The northwest coast of Spencer Gulf, Australia,
is the setting for one of the most colorful and vibrant biological
events: The spawning of Sepia apama, the giant cuttlefish. The greatest
concentration (as many as thousands per acre) is found only on the
few rocky reefs between the industrial port of Whyalla and Point
Lowly, 10 miles northeast. Original
photo of Spencer Gulf area: NASA.
Original photo of Australia: Australian
Department of Environment and Heritage.
A male cuttlefish has distinct white lines
around the edge of its body, and rippling stripes along the body
while guarding a female from insemination by other males. Photo:
you're planning to visit Spencer Gulf in South Australia, chances
are you'll bring a snorkel, mask, fins, and an interest in sex.
Cuttlefish are relatives of the squid and
octopus that live along Australia's southern coast. Males compete
ferociously for the right to fertilize eggs, and that's where the
fun begins, at least, from a voyeur's standpoint.
In the competition to place a packet of sperm
inside a cavity near the female's mouth, big males shoulder aside
little males. But the small guys respond with a bit of treachery.
Instead of fighting a losing battle, they temporarily look like
a female. "The physically smaller males who can't compete with the
larger males 'dress,' or assume the appearance of females," wrote
Bronwyn Gillanders, of the Southern Seas Ecology Laboratories at
the University of Adelaide in our email interview.
When the little fellow adopts the body colors
of a female, males that are busy guarding females figure there's
more female talent in the neighborhood. "The larger male then thinks,
'Wow, I've got two females here,'" Gillanders adds. When the big
guy's attention is focused on a third male, the little fellow darts
in, inseminates the female, and splits. "When the large male turns
away, the little male quickly assumes the colors of a male again
and then zooms in and mates with the female," says Gillanders. "After
that, he swims away."
It's sneaky, but it works.
Surreptitious sex among the cuttlefish has
attracted attention among scuba divers and snorkelers. The burgeoning
ecotourism industry in Spencer Gulf, Gillanders says, is "centered
around the annual breeding aggregation for cuttlefish."
It's quite an undersea red-light district,
Gillanders adds. During spawning, 85 cuttlefish may crowd into 100
square meters of shallow water.
Like all animals, cuttlefish compete for the
right to breed, and battles among males cause injuries and lost
tentacles. To Gillanders, furtive behavior makes sense for little
guys. "Presumably the small males weren't getting in on the action
because they were being outcompeted or dominated by larger males,"
he says. "Any lesion they get from fighting can potentially be fatal
through infection, so this may possibly have lead to them try alternative
tactics, like sneaky sex."
Gillanders and Steve Donnellan, an evolutionary
biologist at the South Australia Museum, are trying to locate other
populations of the giant cuttlefish, and learn whether the various
populations are breeding together and sharing genes.
To answer these questions, Gillanders and
Donnellan have asked
recreational divers to spy on the cuttlefish, especially outside
the main breeding area in northern Spencer Gulf, and note where
individuals are mating. The helpers are also asked to retrieve individuals
so they can study:
and cuttlebone sizes
Eventually, the research will give a picture
of where the cuttlefish lives and whether and how it moves along
the coast. Preservation tactics - especially regarding the size and
location of a marine reserve to protect the cuttlefish - will be
based on whether or not the populations are genetically and ecologically
Cuttlefish are selling in Asian food markets,
and fishing could decimate the giant Australian cuttlefish. Although
the ornate blue cephalopod is not presently endangered, Gillanders
says, it is "highly susceptible to over fishing, because most individuals
only live for one year. If you remove the breeders, there will be
no eggs for the following year class. This removal can have devastating
consequences, especially if their movements are localized."
South Australia Museum