Otolith geochemistry does not reflect dispersal history of clownfish larvae

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Coral Reefs 29 (2010): 883-891, doi:10.1007/s00338-010-0652-z.Natural geochemical signatures in calcified structures are commonly employed to retrospectively estimate dispersal pathways of larval fish and invertebrates. However, the accuracy of the approach is generally untested due to the absence of individuals with known dispersal histories. We used genetic parentage analysis (genotyping) to divide 110 new recruits of the orange clownfish, Amphiprion percula, from Kimbe Island, Papua New Guinea, into two groups: “self-recruiters” spawned by parents on Kimbe Island and “immigrants” that had dispersed from distant reefs (>10km away). Analysis of daily increments in sagittal otoliths found no significant difference in PLDs or otolith growth rates between self-recruiting and immigrant larvae. We also quantified otolith Sr/Ca and Ba/Ca ratios during the larval phase using laser ablation inductively coupled plasma mass spectrometry. Again, we found no significant differences in larval profiles of either element between self-recruits and immigrants. Our results highlight the need for caution when interpreting otolith dispersal histories based on natural geochemical tags in the absence of water chemistry data or known-origin larvae with which to test the discriminatory ability of natural tags.Research was supported by the Australian Research Council, the Coral Reef Initiatives for the Pacific (CRISP), the Global Environmental Facility CRTR Connectivity Working Group, the Total Foundation, a National Science Foundation grant (#0424688) to SRT, and a National Science Foundation Graduate Research Fellowship to MLB

Movements of Diadromous Fish in Large Unregulated Tropical Rivers Inferred from Geochemical Tracers

Patterns of migration and habitat use in diadromous fishes can be highly variable among individuals. Most investigations into diadromous movement patterns have been restricted to populations in regulated rivers, and little information exists for those in unregulated catchments. We quantified movements of migratory barramundi Lates calcarifer (Bloch) in two large unregulated rivers in northern Australia using both elemental (Sr/Ba) and isotope (87Sr/86Sr) ratios in aragonitic ear stones, or otoliths. Chemical life history profiles indicated significant individual variation in habitat use, particularly among chemically distinct freshwater habitats within a catchment. A global zoning algorithm was used to quantify distinct changes in chemical signatures across profiles. This algorithm identified between 2 and 6 distinct chemical habitats in individual profiles, indicating variable movement among habitats. Profiles of 87Sr/86Sr ratios were notably distinct among individuals, with highly radiogenic values recorded in some otoliths. This variation suggested that fish made full use of habitats across the entire catchment basin. Our results show that unrestricted movement among freshwater habitats is an important component of diadromous life histories for populations in unregulated systems

Shedding Light on Fish Otolith Biomineralization Using a Bioenergetic Approach

Otoliths are biocalcified bodies connected to the sensory system in the inner ears of fish. Their layered, biorhythm-following formation provides individual records of the age, the individual history and the natural environment of extinct and living fish species. Such data are critical for ecosystem and fisheries monitoring. They however often lack validation and the poor understanding of biomineralization mechanisms has led to striking examples of misinterpretations and subsequent erroneous conclusions in fish ecology and fisheries management. Here we develop and validate a numerical model of otolith biomineralization. Based on a general bioenergetic theory, it disentangles the complex interplay between metabolic and temperature effects on biomineralization. This model resolves controversial issues and explains poorly understood observations of otolith formation. It represents a unique simulation tool to improve otolith interpretation and applications, and, beyond, to address the effects of both climate change and ocean acidification on other biomineralizing organisms such as corals and bivalves

Variability in Isotope Discrimination Factors in Coral Reef Fishes: Implications for Diet and Food Web Reconstruction

Interpretation of stable isotope ratios of carbon and nitrogen (δ13C and δ15N) is generally based on the assumption that with each trophic level there is a constant enrichment in the heavier isotope, leading to diet-tissue discrimination factors of 3.4‰ for 15N (ΔN) and ∼0.5‰ for 13C (ΔC). Diet-tissue discrimination factors determined from paired tissue and gut samples taken from 152 individuals from 26 fish species at Ningaloo Reef, Western Australia demonstrate a large amount of variability around constant values. While caution is necessary in using gut contents to represent diet due to the potential for high temporal variability, there were significant effects of trophic position and season that may also lead to variability in ΔN under natural conditions. Nitrogen enrichment increased significantly at higher trophic levels (higher tissue δ15N), with significantly higher ΔN in carnivorous species. Changes in diet led to significant changes in ΔN, but not tissue δ15N, between seasons for several species: Acanthurus triostegus, Chromis viridis, Parupeneus signatus and Pomacentrus moluccensis. These results confirm that the use of meta-analysis averages for ΔN is likely to be inappropriate for accurately determining diets and trophic relationships using tissue stable isotope ratios. Where feasible, discrimination factors should be directly quantified for each species and trophic link in question, acknowledging the potential for significant variation away from meta-analysis averages and, perhaps, controlled laboratory diets and conditions

Intrapopulation Variability Shaping Isotope Discrimination and Turnover: Experimental Evidence in Arctic Foxes

Tissue-specific stable isotope signatures can provide insights into the trophic ecology of consumers and their roles in food webs. Two parameters are central for making valid inferences based on stable isotopes, isotopic discrimination (difference in isotopic ratio between consumer and its diet) and turnover time (renewal process of molecules in a given tissue usually measured when half of the tissue composition has changed). We investigated simultaneously the effects of age, sex, and diet types on the variation of discrimination and half-life in nitrogen and carbon stable isotopes (δ15N and δ13C, respectively) in five tissues (blood cells, plasma, muscle, liver, nail, and hair) of a top predator, the arctic fox Vulpes lagopus. We fed 40 farmed foxes (equal numbers of adults and yearlings of both sexes) with diet capturing the range of resources used by their wild counterparts. We found that, for a single species, six tissues, and three diet types, the range of discrimination values can be almost as large as what is known at the scale of the whole mammalian or avian class. Discrimination varied depending on sex, age, tissue, and diet types, ranging from 0.3‰ to 5.3‰ (mean = 2.6‰) for δ15N and from 0.2‰ to 2.9‰ (mean = 0.9‰) for δ13C. We also found an impact of population structure on δ15N half-life in blood cells. Varying across individuals, δ15N half-life in plasma (6 to 10 days) was also shorter than for δ13C (14 to 22 days), though δ15N and δ13C half-lives are usually considered as equal. Overall, our multi-factorial experiment revealed that at least six levels of isotopic variations could co-occur in the same population. Our experimental analysis provides a framework for quantifying multiple sources of variation in isotopic discrimination and half-life that needs to be taken into account when designing and analysing ecological field studies

The great melting pot. Common sole population connectivity assessed by otolith and water fingerprints

Quantifying the scale and importance of individual dispersion between populations and life stages is a key challenge in marine ecology. The common sole (Solea solea), an important commercial flatfish in the North Sea, Atlantic Ocean and the Mediterranean Sea, has a marine pelagic larval stage, a benthic juvenile stage in coastal nurseries (lagoons, estuaries or shallow marine areas) and a benthic adult stage in deeper marine waters on the continental shelf. To date, the ecological connectivity among these life stages has been little assessed in the Mediterranean. Here, such an assessment is provided for the first time for the Gulf of Lions, NW Mediterranean, based on a dataset on otolith microchemistry and stable isotopic composition as indicators of the water masses inhabited by individual fish. Specifically, otolith Ba/Ca and Sr/Ca profiles, and delta C-13 and delta O-18 values of adults collected in four areas of the Gulf of Lions were compared with those of young-of-the-year collected in different coastal nurseries. Results showed that a high proportion of adults (>46%) were influenced by river inputs during their larval stage. Furthermore Sr/Ca ratios and the otolith length at one year of age revealed that most adults (similar to 70%) spent their juvenile stage in nurseries with high salinity, whereas the remainder used brackish environments. In total, data were consistent with the use of six nursery types, three with high salinity (marine areas and two types of highly saline lagoons) and three brackish (coastal areas near river mouths, and two types of brackish environments), all of which contributed to the replenishment of adult populations. These finding implicated panmixia in sole population in the Gulf of Lions and claimed for a habitat integrated management of fisherie

The use of otolith strontium isotopes (87Sr/86Sr) to identify nursery habitat for a threatened estuarine fish

Nursery habitats are larval or juvenile habitats that disproportionately contribute individuals to adult populations of a species. Identifying and protecting such habitats is important to species conservation, yet evaluating the relative contributions of different larval habitats to adult fish populations has proven difficult at best. Otolith geochemistry is one available tool for reconstructing previous habitat use of adult fishes during the early life history, thus facilitating the identification of nursery habitats. In this study, we compared traditional catch surveys of larval-stage longfin smelt (Spirinchus thaleichthys) occurring in habitats of different salinities to corresponding larval-stage salinity distributions of sub-adult/adult longfin smelt estimated using otolith geochemical techniques. This allowed us to evaluate the relative contribution of larvae from waters of various salinities to sub-adult/adult populations of longfin smelt. We used laser ablation MC-ICP-MS on otoliths and an empirically-derived relationship between strontium isotope ratios (87Sr/86Sr) of waters across the estuarine salinity gradient to reconstruct the larval salinity history of longfin smelt. Salinity values from the larval region of sub-adult/adult otoliths (corresponding to standard lengths of ca.10-mm) were compared to corresponding catch distribution of larval longfin smelt (≤ 10-mm) from 4 year-classes (1999, 2000, 2003 and 2006) in the San Francisco Estuary spanning a period when the population underwent a dramatic decline. Though the catch distribution of larval-stage longfin smelt was centered around 4-ppt and did not vary significantly among years, salinity distributions of sub-adult/adult were lower and narrower (ca. 2-ppt), suggesting that low-salinity habitats disproportionally contributed more recruits relative to both freshwater and brackish water habitats and, therefore, may function as important nursery areas. Furthermore, the relative importance of the low salinity zone (ca. 2-ppt) to successful recruitment appeared greatest in years following the longfin smelt population decline. Our results indicate that otolith strontium isotopes (87Sr/86Sr) are a powerful tool for identifying nursery habitats for estuarine fishes

Trace element fingerprinting of cockle (Cerastoderma edule) shells can reveal harvesting location in adjacent areas

Determining seafood geographic origin is critical for controlling its quality and safeguarding the interest of consumers. Here, we use trace element fingerprinting (TEF) of bivalve shells to discriminate the geographic origin of specimens. Barium (Ba), manganese (Mn), magnesium (Mg), strontium (Sr) and lead (Pb) were quantified in cockle shells (Cerastoderma edule) captured with two fishing methods (by hand and by hand-raking) and from five adjacent fishing locations within an estuarine system (Ria de Aveiro, Portugal). Results suggest no differences in TEF of cockle shells captured by hand or by hand-raking, thus confirming that metal rakes do not act as a potential source of metal contamination that could somehow bias TEF results. In contrast, significant differences were recorded among locations for all trace elements analysed. A Canonical Analysis of Principal Coordinates (CAP) revealed that 92% of the samples could be successfully classified according to their fishing location using TEF. We show that TEF can be an accurate, fast and reliable method to determine the geographic origin of bivalves, even among locations separated less than 1 km apart within the same estuarine system. Nonetheless, follow up studies are needed to determine if TEF can reliably discriminate between bivalves originating from different ecosystems