Ecosystem Change Arguments Practice Test

A coral reef experiences a bleaching event. Evidence of ecosystem change: live coral cover decreases from 60% to 25% in 1 year. Population data: reef fish that shelter in coral decrease from 200 to 90; algae-grazing sea urchins increase from 30 to 70; jellyfish increase from 10 to 35. Which statement is supported by the evidence and includes reasoning linking the change to the population response? Arguments must be evidence-based.

A stream near farms had increased fertilizer runoff in spring, raising nitrate levels. Data were collected before the runoff increase and after.

Evidence (before → after): nitrate: 2 mg/L → 9 mg/L; algae: 200 → 900 cells/mL; dissolved oxygen: 8.5 → 4.0 mg/L; trout: 35 → 10 per 100 m.

Which argument best explains the trout population shift using the evidence and reasoning that links the change to the population response?