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Fishery Bulletin 106(2) 
the primary mechanism driving our results. Although 
it was not possible to measure fish before each experi- 
ment, there was no difference in standard length be- 
tween treatment groups for any year, indicating that 
fish in both groups had similar growth rates. 
Alternatively, it is possible that lagoon water lacks 
some physiologically important trace element which 
limits growth. Again, this seems unlikely to fully ac- 
count for our results because P. coelestis do inhabit 
and spawn in the lagoon, albeit not in great num- 
bers, as do other pomacentrid species. This would not 
be expected if lagoonal waters were lacking an ele- 
ment of such physiological importance. Furthermore, 
Ba is not this limiting element because it has been 
clearly shown that Ba concentrations in otoliths are 
indicative of Ba concentrations in water (Bath et al., 
2000; Walther and Thorrold, 2006) and that Ba is not 
influenced by the physiology of the fish (Campana, 
1999). Because there was a significant relationship 
between increment widths and Ba/Ca, it seems likely 
that another mechanism was involved in producing 
the results observed. 
A related study, in which the otolith chemistry of the 
same otoliths used here was examined, indicated sig- 
nificant differences in the otolith chemistry of the two 
treatment groups for 2000 and 2002, primarily driven 
by differences in Ba/Ca and Sr/Ca (Patterson et al., 
2004a). Similar to the results of the present study, no 
difference in otolith chemistry between the treatment 
groups was detected for 2001. The differences in oto- 
lith chemistry between the treatment groups probably 
reflected differences in the composition of the water 
masses (Bath et al., 2000). Oceanographic features 
that may affect water chemistry (i.e. , upwelling, phy- 
toplankton blooms; Patterson et al., 2004a, 2004b) are 
not temporally stable. This may explain why signifi- 
cant differences in otolith chemistry and 
microstructure were found only for fish 
from the 2000 and 2002 experiments. In 
addition, there was a significant relation- 
ship between Ba/Ca ratios and increment 
widths, and annual variation in increment 
widths reflected differences for Ba. No sig- 
nificant correlation was found between Sr/ 
Ca ratios and incremental widths, which 
concurs with previous studies (Kalish, 
1989; Gallahar and Kingsford, 1992). 
The mechanisms by which trace ele- 
ments are deposited into otoliths are not 
entirely understood at this time. There- 
fore, the exact mechanisms by which oto- 
lith chemistry may directly influence 
increment widths remain unknown. Oto- 
liths are composed primarily of calcium 
carbonate in the form of aragonite. Di- 
valent metal ions of similar size to Ca, 
such as those of Ba and Sr, can substi- 
tute directly for Ca in the crystal-lat- 
tice (Campana, 1999). However, other 
elements such as Zn and Mn may occupy 
different positions in the otolith matrix 
(i.e., in the interstitial spaces or in as- 
sociation with the proteinaceous matrix; 
Campana, 1999). Although it is known 
that otolith crystal orientation is pro- 
tein-mediated (Lowenstam, 1981), it is 
not known how physiological stress can 
affect protein deposition, or how trace el- 
ement inclusion may influence increment 
width. The orientation of the crystal-lat- 
tice did not change in fish treated with 
ocean and lagoon waters and crystal 
orientation was similar to other fishes 
(e.g., Linkowski et al., 1993). Elemental 
availability in the location of the trace 
metal inclusions may be capable of cre- 
ating differences in increment width 
by increasing the length, or number, of 
Figure 5 
Scanning electron microscope images of the crystal lattice in otoliths 
of neon damselfish (Pomacentrus coelestis). (A) Image of an otolith of 
an experimental (Expt) fish. “Expt” indicates the area (above the white 
line) where increments were laid down in the otolith of a fish exposed 
to ocean waters. (B) Detail of crystal-lattice from a control fish; (C) 
Detail of the crytalline lattice of a postsettlement control fish; the 
white line indicates the settlement mark. Large white arrows indicate 
the orientation of the crystal-lattice. Scale: increments near the edge 
of the otolith are separated by approximately 1.5 pm. 
