Deep Sea 101: Introduction and What Is the Deep Sea?

This semester I am teaching a full on lecture course in Deep Sea Biology at my institution. It is a great opportunity for me and am very thankful that I can be at an institution that would enthusiastically give a PhD student this opportunity to freely develop this course how I wish. I am 2 weeks in and decided that all the work I am putting into my lectures should be shared with the world! The lectures in the Deep Sea 101 series will be rewritten into manageable blog units instead of posting my slides which I feel need a bit more context. The class is aimed at senior level undergraduates with a background in basic biology and ecology, hence this series will be written as such. I will try to have each new lecture up on Wednesday each week, but make no promises.

This series will be divided into 5 sections:

  1. History of Deep-Sea Exploration and Changing Paradigms
  2. Processed Operating at Ocean Scale Affecting the Deep
  3. Adaptations and Patterns
  4. Diversity of Deep Sea Habitats
  5. The Human – Ocean Relationship

Throughout this series I hope the reader can develop a scientific appreciation for the ocean, understand the value of interdiscplinary science, demonstrate an understanding of the human – ocean interaction and get more comfortable with the scientific literature and how scientists present data. To guide your exploration of the Deep, we are using Tony Koslow’s The Silent Deep, selected chapters from Gage & Tyler’s Deep Sea Biology (1992), and papers from the popular and academic literature. You should enjoy Silent Deep, it is a very readable, nicely produced and illustrated book. It reads like a book, not a text is very affordable, a bargain for its price! (I plan on reviewing it from an instructor’s perspective at the end of the semester). We will also be using review articles from Oceanography, which provide typically well-laid out, well illustrated and readable topical issues written by scientists.

Most people’s conceptions of the deep sea are from Disney cartoons.

What is the deep sea? Opinions differ but the ramifications matter. Older definitions define the deep-sea as less than 200 or 400 meters, sometimes less than 1000 meters. Much of our affect on the deep-sea occurs within the first 1000 meters of the water column. But the average depth of the ocean just less than 4,000 meters so we are even barely aware of the extent of our impact.

Maybe to you the deep-sea means scary, sharp-teeth laden fish like the anglers or bioluminescent creatures and odd jellyfish. You may have heard about the real sexy habitats like hydrothermal vents or deep-sea coral reefs. But you will probably be most surprised to know that the seafloor looks like mud (see left). Occasionally there is a little stick of a sponge, lonely in the abyss. Perhaps a tripod fish moping about. Not much that appears to be going on. Just an endless expense of mud for as far as the walleye can see.

And you would be dead wrong. The muddy seafloor is alive with thousand strong armies of sea pigs on the march, millions of small worms burrowing about, or a wide variety of fish coming and going following ephemeral traces of food. The deep sea is the largest environment on the planet and is extremely variable in both time and space at any given point. The diversity and uniqueness of the deep sea fauna and the variety of deep-sea habitats rivals that of many terrestrial habitats, which we will touch on later in the series.

The ocean is characterized by distinct zones, the transitions of which are marked by thermal or pressure interfaces. In the diagram to the right you can see that the majority of the biomass in a water column occurs in the first 200 meters where the temperatures are still warmer and light penetrates through the water. But as light get filtered out, the temperatures shorten, very little biomass exists in the water column, an area referred to as the twilight zone. It is also one of the least explored and understand parts of our planet. As we approach the seafloor there is more biomass, but it appears to never accumulate so much to even begin to rival the amount of life at the surface. Part of this may be our lack of understanding of what happens in sediment communities. Traditionally we study the things we can see on top of the seafloor and have paid little attention to the infaunal community, those animals that lives among the sediment grains.

Distribution of habitats in the deep sea.

Our understanding of the deep sea is a case study in how technology allows us to peer even closer at every step. We are limited by our own imagination to conceive of devices that will carry us to the bottom of the ocean. Only once have humans gazed at the seafloor near the deepest point in the ocean – the Marianas Trench. A point known as Challenger Deep, in honor of the vessel that paved the way for large-scale, hypothesis-driven oceanographic science. Technology has allowed us to discard a paradigm of a uniform seafloor devoid of life, with few interesting topographic features or geologic history. Instead, with the onset of sonar technology and improved sampling techniques and devices, we’ve discovered an environment with a wide variety of seafloor features from submarine canyons and underwater mountain ranges to abyssal plains and deep trenches. The seafloor is littered with habitats (see left) and our pace of discovery in deep-sea shows no signs of slowing down.

NEXT WEEK: Lessons from the Census of Marine Life

Kevin Zelnio (870 Posts)

24 Replies to “Deep Sea 101: Introduction and What Is the Deep Sea?”

  1. GREAT idea, Kevin (both teaching this class and posting the topics on DSN). I’m jealous that you get to design your own course, and I can’t wait for the rest of it!

    Does your history unit include Agassiz’s belief that creationism wasn’t false because extinction didn’t happen because trilobites are alive in the deep sea? That might be my favorite history-of-science story.

    Also, perdy pictures of deep sea sharks? Please?

  2. Congratulations Kevin! That’s such a great opportunity. And I look forward to seeing how you organize your class (and borrowing ideas for when I eventually do some teaching). I already used that “Finding Nemo” pic in a public lecture I gave, with a similar caption. :)

  3. Of course your institution is enthusiastically willing to let a PhD student develop a full on lecture course—you cost FAR less than a faculty member! LOL! Just being cynical. Seriously, it should be fun. Let me know if you need anything on reproduction or larvae in the Deep Sea. I’ve done a few lectures on these and have scavenged some good material. I’m looking forward to seeing your lecture material!

  4. Awesome Kevin!

    Can I sign up for it and get an independent study credit from there to count here at UCONN? My other seminar course fell through and yours sounds so much more applicable.

    1. LOL, that is between you and your dept. I can send someone there my exams for you to take ;)

  5. Sounds like a great course Kevin! You talk a little bit about how the definition of “deep sea” has changed over time, do you happen to know who said what definition and when?

    One of my committee members has given me this task (I think to make the very point to be careful about what each person actually means by “deep sea” especially in paleontological literature where it could mean intercontinental seaways etc). What I have found so far is that although the starting point gets deeper moving forward from Edward Forbes (pre-Challenger with 50 fathoms/91m), the modern definitions don’t seem to be in agreement with one another. Some say “beyond the continental shelf” or below the euphotic zone, others stick with greater than 200m, and wikipedia says greater than 1000 (these later 2 are definitions for bathyal, didn’t actually define “deep sea”).

    Anyway, if you have found anything in your research for teaching the course that would add to this, I’d be interested in seeing it!

  6. I am glad you got this course. With all that I have learned from you so far, I am sure that your students will get a great picture of that big ol’ ecosystem we hardly ever sea.

    Will you be doing any singing or playing some of your deep sea songs in the class?

  7. Kevin,
    That is a very exciting project! I wish you could come teach this here at Hawai’i Pacific University. We have a very beautiful campus!
    I like the flow of your sections. Sounds like a well-articulated class. Are the pictures in the intro from Claire Nouvian’s book?

    1. Thanks! Give me a job and I’ll teach all sorts of wonderful classes at Hawai’i Pacific University!

  8. Ha, to be honest, I have no idea about the current teaching opportunities, I’m just an undergrad… I’ll further inquire!

  9. Better to have this like lecture in web….thankz for the great attempt…
    An undergrad.Sri Lanka.

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