Whale Poo and Gothenburg Natural History Museum

Hej! I'm in Gothenburg, Sweden this week, and as a Palaeobiology student naturally I made a trip to the Natural History Museum. I have to admit, I had been slightly blinded by London-centrism and forgot that, despite what the London equivalent would have you think, most museums don't require several days to walk around meaningfully. So I was a teensy bit underwhelmed by the size of this museum at first glance. But once inside, I began to see it's charm (not that it's not charming on the outside - set in a huge wooded park within the city). Gothenburg's Natural History museum has the title of holding the world's only mounted blue whale (reportedly - feel free to correct me if I'm wrong). Not only that, once I was stood in front of the thing, I could see that it was mounted on a wooded interior 'skeleton' and contained benches, accessible presumably by the hinged top of it's former skull. Now you can't see that in London.

Mounted blue whale at Gothenburg Natural History Museum. You can just about make out the two rows of blue benches inside.

The importance of whale poo

Recently there's been a lot of news coverage about UK marine megafauna and the 17 key megafauna sites that the Wildlife Trust wants protected along our coastline. (For more on this, you can read this blog post on Ocean Commocean). But what exactly is so newsworthy about these marine megafauna? These animals were fairly untouched in comparison to their contemporaries on land during the Pleistocene extinctions, but over more recent history large marine animals have suffered comparatively unnoticed, due in part to their apparently low commercial value (Lewison et al., 2004). Despite this, they have a big impact on both the marine and terrestrial environment. Whale poo even helps to slow climate change, as discussed in George Monbiot's Conservation blog last month. 

Here's what caught my attention from the post... 

Whales return to the surface to breath and defecate (Lavery et al., 2014). The faeces fertilises the surface water, known as the photic zone - where sunlight penetrates and where photosynthesising plankton live. This iron-rich faeces helps them to grow and multiply.  

In the 1970's, people who wanted more krill suggested that the decline in large whale numbers in the southern oceans would lead to an increase in krill populations. This is called the surplus-yield model (Lavery et al., 2014). They were wrong. Instead krill populations have declined steadily along with the whales. Bad for the whales, bad for the krill and bad for us. So what happened?

By feeding at depth when they dive, then defecating at the surface, the whales are transporting nutrients into the photic zone. Iron, part of the nutrient boost contained in whale poo, is a limiting factor in the southern oceans, and the phytoplankton require it to grow (Smith, 2013). The krill feed on the plankton, and so increased plankton growth supports more krill... On top of this, these photosynthesising plankton collect carbon from the atmosphere, and lock it up for thousands of years when they die and fall to the sea floor. So before their populations began to decline, it's likely whales made a small but significant contribution to the removal of carbon dioxide from the atmosphere. 

From Sciencedaily
Whales are ecosystem engineers. 

Lesson to be learned (again)?

It seems in ecology more and more often we are discovering that we have underestimated the complexity of ecological interactions, and as such our fiddling with parts of the system often results in loss on both sides.

As discussed in my post Trophic Cascades in the Cascade Mountains... , megafauna are key to ecosystem functioning . In the past, ecologists studied ecosystems and found them to be controlled by abiotic factors (climate, geology, nutrients...) rather than by biotic (living) components, such as megafauna. Modern ecology recognises the importance of living components. Large carnivores are particularly vital due to their impact on the populations and behaviour of large herbivores (Monbiot, 2014). These in turn alter the plant community structure and composition, which affects soil erosion, river movement, carbon storage and other processes. So nutrient availability, the shape of the land and atmosphere composition are powerfully affected by living system components.

It seems that the old view came about because the ecologists were studying degraded ecosystems affected by mankind. In a human-impacted system, abiotic factors increasingly rule (Monbiot, 2014). 

Ecosystem connectivity

When humans tip the balance, whales can become part of the problem we created. Roman et al. (2014) suggest that the decline in the great whales (baleen and sperm whales) triggered orcas to switch from feeding on them to seals and sea lions. Then the decline in seals due to (take a guess) human hunting in the Aleutian archipelago, near Alaska, seems to have caused the orcas to switch their diet again to sea otters. 

From seaotters.com
The effect of sea otters on the kelp forest ecosystem. Kelp forests have been described as the rainforests of the oceans. If you're interested there's more info available on the seaotters website

Sea otters, megafauna in their own right, are famous for their part in the kelp forest/ sea urchin trophic cascade disaster, with huge impacts on atmospheric carbon dioxide. 

Sea otters have been heavily hunted along North American coastlines, causing urchins to increase and kelp forests to die. Whales preying on the sea otters, which are now a focus of international conservation efforts, creates another challenge in the restoration of this ecosystem (Monbiot, 2014). 

The video below is from the Planet Earth series, showing the sea urchins in action

Ecosystems are connected more intricately than we often appreciate. This understanding can not only explain some of the mystery behind the megafaunal extinctions of the past, but also help us to understand the ecosystems we have today, and to better protect them to ensure their long time survival as well as our own.

There is so much more in the post by George Monbiot, it's 2000 words long but an easy read so I would encourage you to take a look if you're interested.