The temporal pattern of population abundance, breeding, and recruitment of the marine shrimp Lysmata wurdemanni is described and analyzed. A population inhabiting the rock jetty in Port Aransas, Texas, U.S.A., was sampled monthly for one year and then bimonthly in a second. Abundances were greatest in the summer, declining during the fall to zero values in early winter, with increases in the late winter and early spring. The disappearance of the population in early winter is attributed to its movement beneath the jetty or to some other location inaccessible to sampling. When the population reappeared in late winter to early spring, it contained a high proportion of larger (older) individuals. The breeding season was seasonal but extended. Most female-phase individuals (FPs) incubated broods of embryos continuously during the warmer months (spring through early fall). Spawning of a new brood occurred soon after hatching of the previous one, as shown by the significant positive correlation between the degree of embryonic development (nearness to hatching) in an FP and the degree of ovarian maturation (nearness to spawning) in its ovotestes. Male-phase individuals (MPs) changing to FPs were found throughout most of the year. Their relative abundance was greatest in late winter to early spring when a group of large MPs, far past minimum FP size, finally changed sex. Recruitment occurred primarily in the spring and summer in both years, although its timing and intensity varied between years. The observed pattern of breeding, recruitment, and population abundances of Lysmata wurdemanni is what might be expected of a primarily tropical species living in an area transitional between the tropical Caribbean and warm temperate Gulf of Mexico biogeographical provinces. The breeding pattern of this shrimp, with an unusual hermaphroditic sexual system, is not strikingly unusual or different from that of gonochoristic shallow-water carideans.