Evaluating chemical signatures in a coastal upwelling region to reconstruct water mass associations of settlement-stage rockfishes

Abstract

Characterizing the behavior of larvae prior to settlement is integral to understanding population dynamics because coastal oceanography may facilitate or limit settlement. Otolith microchemistry can be used to determine patterns of fish movement, although there is a limited understanding of how this tool can be applied in coastal marine systems. Our goal in this study was to evaluate the application of otolith microchemistry to characterize water mass associations of settlement-stage marine fish in a coastal upwelling region using a 3-step approach. First, we characterized seawater chemistry of coastal water mass types across multiple years, finding differences in the chemical signatures of strong upwelling, weak upwelling, and relaxation events. Second, we experimentally determined the effect of temperature on the partitioning of trace elements in otoliths for 2 rockfishes (Sebastes spp.) to find that the effect of temperature on otolith partition coefficients was element-and species-specific. Finally, we compared coeval changes in seawater and otolith chemistry of settlement-stage rockfishes that were exposed to naturally variable conditions over an upwelling-relaxation cycle. We subsequently evaluate whether laser ablation inductively coupled plasma mass spectrometry effectively measures otolith chemistry over ecologically relevant time scales. We discovered that elemental concentrations in otoliths respond rapidly to changes in seawater chemistry and reflect equivalent proportional changes. This study provides evidence that elemental signatures are valuable tools for reconstructing larval histories of marine fish in coastal upwelling regions.

Otolith elemental composition reveals separate spawning areas of anchoveta, <em>Engraulis ringens</em>, off central Chile and northern Patagonia

“…Therefore, the higher Ba:Ca ratios we found in fish in the central zone are most probably an effect of upwelling. These findings are concordant with previous observations of Ba:Ca in seawater and fishes in other upwelling areas where increased Ba:Ca has been detected under upwelling conditions (Wheeler et al 2016, Hampton et al 2018. A similar nutrient-like distribution might be expected for Sr (De Villiers 1999), though we found no significant differences in Sr:Ca rations in otoliths between central Chile and northern Patagonia.…”

“…A similar nutrient-like distribution might be expected for Sr (De Villiers 1999), though we found no significant differences in Sr:Ca rations in otoliths between central Chile and northern Patagonia. Wheeler et al (2016) concluded that individual ratios of Sr:Ca in fish otoliths showed little variation in the California upwelling system and did not serve as valuable proxies of oceanic conditions.…”

Coupling biogeochemical tracers with fish growth reveals physiological and environmental controls on otolith chemistry

“…Moreover, otolith Ba:Ca concentrations increase in as little as three days following increased levels of Ba:Ca in seawater (Wheeler et al. ). Therefore, the otolith Ba:Ca profile found in the Bonney upwelling region may reflect reduced concentrations of Ba of the actual water mass being upwelled and alternative (non‐upwelled) sources of greater Ba input into southern Australian marine waters during the autumn/winter months.…”

Otolith chemistry does not just reflect environmental conditions: A meta‐analytic evaluation

“…The ear bones of bony fish (otoliths) provide analogous calcified structures that are widely used to answer a range of biological and ecological questions on fish movements and habitat use based on their element composition (Brennan et al., ; Elsdon et al., ; Gillanders, Izzo, Doubleday, & Ye, ; Izzo, Doubleday, Grammer, Gilmore, et al, ; Reis‐Santos, Tanner, Vasconcelos, et al., ). Otolith chemistry also provides a means of estimating environmental conditions experienced by individual fish over time (Izzo, Doubleday, Grammer, et al., ; Limburg et al., ; Tanner et al., ; Wheeler, Russell, Fehrenbacher, & Morgan, ). However, unlike the aforementioned calcified structures, otoliths are produced by complex multicellular organisms, and the precipitating surface is not in direct contact with the surrounding water.…”