Science topics
Larval development and metamorphosis - Russell Bradford
The Scientist
Hi, my name is Russell Bradford. In 1991 I graduated from the University
of Tasmania with a Bachelor of Science (Honours) degree in Marine,
Freshwater and Antarctic Biology. Shortly thereafter I began working
for the CSIRO as a marine biologist in the field of crustacean taxonomy
and fish ageing. Following on from my early work I was involved
in studies of tuna diets and the interactions between tuna prey
and their environment. Currently I am working in the area of larval
fish ecology.
As you can see I have largely been working at the smaller end of
the size spectrum of marine animals - the zooplankton and micronekton.
The small, often microscopic, world of zooplankton and micronekton
is fascinating. It is a world not often seen. However, it is a world
full of incredible diversity in both shape and form, and provides
the link between the plant life harnessing the energy of the sun
and the larger animals that we more commonly associate with the
marine environment.
My personal interest is in the area of larval ecology and biology.
It is a large, multi-disciplinary field in marine biology that examines
the early life stages of fishes and other marine animals and how
they interact with their surroundings. It involves sampling at sea
in coastal and offshore waters with a variety of fishing nets; taxonomic
studies; live fish rearing and handling techniques; dissection;
examination of fish bone structure (in particular, the ear bones
- or otoliths); looking for linkages between the physical oceanography
and the areas in which larvae has been collected.
Russell's collaboration is with artists Di
Allison and Patrick Hall.
The Research
Larval Ecology and Biology: The larvae of many fish and crustaceans
are poorly studied. Yet they are a key link in the chain between
the fish left in the sea to reproduce and what is available for
the recreational and commercial fisher. The Larval Ecology and Biology
group is studying the links between larval fishes, the physical
environment they live in, and how these larvae contribute to successive
generations.
Many larval forms of common marine animals are vastly different
to their adult forms. In fact, some larval forms were classed as
separate species to the adult form because the differences were
so large. One example is the southern rock lobster. The egg of the
crayfish hatches into a nauplisoma, a stage that lasts hours; the
nauplisoma then transforms into a phyllosoma. The phyllosoma stage
of the crayfish involves about 11 moults (discarding of the exoskeleton)
to allow for growth. At some point (triggered by a cue as yet unknown)
the phyllosoma transforms into the puerulus. It is at this stage
that the larva takes on a recognisable form. The images below illustrate
the changes that take place in the larval phase of the southern
rock lobster.
In a previous project, we looked at some of the links between the
physical oceanography (i.e. ocean currents, salinity, wind patterns,
sea height) and the distribution of the phyllosoma larval stage
of the southern rock lobster. Phyllosoma (meaning leaf body) are
weak swimmers and thus to a large part are subject to the whims
of ocean currents. They are also long-lived; the larval stage lasts
approximately 18 months. As the prevailing currents in the south
and south-east of Australia are west to east, how do phyllosoma
contribute to future generations in the western regions of the southern
rock lobster’s distribution? One possible answer is that phyllosoma
take advantage of eddies within the general circulation (colour
sat image of ocean temp showing eddies). Research into ocean currents
using satellite-tracked drifter buoys has shown that these passive
drifters are capable of returning to their point of release after
about 18 months before becoming caught within the general west to
east circulation (image of sat-tracks).
Eddies, thus, provide a possible means of returning larvae to the
region in which they were born. We do not know, however, what would
tell the larvae that they have returned home and thereby trigger
a change in their body form (metamorphosis) allowing them to swim
to shore and shelter from predators.
Additional information:
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