Fish Communities Before and After a Bleaching Event The goal of this project was to assess how fish communities in Northeast Oahu may have been affected by the 2014-2015 mass bleaching event by examining abundance data from immediately before (2013) and after (2016). I hypothesize that fish abundances will have declined from the 2013 to the 2016 surveys. Kelsey Doughten
Data Description Data files: projectMM.wk1 (main) and projectSM.wk1 (second) 28 samples and 47 species Samples are coral reef surveys, species are fish counts Environmental variables are: Time (year: 2013 and 2016) Depth (zone: shallow, mid, deep) Hard coral cover (percent)
Data Processing Skewness: Outliers (2 SD cutoff): Species data: Avg. = 2.0 (1.0 < skew < 4.2) Environmental data: Avg. = 0.2 (0.0 < skew < 0.4) Outliers (2 SD cutoff): Samples: s1 (+2.66 SD) Species: PSCE (+2.49 SD), PARR (+2.22 SD), and PSEV (+2.17 SD) After log(x+1) transformation and general relativization: Skewness: Avg. = 1.0 (-0.7 < skew < 3.0) One sample was discarded: s1 (+2.92 SD) Two species were discarded: PSEV (+2.55 SD) & PSCE (+2.17 SD) 27 samples and 45 species
Data Analysis
Results Conclusion: 3-dimensional solution Criterion 1: decline in stress with added axis at least 5 Criterion 2: p value < 0.05
Results
Results Coefficient of determination (% variance explained by axes) Orthogonality (independence of the axes)
Results
Results 2016 2013 ACNR CAGA CEPO CHHA CIFA PAFO THBA ACOL CAJA SUBU ACLE CHSO CTST PLIM OXBI SUFR
Results Axis 1: Positive: OXBI (τ = 0.677) and SUFR (τ = 0.536) Secondary consumers Negative: ACLE (τ = -0.519), CHSO (τ = -0.480), CTST (τ = 0.540) Primary consumers Axis 2: Positive: ACNR (τ = 0.487), CAGA (τ = 0.488), CEPO (τ = 0.574), CHHA (τ = 0.549), CIFA (τ = 0.525), PAFO (τ = 0.567), THBA (τ = 0.541) Primary (2), secondary (2), piscivores (2), planktivore (1) Negative: ACOL (τ = -0.512), CAJA (τ = -0.426), SUBU (τ = -0.431) Primary (2) and secondary (1)
Discussion What do these results mean for the hypothesis? No apparent relationship between depth and fish community Slight relationship between coral cover and fish community Strong relationship between the composition of fish communities before the bleaching event and after Suggests possibility for underlying relationship with bleaching Or perhaps something else? What did this exercise teach you regarding your overreaching analysis, methods, and objectives? Community data is complex and NMDS provides a great way to assess many different relationships at once but data exploration is very important to ensure you are getting results actually representative of the real data
Discussion: Next Steps For re-analysis of the data, I would like to do a MRPP test to further investigate the relationship between fish assemblages before and after the bleaching event. To further this study… Assess more environmental variables Structural complexity Actual depths (rather than zones) Different sides of island Other benthic coverage (such as macroalgae, CCA, sand, etc.) Live vs. dead coral cover Add data from 2015 surveys Fish consumer groups