Distribution of mycosporine-like amino acids in the sea hare Aplysia dactylomela: effect of diet on amounts and types sequestered over time in tissues and spawn.

We investigated the interaction of diet and accumulation of UV-absorbing mycosporine-like amino acids (MAAs) in body tissues and spawn of the sea hare Aplysia dactylomela to determine if MAA accumulation reflects type and level of dietary intake. Food sources were the red algae Acanthophora spicifera, Centroceras clavulatum, and Laurencia sp., and the green alga, Ulva lactuca. Adults were maintained on these foods for 40 days, after which feces were collected and tissues separated by dissection. Field animals were similarly sampled at this time. All spawn from experimental and field animals was collected over the study period. Samples, including seaweed foods, were analysed for six MAAs. Overnight consumption experiments using a variety of common seaweeds and one seagrass from A. dactylomela's habitat showed that the four seaweeds selected as foods were among those best-eaten by Aplysia. After 40 days levels of specific MAAs in the tissues of experimental animals showed excellent correlation with those in their diets, suggesting that the MAAs were dietarily-derived. Relative MAA contents in spawn from all diet groups correlated well with those in spawn from field animals. Commonest MAAs in spawn were porphyra-334, shinorine, and palythine, in this order. Concentrations of these MAAs were maintained at constant levels over time in spawn from all diet groups eating red algae and from field animals. Spawn from the Ulva dietary group showed an initial significant decline in MAA concentrations, but levels stabilized after the first 2 weeks. Skin was rich in porphyra-334 and shinorine, and levels of these in experimental animals correlated well with comparable levels in the skin of field animals. Digestive glands contained high levels of asterina-330, particularly those of the Centroceras dietary group, where concentrations reached a maximum of 21 mg dry g(-1).

Hemolymph ion composition and volume changes in the supralittoral isopod Ligia pallasii Brandt, during molt.

We analyzed ion composition and volume of the hemolymph of Ligia pallasii in four different stages of the molt cycle using capillary electrophoresis and 3H-inulin. The main ions in the hemolymph were Na+, K+, Mg2+ , Ca2+, and Cl-. The Ca2+ concentration increased significantly during the molt by 47% from intermolt to intramolt and by 37% from intermolt to postmolt, probably due to resorption of Ca2+ from the cuticle and sternal CaCO3 deposits. The K+ concentration increased significantly by 20% during molt. The hemolymph volume normalized to the dry mass of the animals decreased by 36% from intermolt to late premolt. This was due to a reduction in the hemolymph volume and to an increase in dry mass of the animals during premolt. A sudden increase in the hemolymph volume occurring between late premolt and intramolt served to expand the cuticle. Since the Na+, K+, Mg2+, and Cl- concentrations did not change significantly from late premolt to intramolt, the increase in hemolymph volume suggests an uptake of seawater rather than freshwater.

Use of isolated digestive-gland cells in the study of biochemical and physiological processes in gastropod molluscs.

We describe a method for preparation and maintenance of isolated digestive-gland cells in the abalone, Haliotis kamtschatkana. Viability of the isolated cells was confirmed by the fact that 18 h after preparation the cells exhibited less than 5% staining with trypan blue and actively synthesized glycogen following the addition of glucose substrate. Use of the method in a 15-month study of metabolic activity of the digestive gland of H. kamtschatkana showed significant differences in oxygen consumption of isolated-cell preparations correlated with seasonal differences in somatic and gametogenetic growth, and with relative size of the digestive gland.

Functional Significance of Varices in the Muricid Gastropod Ceratostoma foliatum.

Functional significance of varices in the muricid gastropod Ceratostoma foliatum was investigated from the standpoints of (1) frequency of landing in the two upside-down orientations after short vertical falls of less than five body lengths through seawater and energy costs of righting from these upside-down positions, and (2) scaling relationships of varix areas with other body dimensions. Field manipulations showed that C. foliatum occupied habitats that mostly permit short falls of less than five body lengths upon dislodgment, as might occur during predation by fish. After short vertical falls in the laboratory, animals landed 48% of the time on their aperture sides (upright), 15% on their right sides (on right and middle varices), and 37% on their left sides (on left and middle varices). These frequencies differed significantly from the expected frequencies calculated on the basis of the percentage circumference delineated by each varix pair (50%, 31%, and 19%, respectively). Righting from the right-side orientation was slower and four times more energetically costly than from the left-side orientation, underscoring the advantage conferred by animals, if not landing in the upright position after short falls, preferentially landing on their left sides. Removal of individual varices showed that the large, right varix is most influential in producing this "destabilization." Landings are biased to the side from which rightings are easiest due to a combination of the location of center of mass within the left side of the main body whorl and the broad right varix possibly acting as an upward-trailing vane. Morphometric relationships of shell length, live weight, varix areas, aperture dimensions, and labial spine (tooth) length were investigated over a wide range of body sizes in an attempt to infer varix function. Aperture area scaled allometrically with length. Right-, middle-, and left-varix areas also grew relatively larger as the animals increased in length. In contrast, combined varix areas around the aperture increased in direct proportion with aperture area, forming a broad shelf surrounding the aperture. We infer from this that, in addition to their effects on landing orientation from both long and short vertical falls, the varices of C. foliatum may function to protect the aperture, and thus protect the soft body parts that protrude from it during feeding and locomotion.