Hydranth structure and digestion rate as a function of temperature and salinity inClava multicornis (Cnidaria,Hydrozoa)

Summary 1. Responses to 12 different combinations of constant levels of temperature and salinity were tested in the colonial athecate hydroidClava multicornis. Criteria measured were: (a) length and width of hydranth bodies, (b) number and length of tentacles and (c) rate of digestion.2. Test colonies were obtained by allowing single hydranths — cut off from an individual primary colony — to regenerate via asexual reproduction into new secondary colonies.3. In the resulting — genetically identical — material, all criteria tested vary as a function of the different environments offered.4. In 16, 24 and 32 S hydranth length reaches maximum values at 12°C, followed by 17° and then 22°C. With increasing salinity, hydranth length declines markedly at 12°C, while there is little or no decline at 17°C and a definite increase from 24 to 32 S at 22°C.5. Hydranth width varies less extensively; in general, it follows similar patterns as does hydranth length.6. Tentacle number per hydranth tends to be positively related to the size of the hydranth body; it decreases with increasing temperature. Salinity levels producing maximum tentacle numbers vary with temperature; maxima are found at 12°C in 16, at 17°C in 24 and at 22°C at 32 S.7. Tentacle length — although a more variable criterion — is affected similarly to tentacle number; it attains, however, relatively higher values at 17°C.8. In regard to the hydranth dimensions measured, combinations of low temperatures/low salinities and of high temperatures/high salinities tend to produce maximum values.9. Rate of digestion is taken here to be identical to the time elapsing between completed food intake and defecation. This time span is reduced with increasing temperature. In all temperature levels, digestion time is shortest in 32 S.10. The results presented above compare well with those obtained earlier under similar conditions onCordylophora caspia.11. It is assumed that the structural modifications of hydranths affect rate and efficiency of exchanges between organism and environment and may thus represent a means of metabolic adjustment.

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Hydranthenstruktur und Verdauungsrate als Funktion von Temperatur und Salzgehalt beiClava multicornis (Cnidaria, Hydrozoa)

Kurzfassung Erbgleiche Polypen vonClava multicornisForskål wurden in 12 verschiedenen Temperatur-Salzgehalts-Kombinationen durch asexuelle Vermehrung zu neuen Kolonien herangezogen und an den adulten Hydranthen dieser erbgleichen Sekundärkolonien Länge und Breite des Hydranthenkörpers, Anzahl und Länge der Tentakel sowie die Verdauungsgeschwindigkeit ermittelt. Alle gemessenen Parameter verändern sich — zum Teil sogar erheblich — als Funktion von Temperatur und Salzgehalt. Die Veränderungen der Hydranthendimensionen führen zu Verschiebungen der Oberfläche-Volumen-Quotienten. Da der Stoffaustausch zwischen Kolonie und Umwelt primär im Bereich der Hydranthen erfolgt, kommt diesen Verschiebungen vermutlich eine Bedeutung zu im Rahmen der Stresskompensation (nicht-genetische Adaptation). Die erzielten Ergebnisse bestätigen frühere Untersuchungen vonKinne an dem naheverwandten HydroidpolypenCordylophora caspia.