The distribution of two sea pens (Pennatulidae) in the SW Gulf of California, Mexico with reference to predation

Sea pens (Pennatulidae) are sessile, benthic cnidarians that inhabit soft sediment, and rely on filter feeding to obtain energy. They have a central stalk (rachis) which contains secondary polyps for feeding. Since no previous data has been collected on their distribution, abundance or size in the SW Gulf of California, Mexico, benthic surveys were conducted at depths of 11.0 – 32.6 m near Isla San Fransiscito and El Pardito. Two species (Stylatula elongata and Ptilosarcus undulatus) were observed. The average height ± s.d. (tip to sediment surface) of S. elongata was 9.5 ±3.8 cm (n=37) and was 3.5 ±1.6 cm (n=54) for P. undulatus. Twenty-four S. elongata individuals and five P. undulatus individuals were observed for horizontal movement over a 24 hour period. Three of the S. elongata individuals moved 0.4-1.4cm and 24 others showed no movement. Also, 2 sea pens could not be located (possible retraction into sediment or predation). Four of 37 S. elongata surveyed had predation damage on their tips indicated by a bare rachis. Two octocorallivorous mollusks were collected from these damaged tips and were identified as Neosimnia avena. Sea pens are part of the diet of Chelonia mydas, the endangered Green Sea Turtle, as well as many sea stars and nudibranchs, suggesting they are an important part of the marine food web. A return trip is planned for July 2011 to augment existing distributional and size data and supplement our knowledge of sea pens with observations on predation as well as bioluminescence