Optimization of Macroalgal Density and Salinity for Nutrient Removal by Caulerpa lentillifera from Aquaculture Effluent

Controlling the main source of green tides in the Yellow Sea through the method of biological competition

Macroalgal blooms have become a serious threat to public health, fisheries, ecosystems, and global economies. Since 2007, in the Yellow Sea, China, Ulva green tides have occurred for 15 consecutive years. However, effective control methods are limited. Ulva prolifera attached to Neopyropia aquaculture rafts are believed to be the main source of blooms, therefore eliminating Ulva from rafts could effectively prevent and control blooms. We investigated this phenomenon and showed that macroalgae germination was significantly inhibited by dried Neopyropia yezoensis at concentrations of 1.2, 2.4, and 4.8 g DW^-1. Also, the inhibitory effects of dried N. yezoensis toward U. prolifera gametes at 2.4 and 4.8 g DW^-1 were >90% at day 21. N. yezoensis culture filtrates and thalli were also used to determine dose-dependent inhibition effects on U. prolifera gamete germination. Both were potent and significantly inhibited germination at 1.75-7 g FW^-1; the inhibitory effect 7 g FW^-1 was >90% at day 21. As N. yezoensis thalli exhibited high inhibitory effects in laboratory experiments, we also performed field studies. N. yezoensis on ropes displayed high inhibitory effects on Ulva attachment and growth. Thus N. yezoensis powder, culture filtrates, and thalli displayed strong inhibitory effects on U. prolifera gametes, suggesting N. yezoensis attachment to ropes could be used to control green tides at the source.

Effects of Different Densities of Sea Grape Caulerpa lentillifera on Water Quality, Growth and Survival of the Whiteleg Shrimp Litopenaeus vannamei in Polyculture System

The integrated aquaculture-seaweed system has been identified as a bio-mitigation strategy to overcome environmental damage, improve the efficiency of nutrient use, maintain good water quality, and ensure the system’s sustainability. This study was conducted to determine the appropriate density of sea grape (Caulerpa lentillifera) in polyculture with whiteleg shrimp (Litopenaeus vannamei) in the same culture tank. Five treatments were randomly designed in triplicate tanks where shrimp was monocultured (without sea grape) as a control treatment and four polyculture treatments with different seaweed density levels (0.5, 1, 1.5, and 2 kg m−3) for 56 days. The results showed that polyculture of shrimp and sea grape significantly reduced the concentrations of total ammonia nitrogen (TAN), nitrite (NO2−), nitrate (NO3−), and phosphate (PO43−) in the rearing tanks and significantly improved (p < 0.05) the growth rate (6.67–6.76% day−1), survival (73.3–78.5%), and production of shrimp (3.44–3.87 kg m−3) compared to monoculture (6.24% day−1, 54.8%, and 2.02 kg m−3, respectively). Applying shrimp and sea grape polyculture at a density of 1 kg m−3 provided a relatively better shrimp performance and feed conversion ratio than other seaweed densities, although not significantly different among polyculture treatments. The findings suggested that sea grape could be used at densities of 0.5–2 kg m−3 in polyculture with whiteleg shrimp, of which 1 kg m−3 resulted in higher production and feed efficiency.

The role of Ulva fasciata in the evolution of the microbial community and antibiotic resistance genes in maricultural sediments

This study explored changes in the microbial community and antibiotic resistance genes (ARGs) in maricultural clam sediment after 3-month co-culture with different densities (0, 5 and 12 g L^-1) of seaweed Ulva fasciata (U. fasciata). The maximum removal rates of NO₃^--N, PO₄^3--P, and inhibition of Vibrio culturability occurred at presence of 12 g L^-1U. fasciata. A significant decrease by 14.0% of the total ARGs was found in control sediment without U. fasciata after separation from the original niches, while the total ARGs further increased by 5.58%and 4.65% at presence of 5 and 12 g L^-1 of U. fasciata in compared with control sediment, respectively, strongly related with Chloroflexi, Spirochaetes, Proteobacteria and Bacteroidetes hosts. In addition, U. fasciata favored the decline of absolute gene numbers of some tetracycline resistance genes (tetPB, tetW, otrA, tetT, tetO) and class 1 integron-integrase gene.

Allelopathic inhibitory effect of the macroalga Pyropia haitanensis (Rhodophyta) on harmful bloom-forming Pseudo-nitzschia species

The blooms of harmful microalgae represent a prominent threat to fisheries, public health, and economies throughout the world. Recent studies have shown that certain macroalgae release allelochemicals that can inhibit the growth of bloom-forming microalgae. In this study, we found that the macroalga Pyropia haitanensis significantly inhibited growth of the harmful bloom-forming microalgae Pseudo-nitzschia pungens and Pseudo-nitzschia multiseries. The inhibitory-effect of the live thali of P. haitanensis was highest, followed by that of dry powder, water-soluble extract, and culture medium filtrate. The Pseudo-nitzschia species died 96 h after exposure to 5-10 g fresh-weight L^-1 of P. haitanensis live thalli. Furthermore, an aqueous extract of P. haitanensis suppressed the growth of P. pungens and P. multiseries, thereby indicating that P. haitanensis contains stable allelopathic substances that cause the observed inhibitory-effects. On the basis of these findings, we conclude that the macroalga P. haitanensis would have potential utility in controlling the blooms of Pseudo-nitzschia species.

Wastewater Treatment Processes: Part I

Cheap and plentiful, water was for centuries a manufacturing tool that industry took for granted [...]

Capacity of Caulerpa lentillifera in the Removal of Fish Culture Effluent in a Recirculating Aquaculture System

Aquaculture is one of the fastest growing food producing industries in the world. Aquaculture effluent contains high concentrations of inorganic nutrients. Reduction of these inorganic nutrients in aquaculture effluent is crucial for fulfilling the effluent standards or reuse of aquaculture effluent. This study investigated the effective use of green macroalga Caulerpa lentillifera as a bioremediatory species for nutrient removal from aquaculture effluent by conducting an on-station experiment and measurements. The effluent of a fish culture unit was circulated through a macroalgal culture unit every four days for a total of 60 days, allowing 15 circulations. Concentrations of inorganic nutrients (NO2−-N, NO3−-N, NH3-N, and PO43−) were measured in the integrated system consisting of a fish unit, settling unit, macroalgal unit and extra tank for water circulation in triplicates. Multiple linear regression analysis revealed that the application of the bioremediation system led to a significant reduction in nutrient concentrations within one day, and slightly further in the following two days. On average over the 15 circulations, the first one day of application decreased the concentrations of NO2−-N, NO3−-N, NH3-N, and PO43− by 0.247 mg/L, 81.6 mg/L, 0.682 mg/L, and 0.352 mg/L, respectively. Furthermore, the C:N ratio of macroalgae decreased during the 60-day application period, providing evidence of the nutrient uptake by macroalgae. Based on the European Union (EU) standard and quality criteria of France and the Joint FAO/WHO Expert Committee (JFWEC), the macroalgae grown in the integrated system were at the safe level for human consumption in terms of contents of Cd, Pb, and As. The results of our study imply that recirculating aquaculture systems utilizing C. lentillifera for biofiltration have the potential for effective treatment of aquaculture effluent integrating fish and macroalgae production.