By Paul Caiger
Planet Earth is 71 percent ocean, and the open ocean is by far the largest component of this watery world. A myriad of beautifully diverse life can be found in the pelagic environment, and with the fourth largest EEZ (exclusive economic zone), New Zealand is particularly bountiful in this regard. There are animals that are very familiar to most, such as dolphins and whales, and many fishes and sharks. There are even more that are not.
Most of the life can be found in the shallow sunlit waters near the surface, where the sun’s energy drives the phytoplankton-led food web. Strange beauties can be found, such as the rarely seen glass squid. This is one of about 60 species of cranchid squid, which includes the colossal squid. Most however, are small transparent animals that spend their younger lives near the surface, and progressively get deeper as they transform into adult form. The main chamber is almost completely transparent and filled with ammonia, the only visible parts being the digestive gland and gills. This buoyancy chamber is unique to the family, and is the source of their common name ‘bathyscaphoid’, after resemblance to the bathyscaphe. This individual, who couldn’t swim very fast, repeatedly pulled its head and tentacles inside its mantle to protect itself, and even filled the chamber up with ink, a conserved trait in squid, usually designed to squirt outside its body as a diversion.
Some of my most rewarding time spent in the water in New Zealand has been away from the colourful rocky reefs and kelp forests and out in blue water. As the pelagic environment is an enormous highway, transporting the early stages of the marine organisms far and wide, spring and summer are good times to be in the water. The majority of fishes and invertebrates begin life in the upper layers of the ocean, drifting around as larvae, and this is usually timed with the annual spring phytoplankton blooms. These larvae often look nothing like their adult counterparts, which makes animals normally common to us quite exciting finds. Hugely vulnerable during this time, it is only natural that many larvae seek shelter under floating objects, and these flotsam need only be tiny to support large numbers of animals. On any given summer in New Zealand’s oceanic waters, a myriad of larval and juvenile fishes can be found hiding under floating wracks of seaweed or discarded human objects. Kingfish, a colossal coastal predator, begins life a tiny tiger-striped juvenile, tens of kilometres off the coast of northern New Zealand. These floating oases inevitably attract oceanic predators, and lucky encounters with species such as mahimahi and sharks do occur during the warmer summer months.
Some animals not only begin their lives as larvae in the ocean, but remain there permanently. This requires them to adapt to a life at sea, and often animal groups that we know exclusively as coastal or intertidal are wholly pelagic. These include the pelagic goose-neck barnacle, which clings tightly to floating objects, and uses a soft fleshy stalk to extend into the water column to filter particles. Furthermore, these wracks of floating life support inhabitants such as pelagic crabs, nudibranchs and other wonderful invertebrates.
Without doubt, the pelagic environment is the ideal place for those that are made of jelly. With no boundaries to movement and nothing to run into, the open ocean is a veritable soup of jelly-made organisms. These simple animals maintain an enormous diversity, from tiny hydrozoans, salps and comb jellies to giant jellyfish capable of capturing substantially large prey. In the open ocean, the lion’s mane jellyfish acts as a floating oasis for certain species, such as driftfish and juvenile carangids, providing both a reliable source of food and protection from predators. We commonly see these jelly animals when we are close to the coast, as that is where we dive most. Here they are often near the end of their lifespan, and/or damaged from bumping into hard things. However, to fully appreciate them in all their splendour, you must see them in the pelagic realm.
Of course, the pelagic environment also contains large schools of fish, swimming effortlessly together like one super organism, in constant search of microscopic plankton. Some, such as mackerel, trevally and koheru, are constantly seen travelling around the blue-green waters off New Zealand’s coast. Others, such as blue mao mao and sweep, venture out into deeper water to feed when the currents run strong, retreating regularly to the safety of reefs, caves and archways. There are not many who don’t get excited by the sight of a ‘workup’ when out at sea; the result of schools of fish feeding at the surface, eliciting a chain reaction of predator-prey interactions.
Given the evolution of life on this planet began in the open ocean, it is no wonder that there are so many exciting things in the pelagic zone. A keen eye, the ability to float and somewhat steady nerves are all that is required to enjoy what this place has to offer us.