MERCER02-14
2
conditions (Table 1) and has proliferated as an invasive species inmany areas. It is known to be
present in Europe, the Black and Azov Seas, West Africa, India, Australia, California (San
Francisco Bay in 1901), the Atlantic coast of North America, the Gulf of Mexico, Panama, and
South America.
G. franciscana
is most successful under estuarine conditions, and is capable of
surviving in both tropical and temperate
climates (Vervoort 1964; Figure 2).
Table 1. Environmental Tolerances of
Garveia franciscana.
See Davidson et al
.
(2007) and
Fofonoff et al. (2003) for more details and additional experimental references. See Thompson
(1993) for estuarine field and laboratory studies (JamesRiver, VA).
Parameter
Maximum
Minimum
Optimal
Water Temperature (°C)
30 - 35
0 - 12
10 to 32
Salinity (ppt)
23 – 35*
0 – 1*
5 to 25
ReproductiveTemperature (°C)
34*
9*
15 to 32*
ReproductiveSalinity (ppt)
25
5
10 to 15
*Experimental
Figure 2. Range of
Garveia franciscana
taken fromNEMESISBioregionDistribution (Fofonoff
et al. 2003).
2.2. LifeHistory
Hydroids use stinging cells to stun their prey (zooplankton and epibenthic animals), and tentacles
transport the food in themouth and down to the interconnected brancheswhere it is digested and
distributed to the colony (Lippson andLippson 2006).
Most hydroids reproduce through gonophores (reproductive polyps) that produce microscopic
free-floating hydromedusae. The hydromedusae produce planula larvae (flattened, ciliated,
bilaterally symmetrical larvae) that eventually settle onto hard substrate to form the hydroid
colony.
G. franciscana
lacks a hydromedusae stage and reproduces sexually using gonophores.
Male and female gonophores are born on separate colonies (Vervoort 1964). Eggs are fecundated
in situ (one egg in each female gonophore) and develop into a complete planula inside the
gonophore. The fully developed planula leaves the gonophore after rupture of the peridermal
