Ocean acidification: effects of pH on 45Ca uptake by lobster branchiostegites

Effect of CO2 driven ocean acidification on the mud crab Scylla serrata instars

The decreasing ocean pH seems to adversely affect marine organisms, including crustaceans, which leads to potential threats to seafood safety. The present investigation evaluated the effect of seawater acidification on the edible marine mud crab Scylla serrata instars. The experimental setup was designed using a multi-cell cage based system assembled with 20 pre holed PVC pipes containing 20 individual crabs to avoid cannibalism. The crab instars were exposed to CO₂ driven acidified seawater at pH 7.8 (IPCC forecast pH at the end of the 21^st century), 7.6, 7.4, 7.2, and 7.0 for 60 days. The crabs reared in seawater without acidification at pH 8.2 served as control. The present study revealed a notable decrease in survival, feed intake, growth, molting, tissue biochemical constituents, minerals, chitin, and alkaline phosphatase in S. serrata instar reared in acidified seawater, denotes the adverse effect of seawater acidification on crabs. The significant elevations in antioxidants, lipid peroxidation, and metabolic enzymes in all acidified seawater compared to ambient pH indicates the physiological stress of the crabs' instars. The changes in the metabolic enzymes reveal the metabolism of protein and glucose for additional energy required by the crabs to tolerate the acidic stress. Hence, the present study provides insight into the seawater acidification can adversely affect the crab S. serrata.

Ocean acidification: synergistic inhibitory effects of protons and heavy metals on 45Ca uptake by lobster branchiostegite membrane vesicles

Previous work with isolated outer membrane vesicles of lobster branchiostegite epithelial cells has shown that ⁴⁵Ca²⁺ uptake by these structures is significantly (p < 0.02) reduced by an incremental decrease in saline pH (increased proton concentration) and that this decrease is due to competitive inhibition between carrier-mediated transport of ⁴⁵Ca²⁺ and hydrogen ions. The present paper extends these previous findings and describes the combined effects of pH and cationic heavy metals on branchiostegite uptake of ⁴⁵Ca²⁺. Partially purified membrane vesicles of branchiostegite cells were produced by a homogenization/centrifugation method and were loaded with mannitol at pH 7.0. The time course of 1 mM ⁴⁵Ca²⁺ uptake in a mannitol medium at pH 8.5 containing 100 µM verapamil (Ca²⁺ channel blocker) was hyperbolic and approached equilibrium at 30 min. This uptake was either significantly reduced (p < 0.05) by the addition of 5 µM Zn²⁺ or essentially abolished with the addition of 5 µM Cu²⁺. Increasing zinc concentrations (5-500 µM) reduced 1 mM ⁴⁵Ca²⁺ uptake at pH 8.5 or 7.5 in a hyperbolic fashion with the remaining non-inhibited uptake due to apparent non-specific binding. Uptake of 1 mM ⁴⁵Ca²⁺ at pH 8.5, 7.5, 7.5 + Zn²⁺, and 7.5 + Zn²⁺ + Cu²⁺ + Cd²⁺ in the presence of 100 µM verapamil displayed a stepwise reduction of ⁴⁵Ca²⁺ uptake with the addition of each treatment until only non-specific isotope binding occurred with all cation inhibitors. ⁴⁵Ca²⁺ influxes (15 s uptakes; 0.25-5.0 mM calcium + 100 µM verapamil) in the presence and absence of 10 µM Zn²⁺ were both hyperbolic functions of calcium concentration. The curve with Zn²⁺ displayed a transport K_m twice that of the control (p < 0.05), while inhibitor and control curve J_max values were not significantly different (p > 0.05), suggesting competitive inhibition between ⁴⁵Ca²⁺ and Zn²⁺ influxes. Analysis of the relative inhibitory effects of increased proton or heavy metal interaction with ⁴⁵Ca²⁺ uptake suggests that divalent metals may reduce the calcium transport about twice as much as a drop in pH, but together, they appear to abolish carrier-mediated transport.