Blackwater Diving: An Exciting Window Into the Planktonic Arena and Its Potential to Enhance the Quality of Larval Fish Collections

Abstract

Blackwater diving,'' or nighttime SCUBA diving in epipelagic environments, has become highly popular in recent years because lay participants encounter animals that are difficult and expensive to observe through other methods. These same observations can be priceless for researchers working with these species, so an interface between the scientific communities and recreational divers would be mutually beneficial. In this paper, we describe one such interface through the photography, collection, and DNA barcoding of larval fishes from the island of Hawaii. The images and videos from this activity provide an exciting window into the epipelagic environment and the way larval fishes appear and swim within it. Blackwater diving allows us to see the often-elaborate appendages and other specializations of these larvae as they appear in situ, prior to extensive net and fixation damage. However, blackwater diving remains an almost exclusively recreational pursuit, particularly popular among underwater photographers, who have little interest in (or object to) collecting specimens for scientists. Nonetheless, a logical next step is careful hand collection of specimens for scientific study. Growing numbers of recreational divers around the world have access to an otherwise expensive-to-research habitat. Here we present, for the first time, in situ and post-fixation photos of larval fishes that were hand collected and fixed in 95% ethanol by blackwater divers operating out of Kona, Hawaii, with DNA barcode identifications congruent with morphology and pigmentation where possible. With the right motivation, blackwater diving could augment research in the pelagic ocean and significantly enhance natural history collections and our knowledge of the larvae of marine fishes.

Hydromedusae observed during night dives in the Gulf Stream

“…This method is indeed very promising and several rarely reported medusae species were encountered [see e.g. also Nonaka et al (2021) for a similar study on fish larvae].…”

The Expanding Role of Natural History Collections

“…For example, these specimens include the associated recordings of anuran calls (Fig. 4) and videography and photography of specimens in situ made prior to collection that record behaviors (Nonaka et al, 2021). More generally, specimens can be viewed as including any aspect of the specimen that can be archived, curated, and used to advance the understanding of its biology, including data points related to the physical object.…”

The transcriptional landscape underlying larval development and metamorphosis in the Malabar grouper (Epinephelus malabaricus)

“…More recently, it has also been suggested that the metabolic changes that occur during larval development in teleosts may be regulated by TH, as demonstrated in clownfish [14]. Of note in some cases, like groupers (elongated spines) [16][17][18] or carapids (vexillum appendage) [19], some changes occur very early on and are considered as temporary specialization of the pelagic larval stages, serving as anti-predator defense [20], flotation [21] or camouflage [22]. It is still unclear if these are late developmental processes occurring after hatching or early manifestations of metamorphosis.…”