Growth characters and photosynthetic capacity of Gracilaria lemaneiformis as a biofilter in a shellfish farming area in Sanggou Bay, China

Abstract

Experiments on growth characters and ecological functions of the macroalgae Gracilaria lemaneiformis, collected from south China, were conducted in polyculture areas of kelp and filter-feeding bivalve in Sanggou Bay in Weihai City, Shandong, in north China from May 2002 to May 2003. The results of 116 days cultivation showed that the average wet weight of alga increased 89 times from 0.1 to 8.9 kg rope⁻¹, with an average specific growth rate (based on wet weight) of 3.95% per day. The most favorable water layer for its growth was 1.0–1.8 m below the surface in July and August, with an average specific growth rate of 8.2% per day in 30-day experiments. Photosynthetic activity changed seasonally, with an average of 7.3 mg O₂ g dw⁻¹ h⁻¹. The maximum rate (14.4 mg O₂ g dw⁻¹ h⁻¹) was recorded in July, or 19.3 mg CO₂ g dw⁻¹ h⁻¹, while the minimum (0.40 mg CO₂ g dw⁻¹ h⁻¹) was in April. This study indicated that the culture of G. lemaneiformis is an effective way to improve water quality where scallops are cultivated intensively.