Bioluminescence, Part 2

Bioluminescence is produced by a chemical reaction similar to the one that happens when a glow stick is broken. This reaction releases energy as light. The color of the light that is produced is usually blue or green, but can be red, yellow, or orange, depending on the chemicals used in the reaction. Most animals produce only one color of light, but some fish and worms use two colors of light

Looking for fish beneath cliffs of Laird's Sandstone on Tomales Bay
Photo by Casey Newman, 2011, All Rights Reserved.

Some animals, like fish and shrimp, use photophores, or special organs to produce light. Others, such as jellyfish, have specialized cells scattered over their bodies that glow. Certain species of organisms play host to bioluminescent bacteria, which produce light in exchange for room and board. There are some species of squid that produce bioluminescent ink, which is squirted out as a defense mechanism.  Single celled organisms such as bacteria and dinoflagellates use special compartments in their cell to separate the chemicals that react to produce light, combining the compartments when necessary.

At depths of between 200m and 1000m in the ocean, up to 90% of animals use bioluminescence to blend in with their surroundings. The light that reaches down into those depths is blue-green, and these animals will use bioluminescent photophores (cells or organs that produce light) to match the amount of blue-green light around them, camouflaging themselves.  Other fish that live at those depths produce red light. Many organisms that live that deeply cannot see red light, so the fish that produce it can use the light to see their prey without being seen.  Deeper in the ocean, where conditions are always cold and dark, animals do not need bioluminescence to blend in, but they do use it to attract prey and for communication and courtship. These animals have unique patters of photophores, which may help them to recognize others of their species.

Plainfin Midshipman Fish
Photo copyright Terrence J Fidler, 2006,robots4farms.com

One type of bioluminescent fish, called the plainfin midshipman fish, lives deep in the Pacific Ocean but migrates to the coast in the summer to lay their eggs. These fish are a type of toadfish with no spots or stripes on their dorsal fin. Their photophores are arranged in a U-shape on the underside of their body, and the photophores look like the buttons on a naval officer’s uniform, which is how they get the name midshipman fish. The photophores are used to blend in with the light around them while they are in the ocean, which keeps predators from seeing them from below.

The male midshipman fish returns to Tomales Bay first, digging out a nest in the rocks along the shoreline. The rocks at Nick’s Cove are a favorite spot for these nests. Once there, the males begin to hum to attract females. The hearing of the female midshipman fish is so accurate that they can tell the difference between each male’s hum and find the nest of the hum they like best. Once there, the female will lay her eggs and return to the open ocean. The males fertilize and take care of the eggs, continuing to hum until their nests are full of eggs from many females. The males guard the nest until the eggs hatch and the hatchlings are ready to be on their own.

To hear the plainfin midshipman fish’s hum, visit Discovery of Sound in the Sea: http://www.dosits.org/audio/fishes/plainfinmidshipman/.

Bioluminescence, Part 1

What’s all the fuss about bioluminescence? What IS bioluminescence? 

Sunset over White Gulch on Tomales Bay.
Photo by Casey Newman, 2011, All Rights Reserved. 

It’s the production of light by living organisms. It can be used to attract prey, to communicate, and to help an organism blend in with its surroundings. Bioluminescence is also responsible for the glow that can sometimes be seen on moonless nights in the waters of the ocean. In several places in the world, including our own Bay Area, conditions are perfect for an annual “bloom” of dinoflagellates, a type of single celled organisms that are bioluminescent.

Dinoflagellates are a type of unicellular planktonic organism (whew, what a mouthful). They drift with the currents of the ocean (planktonic), using two whip-like structures (flagella) to move their single-celled selves around a bit. They can photosynthesize, or get energy from sunlight, but some dinoflagellates also eat other, smaller organisms. Most of them have armored plates made of cellulose for a cell wall, which makes them tough for their size (and also beautiful under a microscope). Some dinoflagellate species cause red tides, and release toxins that are harmful to humans. Other species, like the species that is found in Tomales Bay certain times of year, are bioluminescent.

The species of dinoflagellates that bioluminesce operate on a circadian rhythm- they photosynthesize during the day and they only glow at night. Because they only glow when they are jostled, it is theorized that they glow as a defense mechanism. One of their main predators is a type of shrimp, and if they glow when they are about to be eaten, the light will hopefully attract a fish, which will hopefully eat the shrimp. The flash of light may also act as a distraction, blinding the predator to allow the dinoflagellate time to get away.

During certain times of the year, strong winds push the top layer of coastal water offshore, allowing cold, nutrient-rich water to flow up from the ocean floor. This is known as upwelling, and it is responsible for the surge in nutrients that feed an explosion in the population of single celled algae. One species of those algae are the dinoflagellates that produce the light we see on Tomales Bay. Their bioluminescence can occasionally be seen year round, but tends to be strongest in the summer and early fall. The amount of nutrients in the water affects when we can see the bioluminescence and how long it lasts.

The waters of Tomales Bay are a perfect location for viewing the bioluminescence. Tomales Bay has a narrow opening which limits the amount of water that is exchanged during the tides, concentrating the dinoflagelates in the bay. Beds of eelgrass, a plant with long blades, further trap and concentrate the dinoflagellates in the shallow parts of the bay. The northern end of the bay is relatively undeveloped, which keeps light pollution from washing out the flashes of green light when the organisms are moved. 

A paddle through the bioluminescent waters of Tomales Bay is an amazing experience. As we paddle through the water, our boats, paddles, and even hands can jostle the organisms and make them flash. The bioluminescence does not hurt the dinoflagellates, and they can continue to emit flashes of light for hours. On especially dark nights, fish can be seen setting off the bioluminescence as they swim through the waters underneath our boats. The peaceful waters of Tomales Bay provide a protected location filled with wonderful wildlife to paddle past, and the bioluminescence is truly breathtaking.

Sunset on Tomales Bay.
Photo by Casey Newman, 2011, All Rights Reserved. 

Want to know more about bioluminescence? Check out the Bioluminescence Web Page at http://www.lifesci.ucsb.edu/~biolum/, or tune in next week for more information about bioluminescent critters and about a specific type of bioluminescent fish that returns to Tomales Bay every summer.