The Physiological Energetics Of Styela Clava And Its Accumulation Of Heavy Metals

The ingestion and metabolism of ascidian Styela clava were studied in static water system, oxygen consumption rate, ammonia-N excretion rate, filtration rate (FR), clearance rate(CR), ingestion rates (IR), ingestion intension (II) and assimilation efficiency (AE) were measured under different temperatures, and the energy budget equations were established in lab. Based on the semi-static two-compartment model, the bioaccumulation of four heavy metals (Cd²⁺, Pb²⁺, Cu²⁺ and Zn²⁺) by S. clava were investigated, the kinetic parameters (K₁, K₂, BCF, B_1/2) were obtained by non-linear regression. The effects of four heavy metal ions on metabolism were discussed at the same time. The feasibility of S. clara and its metabolizable parameters were explored used as markers of heavy metal pollution in offing marine space.The study on metabolism of S. clava showed that metabolizable parameters increased with increasing individual weight as a power function R=aW^b including oxygen consumption rate, ammonia excretion rate, filtration rate(FR), clearance rate(CR), ingestion rate(IR) and ingestion intensity(II); Oxygen consumption rate increased with increasing temperature, while peaks were found in the range of 20～24℃for ammonia excretion rate, FR, CR, IR, II and AE.The study of food selection indicated S. clava had selectivity to the sizes of particles and could retain more particles around 6μm. In low concentration range, FR and IR of S. clara increased with increasing algal cell concentrations as described by the equation R=aW^b until 10 mg POM·L^-1. Within the range of diet concentration from 2.11 to 20.12 mg POM·L^-1, the relationships between POM and CR as well as IR changed to quadratic as R=aC²+bc+c.The study of energy budget revealed that routine metabolism of S. clava with same size was obviously higher than standard metabolism at different temperatures, oxygen consumption rate increased by 16.7～34.9ï¼…, while ammonia excretion rate increased by 34.0～61.9ï¼…. Ingestion energy, absorption energy, metabolism energy, excretion energy and feces energy all increased with increasing body weight at different temperatures. Respiration energy increased with increasing temperature within the range of temperature from 12℃to 28℃, but critical values were found at 20～24℃for energy of ingestion and absorption, and energy in feces and excretion. In the energy budget equations of different sized ascidians obtained at different temperatures, excretion energy shared a minimal fraction in ingestion energy (3.8～9.4ï¼…), the ratios of feces energy and respiration energy to ingestion energy were 27～54ï¼…and 10～78ï¼…, respectively. The proportion of various energies changed with temperature.S.clava could accumulate heavy metals, and its accumulative action of Cd²⁺ was distinctly higher than that of Pb²⁺ and Zn²⁺, while the accumulation of Cu²⁺ was quite small. The absorbing rate constant k₁ of four heavy metals increased with increasing metal concentration in water as well as bioaccumulation factors (BCF). When the accumulation achieved balance, metal concentrations in organism showed positive correlation to metal concentrations in water. Concentrations of four metals in different organs of S. clava were in the order: germen＞digest gland＞others＞crust. The biological half-life (B_1/2) of four heavy metals were 10～24 days.S. clara's metabolism was influenced by heavy metal ions at the same time of accumulation. Cd²⁺, Zn²⁺ and Pb²⁺ could depress oxygen consumption rate of S. clava, 0.1mg/L Cu²⁺ could improve its respiratory metabolism, while restraint effect occurred when the concentration of Cu²⁺ exceeded 0.5mg/L. Ammonia excretion rates increased in 0.01mg/L Cd²⁺,0.1mg/L Cu²⁺,0.1mg/L Zn²⁺ and 0.01mg/L Pb²⁺, while obvious depress was observed when S. clara discovered in high concentration of metal. Cd²⁺ exhibited controlling effects on filtration rate of S. clava with concentration correlation, while Zn²⁺ boost FR with concentration correlation; 0.1, 0.5, 1 mg/L Cu²⁺ and 0.01, 0.05mg/L Pb²⁺ enhanced FR while 2 mg/L Cu²⁺ and 0.2mg/L Pb²⁺ depressed FR. Four heavy metals all showed restraining effect on O:N with concentration correlation.The four metal ions could affect energy of metabolizing enzymes in S. clara. Cd²⁺, Pb²⁺, Cu²⁺ and Zn²⁺ could depress the activities of alkaline phosphatase (AKP) and Na⁺-K⁺-ATPase with concentration correlation. The activities of SOD descended immediately and then increased again when S. clara exposed to Cd²⁺ and Pb²⁺. Cu²⁺ and Zn²⁺ could increase the activities of SOD at low concentrations, while restrain its activities at higher concentrations.The results suggested that S. clava and its metabolism parameters (O/N, AKP, Na⁺-K⁺-ATPase and SOD) could be used as markers of heavy metal pollution in offing marine space.