118 — Sea hare, Aplysia juliana

 

Aplysia juliana. feeding on Ulva,
Pilot Bay, Mt. Maunganui, January 2016.

This post leads on from my last post regarding sea hares. Aplysia juliana * is a large sea hare (to ~45cm), which is found circumglobally in warm-temperate waters. They come in a variety of colours, from blotchy light brown to an even dark brown.

Aplysia juliana. feeding on Ulva,
Pilot Bay, Mt. Maunganui, January 2016.

Aplysia juliana, feeding on Ulva,
Pilot Bay, Mt. Maunganui, January 2016.

Aplysia juliana is particularly fond of sea lettuce (Ulva sp.) (Fring & Fring 1965). The ones pictured here feeding on sea lettuce and you can see the sea hare in the video devouring a piece.

Aplysia juliana moving over shell hash,
Pilot Bay, Mt. Maunganui, January 2016.

This species is also unusual in that it doesn't produce ink, but instead produces opaline: a white milky secretion. Opaline fulfils a similar defensive role to the ink produced by other sea hares and has been shown to protect sea hares from predation by spiny lobsters (Kicklighter et al., 2005).



Aplysia juliana is unusual amongst sea hares in that the posterior end of it's foot can act as a sucker. What this means is that it can inch it's way along a bit like a leech: reaching the head out and placing it down, then lifting up the posterior end of the foot and bringing that forward, which most other sea hares don't do. This form of motion can be seen the video on the right.

Given the abundance of sea lettuce in Tauranga Harbour in summer during recent years it would be interesting to see if there has been a corresponding increase in this species of sea hare. That's a research project for some one :)

* Quoy & Gaimard, 1832




More info

Sea slug forum: What are sea hares?

Sea slug forum: Aplysia juliana

Fring, H., Fring, C., 1965. Chemosensory bases of food-finding and feeding in Aplysia juliana (Mollusca, Opisthobranchia). Biological Bulletin, 128(2), 211–217.

Kicklighter C. E., Shabani, S., Johnson, P. M., Derby, C. D., 2005. Sea hares use novel antipredatory chemical defenses. Current Biology, 15, 549–554. doi:10.1016/j.cub.2005.01.057

Willan, R. C., Morton, J. E. 1984. Marine molluscs part 2: Opisthobranchia. University of Auckland, Leigh Marine Laboratory, Leigh, New Zealand. 106 pp.