Giant Squid

Description:

Architeuthis dux, also known as the giant squid, is one of the largest species of cephalopod and one of the largest invertebrates, second only to the colossal squid (MarineBio, 2021). They can reach lengths of up to 18 m (~60 feet) and have been relatively difficult to describe due to their solitary nature in the depths of the sea. Most of the giant squid that have been found have either been from the remains of whale stomachs or from dead specimens that have washed up on beaches (Winkelmann et al., 2013). Considering these creatures remained a mystery for a very long time, it was thought that there were multiple species of giant squid. However, mitochondrial studies have recently determined that there is indeed only one species of giant squid. Additionally, these mitochondrial genome studies have shown that the giant squid has low nucleotide diversity, particularly when compared to other marine species. While the exact reasons for this are unknown, one hypothesis is that the population of the giant squid used to be much smaller, perhaps because of predation or competition, but has more recently expanded due to a loss of these predators/competitors as a result of large climatic events (Winkelmann et al., 2013).

Habitat and Distribution:

Architeuthis are found globally, from the eastern Atlantic Ocean and the western Mediterranean Sea down to the waters of South Africa and New Zealand (Roper et al., 2015). They are rarely found in polar and tropical waters, however. One area that has had significant records of Architeuthis, usually in the form of dead specimens floating on the water’s surface, is the western Atlantic Ocean, from Newfoundland to the Gulf of Mexico. Interestingly, no sightings were reported in the mid-Atlantic shores of the United States, between Massachusetts and Florida. Between 1952 and 2011, 28 giant squid specimens were reported or collected, with a rise in sightings beginning in the 1990s. Before the 90s, only 3 or 4 specimens were reported. The rise in specimen sightings is likely due to an increased scientific awareness of the species, as well as a growing interest in them (Roper et al., 2015).

In terms of the habitat of Architeuthis, not much is known considering much of what is known about these creatures comes from their dead bodies. We do know, however, that they live in the Twilight Zone of the ocean at depths of around 300m - 600m (1,000-2,000 feet) (Frey, 2019).

Feeding Habits:

Architeuthis, like other cephalopods, are carnivorous. Just like most aspects of their life, their diet had remained a mystery for a while. However, an analysis of a few specimens’ gut contents shows that they likely feed on fish and cephalopods. Specifically, they feed on active and schooling fish, such as hake and cod, and pelagic cephalopod species, particularly other squid species (Regueria et al., 2013). They may also occasionally feed along the bottom of the sea for benthic fish and crustaceans.

The method in which Architeuthis obtains its food is still up for debate. The presence of active fish in the gut contents, as well as video footage, suggests that the giant squid is an active predator that can attack prey. However, other evidence, such as an estimated daily feeding rate of 0.5-0.8% of their own body weight, indicates a more passive, sit-and-wait style of hunting (Regueria et al., 2013). It is a possibility that the squid will employ both tactics when hunting. However, since evidence for both styles exists, the topic remains up in the air.

In terms of trophic levels, the gut contents of Architeuthis individuals indicate that they play the same or similar roles in deep-sea food webs, regardless of gender, size, or geographic location (Regueria et al., 2013). However, these organisms may differ in trophic levels depending on their age. Carbon and nitrogen isotope levels in their beaks indicate an ontogenetic shift from lower trophic levels as juveniles to higher levels as adults. They have also been shown to only inhabit small areas that are abundant in food (Guerra et al., 2010).

Works Cited

Frey, Michelle. “All You Need to Know about the Giant Squid.” Ocean Conservancy, 26 June 2019, https://oceanconservancy.org/blog/2019/06/26/need-know-giant-squid/.

Guerra, Ángel, et al. “Life-History Traits of the Giant Squid Architeuthis Dux Revealed from Stable Isotope Signatures Recorded in Beaks.” ICES Journal of Marine Science, vol. 67, no. 7, 2010, pp. 1425–1431., https://doi.org/10.1093/icesjms/fsq091.

MarineBio. “Giant Squid ~ Marinebio Conservation Society.” MarineBio Conservation Society, 2021, https://www.marinebio.org/species/giant-squid/architeuthis-dux/.

Nilsson, Dan-Eric, et al. “A Unique Advantage for Giant Eyes in Giant Squid.” Current Biology, vol. 22, no. 8, 24 Apr. 2012, pp. 683–688., https://doi.org/10.1016/j.cub.2012.02.031.

Regueira, M., et al. “What Does the Giant Squid Architeuthis Dux Eat?” Hydrobiologia, vol. 725, no. 1, 2013, pp. 49–55., https://doi.org/10.1007/s10750-013-1662-y.

Roper, Clyde F., et al. “A Compilation of Recent Records of the Giant Squid,Architeuthis Dux(Steenstrup, 1857) (Cephalopoda) from the Western North Atlantic Ocean, Newfoundland to the Gulf of Mexico.” American Malacological Bulletin, vol. 33, no. 1, 13 Jan. 2015, pp. 78–88., https://doi.org/10.4003/006.033.0116.

Smithsonian. “Giant Squid.” Smithsonian Ocean, Apr. 2018, https://ocean.si.edu/ocean-life/invertebrates/giant-squid.

Winkelmann, Inger, et al. “Mitochondrial Genome Diversity and Population Structure of the Giant Squid Architeuthis : Genetics Sheds New Light on One of the Most Enigmatic Marine Species.” Proceedings of the Royal Society B: Biological Sciences, vol. 280, no. 1759, 25 Feb. 2013, p. 20130273., https://doi.org/10.1098/rspb.2013.0273.