Biogeography of Eight Large Branchiopods Endemic to California

Northern California supports eight endemic species of large branchiopods (Crustacea: Anostraca, Notostraca, and Conchostraca), three of which are listed as endangered and one as threatened under the federal Endangered Species Act. Published information on the geographic distribution of these endemics from a biological perspective is scant. This study was initiated to gain a better understanding of the biogeographic distribution and abundance of endemic large branchiopods in California. The primary objective was to investigate several physical features of wetlands that change little over time (e.g., habitat type, potential maximum and average ponding depth, potential maximum ponding surface area and water volume, soil type, and landform) for correlations to species’ presence or absence. The secondary objective was to analyze selected life cycle dynamics (i.e., maximum population longevity, and minimum, mean, and maximum age to maturation and reproduction) for correlations to habitat characteristics. These objectives were accomplished by gathering and analyzing quantitative data on 5,565 wetlands studied in California between 1989 and 1996, and on endemic large branchiopods raised in mesocosms (plastic wading pools) between 1990 and 1996. Large branchiopods were found in slightly less than half the seasonal wetlands sampled during field surveys. Anostracans comprised the majority of these. The three most common large branchiopod species were Lepidurus packardi, Linderiella occidentalis, and Branchinecta lynchi. Endemic species occurred in half the 50-wetland types and on most landforms sampled. Approximately two-thirds of the wetlands sampled were vernal pools. Vernal pools supported a higher percentage of large branchiopod occurrences, and species richness, than any other wetland type. The majority of occurrences of B. lynchi and L. occidentalis are located on High Terrace landforms with Redding, Corning, or Red Bluff soils; these landforms also supported slightly more than half the occurrences of L. packardi. Life cycle analyses of cultured populations revealed that the Midvalley Fairy Shrimp (Branchinecta sp. – not described or named) has the fastest maturation period, followed by B. lynchi, B. conservatio, B. longiantenna, Linderiella occidentalis, Lepidurus packardi, and Cyzicus californicus. Overall, the seven species differed significantly in age of first reproduction (ANOVA:F6,89 = 6.75, P < 0.0001), and maximum population longevity (ANOVA:F6,89 = 15.50, P < 0.0001). However, a multiple range test revealed the anostracans did not differ significantly among each other in age at first reproduction and that Lepidurus packardi did not differ significantly from C. californicus and the four anostracan species: Midvalley Fairy Shrimp, L. occidentalis, B. longiantenna, and B. conservatio. Nonetheless, the age at first reproduction for C. californicus was significantly later than that of anostracan species. Physical wetland parameters (i.e., mean average ponding depth, mean maximum ponding depth, mean maximum ponding surface area, and mean maximum ponding volume) were utilized as predictors to assess the responses of life cycle data (i.e., mean maturation period, mean reproduction period, and mean population longevity period) using linear regression best subsets. Significant linear correlations were obtained when: mean maximum ponding surface area and mean maximum ponding volume were used to predict the response of mean maturation period (F2,4 = 18.71, P < 0.009); mean average ponding depth, mean maximum ponding depth, mean maximum ponding surface area ,and mean maximum ponding volume were used to predict the response of mean reproduction period (F4,2 = 102.24, P < 0.010); and mean maximum ponding surface area and mean maximum volume were used to predict the response of mean population longevity period (F2,4 = 7.39, P < 0.045). CITATION. Pages 124-139 in: C.W. Witham, E.T. Bauder, D. Belk, W.R. Ferren Jr., and R. Ornduff (Editors). Ecology, Conservation, and Management of Vernal Pool Ecosystems – Proceedings from a 1996 Conference. California Native Plant Society, Sacramento, CA. 1998.