Coral reefs are a vision of activity and color during the day but they offer an entirely different world as daylight fades. The nocturnal animals, most of which are predators, come out of their hiding places and look for food. They have big eyes and huge black pupils that allow them to see in the dark.
Coral reefs are amazing places. Any person who has seen a reef is immediately struck by its astounding diversity and density of life. In fact, tropical reefs are distinguished by supporting more species of animal life, in greater abundance and closer to each other than any other natural habitat on earth. Yet, for most snorkelers, many of the reef’s most obvious creatures go unnoticed.
Without reference to observational skills, it is simply that the reef, as a community, never sleeps. Most of its inhabitants do, however, just not at the same time. So if you’ve never snorkeled at dusk, you’re missing half the action. In the fading illumination of dusk snorkelers can view the reef in an entirely new light.
Coral reefs have a “rush hour,” the twilight periods of dusk and dawn when diurnal and nocturnal populations cross paths. During this time behaviors alter radically. One set of creatures is seeking safe haven for rest while others are waking up – hungry. Predation is at its peak. This is one of the most exciting times for snorkelers to observe the reef community.
Visual ability is a fundamental survival skill among creatures of the reef, especially fish. Primarily through vision, most fish accomplish the rigors of their daily routine that allow them to stay alive – finding food, shelter, mates and avoiding predators.
Vision requires light and we find that different species of fish have adapted successfully by evolving eyes that function best under specific lighting conditions.
Specialization is not without its cost. While some eyes are extremely well adapted for the bright light of day, when illumination diminishes so does visual ability. At the end of the day colors are muted and small pupils are unable to absorb enough light to see clearly. In this compromised state of impaired vision, diurnal fish become vulnerable.
Just as the daytime fish see clearly under full sun, other fish see much better in the dim light of dusk. Their eyes are large, with huge black pupils designed to gather and utilize low levels of light. These are the eyes of the twilight hunters.
Although I discovered the thrill of twilight snorkeling simply by staying in the water too long, conscientious dusk snorkelers will enjoy the experience much more if they make some simple preparations. The predominant factor, obviously, is that snorkelers enter the water late in the day with ample light to see but exit the water in what can be nearly complete darkness.
To avoid unwanted complications, I always bring along a submersible light. As the sun goes down and a shadowy gloom replaces brilliant color, our own vision becomes seriously compromised, just like that of the daytime fish. Although unnecessary at the start, in the ensuing darkness using a light reveals many of the newly arrived nocturnal animals. Just as important, using a light will help locate shallow rocks, corals and other potential hazards.
In planning a dusk snorkel I also attach a small flashlight or chemical lightstick to my snorkel. This makes it very easy for my buddy to locate me if necessary.
We all recognize that skin abrasions, especially coral cuts, are best avoided, both for our own comfort and the health of the coral. In the dark, this is always more challenging. As a precaution, I usually cover my body with some type of protective layer. Lycra suits work perfectly but just about any type of clothing will suffice.
In addition to unwanted contact with coral or other objects, it’s also easier to become disoriented in the dark. Some shore entries are done through narrow channels in the reef or from small beaches that, while obvious in the light, can become remarkably obscure in the dark. It’s important to pay special attention to your location when you get into the water so that you may safely find your way out later. Some dusk snorkelers leave a small flashlight, flashing strobe or other illumination on the beach to mark their point of entry. Several months ago in Fiji, we simply tied a lantern to a palm tree and this proved highly effective.
Whenever possible, I prefer to snorkel the area first during the day. This gives me a familiarity with the physical layout under well-lit conditions. It also lets me better appreciate the daytime ecology, making the changes that occur at dusk all the more dramatic.
One final consideration: During the day, with the warmth of the sun, I rarely bring a towel. In the dark, however, after a long immersion in the water, a warm, dry towel is a welcome comfort.
With these few tips, I’m sure you will safely and comfortably enjoy the excitement of snorkeling at dusk. And, at least in terms of reef ecology, you will have the chance to see for yourselves how the “other half” lives.