Abstract
Identifying natal origins of animals is key to determining the relative productivity of natal habitats, dispersal of individuals among local populations (i.e. connectivity), and, ultimately, metapopulation dynamics. As marine fish larvae have a high potential for dispersal, natural tags such as otolith chemistry are often used to determine natal origins. Trace elements may be incorporated into embryonic otoliths while larvae are developing in the egg, resulting in chemical signatures in the pre-hatch region of the otolith that reflect the natal habitat. Our goal was to determine whether the natal origins of 1-3 day old larval capelin (Mallotus villosus), a key forage fish in many northern marine ecosystems, could be determined using otolith chemistry. We sampled larvae from five Newfoundland regions (i.e. embayments: Placentia Bay, St. Mary’s Bay, Witless Bay, Trinity Bay, Notre Dame Bay) during July-August, 2019 to quantify regional differences in otolith chemistry. Additionally, eggs/larvae were field-reared within two regions over multiple years (Notre Dame Bay: 2014, 2015, 2018, 2019; Trinity Bay: 2018, 2019) to quantify interannual variation in region-specific otolith chemistry. Multi-elemental otolith signatures (i.e., Mg, Mn, Zn, Sr, Ba), as determined by Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA ICP-MS), differed significantly among regions, with individuals classified into their natal region with 78% success (region-specific success: 68-100%). Classification success into natal region remained high (67-76%) despite interannual variation in otolith trace element concentrations within regions. Characterizing region-specific otolith chemical signatures that reflect natal origins of capelin larvae is the first step in determining the productivity and relative contributions of different regions of coastal Newfoundland to capelin recruitment.
Highlights
Natal origins of animals are used to evaluate relative productivity of natal habitats and determine dispersal and connectivity of individuals among local populations and metapopulations (Cowen et al, 2007)
Otolith chemistry differed for some trace elements between fieldreared larvae in incubation canisters and preemergent larvae collected from sediments in Notre Dame Bay during 2019, with significant differences in Zn (t38 = 3.24, p = 0.0025), Mn (t42 = 2.504, p = 0.0163), and Ba (t41 = 2.023, p = 0.0496)
Capelin larvae could be correctly classified into their natal region based on otolith chemistry (QDFA: Wilk’s λ = 0.172; approximate F20,210 = 7.332, p < 0.0001; Figure 2) with an overall classification success of 78%
Summary
Natal origins of animals are used to evaluate relative productivity of natal habitats and determine dispersal and connectivity of individuals among local populations and metapopulations (Cowen et al, 2007). To determine the natal origins of fish larvae, tagging or marking is required. Natural tags have determined natal origins of fish larvae, providing important information on local retention (e.g., Jones et al, 1999; Swearer et al, 1999) and connectivity (e.g., Davoren and Halden, 2014). Trace elements in the surrounding aquatic environment are incorporated into the calcium carbonate structure of fish otoliths as individuals grow, allowing chronological reconstruction of environmental histories including natal origin (Campana, 1999; Elsdon and Gillanders, 2003). Ambient water chemistry primarily influences trace element incorporation into the otoliths, other extrinsic factors including salinity and temperature influence trace element incorporation rates (reviewed in Loewen et al, 2016)
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