Every night as the sun dips below the horizon, an extraordinary event unfolds in the ocean: one of the planet’s largest migrations. Deep-sea inhabitants ascend to the surface to feast, offering a unique spectacle for those brave enough to venture into the dark offshore waters known as blackwater diving.
“You’re just out there drifting with the current and checking out all this life that’s in the ocean,” shares Rich Collins, a renowned blackwater photographer and diver associated with the Florida Museum of Natural History.
These incredible blackwater photographs, however, are capturing far more than just beautiful fish. Through careful examination of images provided by Mr. Collins and his fellow divers, scientists are uncovering never-before-seen interactions between young fish and anemones.
A recent study, published last month in the Journal of Fish Biology, documented larval and juvenile fish either concealing themselves behind or actively carrying larval sea anemones. These anemones, close relatives of jellyfish, possess stinging capabilities. While adult anemones typically anchor themselves to the seabed, their larval counterparts drift freely through the ocean currents.
Gabriel Afonso, a doctoral student at the Virginia Institute of Marine Science and the lead researcher of the study, suggests that by embracing a potentially toxic invertebrate, these young fish might be warding off predators. “The fish sometimes seem to be using the invertebrate as a protection,” he noted.
The photographs depict various larval fish species, such as pomfrets and filefishes, gripping larval tube anemones – a type of anthozoan – within their mouths. The study identified four distinct families of fish engaged in these interactions in the pelagic zone, or open ocean.
This strategy is akin to a “poison pill defense,” Mr. Collins explained, effectively telling potential attackers: “Go ahead and eat me, but you’re going to eat this little poison pill at the same time.”
For the anemone, this symbiotic relationship could offer a method of dispersal. However, further research is necessary to fully grasp how and whether both species truly benefit from this unique partnership.
Simon Thorrold, a marine biologist at Woods Hole Oceanographic Institution who was not involved in the research, remarked that the study presents “something new and interesting to think about” for other fisheries scientists. “I had no idea that there was this much diversity in the relationship between fishes and anthozoans,” he added.
Beyond the advantages to individual fish, Dr. Thorrold pondered the broader implications for population survival. This is just one of many new research avenues being opened up by blackwater diving.
Traditionally, the study of juvenile fish involved examining specimens captured in mesh nets, leaving scientists to speculate about their behavior and interactions in their natural open-ocean habitat. “It’s hard enough studying whale sharks, who are 30 feet long, let alone a larval fish that might be 10 millimeters or an inch long,” Dr. Thorrold pointed out.
The larval stage is a critical period in a fish’s life cycle, as the mortality rate during this phase largely dictates how many individuals reach adulthood.
“Marine fish larvae can be as different from the adults they will become as caterpillars are to butterflies,” observed Carole Baldwin, curator of fishes at the National Museum of Natural History, who also was not part of the study.
For those studying larval fish, blackwater photography is nothing short of a “game changer,” according to Dr. Baldwin. These photographs offer glimpses into novel behaviors, developmental stages, colors, and interactions that are rarely observable in preserved specimens. Blackwater photos are truly “like a gold mine,” Mr. Afonso emphasized. Marine scientists frequently comb through social media groups, seeking images that might reveal new species or behaviors, and then reach out to the photographers. This collaboration between the scientific community and diving enthusiasts is “really beautiful,” Mr. Afonso expressed.
Ai Nonaka, a researcher at the National Museum of Natural History, stated that blackwater photography, combined with advanced scientific techniques, is profoundly transforming how scientists approach the study and understanding of the early life stages of marine fish. At the museum, she confirmed, “we now house over 500 larval fish specimens collected directly by blackwater divers.”
Mr. Collins, who has completed hundreds of dives in the Gulf Stream off the coast of Florida, estimates he has contributed approximately 1,000 specimens to the Florida Museum of Natural History. “It’s turned into sort of an avocation, as opposed to just a hobby,” he remarked.
“The thing that people don’t recognize is just how much life there is out there, just beneath the surface,” Mr. Collins added, “and that there’s this amazing migration that happens every day.”