Nutrient and Energy Transport between Estuaries and Coastal Marine Ecosystems by Fish Migration

TLDR

The study assessed whether fish migration of gulf menhaden transports energy and nutrients from estuaries to coastal marine ecosystems. By measuring biomass, energy, and nutrient composition relative to migration patterns, the authors found that transport always moved from estuary to marine system, with magnitude governed by growth, mortality, and fish abundance. Gulf menhaden exported substantial energy and nutrients—about 38 g biomass, 930 kJ, 22.5 g C, 3.1 g N, and 0.9 g P per m² per year—representing 5–10 % of estuarine primary production and comparable in magnitude to passive export but of higher quality, underscoring fish migration as a key pathway for transferring estuarine productivity to coastal waters.

Abstract

Biomass accumulation and changes in body energy and nutrient (carbon, nitrogen, and phosphorus) composition were evaluated relative to the migration pattern of gulf menhaden (Brevoortia patronus) to determine if biotic transport by fish is an important source of energy and nutrients to coastal marine ecosystems. Gulf menhaden transported significant quantities of energy, C, N, and P from a Louisiana estuary to the nearshore Gulf of Mexico. Transport was always out of the estuary to the marine system, although the magnitude depended on the balance between growth and mortality rates and abundance of fish. Average export per year was 38 g biomass, 930 kJ, 22.5 g C, 3.1 g N, and 0.9 g P∙m −2 out of estuaries. This is roughly 5–10% of the total primary production of these estuarine areas. N and P export by fish is of the same magnitude as passive waterborne export; however it is higher quality. This indicates that fish migration can play an important role in exporting the productivity of estuaries to coastal marine ecosystems.