John S. Pearse

DEVELOPMENT, METAMORPHOSIS, AND SEASONAL ABUNDANCE OF EMBRYOS AND LARVAE OF THE ANTARCTIC SEA URCHIN STERECHINUS NEUMAYERI

The development to metamorphosis of the shallow-water antarctic sea urchin, Sterechinus neumayeri, is described for the first time. Developmental stages are similar to those of closely related temperate species with feeding larvae, but the rate of development is extremely slow. Hatching of ciliated blastulae occurs approximately 140, 128, and 110 hours after fertilization at -1.8, -1.0, and -0.5°C, respectively, more than twice the time required for closely related temperate species near their normal ambient temperature. Larvae reared at -1.8 to -0.9°C are capable of feeding 20 days after fertilization and are competent to metamorphose after 115 days. Early cleavage embryos, blastulae, gastrulae, and prism larvae of this species were collected from the plankton adjacent to McMurdo Station, Antarctica, in early November and December, 1984 and 1985. Echinoplutei were not found during this study, but they have been collected from the plankton in other years; there is no evidence that the larvae are demersal. The timing of spawning ensures that feeding larvae are in the plankton during the abbreviated summer peak of phytoplankton abundance in McMurdo Sound. Recruitment of juveniles into the benthos most likely occurs in synchrony with the subsequent period of high levels of benthic chl a concentrations.

Mycosporine-like Amino Acid Content in Four Species of Sea Anemones in the Genus Anthopleura Reflects Phylogenetic but Not Environmental or Symbiotic Relationships

We examine the occurrence of UV-absorbing, mycosporine-like amino acids (MAAs) in four sympatric species of sea anemones in the genus Anthopleura, all collected from intertidal habitats on the Pacific Coast of temperate North America. We compare patterns of MAAs in A. elegantissima of several types: specimens having predominately zooxanthellae (dinoflagellates comprising at least two species) or zoochlorellae as symbionts; those containing algal endosymbionts of both kinds, and naturally occurring aposymbiotic specimens that lack the endosymbionts typically found in most specimens. We also compare MAAs in zooxanthellate specimens of A. sola and A. xanthogrammica, and specimens from the asymbiotic species A. artemisia. Our findings indicate that the complements of the four major MAAs in these species of Anthopleura (mycosporine-taurine, shinorine, porphyra-334, and mycosporine-2 glycine) broadly reflect phylogenetic differences among the anemones rather than the taxon of endosymbionts, presence or absence of symbionts, or environmental factors. An exception, however, occurs in A. elegantissima, where mycosporine-2 glycine increases in concentration with the density of zooxanthellae. Our evidence also shows that A. elegantissima can accumulate MAAs from its food, which may explain the occasional occurrence of minor MAAs in some individuals.

Experimental manipulation of shell color and morphology of the limpets Lottia asmi (Middendorff) and Lottia digitalis (Rathke) (Mollusca: Patellogastropoda)

Abstract We experimentally show that substratum can determine an individual patellogastropods color and morphology. Lottia asmi (Middendorff), previously considered a high-domed, black stenotopic species on trochid gastropods, is similar to other northeastern Pacific limpet species with low profile and tessellated color patterns, when it is translocated to rock substrata. Lottia digitalis (Rathke), a highly variable species with at least two ecological variants that have been considered to be genetically determined, changes between these two forms when translocated from stalked barnacles to rocks. Color changes because the ingested pigments (algal, periostracal, etc.) and other materials (e.g., calcium carbonate) vary between substrata; morphological changes occur as responses to the topographical complexity and constraints of substrata. The geographical distribution of ecological variants of polytypic limpet species, and the ability to achieve cryptic coloration, may be determined by the geographic distributions of algae on which the limpets feed rather than by intrinsic characteristics of the limpets.

Evidence for a Programmed Circannual Life Cycle Modulated by Increasing Daylengths in Neanthes limnicola (Polychaeta: Nereidae) From Central California

Timing of parturition, fecundity, and life span were determined in laboratory cultures of the semelparous, self-fertilizing, viviparous polychaete Neanthes limnicola. Worms were exposed to fixed daylengths (short--8h light: 16h dark; neutral--12h:12h; long--16h:8h), switched between different fixed daylengths, and switched from fixed daylengths to increasing or decreasing daylengths. Timing of parturition was synchronized when under neutral daylength, but became asynchronous under both short and long daylength, as well as when any of the fixed daylength was followed by decreasing daylengths. Worms under neutral daylength had the highest fecundities and shortest life spans, while those under long days had the lowest fecundities and longer life spans. When fixed daylength (short, neutral, long) was followed by increasing daylengths, timing of parturition was synchronized, fecundity was high, and life span shortened. These and earlier published experiments on the influence of seasonally changing photoperiods indicate that the life cycle of the estuarine N. limnicola is programmed to be completed in somewhat less than a year, and that seasonally changing photoperiods modulate it to determine the optimal time of parturition.