Variations in Otolith-Zinc Concentrations of Brown Surgeonfish (Acanthurus nigrofuscus) Between Marine Protected Areas and Fished Reefs
Nichols, Matthew Austin
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As human populations continue to increase, the growing reliance on exploited fish stocks has furthered patterns of declining body size and biomass worldwide. To mitigate these impacts, fisheries managers have implemented a variety of conservation strategies, including marine protected areas (MPA), as these serve as a refuge for fish, resulting in increases in numerous health metrics (fish density, biomass, body-size, and species diversity). By using fish otolith samples previously concluded to have physiological and morphometric differences between MPA and fished reef (FR) fish, this thesis explores the potential of using microchemical analysis of zinc (Zn) to reveal impacts MPAs might have on Brown Surgeonfish (Acanthurus nigrofuscus). To investigate this, the following research questions were proposed: (1) Is there a difference in otolith-Zn concentration between conspecific fish in MPAs and FRs? (2) Is there an age-based difference in otolith-Zn concentrations among conspecific fish and is this difference present between MPAs and FRs? (3) Is there a sex-based difference in otolith-Zn concentrations among conspecific fish and is this difference present between MPAs and FRs? Otoliths collected from fish captured within and outside MPAs in Zambales, Philippines, were sliced, aged, and analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The collected data was calculated for statical significance using linear mixed-effects models (LMM). This study was able to conclude that otolith-Zn concentrations were effective in distinguishing differences between these conspecific fish by MPA status, age, and sex (p<0.0001, p<0.0001, and p=0.0351 respectively). However, these variables were not found to be statistically significant between interactions. Therefore, the microchemical analysis of otolith-Zn concentrations alone does not provide a completed picture of the effects MPAs have on these populations. Furthermore, higher otolith-Zn concentrations were expected from those populations previously determined to show healthier characteristics. Contrarily, the opposite observation was observed in this analysis and warrants additional research. It was only by combining the microchemical analysis, biological profile, literature, and morphometric sample data that we get a potential glimpse into the physiologic and behavioral response of A. nigrofuscus to protective zones.