The contribution of harbour porpoise faeces to the nutrient cycling in the Dutch North Sea

Abstract

This project does research into the relationship between phosphorus (P) availability and harbour porpoise density in the Dutch North Sea, as well as the potential contribution of harbour porpoise faeces to the marine ecosystem's nutrient cycling in relation to phytoplankton growth. Contrary to the initial hypothesis, no clear correlation was found between P measurements and porpoise density. Calculations suggest that the P contribution from harbour porpoise faeces (0,06 kton/year) is minimal compared to river input (16,1 kton/year) in the Dutch North Sea. Comparing this to several other studies on cetacean released nutrients, points out a contribution to nutrient recycling and transportation but a low influence on the carbon (C) fixation. The calculation from this study also finds a low influence on the C fixation and a minimal contribution to the nutrient cycling in the Dutch North Sea and the amount of P made available via porpoise faeces is disproportional when compared to other sources of P. To have a similar P input as from rivers, the harbour porpoise population would have to increase with 267 times.