Date of Degree
Jennifer A. Basil
BRUVS; Cephalopod; Conservation; Learning and Memory; Nautilus; Scavenging
Chambered nautiluses are unique molluscs that differ from their closest relatives, octopus, squid, and cuttlefish, in many ways. Most obvious, nautiluses possess the ancestral trait of an external shell; a shell that has protected them for hundreds of millions of year but is dooming them today. Although nautiloids have survived all five mass extinction events, the lineage is under siege in the current 'sixth mass extinction'. Unregulated, unmanaged, and ongoing nautilus fisheries, particularly in the Philippines and Indonesia, have been depleting populations in a matter of years, some to local extinction, to supply a worldwide demand for the ornamental shell. Although nautiluses are heavily fished and common in the shell trade, there is a considerable lack of information on their biology, ecology, and behaviors. Thus, at this point, we do not have enough basic information about nautiluses to propose management plans and conservation practices. Here, we investigate three aspects of nautilus life history as it relates to conservation by combining laboratory and field studies: navigational tactics, feeding behaviors, and population demography.
Nautiluses learn and remember visual cues to find a goal using a beacon, or constellation of cues around the goal. However, the contribution of kinesthetic, or route memory, as they navigate to the goal, is unknown. Here, we tested the nautiluses' ability to navigate a maze by shifting or removing a visual beacon cue used to identify the goal. We found that after learning that a beacon cued a goal in a spatial maze, nautiluses switched to route memory to find the goal when the beacon was removed. However, this switch was difficult for them. Nautiluses tested with a shifted beacon, 45° relative to the goal, ignored their route memory to orient toward the beacon instead. Only when the beacon was shifted 90° from the learned location, or was removed entirely, did the animals seem to switch to route memory. Thus, it appears that during learning, the beacon overshadows the acquisition of route memory. However, as animals were successful in finding the goal when the beacon was removed, overshadowing was not complete -- nautiluses were able to access route memory when the beacon was removed entirely. Thus, nautiluses exhibit behaviors that indicate they are adapted for an environment with cues that may shift or become unreliable.
Most cephalopods are active predators that rely on a suite of different behaviors to capture live prey. Nautiluses have been characterized as predators, scavengers, and opportunistic scavengers, among other terms. However, no direct evidence has been available to confirm these claims. Here, we used field and laboratory observations to describe what type of prey nautiluses prefer (dead or live) and how they locate and capture prey items. In the field, baited remote underwater video systems (BRUVS) were deployed at four different sites in the South Pacific to depths of 300-400m to record feeding behavior of wild Nautilus. In the laboratory, a mock setup of nautilus habitat was used to test and record the nautiluses' ability to locate and capture dead, and sometimes buried, shrimp. In both settings, the nautiluses exhibited the same foraging behaviors. Remote tracking of the food source was characterized by the cone of search behavior with tentacles extended outward and laterally. Field observations suggested that nautiluses may dig for prey items and laboratory experiments confirmed this ability. Nautiluses were able to locate prey from a distance and then excavate buried prey items. An unexpected result here was that nautiluses showed no foraging or predatory behaviors toward live prey items in the field which suggests that nautiluses may only forage on decaying prey. The foraging and digging behaviors appear to be fixed action patterns in Nautilus, exhibited in the presence of odor stimuli whether the nautilus consumes the food item or not. This would be an ideal adaptation for an opportunistic forager finding food in a dark environment with limited prey items. However, this adaptation has the secondary effect of leaving nautiluses highly vulnerable to being caught in traps baited with dead prey items. In addition, their digging behavior makes them susceptible to accumulating toxins in the sediment that may collect on the ocean floor as a result of increasing coastal development and runoff.
The extant species of Nautilus and Allonautilus (Cephalopoda) inhabit fore-reef slope environments across a large geographic area of the tropical western Pacific and eastern Indian Oceans. While many aspects of their biology and behavior are now well-documented, uncertainties concerning their current populations and ecological role in the deeper, fore-reef slope environments remain. Given the historical to present-day presence of nautilus fisheries at various locales across the Pacific and Indian Oceans, a comparative assessment of the current state of nautilus populations is critical to determine whether conservation measures are warranted. We used baited remote underwater video systems (BRUVS) to make quantitative photographic records as a means of estimating population abundance of Nautilus sp, at sites in the Philippines Islands, American Samoa, Fiji and along an approximately 125 km transect on the fore reef slope of the Great Barrier Reef from east of Cairns to east of Lizard Island, Australia. Each site was selected based on its geography, historical nautilus abundance, and the presence (Philippines) or absence (other sites) of Nautilus fisheries. We found significantly fewer nautiluses with this method than expected in the Philippine Islands site. While there may be multiple reasons for this difference, the most parsimonious is that the Philippines Islands population has been reduced due to fishing. Specifically, historical trap records from the same site demonstrate there have been far more nautiluses at this site in the past.
Effective conservation plans benefit both the species of interest as well as the community. We identify visual and kinesthetic cues and tactics that are important to nautiluses returning to locations in their habitat (e.g., hiding spots, good foraging), and support the hypothesis that nautiluses are strict scavengers, sometimes reliant on digging in the substrate to find food they have found using olfactory cues. We also report on the health of populations in both fished and unfished sites in the Indo Pacific. There is still work to perform, such as identifying preferred habitat type, preferred species of prey, and calculating abundance levels at different areas and at different times. However, without protection, fisheries will continue to deplete nautiluses to extinction, one population at a time, as the fishermen move to new sites when one site is no longer profitable.
Barord, Gregory Jeff, "On the Biology, Behavior, and Conservation of the Chambered Nautilus, Nautilus sp." (2015). CUNY Academic Works.