The Midwater Zone
by Jim Stime, Jr
The midwater, or mesopelagic zone, is located between the ocean's photosynthetic surface and the sea's deep dark bethnic layer. Even though this zone only accounts for one quarter of the entire ocean it contains the majority of the ocean's life.
Scientists have divided the ocean into 5 main layers. These layers, known as "zones", extend from the surface to the most extreme depths where light can no longer penetrate. These zones are where some of the most bizarre and fascinating creatures can be found. As we dive deeper into these vast and unexplored places, the temperature drops, light disappears and the pressure increases at a tremendous rate.
In the past, researchers used nets towed by ships to collect and study organisms drawn from the midwater layers. These nets were capable of catching organisms within certain zones but many deep-sea organisms have bodies so fragile, with water making up the bulk of their mass, that their bodies collapsed while they were being brought to the surface. Many of them were so badly damaged that their original shape was hardly recognizable.
Today, with the advent of blue water diving techniques, submersibles, and deep sea remotely operated vehicles (ROVs), it has become possible to study and observe these organisms in their natural habitats.
Scientists have been surprised at the number and variety of species discovered in the deep ocean's midwater zone. Many of these creatures are soft and gelatinous, from transparent squid, octopuses and jellyfish to large colonial animals called siphonophores.
One such group of deep sea creatures is a very diverse family of organisms called Cnidarians. These organisms include the familiar anemones, corals and jellyfish and live as either a stationary polyp or a free swimming medusa, or in some cases both. All Cnidarians share a similar body plan, they can be simply described as a sac within a sac. These organisms posses no distinct head, digestive or structural organs, but all possess Cnidae, specially modified stinging cells.
Many coastal Cnidarians, such as corals, include packets of light absorbing algae called zooanthellae. The midwater region is where sunlight's reach is too weak for photosynthetic organisms. The only light found at these depths is produced by bioluminescence from the living inhabitants. It has been estimated that 90% of deep sea marine life can produce bioluminescence in one form or another.
The most commonly referred to jellyfish belongs to the class of Scyphozoan. They are disc shaped animals that are seen floating near, or beached on the shore. Within the class of Scyphozoan are the orders of Semaeostomeae, which contains 50 described species of mainly coastal water jellyfish, including the popular Moon Jellyfish (Aurelia) and Sea Nettle (Chrysaora). The order Coronatae include 30, and growing, described species of deep sea jellyfish. The order Rhizostomeae contains 80 described species, which include the Cassiopea jellyfish, who swim upside down as they expose their photosynthetic symbiotic algae to sunlight. The order Stauromedusae consists of 30 described species, which are the non swimming stalked jellies that are generally found in cooler waters. They are vase shaped and fixed by a basal stalk. Their mouth is pointed upwards.
Jellyfish, or Sea Jellies, are made up of 99% water, and are found all over the world and in all the seas, even in some freshwater locations. A jellyfish's body is made up of two layers, and in between is a jelly-like substance, which is how they get their name. Their bodies range in size from less than1 inch to 16 inches, with a few species growing up to 6 feet across and 15 feet in length.
Most wild jellyfish have a very short lifespan and may live for only a few weeks, or a couple of years and feed on small plankton type animals that they capture within their tentacles, which have stinging cells, called nematocysts. It is these stinging cells that the adventurous swimmer may unfortunately swim into, with painful results.
The life cycle of Scyphozoan jellyfish consists of three stages ; Adult male and female jellyfish sexually produce eggs and sperm and that fertilized larvae is, either 'brooded' within the gut of the adult or develops as a free swimming planeload. The planeload settle onto a substrate, called the hydra tuba stage, and develops into a polyp, or scyphistoma. The scyphistoma, which is a sessile or stationary polyp, asexually buds off a small medusa, called an Ephyra.
These Ephyra resemble a small 1/8” diameter snowflake, that pulses. Within about two weeks their dome shaped bell begins to become apparent. After about a month the four trailing oral arms begin to develop. From this point it becomes a growth phase and within four to six months a saleable tank raised jellyfish is ready.
Midwater Systems originally planned to develop a free standing acrylic jellyfish tank but quickly realized that the available livestock for a jellyfish tank was non existent. The local public aquariums were prohibited from exchanging livestock and were guarded with their information. Fees for collection permits are expensive and many collectors are hesitant. Hard to sell a jellyfish tank without jellyfish ! The project now took on a second task, to learn how to produce livestock.
Having acquired an initial batch of tank raised adult Moon jellyfish from a laboratory in the midwest, which produced larvae and the resulting polyps, Midwater Systems was in the tank raised jellyfish livestock business. Recognizing a need and then developing a series of specialty tanks the product line increased to include tanks for holding polyps that are budding, tanks that gently rotate new born Ephyra, to larger grow-out tanks can double as retail holding systems for jellyfish sales.
Along with tank raised jellyfish Midwater Systems has developed a series of patent pending free standing complete system designed to maintain jellyfish, called the Jelliquarium.
The Jelliquarium, known in the scientific community as a plankton Kreisel, is uniquely designed. Water flow is introduced in a method called laminar flow. This creates a gentle flow that keeps the jellyfish in suspension. This flat stream of water acts as a boundary against the edges of the tank and creates a water flow that helps to separate debris in a manner as to not draw the jellies into the filter system and to maintain the gelatinous organisms in suspension.
It is hoped that the Jelliquarium systems and the information presented within this web site will spawn a new facet of the marine aquarium hobby, and a new fascination with keeping jellyfish.