Marine Invertebrates of Bermuda Spotted Sea Hare (Aplysia dactylomela) By Anne Overly Dr. James B. Wood - Editor Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Taxononmy


Phylum:Mollusca
  Class:Gastropoda
    Order:Anaspidea
     Order:Opisthobranchia
       Family:Aplysiidae


Habitat


Aplysia dactylomela lives mostly in high subtidal to intertidal areas on sandy or rocky substrate with dense algae cover. It is reported that it has sometimes be found at depths up to 40 m (Sterrer, 1986). It is also commonly found in shallow waters and tide pools, again, where there is dense algal cover (Miller, 1999). A. dactylomela can be found in these habitats globally in subtropical and tropical oceans.

Ecology


Aplysia dactylomela can reach lengths of 15-16 cm as an adult. It ranges in color from light brown to olive green, with black ring-shaped spots of varying sizes. The shell plate is internal, enclosed in the mantle (Sterrer, 1986). A. dactylomela has mantle flaps used for swimming, and large dorsal parapodia, slightly resembling long ears, from which it derives its common names for its resemblance to a terrestrial rabbit.

Being a gastropod, one might expect Aplysia dactylomela to have a shell, but if one is present, it is not obvious. Like most cephalopods, A. dactylomela does have a fragile internalized shell that is thought to be mainly a vestigial remnant from a shelled gastropod ancestor and is not sturdy enough to provide support (Rudman, 2000).

Aplysia dactylomela feeds mainly on red algae in sea grass beds (Carefoot and Pennings, 2003). Swimming behavior in Opisthobranchs is thought to be related to feeding and defense. Swimming behavior in A. dactylomela may be slightly impaired, however, as sand makes up about 25% of its food intake volume, which weights it down significantly. In studies, A. dactylomela fed a diet high in silicon was less likely to swim and more likely to sink, especially compared to species fed only algae. It is also possible that swimming is related to searching for food, and a well fed Aplysia dactylomela is less likely to swim. This is not certain in the wild, however, as A. dactylomela feeds at night and hides in crevices in the day, so swimming behavior is harder to observe (Carefoot, Pennings, 2003).

Opisthobranch predators include other carnivorous opisthobranchs, such as Aglanja inermisi, which feed on smaller opisthobranchs than itself (Pennings, 1990). Sea turtles have also been known to eat opisthobranchs, and labrid fishes or wrasses have been shown to eat juvenile Aplysia dactylomela (Rogers, 2001). Otherwise, A. dactylomela, among other opisthobranchs are generally avoided by predators because of their toxicity (Rogers, 2002).

Aplysia dactylomela is a simultaneous hermaphrodite exhibiting internal fertilization. Sexually mature individuals may be sperm donor, recipient, or both at once. Individuals do not commonly show a tendency towards being a donor or recipient, except maybe in smaller individuals, which tend towards being sperm donors (Lederhendler, Tobach, 1977). A. dactylomela does not self-fertilize, but it may copulate more than once with the same partner, switching roles of sperm donor and recipient each time (Zaferes, et. al., 1988). In dense populations or aquaria, they have been known to form mating chains of three or more individuals, with the first individual in the chain acting only as a sperm recipient and the last individual being solely a sperm donor, while the one(s) in between act as both simultaneously (Rudman, 2000).



Recent Research


Opisthobranchia are known to release purple ink when disturbed. The ink of Aplysia dactylomela appears to be an irritant, as other organisms, such as other invertebrates and fish, display altered behavior when exposed to it. Behavioral alterations induced by exposure to this ink include increase in mucus production in other opisthobranchs, increased grooming and decreased feeding behaviors in crabs, and flight responses in fish (Carefoot, et. al., 1999). These behaviors would appear to indicate the ink is a defensive mechanism. Other hypotheses about the function of the ink include roles in metabolic excretion, a camouflage mechanism similar to that of a squid, and a warning signal (Carefoot, et. al., 1999).

Aplysia dactylomela eats mainly the red algae Acanthophora spicifera, Centroceras clavulatum, and Laurencia sp., and the green alga, Ulva lactuca. From these algae, they obtain mycosporine-like amino acids (MAAs) which they pass on to their spawn to absorb UV radiation during development. Carefoot, et. al. have done multiple experiments relating amounts of MAAs in adult diets to survival rates of their spawn, and found that adults rich in MAAs produce twice as much spawn adults with lower MAA levels (2000). Along with studies on MAAs, which shield spawn from UV radiation are studies indicating that UV light shortens gestation periods of spawn, and encourages healthier growth (Carefoot, et. al., 1998).

Studies are being conducted on the acquiring of secondary metabolites in sea hares, including metabolites from algae in Aplysia dactylomela. Sea hares appear to accumulate most secondary metabolites from red algae (Rogers, 2000). This data combined with the MAA data would indicate that the ideal food for A. dactylomela is red algae, which appears to provide the most overall benefits to the species.

The environmental impact of Aplysia dactylomela grazing has been studied by Lapointe, et.al. (2004). They describe the total impact of nutrient enrichment combined with selective algal grazing in Norman's Pond Cay, Exumas Cays, Bahamas. Nutrient enrichment has been found to increase algal cover, and therefore grazing, and probably population size, in Pond Cay.



Commercial Importance


Some Opisthobranchs, such as Aplysia kurodai, which eat non-poisonous algae, have some commercial value in Asian countries such as Japan where it is eaten as a delicacy (Masayoshi, 2002). It is not clear if Aplysia dactylomela would be equally non-toxic, being in the same genus and also eating mainly algae. But in general, many Opisthobranchs are poisonous, due mainly to their food source, often to the point of being deadly, and are generally avoided by most predators (Rogers, 2002).

Another member of the same genus, Aplysia californica have been used in medical research for brain studies (Rudman, 2002). The purple ink of Bursatella leachii has been shown to have anti-HIV activity (Rajaganapathi, 2002), and as A. dactylomela has similar ink, it is possible that there could be some potential medical value to it as well. A. dactylomela ink has shown antimicrobial activities that inhibits the growth of bacteria, as well as being toxic to many larger organisms such as brine shrimp (Melo VMM, 1998).

The Lapointe, et.al. study (2004) may also provide insight to potential commercial importance. As A. dactylomela grazes algae, it helps hold back the potentially devastating effects of nutrient enrichment, which can lead to rapid eutrophication of bodies of water. The role of A. dactylomela and other grazers in stemming this process my help save such bodies of water which could have economic importance, whether for ecotourism or habitat for other commercially important organisms or some other factor, making A. dactylomela somewhat commercially important, if only indirectly.



Bermuda Laws


No Bermuda laws were found pertaining to Aplysia dactylomela



Personal Interest


I wasn’t originally particularly interested in opisthobranchs. At first, my only interest was to see a picture of the odd-sounding organism so I could at least have a “face” to go with the name, especially when warned in class not to confuse it with a turbellarian. I wanted to know why it would be confused with a turbellarian. Then I finally saw one, and I thought it looked cool. It has an interesting, ruffle-like shape, especially while swimming, and interesting coloration that that was indeed reminiscent of a turbellarian, even if the shape was different. I was even more intrigued to learn that opisthobranchs are gastropods, but lack an external shell. This didn’t fit with my idea of a gastropod, although the body form was certainly similar enough. I went out to Whalebone Bay one day to spend an afternoon relaxing on the beach (and climbing on the rocks…), and I spotted a few Aplysia dactylomela, which were larger than the nudibranchs I’d seen in lab, and the coloration pattern reminded me somewhat of a leopard. So my interest was slightly piqued. Then one day I was out snorkeling (in Whalebone Bay) and near the end of the trip, my professor and his intern were amusing themselves by “harassing” the A. dactylomela, stimulating the ink-releasing response. I was not previously aware that gastropods released ink, much less purple ink. I thought it was a characteristic limited to cephalopods. So I started to get the idea that maybe sea slugs were more interesting than I had ever thought and could be worth looking into.

When I started this project, I thought Aplysia dactylomela would be extremely commercially important, since so many other molluscs from many taxa are very valuable as food at the very least. Even many animals from the class Gastropoda, of which A. dactylomela is a member, have great value commercially. However, I was slightly shocked to find no references to commercial uses for A. dactylomela specifically, and a very few for the genus Aplysia. I was also slightly amazed to find some sources stating that, because of toxicity, most predators (including humans) avoid A. dactylomela, while other sources claim that it excretes irritants to keep predators away. Perhaps the brightly colored skin and ink provide extra warning for predators, as is the case in so many other bright but toxic organisms.

That Aplysia californica is used for research on the workings of the brain was only slightly surprising to me. I’d herd of similar research on cephalopod brains before, but I thought that it was probably restricted to molluscs with more highly developed brains. I suppose that, both being molluscs, their brains are similar enough to conduct similar research on. Or maybe they are each useful for research on completely different functions. I’m not entirely sure, I didn’t find any sort of papers comparing the two types of research.



References

Carefoot TH, Harris M, Taylor BE, Donovan D, Karentz D. 1998. Mycosporine-like amino acids: possible UV protection in eggs of the sea hare Aplysia dactylomela. Mar. Biol. 130 (3): 389.

Carefoot TH, Karentz D, Pennings SC, Young CL. 2000. Distribution of mycosporine-like amino acids in the sea hare Aplysia dactylomela: effect of diet on amounts and types sequestered over time in tissues and spawn . Comparative Biochemistry and Physiology C-Pharmacology Toxicology & Endocrinology 126 (1): 91

Carefoot, T.H., S.C. Pennings, 2003. Influence of proximal stimuli on swimming in the sea hare Aplysia brasiliana. J. Exp. Mar. Biol. Ecol. 228 (2):223

Carefoot, T.H, S.C. Pennings, Jean Paul Danko. 1999. A test of novel function(s) for the ink of sea hares. J. Exp. Mar. Bio. Ecol. 234 (2):185

Lapointe, B.E., P.J. Barile, C.S. Yentsch, M.M. Littler, D.S. Littler, B. Kakuk. 2004. The relative importance of nutrient enrichment and herbivory on macroalgal communities near Norman's Pond Cay, Exumas Cays, Bahamas: a "natural" enrichment experiment. J. Exp. Mar. Biol. Ecol. 298 (2): 275

Lederhendler, I.I., E. Tobach. 1977. Reproductive roles in the simultaneous hermaphrodite Aplysia dactylomela. Nature 270: 238

Masayoshi, N., 2002 (September 12) RE: Are slugs edible? [Message in] Sea Slug Forum. http://www.seaslugforum.net/find.cfm?id=7822 accessed 2/25/2004

Melo VMM, Fonseca AM, Vasconcelos IM, Carvalho AFFU. 1998. Toxic, antimicrobial and hemagglutinating activities of the purple fluid of the sea hare Aplysia dactylomela Rang, 1828. Brazilian Journal of Medical and Biological Research. 31 (6): 785

Miller, M.D. 1999. The Slug Site. Past Opisthobranchs of the week. http://slugsite.us/bow/nudwk174.htm accessed 2/25/2004

Pennings,S.C. 1990. Predator-prey interactions in opisthobranch gastropods: effects of prey body size and habitat complexity. Mar. Ecol. Prog. Ser. 62, 95-101

Rajaganapathi J, Kathiresan K, Singh TP. 2002. Purification of anti-HIV protein from purple fluid of the sea hare Bursatella leachii de Blainville. Marine Biotechnology 4 (5):447.

Rogers, C., 2002 (March 8) Re: Sea Hare poisoning [Message in] Sea Slug Forum. http://www.seaslugforum.net/find.cfm?id=6390 accessed 2/25/2004

Rogers, C., 2001 (Jan 9) Pycnogonids - Sea Slug predators [Message in] Sea Slug Forum. http://www.seaslugforum.net/find.cfm?id=3407

Rogers CN, De Nys R, Charlton TS, Steinberg PD. 2000. Dynamics of algal secondary metabolites in two species of sea hare. Journal of Chemical Ecology 26 (3): 721

Rudman, W.B., 2002 (September 17). Comment on Which slug is used for medical research? by John H. Garrett III. [Message in] Sea Slug Forum. http://www.seaslugforum.net/find.cfm?id=7959

Rudman, W.B., 2000 (May 8) Sea Hares - mating chains [In] Sea Slug Forum. http://www.seaslugforum.net/seahmat.htm

Rudman, W.B., 2000 (August 30). Comment on Shell of Aplysia by Yoshiaki J. Hirano. [Message in] Sea Slug Forum. http://www.seaslugforum.net/find.cfm?id=2928

Sterrer, Wolfgang. 1986. Marine Fauna and Flora of Bermuda. A Wiley-Interscience Publication.

Zaferes, A, A. Skolnick, E. Tobach. 1988. Interindividual Contact and Copulation in Aplysia dactylomela. Mar. Behav. Physiol. 13:221



Links

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