The world’s deep oceans are sometimes portrayed as dark and empty, but in reality, they’re teeming with life – and light. We know this in part because of U.S. marine biologist Edith Widder, who has been at the forefront of documenting and showcasing some of the organisms that brighten those depths. Widder, 71, has devoted the majority of her career to advancing knowledge on bioluminescence and the technology available to capture it, as retold in her memoir Below the Edge of Darkness: A Memoir of Exploring Light and Life in the Deep Sea (Penguin Random House, 2021). A unique legend, she spoke to us from her home on the east coast of Florida, where she runs the Ocean Research and Conservation Association (ORCA) focusing on preservation and restoration of a local estuary, the Indian River Lagoon.
The kinds of bioluminescence most people are familiar with are fireflies and glowworms. It’s cold chemical light, and the chemicals are produced by living creatures. It turns out there’s a lot of different chemistries that have evolved to do this – we think bioluminescence has evolved as many as 50 separate times – and that’s an indication of how important it is for survival. Most of that has happened in the ocean: on land it’s pretty rare, but in the ocean it’s very, very common.
A lot of them are in the mesopelagic zone [from around 200 to 1,000 meters in depth], which is also called the ‘twilight zone’. There’s still sunlight there, but it’s very, very dim – not enough for photosynthesis. That’s where the largest number of bioluminescent animals are usually found. You also see them in surface waters: you sometimes get bioluminescent dinoflagellate [algal] blooms, called ‘sea sparkle’, which illuminate the waves along the shore.
Some animals use it to help find food. There are animals that have built-in flashlights to be able to see in the dark, or they have a lure to attract prey, like the anglerfish that people know thanks to Finding Nemo. And, some animals use bioluminescence to attract mates, with particular flash patterns from uniquely-shaped light organs.
Light is also used a lot for defense, in a whole variety of ways: some of the most spectacular are those that can release their bioluminescent chemicals into the water in the face of a predator, and then swim away into the darkness: there are shrimp, squid, and even a few fish that have that capability. And then there’s a lot that produce luminescence from their bellies that exactly matches the color and the intensity of downwelling sunlight, so that they can hide out in the mesopelagic zone and not worry about the shadow that they’re casting, which is the ‘search image’ of an awful lot of upward-looking predators roaming around.
When I was 11 years old, my family went on a trip around the world and visited all these wonderful places. One of our last stops was Fiji, where I got to explore a coral reef. After seeing that, I decided I wanted to be a marine biologist. In terms of bioluminescence more specifically, well, the ocean is enormous, and it’s filled with all these animals that are communicating with light; you could make a case for bioluminescence being the most common form of communication on the planet, given the quadrillions of fish, for example, that are using it to communicate. And it’s clearly important to life in the ocean in ways we haven’t even begun to understand yet. We live on an ocean planet with very little understanding of what that means – and yet we’re dismantling our life’s machinery without having first explored it.
I think the biggest has to do with climate change, because we’re managing to acidify and warm the ocean. The ocean is going to be fine – it’ll be different, but it’ll be fine. But we’re going to be in trouble, because we may be altering the ‘rivers’ in the ocean: the massive flows of water, like the Gulf Stream along the east coast of the U.S., that move heat around the planet. Around 10,000 years ago, when these ‘rivers’ became established, our planetary weather systems stabilized to the point where we could have agriculture: before that, they was too erratic. Now, they’re starting to slow down and change, and that’s one reason we’re having weird weather patterns – and it’s only going to get worse.
So there’s that, and then there’s removing every last living thing from the ocean to feed ourselves while filling the ocean with toxins from our plastics, scraping the ocean floor to collect bottom-dwelling creatures, destroying the habitat that has sustained life for hundreds, thousands and millions of years, perhaps, for one haul of shrimp. It makes no sense, and it’s going on: out of sight, out of mind. And then there’s mining and drilling for oil, and all of the damage that that is doing. One reason we’ve survived as long as we have without being more careful is because the ocean has protected us, but we’re overcoming its buffering capacity.
The Indian River Lagoon, where I live, was once described as the most biologically diverse estuary in the U.S. Estuaries are the nursery of the ocean: they’re where many open-ocean fish and other animals come in to spawn, because they provide hiding places, food, and a rich, diverse ecosystem. This one is collapsing, like many around the world, because of the pressures of too many people and all of our pollutants entering the system. So I started ORCA with a feeling of wanting to give back to the ocean: I’ve had the most amazing career exploring it in so many fantastic ways, and I felt like it was time to do that.
I do. I didn’t think I was going to; I thought I was giving it up [to run ORCA]. But I’ve actually been able to do both, because I still collaborate with some colleagues and I’ve been invited on a number of expeditions. There’s going to be a television series next year for National Geographic that details an expedition I was on just a few months ago. So yeah, I still get to go out.
I have a lot of questions about these amazing light organs that animals have evolved and the strange light displays in, for example, some of the jelly animals that don’t have eyes. They’re probably using light to communicate to predators, but the fact that they can have different displays depending on the type of stimulus they receive is fascinating.
There’s one very particular mystery that I’m fascinated by, that I have observed many, many times: it’s called the ‘flashback phenomenon’, where if you’re sitting in a submersible in the dark, and you flash a light two, three, or four times, everything out there flashes back at you. It’s pretty awesome, but for most of my career, I just had to tell people about it – only people that go on submersibles would have been able to see it. Now, we finally have cameras that can record it.
To be able to observe these animals in a world that is usually dark, in a way that doesn’t disturb their behavior, has been a focus of mine for quite a long time. I’m still working with engineers to develop new ways to explore the deep sea, because we have barely begun to do so. The figure you hear most often is that 5 percent of the ocean has been explored, but it’s way less than that if you’re talking about actually visiting. Less than 0.05 percent of the ocean floor has been visited, and then there’s all of that incredible volume above it. So to be able to understand that life, and what part bioluminescent plays in it, requires whole new ways of seeing.
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