Christine Trigg

Calcium concentration in seawater and exoskeletal calcification in the blue crab, Callinectes sapidus

Abstract The blue crab, Callinectes sapidus Rathbun, supports valuable commercial fisheries in the temperate areas of the coastal Atlantic states and US Gulf of Mexico (GOM). Soft crabs form a small part of the total United States blue crab landings, but have a higher market value on a per pound basis than do hard crabs. The soft crab industry depends upon the capture of premolt crabs which are held in open or closed seawater systems until they molt. A major factor limiting profitability is the labor-intensive nature of the shedding operation. Extending the length of time crabs remain in the softshell stage would significantly reduce labor requirements. Exoskeletal calcification in blue crabs is achieved predominantly with calcium absorbed from seawater. In the present study, seawater at a salinity of 12‰, with calcium levels reduced to 60–80% of normal, decreased the calcification rate without increasing shedding mortality. Salinity did not influence calcification rates for crabs shed at 5‰, 12‰, and 25‰, provided calcium concentrations were within the normal ranges for their respective salinities: x =54, 139, and 281 mg/l. Crabs molting over the range of test salinities in waters with normal calcium levels remained soft for ∼4 h. At test salinities with reduced calcium levels, the rate of exoskeletal calcification decreased as total ionic strength of the seawater increased. Crabs shed in low-calcium seawater at 25‰ remained longer in the softshell stage than crabs shed at 5‰ or 12‰. Modifying existing closed system shedding facilities to incorporate low-calcium seawater technology would reduce labor requirements, increase profitability, and produce a higher quality soft crab.

Fishery-Related Morphometric Characteristics of Menippe adina from the North-Central Gulf of Mexico

Abstract Fishery-related morphometric characteristics of the recently described gulf stone crab Menippe adina were measured, providing data applicable to managing the species. Because data used in managing crab stocks have traditionally been based on carapace width, we examined the relationship between propodus length (PL) and carapace width and compared it to similar data for the heavily exploited Florida stone crab M. mercenaria. Claws for M. adina reach harvestable size (70 mm PL, minimum legal size in Florida) when carapace widths are 82 mm for males and 92 mm for females. Menippe adina exhibits allometric growth, and the transition point (carapace width) at which differential growth occurs appears to be related to sexual maturity. Males and females exhibit similar relationships of propodus length to carapace width below the transition point. Above the transition point, males display a greater increase in propodus length per incremental increase in carapace width and enter the fishery at a smaller siz...

Heavy metals in red crabs, Chaceon quinquedens, from the Gulf of Mexico

The red crab, Chaceon quinquedens, is distributed in deep waters of the Gulf of Mexico (GOM) and is most abundant in an area associated with sediment deposition from the Mississippi River. Sediment geochemistry and biological and ecological traits of red crabs favor accumulation of contaminants. Red crabs, sediment, and bottom water samples were taken from three distinct geographic locations representing areas with differing exposure to contaminant laden effluents from the Mississippi River. Inductively coupled plasma spectrophotometry and atomic absorption spectrophotometry were employed to determine levels of heavy metals in red crab muscle tissue. Ion site partitioning was used to determine metal speciation in sediments. Red crabs showed evidence of heavy metal bioaccumulation in all sample areas with high variability in contaminant levels in individual crabs for some metals. Bioavailability of metals in sediment did not always result in accumulation in muscle tissue.