Just another dive on the world’s most isolated islands

It is well accepted that Mount Everest is the tallest mountain on Earth with its summit 8,848m (29,029ft) above sea level. We divers, on the other hand, know that just because there is an ocean, it doesn’t mean the world comes to a stop. We know there are mountains and valleys underwater as well. In fact, if we were to measure a mountain from its summit to where it levels off on the ground and then measure an island from its summit to where it levels off at the bottom of the seafloor, there are some islands that would easily knock down Everest a few steps on the world ranking. This is certainly the case for the Hawaiian Islands. These mountains don’t level off until they have reached the bottom of the Pacific Ocean, which has an average depth of 4,300m (14,000ft.) Interestingly, the Hawaiian Islands are so remote that the closest continent is 3,200 km (2,000 miles) away.

Hot lava hitting the ocean in Volcano National Park (Jonas Stenstrom)

With these things in mind, it is incredible that such a diversity of living organisms even made it to Hawai’i in the first place. A creature would have had to cross half of the deep Pacific Ocean to reach the largest and most isolated mountains in the world, half submerged in water. Living in water or on land, this journey is truly against most odds, and definitely a story worth being told.

Armed with cameras and a high school science classroom in mind, we set out to use the Hawaiian Islands as an example when explaining concepts in colonization of species, succession and evolution. Basically, we wanted to explain how living things had made it to the islands in the first place, and what happened to them once they found themselves isolated in the middle of a giant ocean.

Let’s start by taking a step back and visualize the problem. About 99 percent of the Hawaiian archipelago land mass is made up by the so-called eight main islands. Kauai and Niihau are the oldest of these eight islands, having been formed roughly 5 million years ago. The Big Island of Hawai’i is still being formed by a slow but constant flow of lava on the southeastern coastline around Volcano National Park. The islands are built from lava that seeps out of a stationary magma chamber. As the oceanic crust slowly moves in a northwesterly direction the islands have been formed one by one. The underwater world tells the story of its history, unique composition and exposed location with dark lava tubes and caves and a dramatic drop in depth only a short distance offshore. As the seeping magma cools the new surface becomes new available land to organisms that are present. For a group of islands that have never in history been in contact with the mainland we find the story of its first colonization especially interesting.

The problem here is that many marine inshore species have a planktonic larval stage, meaning that the juveniles are pretty much dependent on wherever the water wants to take them. Most larvae also have a pretty limited life span before they have to settle down and turn into their adult form. Most species would not normally be able to survive the long journey that would be required to reach Hawai’i simply because of their short larval life. But, if you can’t make it by yourself, you could always hitchhike. Corals for example have been found growing on floating pumice rocks or driftwood, which is likely another way these animals first colonized Hawai’i. And even if you managed to defeat the odds and find the place, the next problem is survival and establishment.

Although Hawai’i does not have the same diversity of species as islands closer to the mainland in the Pacific Ocean the abundance of life is still truly amazing. Today there are around 50 recorded species of hard corals around the islands, and about 20% of these are endemic to the islands, meaning they are found nowhere else in the world. Additionally, you can find almost 800 species of mollusks, with around 20% being endemic and more than 500 species of inshore fish of which just fewer than 25% are endemic, one of the highest percentages in the Pacific. So once a species has established, the isolation allows them to evolve separate from their ancestral relatives and give rise to the high percentage of endemic species found today. In fact it has even been said that if Charles Darwin had reached Hawai’i before Galapagos, he would have come up with his theories on evolution a lot sooner.

Hawai’i also gives us a chance to see an impressive display of large marine and pelagic species, including more than 40 documented species of sharks and a great number of whales and dolphins.

We set out to document the Hawaiian Islands history and evolution. And with a limited time to explore the hidden jewels, we were often confined to the easily accessible dives. Dives that I, in a fairly spoiled way, would often classify as “just-another-dive”. Well, I love it when nature over and over again explains that no matter what, there will always be something new to discover, even if you are on “just-another-dive”. There was one particular night of diving in Hawaii that explained this to me in a way I will never forget.

This night was going to be a shallow dive, right next to the boat (and the boat was moored only about a 100m offshore). Wait until after sunset, just roll over and sink, swim 50m under water and a maximum bottom time of 1 hour. We were not even the only divers on location... obviously no records to be broken here, a typical “just-another-dive”… But, the simplicity of the dive soon turned into one of the most majestic nature performances I have ever witnessed.

The divers already on the bottom had organized themselves in a large circle with their lights shining up in a way that made the stage look somewhat like an aircraft landing platform at night. The water was crystal clear but there was a strange murky haze over most of the lights. It was not until I took a better look at my own video light that I discovered that the murky patches were due to an enormous accumulation of small planktonic crustaceans. The dive light attracts an incredible quantity of plankton at night and to many of these small animals it would mean the last light they would ever see. I figured this out just as I got my video camera ready.

The display totally blew me away: seventeen manta rays, up to 15 ft. wide, appeared almost like spaceships looking for a place to land, guided by the dive lights lining the landing platform. Their light colored bellies, all with individual spot patterns, lit up the water like ghosts in the night. A bright belly and a dark colored back is a common feature in the ocean referred to as counter-coloration. Seen from below the animal “blends in” with the light from the surface and seen from the surface the dark back “blends” with the dark depths making the animals harder to spot.

Reaching up to over 20 ft in wingspan and weighing more than 3,000 pounds, these gentle giants are exclusively filter-feeders. Their mouths are equipped with two large cephalic lobes that function to funnel plankton rich water into the mouth where mainly tiny crustaceans and small fish are collected by the five large pairs of gills. The two lobes have also in some cultures given the animal its infamous nickname “Devil Rays” by resembling large diabolic horns. Manta rays (Manta birostris) are cartilaginous fish together with all other rays and sharks. They are found in tropical waters around the world generally between 35 deg. North to South latitude. If you are an animal approaching 20 ft in width and your primary food source is the size of a mere speck in the water, there is a need for a lot of food to survive, and when given the chance to collect some extra food, you can’t pass up the chance. The manta rays sure made the most of the situation and came swooping in over our lights like large trawl nets. The dive was spent in the same spot, enjoying every second of it and we felt like staying down there forever. “Just-another-dive”, but another unforgettable experience.

The mantas almost seemed to put on a show to really explain how special these mountains in the middle of the Pacific Ocean really are. Like we didn’t know already. Over and over again we were reminded of the same thing: even though colonization of Hawai’i started against all odds, the islands today are definitely living examples that nature has an incredible way of working around almost impossible obstacles.

The results of our Hawaiian experiences will be displayed across American high schools in a near future as a video supplement to the new Pearson Biology textbook under the name Untamed Science.

Until next time and as always, we encourage you to Never Stop Exploring Your World.

The Wild Classroom & Untamed Science Crew

The Wild Classroom on location in Hawai'i (Jim Brady)