Critter of the Week: The flowering seapen

Anthoptilum grandiflorum (Verrill, 1879) is a species of Pennatulacea, or sea pen, in the octocoral group of Cnidaria. Octocorals are so named because they have 8 tentacles to each of their polyps.

Sea pens are morphologically distinct from other corals in the octocoral group with a stalk called a shaft or quill that ends in a base called a peduncle and an area with feeding polyps called the rachis. Sea pens use the branches or "leaves" that extend from the quill as mini hydrofoils to lift their feeding polyps into the current. Many sea pens glow mysteriously with a blue-green bioluminescent light when touched.

A whole specimen of Anthoptilum grandiflorum with a slender and terminally pointed muscular peduncle, which it uses to anchor into soft sediment. [Credit: Peter Marriott, NIWA. Oceans Survey 20/20 Bay of Islands.]

Anthoptilum grandiflorum has a long slender and muscular peduncle that it can inflate, which helps it to anchor into soft sediment and stop it from floating away in the current. In seafloor images you can see an example of this. The animals can grow to over 1 m tall.

Anthoptilum grandiflorum on a sandy seafloor in the Bay of Islands, New Zealand. [Credit: Peter Marriott, NIWA. Oceans Survey 20/20 Bay of Islands]

Anthoptilum grandiflorum has a cosmopolitan distribution, which means it is found in lot of different oceans. It is recorded from right around New Zealand in the Pacific Ocean and Tasman Sea, the Gulf of Mexico, the Mediterranean Sea, and in the Atlantic Ocean. It is found from continental shelf depths down to the abyssal parts of the ocean, and in New Zealand we have records from 44–1692 metres.
The polyps of the A. grandiflorum when viewed close-up are very flower-like and it is no surprise that many species of flowering plant also share this species name.

The flower-like polyps of Anthoptilum grandiflorum viewed through a macro camera lens. [Credit: Peter Marriott, NIWA. Oceans Survey 20/20 Bay of Islands]

An extreme close-up on the polyps of Anthoptilum grandiflorum viewed through a macro camera lens. [Credit: Peter Marriott, NIWA. Oceans Survey 20/20 Bay of Islands]

A nursery habitat for fish larvae

A study by some Canadian researchers found that deep cold-water inhabiting sea pen species, including A. grandiflorum, are an important habitat for the larvae of commercially exploited fish species (Baillon et al, 2012). It was concluded in this study that the fish may deliberately release their larvae amongst the sea pens to provide them extra protection from predation. Among different sea pen host species A. grandiflorum was found to have the highest yield of fish larvae living amongst it polyps. A separate study done by these researchers didn’t find any fish larvae in the sea pen digestive tract so there was no evidence for the fish being eaten in a predator/prey interaction. The safe habitat sea pens provide for larval fish is a good justification for why they are important to protect from human impacts on the seafloor.

Vulnerable Marine Ecosystems

Sea pens are classified as Vulnerable Marine Ecosystem (VME) species, which are defined as any ecosystem that is highly vulnerable to one or more kinds of fishing activity or other disturbance, and are identified by the vulnerability of their components (e.g. habitats, communities or species). The South Pacific Regional Fisheries Management Organisation (SPRFMO) Convention includes specific provisions to protect VMEs. The NIWA Invertebrate Collection provides records of these species found in the New Zealand Exclusive Economic Zone, and in the high seas areas outside our zone, via OBIS (Online Biogeographic Information System) to help predict the likely presence of VMEs using habitat suitability models for indicator taxa across the large areas that SPRFMO covers. The sea pen records come from a wide range of projects including those supported by funding from MPI, MBIE, DoC and international agencies.

A guide to the New Zealand sea pens

If you want to learn more about the commonly encountered New Zealand sea pens you can download Sea pens: descriptions for the New Zealand region - a sea pen field guide written by Gary Williams - an international expert on this group.

References and links:

Baillon S., Hamel J-F., Wareham V.E., Mercier A. (2012) Deep coldwater corals as nurseries for fish larvae. Frontiers of Ecology & Environment, 10: 351–356.

NIWA (2016). Vulnerable marine ecosystems in the South Pacific Ocean region. National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand, 202873 records, released on February 3, 2016.

Williams, G. (2016). Anthoptilum grandiflorum (Verrill, 1879). Accessed through World Register of Marine Species on 2016-08-18.

Williams, G.; Tracey, D.; Mackay, E. (2014). Pennatulacea (sea pens) descriptions for the New Zealand region. A field guide of commonly sampled New Zealand sea pens including illustrations highlighting technical terms and sea pen morphology. New Zealand Aquatic Environment and Biodiversity Report No. 132. 22 p.

Research subject: Coral