Pennatula phosphorea (Sea Pen) are colonial marine cnidarians belonging to the order Pennatulacea. Sea pens get their name because they look like a plump, old-fashioned quill pen. They live on muddy or sandy sea bottoms where they can anchor themselves. There are many different varieties of sea pens, only those from some families have the feather-like appearance of a quill pen.

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Sea pens are soft corals that are grouped together with sea whips and gorgonians. Most sea pens grow to between 2 inches and 6 feet, 7 inches in height, but one species living near Antarctica can grow to about 10 feet long. Sea pens range in color from dark orange to yellow and white. Their feather-like shape and ability to live in really deep water are adaptations that sea pens have made. Sea pens are octocorals with multiple polyps, each have eight tentacles and root-like peduncles to anchor themselves in the sea bottom. The larger Sessiliflorae suborder, have club-like or radiating forms instead of feathery structures.

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The sea pen lives on sandy or muddy bottoms, in depths from 45 to 225 feet. They can be found in the Pacific and Indian oceans, or in Europe and the Mediterranean.  In the Puget Sound the number of sea pens average up to about 23 pens per square meter, but their numbers have been declining in the area. Sea pens are common in general, and their only threat to survival comes from humans because of dredges used for oyster harvesting. Species of sea pens living in Scottish waters are protected under the ‘Mud in Deep Water Habitat Action Plan’ of the UK Biodiversity Action Plan (UKBAP).

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Sea pens are suspension-feeding animals. They are a “key-industry species”, defined as a species abundant enough to support a large guild of predators. Phytoplankton and detritus particles are the main food sources of sea pens. They must place their bodies directly into the current flow in order for the polyps to catch particles passing by. Their primary predators are nudibranchs and sea stars. Sea pens emit a bright greenish light when touched and may also force water out of themselves as a defensive act, deflating and retreating into their peduncle. Veretillum sea pens are nocturnal and gather food with their flower-like polyps unfurled.

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Sea pens are important because they provide deep oxygen penetration of soft sediments.  This helps create complex habitats with a higher species diversity in the macrofaunal community. They are very beautiful with their bright colors and sometimes feather-like appearance. Most people may have never heard of a sea pen, but they are an abundant life form and serve as a good food source for other sea creatures.

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Author: Ethan E

Published: 02/2013

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Sources:

http://www.montereybayaquarium.org/animals/AnimalDetails.aspx?enc=VsGX+Lst7QZ0ZBC9MK91Qg==

http://www.livescience.com/15435-sea-pens-corals-marine-deep-water.html

http://en.wikipedia.org/wiki/Sea_pen

http://reefkeeping.com/issues/2005-08/rs/feature/index.php

http://animaldiversity.ummz.umich.edu/accounts/Ptilosarcus_gurneyi/

http://www.asnailsodyssey.com/LEARNABOUT/PEN/penPred.php

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=1367304

www.ospar.org/.../10-11e_seapens_burrowing_megafauna.doc