Nitrate impacts on the Florida apple snail, Pomacea paludosa

Nitrate pollution in springs in Florida has been suggested as a possible reason for declining populations of the Florida apple snail, Pomacea paludosa (Say). No correlation was found between snail density and nitrate concentration measured in six Florida springs. In laboratory studies examining short-term acute impacts of nitrate, adult and juvenile snail 96 h LC₅₀ values could not be determined due to low mortality rates despite nitrate concentrations > 500 ppm. Juvenile snail growth was affected with EC₅₀ values of 504 and 622 ppm nitrate, in two trials, respectively. Juvenile survival during the 14 d growth study fell below 50%, but again nitrate levels were very high (> 500 ppm). Given that snails exhibited little to no response to nitrate concentrations orders of magnitude greater than those found in Florida springs, we suggest that other factors, possibly including natural differences in habitat structure or changes in structure related to exotic plant invasions, may help explain the observed declines in apple snail abundance.     

Histochemistry and ultrastructure of the albumen gland duct of the prosobranch gastropod Pomacea paludosa

Summary

The albumen gland duct passes through the base of the albumen gland. It consists of a single layer of cells composed of ciliated and secretory cells. Sulfated and non-sulfated acid mucopolysaccharides are secreted by the cells of the albumen gland duct. Cell resembling neurosecretory cells are also found between the ciliated and secretory cells. The secretion products probably contribute to the formation of the albumen layer which surrounds the fertilized egg.     

Repair process and enzymatic activity associated with induction of shell regeneration in the invasive species Pomacea canaliculata

ABSTRACT

This study investigated the repair process and enzymatic activity responses after induction of shell regeneration in Pomacea canaliculata. The survival rates, height of regenerated shell, and activities of alkaline phosphatase (ALP) and carbonic anhydrase (CA) were investigated and recorded for 15 days. A triangular piece of shell about 8?mm wide was excised from the ventral region of the shell. On the basis of photographs and enzyme assay, it was concluded both yellow-shell apple snails and black-shell apple snails had high survival rates (100%). The regenerated new shell was initially thin, with the wound sealed 5 days after induction of shell regeneration; after that the regenerated shell thickened. Three snails were sampled at 0, 0.5, 1, 2, 3, 5, 10 and 15 days after shell excision for analysis of enzymatic activity of ALP and CA. Trends of the activity of ALP and CA in the mantle were similar. Initially they both showed a decline on the first day, then rose on following days. Activity of ALP declined to a minimum on the first day, and an activity peak in both colour forms appeared on the fifth day (P?<?0.05) and was maintained for the rest of the experiment. The minimum value of CA occurred after 0.5 days, and a significant increase was also observed on the fifth day (P?<?0.05). This study has revealed that apple snails have good shell regeneration abilities, and that ALP and CA probably play a crucial role in shell growth and regeneration.     

Regeneration of excised shell by the invasive apple snail Pomacea canaliculata

After excision of shell from Pomacea canaliculata, survival rates, repair process, haemocyte response, and calcium content were observed and quantified for three weeks. The following experimental treatments were used: black-colored individuals with large (BL-group) or small (BS-group) shell heights, yellow-colored individuals with large (YL-group) or small (YS-group) shell heights. The survival rates in BL-, YL-, BS-, and YS-groups after making partial excisions of snail shells were, respectively, 93.59, 94.87, 92.31, and 96.15%. Freshly regenerated shell could be seen at 1 day among the four groups after induction of shell regeneration. Regeneration shell filled the wound after 5–10 days. The area of regenerated shell in yellow-colored individuals was larger than that of black-colored individuals, but the thickness of regenerated shell was not significantly different. Multiple (four times) inductions of shell regeneration significantly enhanced the thickness of newly formed shells. Two types of circulating haemocytes (hyalinocytes and granulocytes) were identified under light microscopy based on Wright’s staining. Artificial induction of shell regeneration rendered a significant increase in the number of total circulating haemocytes which was followed by a decrease to pre-wounding levels. This peak value of total circulating haemocytes was 2.86, 2.43, 1.69, and 1.71-fold higher than pre-wounding levels in group BL, YL, BS, and YS, respectively. The number of total circulating haemocytes in yellow-colored individuals was significantly higher than in black-colored. Calcium concentrations in the mantles of snails are favorable for calcium nucleation. It is postulated that calcium content increased in the mantle increase at the start of the experiment and then returned to pre-wounding levels at the end of the experiment. This study shows that apple snails have effective shell regeneration abilities and that haemocytes and calcium transportation appear to play an important role in shell growth and regeneration.     

Studies on the phytoplankton ecology of the Trondheimsfjord. I. The chemical composition of phytoplankton populations

Samples of phytoplankton populations from the Trondheimsfjord, collected in 1970 and the first five months of 1971, have been analysed for carbohydrate, protein, lipid, and phosphorus. Lipid was in all cases less than 10% of the organic dry matter. The $\text{N}\text{P}$ ratio was remarkably constant, but the ratio protein/carbohydrate varied between wide limits. For samples consisting mainly of dinoflagellates, the protein/carbohydrate ratio was always low, due to a large amount of insoluble polysaccharides, probably corresponding to material in the cell walls.For diatoms, the carbohydrates may conveniently be divided into three fractions: 1) an acidsoluble glucan of the β-1, 3-linked type; 2) an alkali-soluble fraction giving a complex mixture of monosaccharides on hydrolysis and, 3) an insoluble glucan. The amounts of acid-soluble glucan varied from 7.7 to 36.5% of organic dry matter and these changes are the main cause of the variation of the protein/carbohydrate ratio of diatom samples. For diatom samples this ratio is a valuable indicator of the physiological state of the population. The variations observed in this study are discussed.