MERCER02-14
4
Laboratory and field experiments were conducted on
Ectopleura larynx
(marine hydroid)
collected from cage nets of Atlantic salmon farms in Norway near the Institute of Marine
Research facility (Guenther et al. 2011). Results of this study showed that short-term immersions
in heated seawater at temperatures of 50 and 60°C significantly reduced the settlement and
survival of
E. larynx
. Actinulae (a type of hydroid larvae) settled well after 1 or 3 seconds of
immersion in water at temperatures of 30 and 40°C. After immersions at 50°C, no actinulae
settled. None of the juvenile hydroids survived after being immersed at 50 or 60°C and exposure
of adult hydroids to 50°C for 1 and 3 seconds resulted in very low survival. Exposure to 60°C
seawater killed all of the adult hydroids.
2.3.2. Biocides
Laboratory experiments showed short-term immersion in acetic acid had detrimental effects on
the settlement of actinulae and survival of both juvenile and adult hydroids (Guenther et al.
2011). Decreasing survival of hydroids at increasing concentrations or immersion times was
observed. None of the juvenile or adult hydroids survived the 5-minute exposure (0.2 and 2 %
concentration). All exposure times to 2% concentration of acetic acid reduced the settlement of
larvae and survival of hydroids to less than 10%.
Field experiments have also shown significant effects of both heat (50 °C for 1 and 3 second)
and acetic acid (0.2% for 1 and 5 minutes and 2% for 1 and 3 seconds) (Guenther et al. 2011).
The biomass (wet weights) of organisms decreased 2-5 days after treatment. There appeared to
bemore effect on biomass from acetic acid exposure. The authors suggest that a combination of
heat and acetic acid (possibly using a 5% concentration of acetic acid)would bemost effective in
treating finfish farm netting for biofouling due to
Ectopleura larynx
.
G. franciscana
has been found to tolerate 200 µL g
-1
of copper (Crooks et al. 2011). Field
experiments (de Rincon and Morris 2003) measuring the settlement of
G. franciscana
on
different materials (steel, aluminum, copper, Plexiglas, glass, carbon steel, polyethylene and zinc
alloy) found that the hydroid had greater adherence on the non-metal surfaces and did not grow
onmaterialswithmore than 30% copper.
Theede et al. (1979) conducted laboratory cadmium tolerance tests on
Laomedea loveni
and
found that the acute toxicity of cadmium on the hydroidwas stronglymodified by abiotic factors.
L. loveni
wasmore tolerant to cadmium at lower temperatures and high salinities. The resistance
to cadmium decreases with rising temperatures. The lowest cadmium concentration affecting
retraction of the polyps is 3µgL
-1
at 17.5 °C and 10 ppt.
At the Surry Nuclear Power Plant in Virginia, several biocides in addition to chlorine (sodium
hypochlorite and sodium bromide are now used as fouling control) were tested against
G.
franciscana
, including ammonium hydroxide, hydrogen peroxide, sodium bromide-hypochlorite
mixture, a surfactant mixture (ClamTrol), and chemically induced anoxia. However, at doses
allowed by their U.S. EPA permit, these treatments were ineffective (Stone and Webster
EngineeringCorp. 1992, seeSection 8).
