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Meet the Zooplankton: Thalia democratica

Imagine a chain of identical sextuplets, linked together and wrapped around their parent; an odd family, to say the least, but that is how the salp Thalia democratica lives. A salp is a gelatinous marine organism that moves by pumping water through its tube-shaped body, filtering-feeding on phytoplankton as it moves.

A single Thalia democratica; image from: http://www.roboastra.com/Ascidacea/images/bras243.jpg

The salp Thalia democratica is commonly found in continental shelf waters, but is most abundant in the Tasman Sea, between Australia and New Zealand, especially during the austral spring season. The most iconic feature of this zooplankter is its ability to produce long chains of identical buds, which may be as long as 6 meters and containing as many as 350 individuals!

A Thalia democratica chain in a diver’s hand. Image from: http://www.diverman.it/images/Salpe-Thalia-democratica05-.jpg

Thalia democratica are well-adapted for filter feeding; a system of 5 muscular rings propels them forward by pumping water through their tube-like bodies. Due to their ability to form dense aggregations and chains, they are capable of outcompeting other common zooplankton like copepods. Thalia democratica is also commonly preyed upon by sea turtles, marine birds, fish, and sea jellies. The importance of salps like Thalia democratica to marine food webs is still being investigated.

Thalia democratica is capable of reproducing both sexually and asexually. Buds are formed at the beginning of Thalia democratica’s sexual cycle and wrap around the body of the parent. These buds develop into chains, which are released into the water before transitioning to a female form. Sperm released by male Thalia democoratica fertilize the females’ eggs. Following fertilization, aggregates may develop testes and produce a single male offspring, which releases sperm into the water before dying.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Script Authors: Jessica Hoeschele and Kait Sanders

Contributing Professor: Dr. Lisa Campbell

Editor: James M. Fiorendino

Meet the Zooplankton: Calanus finmarchicus

Have you ever wondered what the most abundant animal on earth is? The answer is tiny crustaceans known as copepods. The subject of our show today is one species of these tiny but numerous organisms, Calanus finmarchicus. These zooplankton grow to be roughly 3 to 4 mm long. They are widely distributed, but most abundant in the North Atlantic Ocean, specifically the North and Norwegian Seas, off the coast of Canada, and in the Gulf of Maine. Calanus finmarchicus reside in surface waters but have been found at depths of 4000 meters, and they typically live for 1 to 3 years.

An individual Calanus finmarchicus. Image from: https://cdn-a.william-reed.com/var/wrbm_gb_food_pharma/storage/images/7/0/6/7/1507607-1-eng-GB/Study-shows-Calanus-oil-may-benefit-blood-pressure-and-heart-health_wrbm_large.jpg

The diet of Calanus finmarchicus consists of several different species of phytoplankton, including coccolithophores, diatoms, and dinoflagellates. Their life cycle is dependent on the seasonal patterns of their food; Calanus finmarchicus spawns in the spring when waters are warming and phytoplankton bloom, providing abundant food for these copepods. Though spawning typically occurs at night, a behavior that likely reduces predation, female Calanus finmarchicus are the most common predator of their own eggs! So much for nurturing parents.

Within marine food webs, Calanus finmarchicus is an important prey species for fish like herring and mackerel, as well as other invertebrates. They are high in protein, and rich in omega-3 fatty acids. Calanus finmarchicus is also a commercially relevant species to humans. These copepods are harvested to produce calanus oil, a supplement similar to fish or krill oil, or turned into fish feed for aquaculture or home aquariums.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Script Authors: Rebecca Beam and Renee Chastain

Contributing Professor: Dr. Lisa Campbell

Editor: James M. Fiorendino