Changes in midgut gland morphology and digestive enzyme activities associated with development in early stages of the American lobster Homarus americanus

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1986The development of the digestive system, specifically in relation to the midgut gland (hepatopancreas). in early life history stages of the American lobster Homarus americanus is examined in the present study by means of two separate but complementary approaches. A histological study on the light microscope level details the morphological changes which take ·place among the different cell types which form the midgut gland. Included in this portion of the study are scanning electron micrographs of the midgut gland of stage IV larva. Secondly, a biochemical study correlates changes in the activities of digestive protease, lipase, and amylase with the observed changes in the cells of the midgut gland. A sensitive method for detection of crustacean lipase was developed for this study. In order to optimize the assay conditions for measurement of digestive enzyme activities, a series of control tests was performed to determine the effects of several physical and chemical factors. The developmental stages of the lobster which are examined in these studies include: well-advanced embryos at approximately three days prior to hatching, hatching prelarvae, newly hatched and intermolt stage I larvae, intermolt stage II, Ill, and IV larvae, and intermolt stage V and VI postlarvae. Particular attention is paid to specific transitional stages during development. These include: (1) the changeover from yolk metabolism by the embryos to the dependence on exogenous food by newly hatched larvae; (2) the alteration in body form which occurs at the molt from larval stage III to IV; and (3) the change in habitat from the plankton to the benthos which occurs at the molt from stage IV to V. Results of the present study demonstrate that the R-cells (resorptive cells) of the earliest developmental stages, embryo through larval stage III, do not show the characteristic morphology classically ascribed to this cell type. Presumably because young lobsters do not begin to store excess lipids derived from the diet until stage IV, the R-cells do not contain large numbers of lipid vacuoles. By stage VI, however, the i-cells achieve the classic appearance. A previously unreported function for R-cells, that of storage of lipid derived from yolk metabolism in the embryo, is described. F-cells (digestive enzyme synthesizing cells) are present in the midgut gland of embryos a few days prior to the hatch while B-cells (enzyme secreting cells) have developed by the time of hatching. Thus, morphologically the stage I lobster larva appears to possess digestive capabilities prior to ingestion of the first meal. Changes in digestive enzyme activities during early development correlate well with the morphological changes observed in the midgut gland. Activities of protease, lipase, and amylase are very low in the well-advanced embryo and increase slightly by the hatching stage. Enzyme activities more than double by the time the stage I larva attains intermolt, regardless of whether the larva is fed or fasted. Digestive enzyme activities increase further by the time the stage II larva reaches intermolt; in general there is no significant difference in the levels of enzyme activities measured in the older stages (II through V). The results of a more detailed time course examination of the levels of digestive enzyme activities in relation" to first feeding by the stage I larvae are presented. Although there is a trend for slightly increased protease and amylase activities as the stage I larvae get older. the lipase activity is constant. Lobster larvae normally hatch in late spring and early summer but larvae can be induced to hatch during the winter by maintaining the eggs at higher than ambient water " temperatures. There is no consistent difference in digestive enzyme activities measured for larvae which hatch during the summer compared to those which hatch during the winter. The influence of molt stage on the activity of digestive enzymes in wild caught stage IV larvae is also discussed. Only minor variations in lipase and amylase activity are detected during intermolt and premolt and in general there is no significant effect. Protease activity is significantly greater at Do. This work describes new findings on several aspects of digestion among early life history stages of a marine decapod crustacean and has added to our understanding of the functional morphology of the midgut gland during early development.Financial support given by the WHOI Education Office and the Tai-Ping Foundation which sponsored my Tai-Ping Predoctoral Fellowship. This research was funded in part by the United States Department of Commerce. NOAA. Office of Sea Grant

Climate-related hydrological regimes and their effects on abundance of juvenile blue crabs (Callinectes sapidus) in the northcentral Gulf of Mexico

The abundance of juvenile blue crabs (Callinectes sapidus) in the northcentral Gulf of Mexico was investigated in response to climate-related hydrological regimes. Two distinct periods of blue crab abundance (1, 1973–94 and 2, 1997–2005) were associated with two opposite climaterelated hydrological regimes. Period 1 was characterized by high numbers of crabs, whereas period 2 was characterized by low numbers of crabs. The cold phase of the Atlantic Multidecadal Oscillation (AMO) and high north-south wind momentum were associated with period 1. Hydrological conditions associated with phases of the AMO and North Atlantic Oscillation (NAO) in conjunction with the north-south wind momentum may favor blue crab productivity by influencing blue crab predation dynamics through the exclusion of predators. About 25% (22–28%) of the variability in blue crab abundance was explained by a north–south wind momentum in concert with either salinity, precipitation, or the Palmer drought severity index, or by a combination of the NAO and preci

Biochemical Composition of Embryonic Blue Crabs \u3ci\u3eCallinectes sapidus\u3c/i\u3e Rathbun 1896 (Crustacea : Decapoda) from the Gulf of Mexico

Blue crab Callinectes sapidus embryos from the Mississippi Sound were sampled in spring and in late summer to determine patterns of biochemical composition and of yolk utilization during embryogenesis and to ascertain potential seasonal differences in biochemical composition. The diameter of spring embryos was similar to 6% greater than summer embryos but this significant size difference was due to increased water content, not to increased organic content. The general trend in initial biochemical composition was similar in both seasons; protein was the primary component at similar to 50% of initial dry weight followed by lipid (similar to 30%), ash (similar to 8%) and carbohydrate (6%). The general trend for utilization of organic reserves during embryogenesis was also similar seasonally. Lipid was the primary component metabolized during embryogenesis (44-48% of initial stores were utilized) followed by protein (13-16% utilized) and carbohydrate (similar to 13% utilized). Calculated on a dry weight basis, spring embryos had significantly lower lipid but significantly higher ash than summer embryos; there were no significant seasonal differences in protein or carbohydrate. Caloric expenditure on a dry weight basis was significantly different seasonally. There appear to be geographic differences among blue crabs; our results differ from those of a previous study of blue crab embryos from North Carolina waters

Climate-Related Hydrological Regimes and Their Effects on Abundance of Juvenile Blue Crabs (\u3ci\u3eCallinectes sapidus\u3c/i\u3e) in the Northcentral Gulf of Mexico

The abundance of juvenile blue crabs (Callinectes sapidus) in the northcentral Gulf of Mexico was investigated in response to climate-related hydrological regimes. Two distinct periods of blue crab abundance (1, 1973-94 and 2, 1997-2005) were associated with two opposite climate-related hydrological regimes. Period 1 was characterized by high numbers of crabs, whereas period 2 was characterized by low numbers of crabs. The cold phase of the Atlantic Multidecadal Oscillation (AMO) and high north-south wind momentum were associated with period 1. Hydrological conditions associated with phases of the AMO and North Atlantic Oscillation (NAO) in conjunction with the north-south wind momentum may favor blue crab productivity by influencing blue crab predation dynamics through the exclusion of predators. About 25% (22-28%) of the variability in blue crab abundance was explained by a north south wind momentum in concert with either salinity, precipitation, or the Palmer drought severity index, or by a combination of the NAO and precipitation

Biochemical Composition of the Deep-Sea Red Crab \u3ci\u3eChaceon quinquedens\u3c/i\u3e (Geryonidae): Organic Reserves of Developing Embryos and Adults

Deep-sea red crabs Chaceon quinquedens (Smith) were collected in traps at depths of 860 and 1043 m in the northern Gulf of Mexico. Ovigerous crabs were maintained in the laboratory and the developing embryos were sampled every 2 wk until hatching. Proximate analysis (lipid, protein, carbohydrate, and ash) of embryos was performed to determine patterns and rates of organic reserve utilization during embryogenesis. Midgut gland, gonads, and clutch (as appropriate) of adult crabs (males, non-ovigerous females and ovigerous females) were analyzed for the same components as the embryos. Red crab embryos exhibited different patterns of yolk deposition and subsequent depletion of yolk components during embryogenesis. There was a range of lipid to protein (L:P) ratios among the different clutches examined, indicating plasticity in the relative proportions of lipid and protein yolk. The energy used for embryogenesis was estimated by converting the amounts of lipid, protein and carbohydrate in the embryos to their caloric equivalents; final values, taken from 9 mo-old embryos whose siblings were hatching as zoeae, were subtracted from the initial values of sibling embryos sampled at the time of collection (2 to 3 mo old). The amount of energy consumed during embryogenesis in the laboratory was relatively constant (0.12 to 0.13 cal egg-1). There was considerable variability among the concentrations of organic reserves in the midgut gland of adult crabs and in the ovaries of females. Variations in midgut gland L:P ratios and ovaries were related to the reproductive status of the females, but there were no trends related to depth of capture

Lipids and Fatty Acids of the Benthic Marine Harpacticoid copepod \u3ci\u3eHeteropsyllus nunni\u3c/i\u3e Coull During Diapause: A Contrast to Pelagic Copepods

Many free-living copepods produce and store lipids prior to entering diapause (long-term dormancy). Heteropsyllus nunni Coull is the only marine harpacticoid copepod known to undergo any form of diapause. This study presents the first information on the types of lipids and fatty acids produced for long-term diapause in this benthic species. Sexually immature adults of H. nunni undergo diapause within a pliable self-made cyst. Prior to entering diapause (which lasts 3–4 months), they produce and store large amounts of orange lipid. The lipids apparently are utilized during diapause. Although some residual lipids remain, chiefly around the gonads, after the copepods emerge from their cysts, the lipid stores are visibly reduced. Typically, the copepods mate and produce eggs within 48 h after diapause is terminated. Light level and confocal laser scanning microscopy revealed that the lipid stores are distributed throughout the body in numerous oil droplets and not as a single oil sac, as seen in many marine calanoid copepods prior to overwintering (winter diapause). Transmission electron microscopy showed lipid spheres within the gut epithelium and large droplets of lipids stored extracellularly. Confocal laser scanning microscopy of copepods in pre-diapause, during diapause (encysted), post-diapause (recently excysted), and in reproductive condition, revealed that lipid stores are reduced following diapause, but are not totally absent. Analysis of lipid classes showed that H. nunni store predominantly wax esters/sterol esters (83% of total lipids) during diapause. The predominant lipid is most likely wax esters, as sterol esters typically are found only in small amounts in copepods. Fatty acid (FA) profiles of the copepods in diapause showed 16:0 to be most abundant followed by 16:1n-7 and 18:0; other FA occurred at concentrations \u3c10% of total FA. Three polyunsaturated fatty acids (PUFA), 20:5n-3, 18:2n-6 and 20:4n-6, were found at concentrations \u3c2% of total FA. These PUFA are essential fatty acids in H. nunni, obtained through dietary sources. The lipid classes and fatty acids present in H. nunni during diapause are compared to those of other copepods, some in a state of diapause and others not. It appears that lipid class and FA profiles are indicative of genetic makeup, type of diet or amount of food consumed prior to dormancy. Some classic paradigms of lipids and their association with copepod diapause are re-evaluated