Effect of ocean acidification on otolith development in larvae of a tropical marine fish

© The Author(s), 2011. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 8 (2011): 1631-1641, doi:10.5194/bg-8-1631-2011.Calcification in many invertebrate species is predicted to decline due to ocean acidification. The potential effects of elevated CO2 and reduced carbonate saturation state on other species, such as fish, are less well understood. Fish otoliths (earbones) are composed of aragonite, and thus, might be susceptible to either the reduced availability of carbonate ions in seawater at low pH, or to changes in extracellular concentrations of bicarbonate and carbonate ions caused by acid-base regulation in fish exposed to high pCO2. We reared larvae of the clownfish Amphiprion percula from hatching to settlement at three pHNBS and pCO2 levels (control: ~pH 8.15 and 404 μatm CO2; intermediate: pH 7.8 and 1050 μatm CO2; extreme: pH 7.6 and 1721 μatm CO2) to test the possible effects of ocean acidification on otolith development. There was no effect of the intermediate treatment (pH 7.8 and 1050 μatm CO2) on otolith size, shape, symmetry between left and right otoliths, or otolith elemental chemistry, compared with controls. However, in the more extreme treatment (pH 7.6 and 1721 μatm CO2) otolith area and maximum length were larger than controls, although no other traits were significantly affected. Our results support the hypothesis that pH regulation in the otolith endolymph can lead to increased precipitation of CaCO3 in otoliths of larval fish exposed to elevated CO2, as proposed by an earlier study, however, our results also show that sensitivity varies considerably among species. Importantly, our results suggest that otolith development in clownfishes is robust to even the more pessimistic changes in ocean chemistry predicted to occur by 2100

Life-history characteristics of coral reef gobies. II. Mortality rate, mating system and timing of maturation

High adult mortality rate is expected to select for early maturation. However, physiological constraints or size-related reproductive benefits might select for delayed maturation, especially in small-bodied species. Additionally, the mating system and the relative intensity of mate competition can modify the timing of maturation. Here, we investigate the influence of mortality rate and mating system on the timing of maturation in 5 species of small coral reef goby that are either polygynous (Asterropteryx semipunctatus and Istigobius goldmanni) or monogamous pair-spawners (Amblygobius bynoensis, Amblygobius phalaena and Valenciennea muralis). All 5 species experienced high annual adult mortality rates with annual survivorship of ≤2.3%. The mean size at maturity, compared to maximum adult size, was smaller than is typical for fishes, indicating selection for early maturity in all of these species. The season of growth had little effect on size at maturity, but had a considerable effect on age at maturity, with summer-growing individuals exhibiting a younger mean age at maturity than winter-growing individuals. As predicted, males of the 3 monogamous pair-spawning species matured earlier and smaller than females (A. bynoensis and A. phalaena) or at the same time as females (V. muralis), but contrary to expectation, males of the 2 polygynous species (A. semipunctatus and I. goldmanni) did not mature later and at a larger size than females. Overall, the timing of maturation in these species is consistent with predictions from general life-history theory, however, the sex-specific timing of maturation may be influenced by body size constraints and the mating system

Evolution of mating systems in coral reef gobies and constraints on mating system plasticity

Social and mating systems can be influenced by the distribution, abundance, and economic defendability of breeding partners and essential resources. Polygyny is predicted where males can economically defend multiple females or essential resources used by females. In contrast, monogamy is predicted where neither sex can monopolise multiple partners, either directly or through resource control, but where one mate is economically defendable. The mating system and reproductive behaviour of five species of coral reef goby were investigated and contrasted with population density and individual mobility. The two most abundant species (Asterropteryx semipunctatus and Istigobius goldmanni) were polygynous. In contrast, the less populous and more widely dispersed epibenthic species (Amblygobius bynoensis, Amblygobius phalaena and Valenciennea muralis) were pair forming and monogamous. All five species had low mobility, mostly remaining within metres (3 epibenthic species) or centimetres (2 cryptobenthic species) of a permanent shelter site. Interspecific differences in the mating system may have been shaped by differences in population density and the ability of reproductive individuals to economically defend breeding partners/sites. However, in a test of mating system plasticity, males of the three monogamous species did not mate polygynously when given the opportunity to do so in experimental manipulations of density and sex ratio. Mate guarding and complex spawning characteristics, which have likely co-evolved with the monogamous mating system, could contribute to mating system inflexibility by making polygynous mating unprofitable for individuals of the pair forming species, even when presented with current-day ecological conditions that usually favour polygyny

Life-history characteristics of coral reef gobies. I. Growth and life-span

Life-history theory predicts that small species will exhibit short life-spans and fast growth rates; however, previous studies indicate that a positive relationship between size and maximum age may not be universally applicable to coral reef fishes. Here, we investigate the growth and life-span of 5 small species of coral reef goby (family Gobiidae): Istigobius goldmanni, Asterropteryx semipunctatus, Amblygobius bynoensis, Amblygobius phalaena and Valenciennea muralis. All 5 species were relatively short-lived, with the oldest individual sampled ranging from 11 to 16 mo depending on species and sex. Rapid growth occurred over much of the size range of all 5 species and, in contrast to most reef fishes, relatively little or no time was spent at an asymptotic size. Patterns of growth were best described by a Broken Stick model for I. goldmanni, and by either a Broken Stick model or the von Bertalanffy growth function for the other 4 species. Summer-growing individuals had higher growth rates than winter-growing individuals, but this did not affect the overall patterns of growth. Sex-specific differences in growth were evident for I. goldmanni and A. semipunctatus, with males growing faster and attaining a larger maximum size than females. In contrast, there was no significant difference in growth between male and female A. bynoensis, A. phalaena and V. muralis. This pattern may be related to interspecific differences in intensity of sexual selection, mating system, and reproductive behaviour. Overall, the patterns of growth and life-span of these 5 small species conformed to traditional concepts of life-history theory

Validation of otolith growth-increment periodicity in tropical gobies

We assessed the efficacy of tetracycline, calcein and strontium chloride for validating the periodicity of otolith growth-increments in eight species of tropical marine gobies (family Gobiidae). We compared the number of fishes in which the otoliths were successfully marked when each of these chemicals was administered by intraperitoneal injection or immersion bath at a range of doses and immersion times. All three chemicals could produce a detectable mark in the otoliths of five reef-flat gobies, Asterropteryx semipunctatus, Amblygobius bynoensis, Istigobius goldmanni, Valenciennea muralis and Amblygobius phalaena; however, tetracycline injection at 50 mg kg−1 is recommended because it produced a brighter otolith mark than calcein and is cheaper and quicker to detect than strontium chloride. Calcein immersion treatment of 125 mg l−1 for 24 h was the most successful treatment for two estuarine gobiids, Favonigobius reichei and Glossogobius biocellatus. No treatment produced a detectable mark in the otoliths of the coral-dwelling goby Gobiodon histrio. Adequate care in the preparation of otoliths was found to be essential for detection of the validation mark produced by tetracycline and calcein. Otolith growth-increments were deposited daily in the seven species of goby for which validation was possible

Seawater carbonate chemistry and clownfish Amphiprion percula size and otholith development during experiments, 2011

Calcification in many invertebrate species is predicted to decline due to ocean acidification. The potential effects of elevated CO2 and reduced carbonate saturation state on other species, such as fish, are less well understood. Fish otoliths (earbones) are composed of aragonite, and thus, might be susceptible to either the reduced availability of carbonate ions in seawater at low pH, or to changes in extracellular concentrations of bicarbonate and carbonate ions caused by acid-base regulation in fish exposed to high pCO2. We reared larvae of the clownfish Amphiprion percula from hatching to settlement at three pHNBS and pCO2 levels (control: ~pH 8.15 and 404 µatm CO2; intermediate: pH 7.8 and 1050 µatm CO2; extreme: pH 7.6 and 1721 µatm CO2) to test the possible effects of ocean acidification on otolith development. There was no effect of the intermediate treatment (pH 7.8 and 1050 µatm CO2) on otolith size, shape, symmetry between left and right otoliths, or otolith elemental chemistry, compared with controls. However, in the more extreme treatment (pH 7.6 and 1721 µatm CO2) otolith area and maximum length were larger than controls, although no other traits were significantly affected. Our results support the hypothesis that pH regulation in the otolith endolymph can lead to increased precipitation of CaCO3 in otoliths of larval fish exposed to elevated CO2, as proposed by an earlier study, however, our results also show that sensitivity varies considerably among species. Importantly, our results suggest that otolith development in clownfishes is robust to even the more pessimistic changes in ocean chemistry predicted to occur by 2100