Nutrient enrichment, followed by economic development, has already had a significant impact on the costal ecosystem of China. Field investigations on seaweed beds adjacent to Lingshui River in Dalian were conducted in present studies to elucidate the response of the seaweed communities to the sewage effluents along a natural nutrient gradient. Further, the studies were conducted in the laboratory on the uptake and growth kinetics of NO₃ ^–, NH₄ ⁺ and PO₄ ^3– of the clone of Enteromorpha linza, r-strategic green alga dominating in the nutrient-rich estuaries, and Ceramium tenerrimum, k-strategic red alga distributing in the oligotrophic areas. Comparative analyses were carried out on the absorption and utilization of nutrient, and reproduction strategies of the two species to explain the responses of seaweed communities to different nutrient environments. The results show that with the decrease of environmental nutrients, species number of seaweed increases, and the coverage of dominant species decreases. According to the response of seaweed communities to nitrogen nutrient, it is considered that the threshold of category I of inorganic nitrogen in the current seawater quality standard should be revised from the current 14.29 μmol/L to 6.69 μmol/L. In a nutrient-rich area, increasing nutrient concentration promotes the competitiveness and fertility of shoots of r-strategic seaweeds, which makes them occupy a large number of space niches and form dominant populations, resulting in decreasing of the diversity of seaweed communities. However, in the oligotrophic environment, r-strategic algae is limited in the fertility of shoots, occupying only small amount of space niche, while those k-strategic algae with high efficiency in nutrient utilization shows greater competitiveness and could quickly break through early environmental sieves and grow into adults, which contributes to the rich diversity of seaweed communities.