Growth and reproduction as a function of temperature and salinity inClava multicornis (Cnidaria,Hydrozoa)

Summary 1. Rates of growth (length increase of stolons) and of asexual reproduction (increase in number of polyps) were determined in secondaryClava multicornis colonies of a clone exposed to 12 different combinations of water temperature and salinity (12°, 17°, 22° C; 16 , 24 , 32 , 40 S). Sexual reproduction (via gonophores) has been observed only at 12° and 17° C; temperature and salinity ranges are narrower for sexual than for asexual reproduction.2. The data obtained are insufficient for a detailed analysis; they provide, however, interesting insights into the variability of growth and reproduction ofC. multicornis caused by different intensities of temperature and salinity.3. It appears that temperature requirements for maximum colony increase are reduced as the colony grows older.4. One feeding period per 24 hours seems insufficient for maximum growth and reproduction at the higher temperature levels, especially at 22° C.5. The different degrees of environmental stress endured during the initial period of transfer into the test combinations of temperature and salinity have affected the resulting colony size at least up to an age of 39 days. More appropriate criteria for assessment of rates of growth and reproduction are therefore the doubling times (number of days within which stolon length and polyp numbers taken 20 days after initiation of experiments have doubled).6. On the basis of doubling time values, increase in stolon length is progressively reduced with increasing water temperature (12°, 17°, 22° C). At 12° and 17° C stolons grow fastest in 32 , followed by 24 , 16 and 40 S; at 22° C stolon growth rates are identical in 32 and 24 S.7. Doubling times of polyp numbers per colony show a less obvious trend. In 56-day-old colonies, however, stolon length and polyp number are modified to similar degrees by the various temperatures and salinities offered. The sequence of temperatures causing fastest increase in polyp number is 12°>17°>22° C; the respective sequence of salinities reads: 24 , 32 , 16 , 40 S.8. Stolon length and polyp number per colony increase exponentially; most curves obtained exhibit undulations indicating endogenous growth rhythms.9. During the initial period of transfer into the final test media, asexual reproduction via budding seems to have been stimulated by a reduction in salinity.10. The doubling times obtained forC. multicornis are considerably longer than those found forCordylophora caspia and indicate that our culture conditions may have been suboptimal.

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Wachstum und Reproduktion als Funktion von Temperatur und Salzgehalt beiClava multicornis (Cnidaria, Hydrozoa)

Kurzfassung Einzelpolypen eines Klons vonC. multicornis Forskål wurden schrittweise in 12 verschiedene Temperatur-Salzgehalts-Kombinationen überführt und — während sie zu neuen Kolonien heranwuchsen — das Längenwachstum ihrer Stolonen, die Geschwindigkeit ihrer asexuellen Vermehrung durch Knospung neuer Hydranthen sowie die Gonophorenausbildung (sexuelle Fortpflanzung) registriert. Die erhaltenen Daten sind unzureichend für eine detaillierte Analyse, gewähren jedoch interessante Einblicke in die Bedeutung der verschiedenen Temperatur- und Salzgehaltsbedingungen für Wachstum und Vermehrung. Die anfängliche, schrittweise Überführung in die Testmedien verursacht per se Leistungsunterschiede, deren Auswirkungen sich mindestens bis zu einem Alter von 39 Tagen verfolgen lassen. Doubling times stellen daher objektivere Kriterien dar als absolute Zuwachswerte. Die doubling times von Kolonien, welche länger als 20 Tage in den Testmedien gewachsen waren, zeigen eine Verringerung der Stolonenzuwachsrate mit steigender Temperatur (12°, 17°, 22° C). Die Reihenfolge der fördernden Wirkung der einzelnen Salzgehaltsstufen ergibt sich zu 32 , 24 , 16 , 40 S. Im Prinzip ähnliche Verhältnisse liegen hinsichtlich der asexuellen Vermehrungsrate vor. Bemessen an den getesteten Kriterien scheinen die Temperaturansprüche mit zunehmendem Koloniealter abzunehmen. Die errechneten doubling times sind wesentlich länger als beiCordylophora; möglicherweise deutet dieser Unterschied auf inadäquate Kulturbedingungen (Fütterung, Wasserbewegung) hin.

     

Vertical zooplankton distribution on the northeastern Florida shelf and its relation to temperature and food abundance

The vertical distribution of abundant zooplankton on the northeastern(NE) Florida shelf was measured and related to depth, temperatureand concentration of particulate matter. High particle concentrationswere observed in low-temperature near-bottom intrusions of upwelledGulf Stream water. Patterns of vertical distribution differedamong the abundant zooplankton taxa. Abundances of the calanoidsEucalanus pileatus and Temora turbinata, late copepodids andadults of the cyclopoid Oncaea sp., the cladcceran Penilia avirostrisand larvae of the cephalochordate Branchiostoma sp. generallyincreased with increasing depth. E. pileatus, T. turbinata,Oncaea sp. and P. avirostris increased with increasing concentrationof paniculate matter. Abundances of young specimens of the tunicateOikopleura, the calanoid Centropages furcatus and during oneperiod, the cyclopoid Oithona sp. were greatest in the uppermixed layer and the thermocline. The abundance of Eucalanus,T. turbinata and the late copepodids/adults of Oncaea showeda significantly positive conelation to the abundance of paniculatematter.     

Ammonium release by juveniles and adult females of the subtropical marine copepod Eucalanus pileatus

Release rates of ammonium by nauplii, copepodid stages (CIIand CIV) and adult females of the marine copepod Eucalanus pileatusat 0.1 and 3.0 mm³ 1^–1 of the diatom Thalassiosira weissflogiiwere determined at 20°C. When food was abundant, animalsof all stages released ammonium at similar rates per unit ash-freedry weight [24–35 nmol NH₄(mg AFDW)^–1 h^–1on average]. At low food levels, CIVs and adult females releasedammonium significantly more slowly than did the naupliior CIIs[28 and 24 versus 51 and 50 nmoles(mg AFDW)^–1h^–1].Because they weighed less (50%), low-food nauplii and CIIs hadhigher calculated weight-specific excretion rates, than high-foodones of the same stage but release rates per copepod were similarin the two food regimens. In contrast to the early life stages,the CIVs and adult females released less ammonium per copepodin the low-food than in the high-food environment. ¹GLERL - Contribution No. 380     

Feeding, growth and food conversion of the marine cladoceran Penilia avirostris

Ingestion and clearance rates, feeding behaviors and life historyvariables of the marine cladoceran Penilia avirostris were evaluatedover a range of food concentrations encountered in nature (0.01–3.0mm³ 1^–1 of Isochrysis galbana). Ingestion rates increasedand clearance rates decreased with increasing food concentration.No maximum feeding thresholds were observed over the range ofalgal concentrations offered. Weight-specific ingestion ratesdecreased with increasing body weight. Feeding behaviors suchas mandibular activity, abdominal claw rejections of cloggedfeeding structures and feeding appendage activity decreasedat a food level of 0.3 mm³ l^–1 of l. galbana. Peniliaavirostris had very poor survivorship at extremely low (0.01mm³ l^–1 and high (3.00 mm³ l^–1) food levels. Mortalitywas hardly affected at food levels of 0.03–1.0 mm³ l^–1Reproduction did not occur at food levels of     

Caloric content of larvae of the brine shrimpArtemia salina

Summary 1. Caloric contents ofArtemia salina nauplii and larvae have been determined by employing a combustion calorimetry. Freshly hatched nauplii contain on an average 5953 cal/g organic substance; the respective value for 7-day-old (2 mm long) larvae is 5854 cal/g.2. The effect of starvation on the caloric contents was investigated. After a 72 hour starvation period, nauplii contain 5430 cal/g organic substance, 2 mm long larvae 5115 cal/g.3. The ash contents (expressed as % of body dry weight) ofArtemia larvae increase as a function of the length of the starvation period.4. After determining the weight of the nauplii, the caloric content of a single nauplius was calculated after different periods of starvation. It ranges from 0.00924 cal per freshly hatched nauplius to 0.00459 cal per nauplius starved for 96 hours.

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Kaloriengehalt von Larven des SalinenkrebsesArtemia salina

Kurzfassung Der Energiegehalt frisch geschlüpfter Nauplien (5953 cal/g organische Substanz) und 2 mm langer Larven (Metanauplius IV, 5854 cal/g organische Substanz) vonArtemia salina Leach wurde mit einem Parr 1412 Bombenkalorimeter ermittelt. Ferner wurde der Einfluß verschieden langer Hungerperioden auf den Kaloriengehalt dieser Tiere untersucht. Nach 72stündigem Hungern wurden für die Nauplien 5430 cal/g organische Substanz und für die 2 mm langen Larven 5115 cal/g organische Substanz ermittelt. Der Aschegehalt der Tiere stieg mit zunehmender Dauer der Hungerperiode. Anhand des Gewichts der geschlüpften und hungernden Nauplien wurde der Kaloriengehalt einzelner Tiere bestimmt: er reicht von 0,00924 cal pro Tier (gerade geschlüpfter Nauplius) bis 0,00459 cal pro Tier (Nauplius, 96 Stunden ohne Futter).

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Dedicated to Professor Dr.Friedrich Krüger on his 65^th birthday, August 18, 1967.     

On the ecology of marine cyclopoid copepods (Crustacea, Copepoda)

The goal of these studies was to improve our understanding ofhow Oithonidae and Oncaeidae can exist in nearly every partof the ocean. In particular, it was intended to obtain quantitativeinformation on reproduction rates and the longevity of adultfemales, and on feeding and growth rates of Oncaeidae. Whenfeeding at relatively high food levels, early copepodids ofOncaea mediterranea ingested     

Variability due to feeding activity of individual copepods

This paper addresses (the inter- and intraindividual) variabilityin release rates of fecal pellets of early copepodids (Cll)and adult females of the calanoid copepod Eucalanus pileatus.The intervals between releases of fecal pellets of tetheredindividuals were used as a measure of feeding activity. Earlycopepodids represented animals with a known, and adult femalesthose with an unknown, and probably highly variable history.Food concentration had a significant effect on the frequencyof pellet release by adult females, but not by CII. There wereno significant differences in release intervals among femalesat the lowest food level, but significant differences at middleand highest food concentrations. These differences could bepartly attributed to different history (seasonally). The coefficientof variation (CV) as a measure of variability, rarely exceeded30% for females and was always <30% for CII. For most individuals,the CV was <20%. The range in the frequency of pellet releasewas almost always less than factor of two. Our data indicatethat in pellet release frequency, variability in feeding behaviorwithin and between individual E.pilealus is rather low comparedto data on feeding rates, and is attributed largely to the appliedprocedures.     

Perceptive performance and feeding behavior of calanoid copepods

The goal of this study was to determine variables associatedwith calanoid feeding behavior, and thus, to improve our understandingof the basics of calanoid feeding rates. These variables includedperiods and frequency of appendage motion, rates of cell clearance,distance at which a copepod first reacts to a cell which iseventually captured, and rate of water flow through the areacovered by the motions of a copepod's feeding appendages. Theeffects of these variables on feeding rates were determinedfor copepodids and adult females of the calanoid copepod Eucalanuspileatus at phytoplankton concentrations covering the rangeencountered by this species on the south-eastern shelf of theUSA. Our results indicate that the distance at which E.pileatusperceives phytoplankton cells increases {small tilde}2-foldas food concentrations decrease from 1.0 to 0.1 mm³ l^–1.These results lead us to hypothesize that this is due to increasedsensitivity of chemosensors on the copepods' feeding appendages.This 2-fold increase in perceptive distance amounts to a near4-fold increase in perceived volume which is close to the 6-foldincrease in volume swept clear (VSC) from 1.0 to 0.1 mm³ l^–1of Thalassiosira weissflogii. We assume that the increases inVSC by planktonic copepods, when food levels are below satiation,are largely a function of the sensory performance of the individualcopepod.     

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 multicornis Forskål 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.

     

Effects of small-scale turbulence on feeding rate and gross-growth efficiency of three Acartia species (Copepoda: Calanoida)

Experiments designed to test the effects of small-scale turbulenceon the feeding rates and gross-growth efficiency of calanoidcopepods have been performed within a wide range of controlledfood concentrations. Turbulence significantly enhanced feedingrates only at food concentrations lower than the ingestion saturatinglevel. Gross-growth efficiency (the quotient carbon-egg production/carbon-foodingested) of the different Acartia species studied showed differentpatterns of response to turbulence, in agreement with the hydrodynamiccharacteristics of their habitat. Furthermore, experiments conductedon Acartia clausi at two different intensities of turbulenceindicate a shift in the response, with enhancement of feedingat low intensities of turbulence and negative interference athigher intensities.