Mountains under the sea

As some of my friends and family know, the last couple of weeks have been extremely eventful and emotional for me here in New Zealand but let's be honest: I've been a horrible blogger thus far. I was in Christchurch when the earthquake hit on February 22nd and while the story of my experience would probably make a good blog post of sorts, what I’d rather do is give you some resources to help the people of Christchurch and move on to something more science-like. So if you are able, and feel so compelled, please donate to the NZ Red cross to help the effort in Christchurch by clicking here.

So, on to the mountains of the sea…

If you think you can plan a trip to the world’s longest mountain range and gaze in awe at its magnificent peaks, you’re wrong. You would have trouble getting to the longest mountain range on earth, as it is in the ocean. The mid ocean ridge (MOR) extends for 80,000 kilometers (while length of continuous mountains is ~65,000 km) and runs throughout the world’s ocean. Fore reference, the earth’s circumference is roughly 40,000 km!

Here's a map from wikipedia (the pink shows the MOR system):

Like on land, the mountain ranges of the oceans (including the MOR and others) outline the planet’s subduction zones and spreading centers, where tectonic plates crash into each other or are pulled apart, dramatically destroying and creating the earth’s crust. And here’s the cool thing about the ocean, in addition to the MOR, there are thought to be hundreds of thousands of seamounts, or undersea mountains, splattered across the globe (think Jackson Pollock).

Seamounts are a hard geological feature to define (pun intended). If you ask any number of ocean scientists to do so, you are likely to get a range of answers depending on discipline. If you are going to be a serious geologist about it, an underwater feature is only a seamount if it rises more than 1,000 meters off the seafloor. However, we biologists are more likely to clump much smaller features—down to 100 meters in altitude—into the definition. I’ve discovered that in New Zealand, some of the legislation about seamounts uses this broader definition, much to the chagrin of the fishing industry. Here’s why.

Many commercially valuable deep-sea fish like orange roughy (pictured below), and oreo (yes, that's a kind of fish!) aggregate on seamounts. Because of the way the ocean currents interact with these bathymetric features, lots of the nutrients and food necessary for benthic invertebrates and pelagic fish alike to thrive are in high abundance at seamounts. It follows, then, that fisheries would target seamounts while trawling for fish, and who’s to blame them? But when we think about managing the fisheries and try to understand the effects that fishing has on the marine environment, we must consider the impact that trawling will have on the benthic habitat and the organisms within that habitat. When writing the laws, however, if one uses the broader definition of seamount, then more features will be subject to whatever regulation is being imposed, thus explaining the aversion of some fisheries advocates to the use of a more lenient definition.

Orange Roughy on a seamount (this photo was taken by one of my advisors, Malcolm Clark, from NIWA. This particular file is from 3news.co.nz):

Some people find it hard to relate to the marine environment. What’s below the low tide mark remains hidden to almost all people and many marine species continue to be eaten but never seen. Think about how many times you may have eaten fish sticks or fish and chips; now try to think about what cod or haddock look like. Can you? If that was an easy one for you, what about the deep-water coral and other benthic invertebrates often caught as bycatch? As the animals we eat remain largely mysterious, we find the environment from which they came to be virtually unimaginable.

If you decide to follow this blog as I share with you my journey as a graduate student through the world of deep-sea science, I hope that you will soon find yourself as enthralled with the deep sea as I am!

Until next time,

E