| Abstrakt: |
In a eutrophic embayment (Waquiot Bay, Massachusetts), cladophora vagabunda (L.) van den Hoek occurs in thick (sometimes >1 kg dry wt [SUP-2]) nearly monospecific unattatched mats in deeper regions (2 m), whereas gracilaria tikvahiae McLachlan is largely restricted to shallow (<1 m) areas. We explored these distribution patterns, investigating competitive interactions between these opportunistic species by varying the limiting resource, photon flux density (PDF), and species composition under conditions of N sufficiency in microcoms. Under lower biomass loading, neither species showed a difference in growth rates in single-and mixed-species stands. With a 25% increase in initial biomass loading. Gracilaria tikvahiae had significantly higher growth rates under saturating PDF and consistently showed greater performance when grown in single-species rather than in mixed-species stands. While growth rate was 2× Greater for C vagabunda in single species than in mixed-species stands at saturating PFD this pattern was reversed under limiting irradiances. In mixed-species stands at high PFD (comparable to shallow regions of the bay), the growth rate of C. tikvahiae was over 4× Higher than that of C vagabunda Cladophora vagabunda grew at a faster rate than G. tikvahiae only in the low PFD, mixed-species treatment results of this study suggest that the observed distributional patterns of these macroalgae are due in part of interspecify exploitative competition but that tolerance of low PFD by C, vaganunda has led to dominance of these species in distinctive regions of the embayment. [ABSTRACT FROM AUTHOR] |
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