INFLUENCE OF TROPHIC ROLE AND LIFE-CYCLE DURATION ON TIMING AND MAGNITUDE OF BENTHIC MACROINVERTEBRATE RESPONSE TO WHOLE-LAKE ENRICHMENT

Phosphorus and nitrogen additions over a 3-year period (1991-1993) sig nificantly increased the abundance of most benthic macroinvertebrate t axa collected on artificial substrates in a small oligotrophic lake in insular Newfoundland relative to a nearby control lake. The speed and magnitude of response was related to both the trophic role and the li fe-cycle duration of the taxa. This created a response continuum with small, fast-growing herbivores such as sphaeriid clams and gastropods demonstrating more pronounced and more rapid abundance responses than longer lived detritivores such as Ephemeroptera, which, in turn, had q uicker responses than long-lived predators. These observations support the hypothesis that these benthic communities are controlled by botto m-up resource processes during the initial years of enrichment and pro vide the basis for expecting future enhancement of benthivorous salmon id populations in the fertilized lake.