Discovering Deep-Sea Corals of the Phoenix Islands 2

Healing from Open Wounds
Corallivory is the term for predation upon live corals. Organisms like fish and invertebrates can eat the tissue, skeleton, and mucus of the coral colony. The coral usually survives the interaction but is left with an open wound. While these encounters are well studied in shallow coral reefs, little is known about how deep-sea corals respond to wound infliction by their predators.

Deep-sea corals are slow-growing, adapted to thrive under incredible pressure and darkness, and live for hundreds to thousands of years. How they are able to do so while also sustaining external damage and fending off microbial infection is a question Rotjan and her team hope to answer. Understanding how deep-sea corals’ immune systems respond to physical damage from their predators will provide insight into deep-sea coral health and is important knowledge that may give insight into the evolution of our own immune systems.

Benign Bacteria
During the 2017 expedition, Anna Gauthier, a Ph.D. student on the science team co-mentored by Rotjan and Kagan, attempted to culture microbes found during the ROV dives in PIPA while on-ship. Her culture collection included bacteria from the sediment, the corals, the water column, and even the intestine of a seastar. Her efforts yielded over 200 new species of bacteria; an incredible and important discovery because all 200 of them have novel lipopolysaccharide (LPS) structures. LPS structures make up the fatty outer membrane of cell-walled bacteria and are commonly used in the development of novel human therapeutics.

Innate immunity is the immune system mammals are born with and is the first line of defense in protecting the body against pathogens. The rules of mammalian innate immunity state that humans should be able to universally detect microbes in our environment unless they are specifically co-evolved to evade detection, for example, microbes that are either beneficial or harmful. Co-evolved microbes include gut bacteria which help us digest our food and Streptococcus bacteria which causes strep throat.

A New Discovery
Until the discovery by Gauthier, Kagan, Tekiau, Rotjan, and others, scientists believed microbes were globally detectable by mammalian immune systems. However, when these deep-sea microbial LPS were tested on mice and human cells, the cells were unable to detect them. In laboratory tests, mammalian immune systems treated them as if they were as benign as a water molecule, which has massive implications for the development of novel therapeutics and necessitates a revision of mammalian innate immunity. It is now clear that the rules of mammalian innate immunity are locally (not globally) defined. In other words, mammals will detect the microbes we interact with, but may not universally be able to detect microbes from foreign environments like the deep-sea.

The investigation into deep-sea microbes will continue on this expedition; this time the team will culture and test the response of deep-sea corals to diverse bacteria while at sea. They will continue to question the universality of immune theory by examining how deep-sea microbes interact with novel cells. The potential outcomes help to further justify the importance of marine conservation for the future of healthy ecosystems, and healthy humans.

A Truly Collaborative Team
PIPA was originally conceived as a “gift to humanity” from Kiribati, but until 2017, the deep sea remained a wrapped present. Now, several deep-sea expeditions later, and with previous work in the region by Rotjan, Shank, Auscavitch, Kennedy, Gauthier, Cordes, and others, it is clear that PIPA harbors a stunning diversity of colorful deepwater corals, sponges, and other invertebrates, as well as a suite of unknown bacteria with transformative potential for human medicine. The science team on Falkor will be working to achieve complementary goals that include describing new species of coral and invertebrates that live among them; characterizing patterns of corallivory from deep-sea transects; at-sea microbial and corallivory experiments; and simultaneously characterize the deep-sea environment of the full Phoenix Islands archipelago.

Though the team will be working only in US waters this trip, the team also includes a Kiribati collaborator on board, who will assist with the science. The relationship with this special no-take MPA genuinely showcases the importance and value of scientific collaboration and international partnership. It is in this collaborative spirit that the US-Kiribati team heads to United States waters to complement previous work in Kiribati waters, with a long science to-do list that will shed light on this critical ecosystem.