Environmental degradation characterizing the
waters and shores of the Gulf of Mexico is a
result of anthropogenic pollution, including
pollution through inorganic and organic
phosphates. Phosphates are present in
coastal marine environments as a result of
their seasonal application in agriculture.
Increases in inorganic phosphates, used in
fertilizers, are traditionally linked to
eutrophication and the formation of
hypoxic/anoxic zones, and levels of mean
ambient concentrations of 3.2 mg/l-1 of
inorganic sodium phosphate have been
determined for bay systems in the Gulf of
Mexico. Organic phosphates, components of a
variety of insecticides, are known to directly
affect neuromuscular transmission by
inhibiting the enzyme acetyl cholinesterase,
an enzyme used in muscle relaxation.
Concentrations of organic phosphates in
nearshore environments are not available, but
organophosphorous pesticides application
has been estimated as 4,600,000 kg per year
for agricultural lands surrounding the Gulf of
Mexico. The geographic range, abundance in
potentially phosphate polluted areas,
ecological importance and relative immobitlity
of the sea urchin Lytechinus variegatus make
it an ideal organism for ecotoxicological
testing.
L. variegatus is known to survive chronic
exposure to sublethal sodium phosphate
(inorganic, concentrations as high as 3.2
mg/liter) and triethyl phosphate (organic,
concentrations as high as 1000 mg/liter).
However, chronic exposure to low (0.8 mg/liter
inorganic and 10 mg/liter organic phosphate),
medium (1.6 mg/liter inorganic and 100
mg/liter organic phosphate) or high (3.2
mg/liter inorganic and 1000 mg/liter organic
phosphate) sub-lethal concentrations of these
phosphates inhibits feeding and fecal
production, feeding absorption and behavioral
responses. Subsequently, muscular activity
and acetyl cholinesterase activity are reduced
in individuals maintained in organic
phosphate, while no reductions were
recorded in individuals maintained in
inorganic phosphate. Bacterial clearance is
temporarily suppressed in individuals
maintained in inorganic phosphates showing
recovery after a 2-week exposure period, while
individuals maintained in organic phosphate
did not display recovery of bacterial clearance.
Gonad production, oocyte diameter and
gonadal volume fractions decreased in
individuals maintained in increasing
concentrations of both phosphates, with no
recovery over a 2-month exposure period.
Fertilization of gametes from unpolluted
individuals was reduced when exposed to
increasing concentrations of both
phosphates, but development recovered at the
64-cell stage in individuals maintained in low
inorganic phosphate concentrations. At the
prism stage, embryos exposed to all inorganic
phosphate concentrations had recovered,
while no recovery was observed in embryos
maintained in organic phosphate
concentrations.
These experiments indicate that L. variegatus
exposed to chronic inorganic and organic
phosphate concentrations are inhibited in
their metabolic and, subsequently, many
important physiological processes. Changes
in physiological processes are likely to be
attributed to reduced feeding and absorption
rather than direct effects of phosphates.
Impaired reproductive ability and
development, in particular, may reduce
populations of L. variegatus in shallow bays in
the Gulf of Mexico, which could have
ramifications affecting community structure.