In The Blink Of An Eye (21 page)

The traps were tested near Sydney. At the Australian Museum thick rope was sectioned into 50-metre lengths. This was coiled carefully - a
poorly coiled rope can quickly resemble a plate of spaghetti and be just as useful - and baled on to ‘The Flying Scud'. House bricks were also loaded on to the boat, along with orange plastic buoys. ‘The Flying Scud' was towed out to the coast, stopping at a petrol station along the way to buy frozen pilchards. Frozen pilchards sell well in Australia, where fishing is popular and pilchards make suitable bait.

Figure 4.2
A typical scavenging isopod, amphipod and ostracod (seed-shrimp).

On board ‘The Flying Scud', a pilchard was placed inside the smallest chamber of each trap. The traps were individually tied to two house bricks and one end of the 50-metre length of rope. The other end of this rope was tied to a buoy, and the whole apparatus was then hurled overboard to a depth of 25 metres. The length of the ropes had to be greater than the depth of the water in which they trailed, so that, as the traps rested on the seabed, the rope provided some ‘give' in strong currents. Notes were made of the positions of each trap in relation to objects on the shoreline.

The following morning, ‘The Flying Scud' returned to the study site to recover the traps. Finding the buoys was not so easy, and some traps were lost. But the traps retrieved were opened on board - and everyone was happy. Jim had caught his amphipods and isopods. The test run
was a success, although it was clear that improvements to the protocol were necessary if the more turbulent seas off Australia were to be prospected. The marine snail community introduced one unanticipated problem, however. Sometimes they too were attracted to the smell of fish, and in a frenzied bid to dine on the pilchard, they became jammed in the entrance hole, thus spoiling the traps. News also arrived from the fisheries industry of some gigantic isopods living in deep waters off the north-east coast of Australia - and they were feeding on dead fish. All of this called for adjustments to the trap design.

Jim Lowry opened his map of the south Pacific and pinpointed his targets. Several towns were marked at different latitudes, from New Guinea in the north, traversing the eastern Australian coast to Tasmania in the south. From each town, traps would be set along a line of latitude, beginning at 50 metres deep and ending at 1,000 metres. The expedition was starting to get serious.

Behind the scenes, the SEAS project was taking shape. Jim managed to recruit several students and technicians at the Australian Museum to work on his new traps - the deadline for his first boat launch was approaching. A production line unfolded and the finished traps were piled on to a huge trailer at great speed. The new traps were all covered with metal grids to keep out the snails. And to counter the giant deep-sea isopods anticipated, the traps were placed inside much larger structures, which were actually modified lobster traps. All the equipment could be stacked, so a single trailer, albeit fully laden, was adequate.

The deeper sampling sites called for a bigger boat, and ‘The Flying Scud' was retired. Commercial fishing vessels were chartered from each town, and these were equipped with a global positioning system, or GPS. This system employs satellites to locate precisely any coordinates, even at sea, and so traps could theoretically be found easily. But to fight the stronger currents in these deeper seas, and keep the traps in their original positions, anchors and heavier lead weights entered the equation. A certain amount of drift was still predicted, so the markers at the surface were upgraded too to prevent them being dragged under. Huge buoys and flags were tied on to the cage-like trailer, which was beginning to look like a travelling circus wagon. And the great bundles of
rope, now up to a kilometre and a half long, only confirmed the resemblance.

The SEAS bandwagon rolled into Cairns in north-eastern Australia in 1990, and the expedition was launched. Everything went smoothly. The traps were set one afternoon, and most were collected successfully the following morning. Amphipods and isopods were recovered, and nearly all were new species. The Australian Museum jeep towed the gear to the next site and the sampling continued . . . and so on. At each port of call a different fishing vessel awaited, each equipped with a different captain and crew.

The SEAS project was a great success in that hundreds of new species were recovered during the original sampling expedition and in the repeats. Interestingly, as will become evident, the species tended to get larger as the depth increased.

The ecological results of the SEAS project are in the throes of being published. All I can say here is that they reveal, for the first time, the fate of the better known fish and other marine animals in one of the largest environments on Earth. For the first time we will understand the biology of the crustacean scavenging community, which will have all sorts of implications in fisheries practices and management. We won't be able to produce a management plan for the seas, and ultimately preserve our fisheries industry and marine biodiversity, if we don't know what's down there. The SEAS project is a wonderful success story, but it was the results of the isopod part of the research that are relevant to this chapter.

Steve Keable, a member of the SEAS team interested specifically in the isopod catches, set some traps by hand in shallow water on the New Guinea leg of the trip. He did catch isopods, but decided to cut his plans short when, surfacing from a dive one day, he spotted a local tribesman standing astride a large rock, bow in hand with an arrow strung and pointing in his direction. Steve continued with his shallow-water sampling in safer waters off Australia, and with considerable success. Faced with so many new species of shallow-water isopods, he left the deep-water species to Jim Lowry, who could not resist these amazing forms.

It was the shallow waters that revealed the greatest diversity of
scavenger species. As the trap localities became deeper, the number of species caught became fewer. The total number of individuals became fewer too, but not so the total weight of the catches - the animals were getting bigger. And they were dominated by those giant isopods that fishermen had warned of, known as
Bathynomus
.
Bathynomus
was no longer a myth to the SEAS team.

The deep-sea traps were hauled to the surface by a winch. Each trap came into view in the water as it was lifted closer to the ship, at which point members of the crew leant over the hull to heave it on board. It was immediately obvious there was a living animal in the trap. Large crab-like legs began to poke out through the holes in the large outer trap, and scraping sounds were heard as sharply pointed feet crawled over the rigid plastic sides of the trap. The whole trap moved around as it lay on the deck, surrounded by the onlooking crew. Then the trap was opened.

Everybody
gasped. What appeared beggared belief, best described as something out of science fiction. One is invariably taken aback by an encounter with the unknown, and here the crew were witnessing something they had never seen before - not on TV, not in books and not in aquaria. By science fiction I refer to movies about aliens or, more appropriately, those 1960s cult classics where giant tarantulas or ants chased helpless humans some ten times smaller than them.

Out of the deep had risen an isopod that looked like a woodlouse. But this creature could never be mistaken for a woodlouse - it was fifty times bigger. This was
Bathynomus
. The fishermen's legend had come to life, and giant, robust isopods were now roaming the deck. At fifty times their normal size, the jaws of a woodlouse look quite fiercesome, and their steps seem almost mechanical. Their heads, face on, look like stormtroopers from
Star Wars
, and their bodies resemble small but significant tanks, some half a metre long.
Bathynomus
indeed appears more machine than animal (see Plate 13).

It took a while for the unfamiliar to become the familiar, and the sight of a
Bathynomus
scurrying across the deck like an armoured vehicle, with jaws chomping, continued to be breathtaking. Those fortunate enough to see elephants in Africa, tigers in Nepal and bears in Canada should try adding
Bathynomus
to their list.

Something
Bathynomus
shared in common with these animals was its eyes, but
Bathynomus
lives in waters up to a kilometre deep, so what use are eyes here? Well,
some
sunlight exists, even at these depths, although only the blue component remains. And like the eagle owl, which also lives under dim light conditions, the eyes of
Bathynomus
are big. So in parts of our planet that remain too dim for us to see, but are reached by sunlight all the same, there live other animals exercising vision.

At a kilometre in depth, the sea is comparable to night-time on land in that light as a stimulus to behaviour and as a selection pressure to evolution is greatly reduced. But it is still present. This is not the completely dark scenario towards which I am aiming in this chapter, but it is a step in the right direction. Again we can learn that, where light is greatly reduced, biodiversity diminishes in unison. As the SEAS traps were set deeper, the number of species in their catches was reduced.

The deep sea is extremely interesting because there are many more amazing and unknown creatures to be discovered. New finds continue to enthral us every year. And the trend towards gigantism seems to hold, along with the low diversity levels as compared with shallower, brighter environments. Taxonomists studying sea spiders - marine members of the arthropod phylum most closely related to true spiders - also confirm that deep-sea faunas are discernible for their low species diversity while sometimes displaying an amazingly high abundance for a single species. The considerable size and weight of animals in the deep sea suggest that resources are not always limiting. But the reduction in light is a major factor in the reduction of evolution in the deep sea, implied by the depleted variety of species.

Many deep-sea animals share the ‘big eye' characteristic of
Bathynomus
. Fish, squids and shrimps, to name but a few, have larger, more sensitive eyes in the deep. Evolution has continued to provide adaptations to light here, even though the light is extremely low. Light must really be a powerful stimulus. But I won't dwell any longer on the adaptation to reduced light found in animals today, partly because some animals produce their own light in the deep sea. Even where light is extremely dim, selective pressures still act on animals to be adapted to light - to see it and even produce their own, although
Bathynomus
is not one of the light producers. This self-produced light, known as bioluminescence, will be described in Chapter 5. Here it may only complicate matters, although the general light field can still be described as low in the deep sea.

To get the picture of life in complete darkness we must head for caves. But before leaving the deep sea, I will return to
Bathynomus
and another lesson it can teach us - that, in contrast to the outcomes described in Chapter 3, the pace of evolution slows in environments with little light.

Steve Keable set about describing the isopods caught in shallow waters. There were clearly many new species - the contents of the shallow-water traps could be easily sorted into groups based on appearance. Museum volunteers without previous experience of either isopods or taxonomy could carry out this task. There were many obvious characteristics separating species A from species B. Some species had legs covered in spines, some without spines. Some had long antennae, others short antennae. And so on. The identification, and consequently the taxonomy, was straightforward for the shallow water isopods, but enhanced by Steve's refined taxonomic methods characteristic of the Lowry group.

To summarise, in shallow water evolution had resulted in many species of isopods, partly in response to the increase in niches created by light. And each species was considerably different - many genetic mutations had taken place over a limited time period, so evolution had been rapid where light levels were high. But how can I talk about time here, when all we have to examine are the species alive today? Surprisingly I can offer some justification. My evidence derives not from the fossil record of isopods - unfortunately that is inadequate. Instead clues can be drawn from the history of the Earth - plate tectonics, as described in Chapter 2.

The Australian plate is part of the Earth's crust. It consists of terrestrial land, and the submerged continental shelf and continental slope. The continental shelf inclines gently from the sea shore to a depth of about 200 metres. Then the continental slope commences as the sea floor plunges rapidly towards the Abyssal Plain, another gently sloping part of the sea floor, beginning at about 5,000 metres in depth. The
base of the continental slope marks the edge of the Australian plate. So animals living on the sea floor down to depths of at least 1,000 metres are obviously well separated geographically where they occur on different plates. A species could conceivably occupy a large part of one plate, within a range of depths, by circumventing the land. But animals cannot migrate to other plates. They are divided by deep ocean, or forbidden territory. However, as described in Chapter 2, the different plates of today were once joined, but became separated throughout geological time. The consequence of this for animals is that species separated geographically today evolved from ancestors once living together on the same plate. It's also interesting to point out in this chapter that the Australian, Indian and Mexican plates (or continental slopes) were completely separated 160 million years ago.