  As we have seen one is the influx of nutrients and the second is the ability to hold these nutrients in the system.  If you only had phytoplankton and krill in a region, the krill would  eat the phytoplankton and new phytoplankton would grow at a rate that depended on the amount of nutrient coming from outside of the environment.  Feces and dead krill would sink to the bottom of the ocean and nutrients would be lost from the surface.

The ultimate limiting factor in the growth of algae is the amount of sunshine falling on the water.  With an unlimited supply of nutrients in the water, the maximum amount of  sun energy can be used.  However, as nutrients are depleted, the total productivity is limited by the nutrients left in the system**.  In oligotrophic environments, productivity is very low despite the amount of sunshine falling on the water.  Whales, feeding on the surface, are  continually  mineralizing* the krill and excreting nutrients in a form that can be taken up by the algae.  More sun energy is being used and nutrients are being fixed into whale biomass.  Krill grow at a huge rate, fed by the huge primary productivity.  Nutrients entering the system are captured and kept at the surface.    This is a very simplistic painting of the picture.  There are many many other parts to the web of life that capture and use feces from all the surface organisms and mineralize them and all of them conspire to keep nutrients in the photic zone.  Add to this the  upwelling and the nutrient pumping due to the whales and productivity can be truly astounding.  So, whales not only pump nutrients from below the photic zone but contribute to keeping the nutrients within the photic zone.

*Mineralization:  The break down of proteins, sugars, starches etc into a form in which algae can utilize them.
** The law of the minumum which states that the growth rate of an organism (or a system) is proportional to the input which is smallest in comparison with the amount just needed for unlimited growth.

The law of the Minimum Resource

Widening out our horizon a little, the same idea holds true in the ocean when looking at the productivity of an area.  Water is no problem as growth is in water.  Nutrients can be present in larger or smaller quantities depending on upwelling, biological activity and so forth.  The ultimate limit over which we have not control is sunshine.  It powers the bottom layer of productivity, the phytoplankton, and determines the maximum productivity that can occur.  When looking at a fisheries such as the Anchovy off Peru, it is interesting to note that anchovy are at the third trophic level.  They eat zooplankton that in turn eats phytoplankton.  The total productivity of Anchovy is therefore only about 1% of the productivity of phytoplankton#.

#as a rule of thumb, 10% of the biomass of any trophic level is passed on to the next level.  100kg of phytoplankton makes 10kg of zooplankton which makes 1kg of penguin which makes 0.1kg of sea lion.

The bottom line is that with their dual function of bringing nutrients from below the photic zone and of keeping the nutrients at the surface, whales greatly enrich the environment for the growth of other organisms, some of which are commercially exploitable fish. 

Another aspect of the story involves where whales go to give birth.  This is generally in tropical waters such as around our Pacific Islands or in the Gulf of California.  The adult whales for the most part do not feed there but they nurse their young and the young poop nutrients out into the water.  By killing whales we are robbing people in these tropical waters of their source of food.

To anyone that doesn't buy the argument that we should not kill whales because they are such magnificent animals or because they are good for tourism, perhaps this is a more hard nosed argument for leaving them alone.  Whales increase the productivity of fish.


1 comment:

Anonymous said...

William, I have never for a moment even thought about whale poo - how fascinating.