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Copepoda, Harpacticoida) in Laboratory and Field Populations

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Copepoda, Harpacticoida) in Laboratory and Field Populations DEVELOPMENT, BODY LENGTH, AND FEEDING OF TIGRIOPUS CALIFORNICUS (COPEPODA, HARPACTICOIDA) IN LABORATORY AND FIELD POPULATIONS BY JAMES J. POWLIK, ALAN G. LEWIS and MAYA SPAETH University of British Columbia, Department of Oceanography, 6270 University Blvd., Vancouver, B.C., Canada V6T 1Z4 ABSTRACT Development of the harpacticoid copepod Tigriopus californicus was observed under tempera- ture and salinity regimes representative of seasonal conditions in the splashpools of Barkley Sound, Canada. Cultures were maintained in natural sea water representing either summer (18-20°C; 30-32‰ salinity) or winter (10-15°C; 20-25‰ salinity) conditions and compared to concurrent samples from field populations. Development of nauplii (stages N-I through N-VI) occurred in 10 days under "summer" conditions and 12 days under "winter" conditions; copepodite develop- ment (stages C-I through C-VI) was similarly delayed from 11to 18 days at the lower tempera- ture/salinity. Total generation time (egg to adult) was 21 days for the higher temperature/salinity values, and 30 days at the lower values, although no net difference in body length was observed. Clutch size was 17±4.2 eggs (mean± S.E.) at 10-15°C and 15.3± 8.1 eggs at 18-20°C for gravid females in culture; field specimens had a mean clutch size of 17.9± 2.5 eggs at 10-15°C, increasing to 27± 4.2 eggs.clutch-1 during the summer months (July and August), and possibly indicative of the quality and supply of food available in situ. Non-viable progeny accounted for 10± 8.1 % and 10.8± 7.8% of all eggs under "summer" and "winter" conditions, respectively. A synthesis of these results with several studies using T. californicus and its congeners in evaluations of feeding, fecundity, organism development, and toxicity studies is also provided. RÉSUMÉ Le développement du copépode harpacticoïde Tigriopus californicus a été observé sous des régimes de température et de salinité représentatifs des conditions saisonnières dans les flaques supralittorales de Barkley Sound, Canada. Les cultures ont été maintenues dans de l'eau de mer naturelle présentant les conditions estivales (18-20°C; 30-32‰ de salinité) ou hivernales (10-15°C; 20-25‰ de salinité) et comparées à des échantillons des populations locales. Le développement des nauplii (stades N-I à N-VI) s'est produit en 10 jours dans les conditions "été" et en 12 jours dans les conditions "hiver"; le développement des copépodites (stades C-I à C-VI) a de même été retardé de 11 à 18 jours aux température et salinités basses. La durée totale d'une génération (de l'oeuf à l'adulte) a été de 21 jours pour les températures et salinités hautes, et de 30 jours pour les températures et salinités les plus basses, bien que l'on ait observé aucune différence nette dans la longueur du corps. La taille des pontes était de 17± 4,2 oeufs (moyenne±S.E.) à 10-15°C et 325 15,3 ± 8,1 oeufs à 18-20°C pour les femelles gravides. Sur le terrain, les spécimens avaient des pontes d'une taille moyenne de 17,9± 2,5 oeufs à 10-15°C, croissant à 27± 4,2 oeufs. ponte-1 durant les mois d'été (juillet et août), ceci étant peut-être indicatif de la qualité et de la quantité de la nourriture disponible in situ. Le progéniture non viable s'élevait à 10± 8,1% et à 10,8± 7,8% de tous les oeufs dans les conditions "été" et "hiver", respectivement. A également été fournie une synthèse de ces résultats et de plusieurs études sur T californicus et ses congénères dans les domaines de l'alimentation, de la fécondité, du développement et de la toxicité. INTRODUCTION "Growth is the only evidence of life." John Henry Newman (1864) Harpacticoid copepods of the genus Tigriopus Norman, 1868 have been pop- ular and successful subjects of laboratory study for at least the past five decades. Their small size, remarkable fecundity, short generation time, and tolerance to extreme or sudden fluxes in the supporting aqueous medium are attributes that have served to promote the use of Tigriopus congeners in a diverse array of ex- perimental applications. Examples specific to Tigriopus californicus Baker, 1912 include evaluations of copepod feeding (Lear & Oppenheimer, 1962; Sullivan & Bisalputra, 1980; Syvitski & Lewis, 1980) and the use of copepods as food for fish culture (Morris, 1956; Fahey, 1964); response to pollutants or thermal and osmotic stress (Chipman, 1958; Huizinga, 1971; Kontogiannis, 1973; Kon- togiannis & Barnett, 1973; McDonough & Stiffler, 1981; O'Brien et al., 1988; Misitano & Schiewe, 1990; Burton, 1991); sex determination and development (Vacquier & Belser, 1965; Egloff, 1966; Palmer et al., 1993); fecundity (Burton, 1985); and genetics (Ohman, 1977; Burton et al., 1979; Burton & Swisher, 1984; Burton, 1987, 1990; Brown, 1991, to list only a few examples). Indeed, all Tigri- opus congeners may claim an equal diversity of applications, but a cataloguing of these is beyond the intent of the current study. The development of Tigjriopus japonicus Mori, 1938 has been described by Igarashi (1963a, b), and illustrated extensively by It6 (1970) and Koga (1970). Fraser (1936) and Bozic (1960), respectively, document the natural history and taxonomy of T. fulvus (Fischer, 1860), while Comita & Comita ( 1966) and Har- ris (1973) provide the benchmark studies for the egg production, growth, and physiology in T. brevicornis (0. F. Mijller, 1776). Burton (1985) details the mating system of T. californicus and Huizinga (1971) cursorily discusses the development of T. cal?fornicus and maintenance of the organism in culture. A number of studies have addressed related population-level responses of Tigriopus copepods in laboratory culture, including dormancy of life-history stages (Fraser, 1935; Kasahara & Akiyama, 1976), development and brood production (Igarashi, .
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