Differences in Juvenile Plaice and Flounder Otolith Microchemistry from the Inner Danish Waters Elliot J
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Differences in juvenile plaice and flounder otolith microchemistry from the Inner Danish Waters Elliot J. Brown Patrick Reis-Santos Bronwyn M. Gillanders Josianne G. Støttrup Introduction – the wider project Describing juvenile habitat quality for recreationally important fish species of the Inner Danish Waters. 1. [Presence/Absence, Density, Growth] ~ [Physical Factors] + [Biological Factors] VS [Presence/Absence, Density, Growth] ~ [Physical Factors] 2. [Presence/Absence, Density, Growth] ~ [Physical Factors] 3. Apply models to identify potential juvenile habitats European Flounder European Plaice Platichthys flesus Pleuronectes platessa 2 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Introduction – this specific project 4. Can otolith microchemistry be used to correctly assign individuals back to juvenile growth regions across contiguous areas? Vasconcelos et al, 2007 Bailey et al, 2015 Beck et al, 2001 3 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Introduction – this specific project Question 1. • Is there a difference in the levels of different elemental components of sagittal otoliths between hybridising(?) con-familials (flounder and plaice) where they are living together? Question 2. • Is it possible to differentiate between contiguous coastal juvenile habitat areas for plaice using otolith microchemistry? 4 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW n = 113 Field Collections n = 37 n = 36 5 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Field Collections • Fish killed benzocaine at 250g/mL in aerated seawater. • Once all opercula movements and reactions to stimuli had ceased fish were: – Measured to the nearest millimetre – Quick frozen on dry ice before – Stored in a -18°C freezer at the end of the day. • Back in the lab: – Defrosted – Weighed and measured again – Fin Ray counts were made for the dorsal, anal and caudal fin. • Plaice: 499 • Sagittal Otoliths: • Flounder: 147 – Dissected out – Cleaned in milli-q water – Dry stored in individual plastic bags 6 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Otolith Microchemistry • Question 1. Plaice vs Flounder – 20 sites – 37 pairs of flounder and plaice • Question 2. Plaice Distribution – 7756 sites – 499150 individuals – Selected from 4 “regions” 7 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Otolith Microchemistry • SelectedLaser Ablation otoliths: – Inductively Coupled Plasma Mass Spectrometry – MLAounted-ICPMS in indium laced epoxy • University– Thin transverse of Adelaide’s sections microscopy taken through department the core – Hand polished down to the primordium – Sections mounted on glass slides with indium laced crystal-bond. • Edge spots from ventroproximal region • Ba, Cu, Fe, K, Li, Mg24, Mn, Na, Sr 8 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Data Analyses • Implemented via “CAPdiscrim” function (Kindt R; 2017) – Within “BiodiversityR” (v.2.8-4) for R (Kindt, R. & Coe R.; 2005)) • For Plaice Distribution: – Checked # of “regions” with Bayesian Information Criterion – 4 groups was the best fit. • Implemented via “BIC” function in “mclust” (v.4) package for R – (Fraley, C. et al; 2012) 9 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Results – flounder vs. plaice • 76% of individuals were correctly assigned to their species – 72% of plaice – 82% of flounder >cap_flvspl$manova approxF Df Pillai num Df denDf Pr(>F) y[,group] 1 0.30435 2.5455 8 64 0.009804** Residuals 74 Signif.codes: ‘***’<0.001 ‘**’<0.01 ‘*’<0.05 ‘.’<0.1 10 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Results – plaice distribution • 63% of individuals correctly assigned to their region of origin. – The Belt Seas 80% – Northern Kattegat 65% – Skagerrak 53% – Southern Kattegat 53% – ~F = 9.7, p < 0.0001 11 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Limitation – plaice distribution • Number of regions was originally arbitrary. – Subsequently backed up with BIC model selection • Region boundaries are poorly defined. 12 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Conclusions Question 1. • Significant differences in the elemental composition of flounder and plaice otoliths. – Differences not strong enough to do away with other forms of identification. Question 2. • There are significant differences in the elemental composition of juvenile plaice from different regions of the Inner Danish Waters. • It is possible to correctly assign juvenile plaice to the regions of their juvenile growth habitat. – However, limitations in the approach applied to contiguous regions mean that there are still high levels of mis-classification. – A continuous, spatially modelled approach may prove more appropriate. 13 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW Questions 14 DTU Aqua, Technical University of Denmark Juvenile plaice and flounder otolith 12-11-2017 microchemistry from the IDW.