Cephalopod Awareness Days
Searching for Nautilus in National Marine Sanctuary of American Samoa
By Clarissa Lam
"Shellebrating" Common Ancestry
In the depths of the Pacific Ocean, a small, ancient creature slowly bobs up and down along the ocean floor in search of food. Its bright and unique shell sets it apart from the other, darker sea creatures in its habitat. Meet the nautilus!
While nautiluses reside in the Western Pacific Ocean, other cephalopods — a group of marine invertebrates with well-developed eyes and nervous systems, including squids and octopuses — can be found in national marine sanctuaries throughout the United States. An octopus nursery was discovered in Monterey Bay National Marine Sanctuary in 2018, and many different octopus and squid species have been documented in sanctuaries such as Florida Keys National Marine Sanctuary, Channel Islands National Marine Sanctuary, and Flower Garden Banks National Marine Sanctuary.
Although nautiluses fall into the cephalopod family, they differ greatly from their cephalopod cousins: cuttlefishes, squids, and octopuses. Within the class Cephalopoda, there are two subclasses: Coleoidea, which includes cuttlefishes, squids, and octopuses; and Nautiloidea, which includes nautiluses.
A key difference between the two subclasses is the nautilus' famous shell. What many people do not know is that the early ancestors of modern coleoids did have hard external shells, similar to the nautilus. As the animals evolved, different coleoids displayed different shell shapes, and the animals would wrap their soft mantles around their hard shells. In some, the shell became fully internalized, like a backbone, and reduced in size. This lightweight internal shell structure was known as a gladius and can still be found in all modern squid species. In many octopuses, the shell has been completely lost!
A "Living Fossil" Faces Climate Change
In American Samoa and across the world, ocean acidification and rising water temperatures are becoming the norm. An increasingly acidic ocean dissolves the skeletons and shells of coral and other calcifying ("shell-building") organisms, including the magnificent shell that makes the nautilus so beloved.
"Because the water is more acidic, there are less carbonate ions available for animals to build their calcium carbonate shells or skeletons" said Valerie Brown, research coordinator for National Marine Sanctuary of American Samoa. "It's just simple chemistry. They have to be able to pull the carbonate from the water and if it's been bound as an acid because of the increase in carbon dioxide in the water, then it makes it energetically more expensive for them to build those shells."
Nautilus prefer temperatures below 77°F, so rising ocean temperatures may make some of the areas they currently inhabit too warm. They may seek cooler temperatures by moving to deeper waters. However, this may not be possible as their shells aren't strong enough to survive at depths below 2,600 feet.
There is still hope for the nautilus, however. Considered a "living fossil," they evolved roughly 500 million years ago, and have survived more than a few of Earth's mass extinction events, including the meteor that killed the dinosaurs and 75% of Earth's species 66 million years ago. Their deep water home acted like a bunker, insulating them from the harsher changes to the world above them.
The nautilus differs from other cephalopods in more ways than one. Most cephalopods have eight to ten arms, but nautiluses can have over 90! They don't have the suction cups that are so often associated with their close relatives, and instead, they are covered with small ridges and coated with a sticky secretion to help them grip food and place it in their mouths.
Because of their more passive existence, nautiluses do not propel themselves in the same way that coleoids do. Instead, nautilus shells have multiple chambers, typically starting off with seven or eight small chambers when they first hatch, and developing as many as 30 chambers as they grow older. Using a special organ inside their shell, the nautilus can control the distribution of fluids and gases in each chamber, giving it control over its buoyancy and allowing it to float up and down.
Nautiluses also stand apart from other cephalopods in terms of their lifespans. While most cephalopods live between three to five years, nautiluses can live for over 20 years, and they do not reach maturity for 10 to 15 years.
To top off everything that makes these creatures unique, nautiluses only reside in specific areas of the world. They are mainly found in the western Pacific Ocean and coastal areas of the Indian Ocean, but can also be found in the waters near American Samoa.
Nautiluses in the National Marine Sanctuary of American Samoa
Of all the areas in the National Marine Sanctuary System, the American Samoa sanctuary is the most remote and is thought to support the greatest diversity of marine life. It was originally the smallest sanctuary, with just 0.25 square miles established in 1986 within Fagatele Bay. However, in 2012, the sanctuary was expanded to include five additional protected areas, making it the largest in the National Marine Sanctuary System with 13,581 square miles of nearshore coral reef and offshore open ocean waters across the Samoan Archipelago.
Due to the recent expansion, there is still a vast amount of the sanctuary left to explore, especially in the deeper waters where nautiluses may reside — typically between 350 to 1,000 feet, and sometimes as deep as 2,600 feet! While live nautiluses have yet to be observed within the sanctuary, scientists aboard a submersible found a perfectly intact shell in Fagatele Bay in 2005 and many nautiluses have been found and filmed in Taema Bank, off the main island of American Samoa, Tutuila. According to Brown, the discovery of nautiluses at Taema Bank indicates there is a good chance they are also found within the sanctuary, which has many ecological similarities.
Dr. Gregory J. Barord of University of New York and a team of colleagues used a baited remote underwater video system to record two larger adult nautilus and one juvenile nautilus at Taema Bank.
"We're now expanding our science program, and we're gearing up to try to get equipment to be able to explore mesophotic depths and the deeper areas that nautilus may inhabit," Brown said.
Nautiluses were also recently listed as Endangered by NOAA Fisheries through the Endangered Species Act, which is further propelling sanctuary scientists to figure out where in the sanctuary they may reside and how climate change may affect their survival in these areas.
"They are part of the ecosystem here [in American Samoa], so we do want to make sure that they're protected within the sanctuary waters to the fullest extent possible," Brown said.
Encountering nautiluses inside the sanctuary on future research expeditions could give scientists the ability to monitor and protect their population and learn more about the role these animals play in the waters of American Samoa. Researchers working in the sanctuary will look for nautilus and other mesophotic sea creatures during surveys in 2021 and 2022 using scuba divers on rebreather systems and a remotely operated vehicle.
Video courtesy of the NOAA Office of Ocean Exploration and Research, 2017 American Samoa. This expedition was part of the three-year campaign to support science and management decisions within and around U.S. marine protected areas in the central and western Pacific.
"We're excited to see if we can confirm the presence of nautilus in the sanctuary in the coming years," Brown said.
As we wait in anticipation to discover if nautiluses contribute to the rich biodiversity of National Marine Sanctuary of American Samoa and as we celebrate the fascinating diversity of cephalopods during this year's Cephalopod Awareness Days (Oct. 8-12), we hope you appreciate everything that makes nautiluses, and all other cephalopods, an essential part of the marine ecosystems they inhabit, within and outside of your national marine sanctuaries.
Clarissa Lam is a student at Reed College and a Virtual Student Federal Service intern for NOAA's Office of National Marine Sanctuaries.