Newswise – There are more than 300 species of squid living in diverse habitats that include coral reefs, seagrass beds, sand flats, and polar ice regions where they feed on lower trophic levels. Best known for its eight arms (octopus comes from the Greek, octópus, which means “eight feet”), the behavioral ecology of these mysterious sea creatures, particularly the octopuses that share their habitat, is important in understanding their role in community structure and Biodiversity of an ecosystem. Coexistence has been well studied in many species, but rarely in cephalopods such as octopuses.
Researchers from Florida Atlantic University in collaboration with the Marine biology laboratory in Woods Hole, performed the first on site, Long-term study (three years, 371 hours of diving) in a lagoon in South Florida on two species of octopus. The aim of the study was to find out how Octopus vulgaris (common octopus), a medium-sized octopus that is widespread in tropical and temperate seas around the world and Macrotritopus defilippi (Atlantic long-arm octopus), a small species of octopus found in the Atlantic, Mediterranean, and Caribbean, coexist by studying their feeding habits and tactics, diet, behavior, and activity or inactivity.
The study’s rigorous fieldwork included direct observations through diving combined with active and remote video recordings. What the researchers discovered published in the Journal of Experimental Marine Biology and Ecology, is that these two octopus species coexist in a shallow Florida lagoon through very different behaviors and habits – even at high density.
Previously, the research team had discovered that there is a fine division of habitat between these species, but that they still inhabit the same general areas and could use multiple resource-sharing mechanisms to varying degrees. The diet, periods of activity, and foraging of the common octopus have not been studied in this South Florida lagoon and have never been studied in the presence of the Atlantic long-arm octopus. For the Atlantic long-sleeved octopus, there are no reports of feeding or foraging and only two reports of activity duration, which are contradicting.
“Incorporating species-specific behavior is a key tool in understanding octopus ecology and coexistence,” said Chelsea O. Bennice, Ph.D. Department of Life Sciences, FAU Charles E. Schmidt College of Science; and deputy director of FAU RISING UP Programs too Advance S.TEMC.Community E.commitment through neuroscience D.Discovery, within the Stiles-Nicolson Brain Institute on the John D. MacArthur Campus on Jupiter.
Along with foraging, Bennice and co-authors W. Randy Brooks, Ph.D., FAU Department of Biological Sciences; and Roger T. Hanlon, Ph.D., Marine Biological Laboratory, decided to examine the feeding and activity periods for each species as potential resource sharing mechanisms, since they are the primary niche dimensions that normally go along with the habitat they are previously studied are divided between the species.
The results showed that the common octopus was mainly nocturnal (active at night), foraging on hard soil and mainly ate clams such as oysters, clams and scallops, while the Atlantic long-arm octopus was exclusively diurnal (active during the day) and foraging was soft soil and only eaten crustaceans such as crabs and prawns.
Both species exhibited a saltatory (stop and go) tactic dominated by speculative ground-searching, behavior guided by visual scanning and decision-making followed by tactile efforts of the arms and chemotactile suction cups. Species-specific behaviors were parachute attack (common octopus), imitation of flounder swimming (Atlantic long-arm octopus) and tripod posture (Atlantic long-arm octopus).
“We found clear differences in substrates and prey types as well as periods of activity. Since each species also hides in different ways – the common octopus in mussels or hard substrate cavities and the Atlantic long-arm octopus in holes and cavities in the sand – we now understand together how these two species can coexist even at relatively high densities, “said Bennice. “Additional behavioral studies can help us better understand the environmental requirements for cephalopods, an important group in many marine food webs.”
Funding sources for this project included the Broward Shell Club, the Palm Beach Fishing Club, and the Animal Behavior Society. The Sholley Foundation partially funded this Hanlon research.
About Florida Atlantic University: Florida Atlantic University, founded in 1961, officially opened in 1964 as the fifth public university in Florida. Today the university looks after more than 30,000 undergraduate and postgraduate students at six locations along the southeast coast of Florida. In recent years the university has doubled its research spending and outperformed its competitors in academic achievement. Through the coexistence of access and excellence, FAU embodies an innovative model in which traditional performance gaps disappear. The FAU is named a Hispanic Institution, rated by the US News & World Report as one of the best public universities, and by the Carnegie Foundation for the Advancement of Teaching as an institution with high research activity. For more information, visit www.fau.edu.