Tag Archives: Pelagic

Pyrosomes Everything You Never Knew You Wanted to Know

So this is a pyrosome? Cool, what does that mean?!?

PyrosomesPyrosomes are colonial organisms made up of hundreds to thousands of individual tunicates called Zooids! Our pyrosome friends may appear like a strange species of jellyfish however they are more closely related to us! This is because they posses a spinal cord and are taxonomically grouped with the Chordata Phylum. Scientist use this method called taxonomy to group and organize all organisms on earth based on similar characteristics. To be part of the Chordata phylum the shared characteristic required is a notochord, like a back bone. This is what separates Pyrosomes from the Jellyfish which classified as an invertebrate meaning an organism without a backbone!

The Taxonomy break down looks like this:

Kingdom: Animalia

Phylum: Chordata

Subphylum: tunicate

Class: Thaliacea

Now that we are starting to wrap our minds around what a pyrosome is, what is it doing out in the ocean?

Pyrosomes are free-floating colonies of zooids in the pelagic open ocean where they filter feed on microscopic plankton. The colonies of zooids are connected by tissue communicate and coordinate behavior such as propelling the colony through the water. Each individual zooid pulls water from the outside to its microscopic plankton filtration station, once that water is filtered the zooid expels the water into the inside of the cylinder body. The volume of water being filtered by each individual zooid gives the colony propulsion mobility. Pyrosome colonies can range in size from a few centimeters and up to 60 feet long! The giant pyrosome can grow large enough a human can swim though the internal cavity! The zooids grow though the process of asexual reproduction to make new identical zooids that enlarges the colony. Sexual reproduction is used to create a new colony.

How can pyrosomes affect our oceans?

Pyrosome populations can explode into what scientist call a “bloom” with hundreds to thousands of colonies. A bloom of pyrosomes may have a big impact on the benthic food webs. When the pyrosome dies, its gelatinous body sinks rapidly to the oceans bottom creating a pyrosome buffet for all the bottom dwelling critters!

Why are pyrosomes so fascinating?!?

Pyrosomes are a somewhat rare occurrence on Catalina Island but when they arrive they have our full attention here at CIMI. What makes them so fascinating is their ability to produce bioluminescent light! Together the colonies of zooids communicate and when one zooid emits light, they all do! They can produce enough light to see from many yards away as they are washing up on the beach or propelling themselves through the water column.

pyrsomes at night
















Photo Credit: Heather Peterson





Do fish sleep?

Did you have the chance to go on a night snorkel while you were at CIMI? If so, you may have seen all kinds of fishes actively swimming around – even in those late hours of the night! You may have asked yourself, if they’re moving around with their eyes open during my day snorkel and my night snorkel… when do these animals sleep? Do they sleep at all?!

fish sleep

Credit: The Fisheries Blog

The question of sleep in fish is a complicated one. Generally, we associate sleep in mammals with three distinguishing factors: (1) closed eyes, (2) a circadian, or daily, period of rest, and (3) reduced activity in the neocortex, a special part of the brain that helps with sight and hearing. Fish, however, lack both eyelids and a neocortex! So the question of sleep is more about the fish’s behavior, and whether they exhibit this circadian period of reduced activity and responsiveness to stimuli. For most species of fish, this is the case! Many species like our favorite garibaldi, kelp bass, and blacksmith, rest at the bottom of their habitats at night with no detectable eye movement, lower respiratory rates, and slowed responses to stimuli. You can even see some sleeping in our tanks!

fish sleep 1

Credit: Phil Watson, shaaark.com

There are exceptions to this, however. Many researchers believe that pelagic species, ones that live in open ocean environments, continually swim in order to maintain ram ventilation of their gills and sustain breathing. These pelagic species include many types of sharks, tunas, bonitos, and mackerels.

fish sleep 3

What’s more, some shallow water species that do generally sleep may stop sleeping during certain periods of their life, like migrations or while caring for their young! Hey, sound familiar?

fish sleep 2

Pelagic: Open Ocean Fish

Ahoy there landlubbers! Todays catch are pelagic fish species, meaning fish that are found away from the shore. The open ocean accounts for almost two thirds of our planets surface and is habitat for eleven percent of all marine species. Its an immensely vast area that we know very little about and survival is often times extremely difficult. Many fish in the environment have special adaptations which allow them to be successful. The fish range from the small nearshore bait fish; sardines and herring, to the powerful bluefin tuna and oceanic sharks. Particular species that draw our interest are the large ocean hunters including the billfish and tunas.

These massive fish have lots of obstacles to overcome to make it in basically a marine desert. Their large size comes at the cost of developing tremendous power to propel them through the water, sometimes for Marlin upwards of 60mph. Tuna have incredible muscle composition, having higher concentrations of red muscle which allows them to cruise at high speeds for extended periods of time. Bodies of fish have either red or white muscle. The red muscle (densely packed with blood) is what will allow fish to maintain speed for a while. Whereas the white muscle is what allows fish quick burst of speed. Tunas and marlin are also the closest fish to being independent of the environment temperature wise and are shown to alter their body temperature dependent on the external environment. Pretty crazy stuff to think that fish have come close to something we mammals take for granted!

Many open ocean fish have many physical characteristics that allow them to be the kings of their open ocean playground. the main way this is done is be retracting their fins when in pursuit of prey. Tuna and marlin have special slots along their bodies for their fins to slide into giving thus almost eliminating drag and giving the fish almost the complete shape of a torpedo shooting through the water. And if you’ve ever seen a fish from this environment close up you will notice an interesting keel shape near their tails. This acts to stabilize the fish and minimizing water resistance. Fish in this environment have completely fascinated people for many years and there is still so much to learn from them. With overfishing and by catch a major issue for many species in this are (due to high economical value) many scientists predict a sharp decline in numbers of individuals. Marlin and Tuna are amazing animals with amazing adaptations making them the true rulers of the Pelagic environment.


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