Life of the Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 155

established, this zooplankton began to release a stream of faecal pel-
lets from the surface to the depths, together with discarded gelatinous
feeding nets that some of them produced and—ultimately—their
own bodies. To us as fussy humans it is not the most appetizing food
supply (oceanographers call it 'marine snow', or more bluntly the 'fae-
cal express'), but it is one of the main reasons why the deep ocean is
not 'azoic'—or lifeless—as that amiable Victorian-era rebel Edward
Forbes thought (see Chapter 5). Indeed, this constant stream of poo
maintains the ecosystem of the deep ocean. Without it, much of the
organic material fixed by phytoplankton would stay in the surface
layers and never reach the seabed. Only when it is clumped together
does it lose its buoyancy and sink, and it is the role of zooplankton
and of its predators to deliver this vital resource to the sea bottom.
The Cambrian closed and the Ordovician began. A rapidly evolving
and diversifying plankton in the water column may have seeded yet
greater complexity on the seabed. In these Ordovician ecosystems
there lived myriad marine phytoplankton providing the primary
food, zooplankton eating them and being eaten by arthropods, that
were in turn preyed on by larger arthropods and nautiloid molluscs,
all contributing to a faecal stream that fed the organisms at the sea-
bed. It was, therefore, a seabed that crawled with life. Snails fed on the
detritus falling from above, while predatory sea urchins and starfish
prowled around, and brachiopods, bryozoans, and corals attached
themselves to any hard surface available. The sediment below stirred
too, to the movement of burrowing worms and arthropods, and myr-
iad tiny organisms lived as meiofauna, hiding between the sediment
grains. Above the seabed, forests of sea lilies swayed elegantly in the
current, filtering edible particles from the water. This is a marine
world in many ways like our own, peopled with hundreds of species.
It is the time that geologists call the Great Ordovician Biodiversifi-
cation Event (or GOBE for short), when worldwide a much greater