Anthropogenic versus fish-derived nutrient effects on seagrass community structure and function.

Area of Science:

• Marine Ecology
• Nutrient Cycling
• Coastal Ecosystems

Background:

• Human activities globally alter nutrient dynamics through various pathways, impacting ecosystems.
• Seagrass ecosystems are particularly vulnerable to altered nutrient loads from anthropogenic sources and consumer activities.

Purpose of the Study:

• To simulate altered nutrient supply and ratios (nitrogen:phosphorus) from anthropogenic fertilizer and fish excretion in seagrass ecosystems.
• To test ecological theory predicting primary producer dynamics based on resource dynamics.
• To understand the impact of different nutrient sources and their interactions on seagrass structure and function.

Main Methods:

• Simulated scenarios of altered nutrient supply and nitrogen:phosphorus ratios.
• Investigated nutrient inputs from artificial fertilizer and fish excretion.
• Measured ecosystem functions, plant/algae community structure, seagrass growth, and density.

Main Results:

• Artificial fertilizer significantly altered ecosystem functions, increasing seagrass growth by up to 140%.
• Fish-mediated nutrients and their interaction with anthropogenic nutrients most affected community structure, increasing evenness by ~140%.
• While single nutrient supply (N or P) predicted some responses, no single nutrient explained the majority of outcomes, highlighting complex interactions.

Conclusions:

• Seagrass structure and function responses to nutrient changes are complex and not fully predictable by a single nutrient.
• Community structure is best explained by phosphorus (P), the limiting nutrient, while growth and density are best explained by nitrogen (N).
• Effective management of imperiled seagrass ecosystems requires addressing multiple simultaneous nutrient inputs.