Abstract
The rise of atmospheric CO₂ due to climate change is causing the average sea surface temperature to rise along with the amount of CO₂ dissolved in the ocean. Many organisms like tropical fish are already living at their environmental limits in terms of thermal and pH levels, and little is known about the effects increased stresses will have on their development. The effects of increased temperatures on muscle fiber development and standard length were investigated in a juvenile tropical fish, Amphiprion bicinctus in the Red Sea. Fish were collected from four sites within the Red Sea (Eilat, Israel; Nuwayshiziyah, northern Saudi Arabia; Thuwal, Saudi Arabia, and Al Lith, Saudi Arabia). It was predicted that muscle fiber sizes and standard lengths would vary in relation to latitude and temperature of the site location according to the predictions based on a trade-off between oxidative capacity (selection for smaller fibers) and power (selection for larger fibers). While the sizes of the fish from different sites were found to be significantly different, the stage of muscle development was similar, that is, the primary muscle fiber size had reached maximum size and was thus comparable across all populations. Statistical analysis revealed that muscle fibers varied by site location (p=5.148e⁻⁰⁷). Post-hoc Tukey testing revealed that the middle two sites (Northern Red Sea and Thuwal) were not significantly different from each other and the two latitudinal extremes (Eilat and Al Lith) had fish that also did not significantly differ from each other. The effects of decreased pH levels on muscle fiber development and standard length were also investigated in larvae of another anemone fish Amphiprion clarkii (pH 8.2, pH 7.8, pH 7.6, pH 7.2). It was hypothesized that individuals subjected to decreased pH levels would have smaller primary muscle fibers and delayed calcification of bone at the most extreme pH level compared with controls. The fiber size did not significantly depend on treatment (p=0.206) and standard length (p=0.327). As well, parhypural bone calcification in fish was marginally less in pH 7.3 than in pH 8.2. These studies of juvenile Amphiprion spp. provided evidence suggesting local population adaptation of primary muscle fiber size in the field, and no evidence for a muscle fiber response to a gradient of increased acidification in the larval environment.