Describe the role of estuaries as nurseries and how dissolved oxygen dynamics influence juvenile fish and crustaceans.

• A. Estuaries provide shelter and abundant prey; tidal flushing delivers oxygenated water, but stagnant zones can create hypoxia that harms juvenile life stages.
• B. Estuaries have no nursery value; oxygen levels remain constant; juveniles thrive in stagnant zones.
• C. Estuaries are primarily salt flats with poor productivity; oxygen is always abundant.
• D. Estuaries' nurseries rely on anoxic conditions to stimulate certain species.

Answer: (A)