Temperature and larval development of Carcinus maenas (Decapoda) in the laboratory; predictions of larval dynamics in the sea

Larvae of Carcinus maenas (L.) (Decapoda, Brachyura, Portunidae) were reared in the laboratory from hatching to metamorphosis. Developmental times of subsequent stages at d~fferent constant temperatures (6, 12, 12.5. 18. 25°C) were recorded. Temperature-dependent development of each larval stage can be expressed by a power function. A model is presented which combines these results with the long-term mean temperature curve of Helgoland waters (North Sea). Hence prediction is possible of occurrence and presence of C. maenas larvae in the natural environment relative to their hatching date. On the basis of main hatching activities in nature, qualitative larval dynamics in Helgoland waters are discussed. To test the usefulness of the model, C. maenas larvae were reared in the laboratory from hatching to metamorphosis under simulated varying in situ temperatures. Results of this experiment correspond very well with model predictions. INTRODUCTION hatching to metamorphosis at several constant temperatures. Data from this temperature-dependent larval It is well established that temperature is one of the development were combined with data from the longmost important environmental factors in nature. term mean temperature curve of Helgoland waters. Biochemical and physiological reactions have Some work has already been done on the basis of this optimum temperature ranges, beyond which basic concept (Anger & Nair 1979, Dawirs 1979, 1982a, mechanisms of living organisms cease to function. Harms 1982, Anger 1983). Consequently, much effort has been undertaken to elucidate relations between temperature and development, growth, and metabolism of decapod crustacean MATERIAL AND METHODS larvae in the marine environment (for references see Dawirs 1982a). In most of these investigations the Obtaining and handling of larvae. Gravid Carcinus range of possible physiological responses was related maenas females were collected from the rocky intertito constant temperature conditions. dal region of northern Helgoland and taken to the Dynamic processes, however, play an important role. laboratory. Maintenance of ovigerous crabs, and larval Environmental temperatures in boreal seas, for examcollecting and handling methods, were performed as ple, reveal short-time and seasonal fluctuations. Many described by Dawirs (198213). A total of 500 larvae were dynamic processes are controlled by the characteristic reared under both constant and variable temperature annual course of varying water temperature. conditions. To analyse larval dynamics of Carcinus maenas in Individual larvae were kept in small glass vials conHelgoland waters, 2 questions were posed: (1) To what taining 20 m1 of filtered (1 pm) natural sea water from extent is the duration of larval development influenced Helgoland (31 to 33 %O S), in constant 6, 12, 12.5, 18 or by water temperature? (2) Is it possible to predict the 25°C. They were fed newly-hatched brine shrimp nauoccurrence and presence of subsequent larval stages in plii, Artemia spp. (ca 10 nauplii ml-l). nature relative to the date of hatching? To answer Temperature varied gradually to simulate the these questions, C. maenas larvae were reared from annual course of in situ temperature. Fig. 1 illustrates O Inter-Research/Printed in F. R. Germany 298 Mar. Ecol. Prog. Ser. 24: 297-302, 1985 Jan I Feb I Mar 1 Apr I May I Jun I Jut 1 Aug Sep I Oct [ Nov ( Dec Fig. 1. Design of temperature and daylength regulation (steps) of the experimental chamber. Curves illustrate the simulated annual course of temperature and day length these changes together with the resulting idealized Table 1. Carcinus maenas. Temperature-dependent developtemperature curve, Natural daylength was simulated ment of larvae described by power functions. D: development duration (d); T: water temperature ("C); a: constant; b: regresconcurrently by gradual changing of daily light-dark sion coefficient; r: correlation coefficient; p: level of signifiratios (Fig. 1). Larvae reared under these conditions cance originated from females which had also been kept in this temperature cabin. Thus egg incubation also took place under the simulated natural temperature regime. Simulating larval dynamics in the sea using laboratory and field data. The long-term mean water temperature near Helgoland increases from about 4°C in February to about 17°C in August, and decreases thereafter. Using data in Weigel (1978), the course of daily water temperature can be expressed by the following parabolae: Jan 1st Jun 14th: T = 5.6067 0.0785 d + 0.00074 d2 Jun 15th Oct 14th: T = -36.7493 + 0.4630 d 0.00099 d2 Oct 15th Dec 31st: T = 68.6692 0.2562 d + 0.00023 d2 where T = temperature ("C); d = day of the year (1 to 365) (Anger 1983). Estimation of in situ duration of larval development was made as follows: (1) Field temperature on the day of hatching (T) is determined by 1 of the above 3 parabolae. (2) This temperature enters the power function describing temperature dependent developmental duration of zoea 1 (Table 1). By this means, theoretical stage duration is calculated on the assumption that field temperature (T) remains constant. (3) One d after hatching, water temperature in the field becomes either somewhat warmer or cooler, depending on season. The calculated theoretical stage duration thereInD = a b l n T