Rewilding the Sea - Feral: Rewilding the Land, the Sea, and Human Life - page 240

extracted again. As the great beds were smashed by fish trawlers and
oyster dredgers, the sea's filters were shut down at the same time as
the crust of life was broken, releasing the mud that lay beneath. Even
the Humber estuary - a mud bowl whose waters are now as murky as
a hedge fund's tax returns - was once lined with oyster reefs. On the
tidal slops, Callum Roberts tells us, you can still find oyster shells
'smoothed by more than a century of tides'. By creating, through the
accumulation of cemented shells, a hard bottom onto which other
oysters could attach, the shellfish, like cod and green turtles, engi-
neered the environment that suited them. They also provided a
substrate onto which many other species could attach, in turn creat-
ing habitats for yet more wildlife.
In Chesapeake Bay on the Atlantic coast of the United States
there were sufficient oysters, according to one paper, to have 'filtered
the equivalent of the entire water column every 3 days'. 32 As the
early colonizers broke the land, much of the soil - and the nutrients
it contained - began to wash into the sea. This process - called
eutrophication - has been blamed for the periodic bloom of plant-like
plankton, whose decay and nocturnal respiration sucks the oxygen
out of the water, killing many of the animals the bay contains. This
plankton contains species which poison the water, causing lethal
red tides. Fascinatingly, however, despite the great dump of nutrients
into the bay from around 1750 onwards, it was not until the 1930s,
when the oysters had been more or less fished out, that such disasters
began to occur. 33 The oysters filtered and consumed the plankton, pre-
venting it from blooming and from poisoning the ecosystem. The
damage, from the 1930s onwards, was self-perpetuating. As the oys-
ters were reduced to the point at which they could no longer keep the
water clear, they began to suffer from a lack of oxygen and the over-
abundance of sediments. This made them susceptible to disease, which
further reduced their number. The report describing this effect remarks
that Chesapeake Bay, the Baltic, Adriatic and parts of the Gulf of
Mexico, are now 'bacterially dominated ecosystems'. 34
The Black Sea also appears to have been transformed by the removal
of some of its dominant species. After its predators - such as dolphins,
bonito, mackerel and bluefish ( Pomatomus saltatrix ) - were reduced by
commercial fishing, the plankton-eating fish they preyed on proliferated.