Developing an indicator of nutrient enrichment in coastal estuaries and lagoons using tissue nitrogen content of the opportunistic alga, Enteromorphaintestinalis (L. Link)

We explored the use of an opportunistic green alga, Enteromorpha intestinal is (L. Link), as an indicator of N enrichment in a southern California salt marsh. In conjunction with N additions to cordgrass (Spartina foliosa, Tri n) in April, June and August 1995, mesh bags containing N-starved algal tis sue were placed within cordgrass patches, at their edges along islands, and in adjacent channels. After 1 week in the field, recovered algal tissue wa s used to test detection of two levels of total N supply tone twice as high as the other), as well as no added N (control). Tissue N concentration, ca lculated as the percentage change in N, was the best of several algal measu res at discerning differences in N availability in any month. In both April and June, tissue N declined from the marsh plain to the channels, reflecti ng declining N supply. Tissue N concentration also reflected differences in the total quantity of N added. Within the channels adjacent to fertilized areas, algal tissue N was similar to control areas, suggesting that N addit ions to cordgrass are not resulting in eutrophication of open waters. In Au gust, the algae detected N additions on the marsh plain, but survivorship w as poor; other algal species may be better indicators of enrichment in late -summer. With further investigation, the technique presented in this paper has the potential to be developed into a useful bioassay for detecting eutr ophication of coastal salt marshes and lagoons. (C) 1998 Elsevier Science B .V. All rights reserved.