Articles

Changes in the protein, RNA and DNA content related to nitrogen (N) and phosphorus (P) starvation were studied in the marine dinoflagellate Heterocapsa sp. grown in batch cultures. In both cases of nutrient starvation, metabolic adaptations affected protein and RNA pools, while the DNA content per cell remained approximately constant. N starvation led to a parallel decrease in protein and RNA concentration which caused the protein/RNA ratios to remain constant. A dramatic decrease in the RNA content characterized the P-starved cultures, although protein synthesis continued. The ribosomal RNA content was lower than expected given the continuation of protein synthesis. It is suggested that protein/RNA ratios could be used as an indicator of P starvation, while protein/chlorophyll ratios would characterize N starvation

The effect of nitrogen (N) and phosphorus (P) depletion on the cell volume and pigment composition of the marine dinoflagellate Heterocapsa sp. was studied. Cell size increased under both N or P starvation, but the change was faster when P was limiting. Quantitatively. N deficiency resulted in greater pigment loss than did P deficiency, thereby corroborating the relationship between pigment synthesis and N metabolism. It is suggested that the synthesis of pigments is primarily stopped at a transcriptional level (from DNA to RNA) under P limitation and at a translational level (from RNA to proteins) under N limitation. Almost all pigments underwent a parallel decrease during the stationary phase and no clear changes in pigment ratios were found. As an exception, a pigment identified as diatoxanthin accumulated in the algae when cell growth ceased. This occurred regardless of the growth-limiting nutrient and became more pronounced as cell deterioration progressed.

Keywords: Spawn, protoconch, Cerithium, Euspira.

Spawn morphology and subsequent development are described and illustrated from laboratory observations for two species of marine prosobranch gastropods, Cerithium alucaster (Brocchi, 1814) and Euspira fusca (Blainville, 1825). The spawn of C. alucaster consisted of a white and amorphous, irregularly coiled string. The egg capsule had a mean diameter of 155 mm. Shell dimensions of the free-swimming larvae at hatching were 130 mm length and 90 mm height. The appearance of the protoconch I and the beginning of protoconch II surface was smooth, as seen with scanning electron microscopy. The spawn of E. fusca had a flat ribbon shape, coiled to form an incomplete circle. Eggs were spheroidal in shape, with a mean major diameter of 396 mm and were placed in two layers. Development was direct. Shell dimensions at hatching were 276 mm length and 196 mm heigth. The protoconch was smooth with granular spiral lines on its dorsal part. The spawn of each species was similar to the general pattern exhibited by other species of their respective families.

The early stages of development of three blenniid species, Aidablennius sphynx (6.7–15.8 mm BL), Coryphoblennius galerita (4.3–13.9mm BL), and Lipophrys canevai (3.5–10.4 mm BL) are described from specimens collected in the western Mediterranean. The characteristics used for identification included meristic, developmental, morphological and pigmentation characters. Distinguishing characters of these species useful in differentiating them from other species of blenniids for which early stages are known in the Mediterranean are presented. Information on the occurrence of larvae and juveniles of these species off the Catalan coast (north-western Mediterranean) is also given.

Keywords: Bacterivory . Mathematical methods . FLB

We develop a method to calculate grazing on bacteria determined by the disappearance of marked cells or particles. The method uses an exponential model based on population dynamics. We also describe 2 linear approaches: one is a model currently in use that takes into account only the initial proportion of marked cells; the other also includes their final proportion. An expenmental data set 1s used to compare the 3 models. The first linear model tends to underestimate grazing due to lack of information concerning the final proportion of marked cells. The second linear model, whch does take into account the final abundances of marked and natural cells, results in a good approximation to the exponential. We conclude that consideration of the final proportion of marked to natural cells IS crucial to correctly estimate bacterial grazing

A simple method of providing a regular supply of live food for the experimental culture of paralarval cephalopods is described. The primary food source utilized was hatched zoeae of large laboratory populations of the hermit crab, Pagurus prideaux. Zoeal size, swimming behaviour, and distribution in the water column make these zoeae a suitable live prey for rearing early post-hatching planktonic stages of cephalopods and probably other marine zooplanktivores. Ovigerous P. prideaux females were collected from the sea throughout the year at depths between 10 and 90 m in the NW Mediterranean and maintained at densities of up to 500 specimens .rnP2. One month after spawning in aquaria, 38% of the females of P. prideaux started to incubate a second clutch of eggs. Other decapod crustacean species, such as Liocarcinus depurator and Dardanus arrosor, were maintained to use their zoeae as a food source for cephalopod paralarvae. P. prideaux zoeae were used as the sole or main food resource for rearing Loligo uulgaris and Octopus uulgaris, during the first 2 months of life. First feeding and initial growth in L. uulgaris and 0. vulgaris paralarvae can be successfully stimulated using decapod zoeae with a total length equivalent to 50-100% of the cephalopod’s mantle length.