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AD 2016 Q4

Alert Diver is the dive industry’s leading publication. Featuring DAN’s core content of dive safety, research, education and medical information, each issue is a must-read reference, archived and shared by passionate scuba enthusiasts. In addition, Alert Diver showcases fascinating dive destinations and marine environmental topics through images from the world’s greatest underwater photographers and stories from the most experienced and eloquent dive journalists in the business.

LIFE AQUATIC MARINE

LIFE AQUATIC MARINE BIOGEOGRAPHY unexso @unexsobahamas fish or invertebrate might evolve into two or more species over time. As sea levels rise and land barriers are once again covered with water, expanding marine habitats allow the now genetically dissimilar populations to mix again. Thus, climatic events in combination with tectonic movements have caused previously isolated species to evolve, congregate in and disperse from the Coral Triangle. HABITATS AND NICHES Geography, climate, plate tectonics, recurring ice ages and oceanic current circulation play large roles in species’ aggregation in and dispersal from given regions, but another vital factor in determining a place’s biomass and biodiversity is the number of habitats and niches available. The more habitats and niches, the more species an area will have. For example, the cold, coastal waters of Cape Cod, Mass., offer few habitat differences, while the seascape among the islands of Indonesia offers many. Flooded by daily tides, extensive mangrove forests support juvenile fishes. Seagrass meadows also act as nurseries for a large number of reef dwellers. Nearby lagoons offer protected patch reefs as habitats for large reef fishes. The threedimensional, honeycomb structure of barrier reefs adds even more niches. VARIETY, NOVELTY AND ADVENTURE Marine biogeography — the wild array and distribution of underwater life — is a vital ingredient in making recreational diving the adventure that it is. Each time divers venture beneath the surface, no matter where in the world, they have the opportunity to observe a creature, a behavior or a relationship that they never seen — and perhaps one that no one has ever seen. It is now estimated that there are roughly 8.7 million species on Earth. Somewhere between 35,000 and 60,000 reef dwellers have been described to science, including many, but certainly not all, shallow-water fish and invertebrates. At present, about 76 percent of the world’s coral species and 37 percent of all reef fishes, an estimated 3,000 species in all, flourish within the Coral Triangle. Beyond simply keeping divers fascinated, this biodiversity is a vital cog in the interconnected ecosystems of planet Earth. Every species and individual plays a role, and humans cannot separate themselves from this interconnectedness. “Our understanding of the origin of diversity and distributional patterns in the Indo-West Pacific is still rudimentary,” Paulay said. So far it has been impossible to unravel the mysteries and explain all the reasons underlying coral reef life. Besides a handful of well-studied fish and invertebrates, most coral reef dwellers are not well understood because of the difficulties in studying them. It is clear no single explanation for the distribution of plants and animals will suffice — a variety of complicated processes are at work, and they create a plethora of unique diving situations around the world. One of the most captivating aspects of this planet is that life, which is constantly and continually evolving, is unevenly distributed. The observable variability of species that inhabit each diving destination is what drives recreational diving around the world. It’s a big part of what keeps divers enduring long travels across the globe — the will to be in the midst of flourishing and ever-evolving life, discovering just a bit more about the unknown, no matter how far we must go. AD 42 | FALL 2016

RESEARCH EDUCATION MEDICINE 44 DAN WAS THERE FOR ME / 46 ADVANCED DIVING / 50 RESEARCHER PROFILE 54 CHAMBER CRISIS / 56 FROM THE MEDICAL LINE / 60 SAFETY 101 62 SKILLS IN ACTION / 64 INCIDENT INSIGHT With a largely transparent body interspersed with opaque white muscle lines, the Melibe colemani nudibranch is very difficult to spot among the soft corals on which it resides. When it feeds, it expands its massive mouth as if casting a net, nearly doubling its size. This one was seen in Anilao, Philippines. MIKE BARTICK ALERTDIVER.COM | 43