Marine Invertebrates of Bermuda Grass octopus (Octopus macropus) By Rachel Wigton and James B. Wood (Ed) Abstract Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Abstract


Octopus macropus is primarily found in the Mediterranean and Caribbean Seas, as well as the tropical western and eastern Atlantic Ocean. O. macropus is characterized by long arms, with the first pair being longer than the others, and a shallow web. It is red in color with large white spots over its entire body and paired white spots down the arms. The body measures up to 15cm and the arms to more than a meter. O. macropus is exclusively nocturnal and has a narrow range of prey species. Most of the research done on this species is concerned with larval development and activity patterns.

Taxonomy


Phylum: Mollusca
  Class: Cephlopoda
    Order: Octopoda
      Family: Octopodidae

Molluscs are characterized by a radula, muscular foot and shell (Sterrer 1986). In the class Cephalopoda the shell is mostly reduced, modified or absent, and is enclosed by the mantle (except in Nautiloidea) (Sterrer 1986). Members of the order Octopoda have 8 appendages with unstalked suckers (Sterrer 1986).


Habitat


The Octopus macropus species complex is found in shallow temperate and tropical waters throughout the world (Norman 2003). A species complex is a group of species that are reproductively isolated from each other but are not morphologically distinguishable (Norman 2003). They are found in the Atlantic, Pacific and Indian Oceans as well as the Mediterranean and Caribbean Seas (Norman 2003). O. macropus is very common in the near shore and deeper bottom regions of the Mediterranean Sea where it was first discovered (Boletzky et al 2002). O. macropus is also commonly seen in the tropical western and eastern Atlantic Ocean (Boletzky et al 2001). O. macropus is one of two octopus species commonly found in Bermuda, the other being Octopus vulgaris (Sterrer 1986). O. macropus lives near shore and its habitat overlaps that of O. vulgaris. However, O. macropus tends to live deeper than O. vulgaris (Meisel et al 2006). The depth range of O. macropus in Bermuda is 1 to 17 meters (Sterrer 1986). O. macropus prefers sand and rubble and is capable of burrowing in the sand (Norman 2003). The common name for O. macropus in Bermuda is the grass octopus because it often inhabits the grass beds in the flats behind reefs (Sterrer 1986). O. macropus has also been recorded in enclosed waters with rocky, sandy or grassy bottoms (Sterrer 1986).



Ecology


Activity:
Octopus macropus is active only at night (Meisel et al 2006; Norman 2003). These octopuses use light as a time cue for nocturnal activity (Meisel et al 2006). This is an adaptation to exogenous cycles such as the change between night and day, food availability, and activity of prey and predators (Meisel et al 2006). Octopus vulgaris shares the same genus and macrohabitat as O. macropus, however O. vulgaris is diurnal, or active during the day (Meisel et al 2006). This difference may reflect the activtiy of the two species. O. macropus is much less active and aggressive than O. vulgaris. O. macropus also has a more narrow range of prey (Meisel et al 2006). These differences may reduce competition through temporal spacing of activity since these species live in the same habitat (Meisel et al 2006).

Reproduction:
Octopuses are solitary animals so mating does not typically include courtship displays, long term pairing or monogamy (Hanlon and Messenger 1996). Octopus species have seperate sexes that look alike except for a hectocotylized third right arm in the males (Hanlon and Messenger 1996; Wells 1978). This hectocotylus is a specialized arm with a hollowed out groove into which a spermatophore sac fits (Hanlon and Messenger 1996). The hectocotylized tip of the third right arm of Octopus macropus is very long and slender (Sterrer 1986). Males also have some larger suckers at the bases of the second and third arm pairs (Wells 1978). Male Octopus vulgaris reach sexual maturity at an earlier age than females (Silva et al 2002). This is not an issue because the females are able to store sperm in the oviducal gland (Hanlon and Messenger 1996). Males and females of O. vulgaris die after their eggs hatch, which is typical of other octopus species as well (Hanlon and Messenger 1996). Before mating can commence the male and female octopus must meet. When a male octopus senses an intruder into its den, it will either pale and spread its interbrachial web, to make it appear larger, or remain dark to stay hidden (Wells 1978). The male will then try to envelope the intruder in its web and probe with its hectocotylus (Wells 1978). Once contact is made, if the intruder is another male the two octopuses will fight, if it is a female she will usually submit (Wells 1978). Since courtship is reduced there are no specific coloration patterns or postures used during mating. However, the male may display its large suckers so that the female is able to confirm his gender (Hanlon and Messenger 1996). The male will then insert his hectocotylus into her mantle cavity and deposit the spermatophores (Wells 1978). There have been no specific observations of the reproductive behavior or reproductive season of Octopus macropus.

However, there are several observations of larval development for O. macropus. The embryonic stages for O. macropus closely resemble those of other octopodid species. Spawning for O. macropus is estimated to be in winter and early spring (Sterrer 1986). The first record of spawning and embryonic development was made by Boletzky et al (2001). In this study a female was mated with two males in June and proceeded to lay more than 1000 eggs in September. The eggs were attached, by the female, to a hard substrate individually or in small clusters (Boletzky et al 2002). This forms a sheet of eggs on the walls of the den in which the female broods. Eggs are flask shaped (Boletzky et al 2002). The female died two weeks after the last hatchlings were observed. The female dies shortly after the eggs hatch because after the eggs are laid she stops eating and all of her time is spent brooding the eggs (Hanlon and Messenger 1996). Brooding includes cleaning and aerating the eggs (Hanlon and Messenger 1996). The newly laid ova measured 4.0x1.2mm (Boletzky et al 2001). These are much larger than those laid by Octopus vulgaris, however they are still small relative to the body size of O. macropus (Boletzky et al 2002). The newly hatched octopuses were 4mm in dorsal mantle length. They start as active swimmers and feed on planktonic organisms. The hatchlings are planktonic, but are micro-nektonic in terms of swimming and hunting behavior (Boletzky et al 2002). The hatchlings will sometimes spread their arms and use their suckers to attach to the substrate (Boletzky et al 2002). The hatchlings were also readily attacking and seizing crustacean larvae. The length of the planktonic/micro-nektonic stage for O. macropus is unknown, however it is possibly shorter than the two month long planktonic stage for O. vulgaris (Boletzky et al 2002). This prediction that life style switching may occur early is based on the spontaneous attachment to hard substrate by the hatchlings (Boletzky et al 2002).

Prey:
Octopus macropus has a more narrow range of prey species than an octopus species living in the same habitat, Octopus vulgaris. O. vulgaris consumes a variety of molluscan and crustacean prey. O. vulgaris seems to have more of a generalist and flexible lifestyle than O. macropus. Octopus only have one visual pigment but are able to detect prey through shape, movement, features, and scent (Fiorito and Gherardi 1999). One method that octopuses use to hunt is by groping, or feeling along the bottom, under rocks and in the sediment with their arms for prey (Fiorito and Gherardi 1999). They may also use their web to cover a prey item (Hanlon and Messenger 1996). They can also use their siphon to jet water into the sediment and expose prey (Hanlon and Messenger 1996). Once the prey item is obtained the octopus will use its radula to drill a hole through the shell or exoskeleton (Fiorito and Gherardi 1999). Bivalves can be pulled apart using the octopus’s arms and suckers or can be drilled (Fiorito and Gherardi 1999).

Predation:
Octopuses have many predators including pinnipeds (not found in Bermuda), large predatory fish (for example the Barracuda) and eels (Hanlon and Messenger 1996). Octopuses have two methods of evading predators. The first is camouflage or crypsis, where the octopus will match the color and/or texture of its surroundings (Hanlon and Messenger 1996). Octopus are able to change their color by expanding and contracting elastic pigment sacs called chromatophores (Ferguson and Messenger 1991). Changes in color are also achieved through th euse of iridophores and leucophores (Froesch and Messenger 1978). If camouflage fails to fool the predator the octopus will try other defense mechanisms. These include flight, inking, deimatic behavior (bluffing or threatening actions), defensive postures, and deflective markings (Hanlon and Messenger 1996). When Octopus macropus is disturbed, it flushes brick-red and its white spots become more prominent (Sterrer 1986).

Recent Research


There has not been much research done on Octopus macropus. Most of the literature available is on larval development. Boletsky et al (2001 and 2002) did two separate studies on the development of O. macropus from the spawning to the planktonic/micro-nektonic stage. Meisel et al (2006) did a study on the contrasting activity patterns of O. macropus and Octopus vulgaris because the two species share the same macrohabitat and genus. Future research could include prey preference, reproductive behavior, physiology and defensive/predator avoidance behavior. The work on larval development could also be expanded to look at what happens after the planktonic/micro-nektonic stage.

Commercial Importance


There is currently no literature on the commercial fishery of Octopus macropus. However, Octopus vulgaris, which is commonly in the same habitat as O. macropus, is caught for commercial purposes. Octopus is a delicacy in many countries, especially those whose diet is comprised strongly of seafood, and is prepared in a variety of ways (Hernandez-Garcia et al 1998). O. vulgaris accounts for about fifty percent of the total world octopus catch (Hernandez-Garcia et al 1998). The octopus are usually caught using otter trawls and sometimes octopus pots (Quetglas et al 1998). Fishery of O. vulgaris usually occurs on their breeding ground since it is shallow and there are larger numbers (Quetglas et al 1998). Since O. macropus shares the same habitat this fishery may also affect their population density, prey species and behavior.

Bermuda Laws


Bermuda laws in the form of MPAs and no collection zones help to protect Octopus vulgaris and Octopus macropus and the habitats in which they live. In 2000, Bermuda passed the Customs Tariff Amendment (No 2) Act in which it was stated that all mollusk species meant for human consumption are subject to a tax of ten percent per kilogram.

Personal Interest


I have been interested in marine biology since my family used to take walks on the beach near my house and my dad would have contests to see who could find the most interesting thing. Going into college in the marine biology program I was very unsure of what I wanted to study because I was interested in everything. One of the professors that was teaching a few of my classes does research on cephalopod environmental physiology. I always thought his classes were really interesting so I asked if I could help out in his lab. He did me one better and invited me on a research cruise. The research cruise was in the Gulf of California and most of the work was on the metabolism and vertical migration of the Humboldt squid. This trip is what really made me want to study cephalopods because I think that they have a lot of interesting physiological adaptations to living in a variety of different habitats. I am especially interested in octopus. This may be due to volunteering at New England Aquarium. I volunteered in the cold marine gallery and helped to feed a giant pacific octopus named Gueneviere. I thought it was really cool how curious she was and how she seemed to have her own personality. When I decided to come to Bermuda I really wanted to do my research project on octopus. I am very interested in physiology and in particular metabolism. So for my research project I will be doing metabolism (from measurements of oxygen consumption) of Octopus macropus. In the future I hope to do more work on octopus.

References

Boletzky, S.V., M. Fuentes, N. Offner. 2001. First record of spawning and embryonic development in Octopus macropus (Mollusca: Cephalopoda). J. Mar. Biol. Ass. U.K. 81:703-704.

Boletzky, S.V., M. Fuentes, N. Offner. 2002. Developmental features of Octopus macropus Risso, 1826 (Mollusca, Cephalopoda). Vie Et Milieu-Life and Environment. 52(4):209-215.

Fiorito, G. and F. Gherardi. 1998. Prey-handling behavior of Octopus vulgaris (Mollusca, Cephalopoda) on Bivalve preys. Behavioural Processes 46: 75-88.

Ferguson, G.P. and J.B. Messenger. 1991. A countershading reflex in cephalopods. Proc. Royal Soc. Lond. 243: 63-67.

Froesch, D. and J.B. Messenger. 1978. On leucophores and the chromatic unit of Octopus vulgaris. J. Zool., Lond. 186:163-173.

Hanlon, R.T. and J.B. Messenger. Cephalopod Behavior. Cambridge: Cambridge University Press, 1996.

Hernandez-Garcia, V., J.L. Hernandez-Lopez, J.J. Castro. 1998. The octopus (Octopus vulgaris) in the small-scale trap fishery off the Canary Islands (Central-East Atlantic). Fisheries Research 35: 183-189.

Meisel, D.V., R.A. Byrne, M. Kuba, J. Mather, W. Ploberger, E. Reschenhofer. 2006. Contrasting Activity Patterns of Two Related Octopus Species, Octopus macropus and Octopus vulgaris. J of Comparative Psych. 120: 191-197.

Norman, M. 2003. Cephalopods: A World Guide. Conchbooks. Hackenheim, Germany.

Silva, L., I. Sobrino, and F. Ramos. 2002. Reproductive Biology of the Common Octopus vulgaris Cuvier, Cuvier 1797 (Cephalopoda: Octopodidae) in the Gulf of Cadiz (SW Spain). Bull. Mar. Sci. 71(2): 837-850.

Sterrer, W. 1986. Marine Fauna and Flora of Bermuda: A Systematic Guide to the Identification of Marine Organisms. John Wiley and Sons, Inc.

Wells, M.J. 1978. Octopus: Physiology and Behaviour of an Advanced Invertebrate. Chapman and Hall Ltd. London.

Links

Octopus macropus escaping through a 1 inch hole
The Cephalopod Page
CephBase
Bermuda Law Database