Pyrosome - WikiHQ

Pyrosomes are free-floating colonial tunicates in family Pyrosomatidae. Pyrosomes consist of colonies of small zooids. There are three genera, Pyrosoma, Pyrosomella and Pyrostremma, and eight species. They usually live in the upper layers of the open ocean in warm seas, although some may be found at greater depths. and the name Pyrosoma derives from the Greek words pyro, meaning "fire", and soma, meaning "body". Pyrosomes are hermaphroditic and reproduce via a two-part process. They have the ability to create massive blooms that may affect pelagic food webs.

Description

Pyrosomes are commonly called "sea pickles", due to their tube-like gelatinous structure. Other nicknames include "sea worms", "sea squirts", "fire bodies", and "cockroaches of the sea".

Each zooid opens both to the inside and outside of the "tube". The zooids draw in ocean water from the outside into their internal filtering mesh called the branchial basket, extracting the microscopic plant cells on which it feeds, and then expelling the filtered water to the inside of the colony's cylinder.

Pyrosomes are brightly bioluminescent, flashing a pale blue-green light that can be seen for many tens of metres. Pyrosomes are closely related to salps, and are sometimes called "fire salps". Sailors on the ocean occasionally observe calm seas containing many pyrosomes, all luminescing on a dark night.

Anatomy and morphology

thumb|Drawing of a pyrosome. Clearly shows the individual zooids that appear as small bumps on the surface of the tubular structure.

A single individual of a pyrosome colony is referred to as an ascidiozooid, or zooid. A pyrosome colony contains many zooids which form a gelatinous tube, the walls of which range from 0.2 - 2.0 cm.

The zooids that make up a pyrosome are typically only a few mm long. Colonies of these zooids, which are bound together by a notochord and shared tissue, form a tube-like, hollow structure that is typically between 1 inch and 2 feet in length. However, giant pyrosomes can reach up to 60 feet in length, with a hollow opening up to 6 feet (2 meters) wide. There have been some instances in which deep sea scientists have swum inside of a giant pyrosome's hollow body.

Pyrosomes are transparent and gelatinous, with a slimy yet bumpy texture. Zooids appear as small bumps on the colony, although the colony appears nearly smooth with perforated holes for each zooid on the inside. Each zooid has a stomach that can be seen through the transparent body of the colony. These stomachs have been compared to "wire baskets". Pyrosomes may use bioluminescence to signal danger or otherwise communicate with individuals of the same or nearby colonies. These bacteria live within the host cells, which assumably control bacterial light emissions, a phenomenon rarely seen in other bioluminescent marine organisms.

Food chain niche

Pyrosomes are filter feeding tunicates that consume small particles like phytoplankton and detrital matter. That being said, their predator to prey mass ratio is very large at almost 50 million : 1.

Pyrosomes are essential members of the food chain on multiple fronts. Pyrosomes feed on large numbers of microbes, fall after death, vertically migrate while producing marine snow, and are prey for marine mammals, seabirds, turtles, or fish. During their daily vertical migration of up to 900m or falls after death, Pyrosomes are prey to at least 62 pelagic organisms (like turtles and sea lions) and at least 33 benthic organisms (like sea urchins and crabs). Therefore, their role as contributors to the marine carbon cycle is likely very essential.

Taxonomy

thumb|Pyrosoma atlanticum by a tide pool in California

According to the World Register of Marine Species, the family is divided into two subfamilies and three genera, containing eight species.

Subfamily Pyrosomatinae Lahille, 1888
Genus Pyrosoma Péron, 1804
Pyrosoma aherniosum Seeliger, 1895
Pyrosoma atlanticum Péron, 1804
Pyrosoma godeauxi van Soest, 1981
Pyrosoma ovatum Neumann, 1909
Genus Pyrosomella van Soest, 1979
Pyrosomella operculata (Neumann, 1909)
Pyrosomella verticillata (Neumann, 1909)
Subfamily Pyrostremmatinae van Soest, 1979
Genus Pyrostremma Garstang, 1929
Pyrostremma agassizi (Ritter & Byxbee, 1905)
Pyrostremma spinosum (Herdman, 1888)

The three genera of pyrosomes, Pyrostremma, Pyrosomella, and Pyrosoma, have morphological similarities and differences. Most pyrosome colonies are finger-shaped, but there are two exceptions in the Pyrosoma genera; P. godeauxi and P. ovatum have a more globular appearance. Generally, pyrosomes have limp tests, or outer coverings. However, in some cases, Pyrosoma have tough, elastic tests. Each genera has test projections, those of Pyrostremma being triangular and spiny, Pyrosomella smooth, and Pyrosoma long and blunt. Multiple different cellular types have been found to be distributed in the tunic of Pyrosome atlanticum, Pyrosomella verticillata, and Pyrostremma spinosum. These cell types include Tunic amebocytes, which are found to be motile and shaped asymmetrically. They are also found to either contain granules or phagosomes within them. Another cell type is known as Spherical Tunic cells, in which contain spherical vesicle that often contain eosinophilic and acidic substances. Net cells form a net in which the cell's elongated filopodia connect with each other, forming a network. This network maintains a tension in order to reinforce the colony shape and support the cell's cloacal cavity. Multicellular cords also exist between the tunic cells and the zooids, and are known as test fibers. They are hypothesized to maintain and control muscle contractions of the zooids.

Geographic distribution

Pyrosomes are globally distributed organisms, with recorded sightings in every ocean, with the exception of the Arctic Ocean, and are typically latitudinally confined within 50°N and 50°S. However, some pyrosome species have been shown to expand their geographic range in response to increasing ocean temperatures, which has unknown implications for the already existing ecosystems. Since pyrosomes are food-limited organisms, they may take advantage of these circumstances to increase reproduction. In 2017, pyrosomes were observed to have spread in unprecedented numbers along the Pacific coast of North America as far north as Alaska. The causes remain unknown, but one hypothesis is that this bloom may have resulted in part from unusually warm water along the coast over several preceding years. Also, weak upwelling off the coast of northern California creates an ideal environment for blooms.

Scientists have observed that large blooms can hurt pelagic food webs, for an increased population leads to increased grazing pressure, ultimately affecting the transfer of energy in these environments.