Zur chemischen Zusammensetzung der CtenophorePleurobrachia pileus in der Kieler Bucht

Abstract

On the chemical composition of the ctenophore Pleurobrachia pileus in Klel Bight.The chemical composition of the ctenophore Pleurobrachia pfleus was investigated in March, May and July 1981 in Kiel Bight, western Baltic. The results of all determinations yielded low values compared with other zooplankton groups. Dry weight made up 1.95 to 2.28 % wet weight with a minimum occurring in May. Ash-free dry weight amounted to 28-37 % of the dry weight but exhibited a maximum in May. Carbon and nitrogen analyses yielded amounts of between 2.6-4.7 % of the dry weight and 0.5-1.0 % of the dry weight, respectively. Both elements reached lowest levels in May. Proteins reached a minimum in May, too, and values ranged between 2.5 and 5.1% of the dry weight. However, hpids as well as carbohydrates exhibited highest values in May and ranged from 0.8 to 1.6 % and 0.8-1.1% of the dry weight, respectively. The C : N values increased between March and July from 3.7:1 to 6.7:1, indicating a decline in protein content. To relate the biochemical compounds to organic matter I used three different approaches: (1) On the basis of ashfree dry weight, carbohydrates remained constant whereas lipids increased from March to July. A minimum of proteins occurred in May. The three compounds made up only 14-22 % of ash-free dry weight. (2) Organic matter approximately equals organic carbo~ content multiphed by 2. Proteins, lipids and carbohydrates summed up reached 61-100 % of this reference value and the seasonal course of these compounds changed in a drastic way: proteins decreased, whereas hpids as well as carbohydrates showed a relative maximum in May. (3) Finally, the carbon content of each biochemical compound was calculated in relation to total carbon content measured via C/N analysis. On this basis, 63-105 % of total carbon were recovered, and the course of seasonal changes agreed with that of the second approach. A comparison of these three approaches suggests that comparative calculations based on carbon measurements are more valid than those based on ash-free dry weight. The results show that seasonal changes in the amount of organic matter and the biochemical composition occurred. Dry weight was lowest in May, which could be due to the low salinity environment recorded at that time and the corresponding low salt content of the tissue. The observed relative maxima of lipids and carbohydrates in May may be explained by good food conditions since high zooplankton densities are characteristic for this month in Kiel Bight.

Effect of starvation on the biochemical compositions and respiration rates of ctenophores Mnemiopsis leidyi and Beroe ovata in the Black Sea

“…According to Dudkin et al (2002), Beroe in the course of the starvation has utilized glucose and metabolic carbohydrates most intensively especially in comparing with the utilization of protein and of structural carbohydrates. These changes in the biochemical composition of starved specimens of both B. ovata and M. leidyi in general did not differ from those that were observed in the ctenophore Pleurobrachia pileus from the North Sea (Hoeger, 1983;Schneider, 1989).…”

“…Although, there is supposition, that for some species the total lipid could be an exception in this respect (Schneider, 1989): sometimes their large amounts testified rather to starvation than provision of feeding for ctenophores (Figures 4-6).…”

“…The main organic compounds and their ratios usually do not permit us to determine the duration of fasting and food supply in these gelatinous animals. Although, there is supposition, that for some species the total lipid could be an exception in this respect (Schneider, 1989): sometimes their large amounts testified rather to starvation than provision of feeding for ctenophores (Figures 4-6).…”

“…The experiments discovered no significant differences between the proximate biochemical composition of freshly collected and starved gelatinous animals. So, it is still unclear, if predominant organic compounds could be characteristics of the ctenophores' condition (Schneider, 1989). In this paper, we report how starvation affects the biochemical composition and respiration rate of ctenophores M. leidyi and B. ovata, which have been investigated insufficiently in this respect.…”

Does the nutrient stoichiometry of primary producers affect the secondary consumer Pleurobrachia pileus?

“…So, the hypothesis based on the study of Borodkin and Korzhikova (1991), that due to their relatively high phosphorus content Pleurobrachia, or perhaps even all ctenophores, is expected to show phosphorus limitation quickly, clearly needs to be rejected. In fact, several studies (Schneider 1989;Anninsky et al 2005) have indicated a very high content of proteins in ctenophores, which is corroborated by the low C:N values found by Kremer and coworkers (Kremer 1977(Kremer , 1982Kremer et al 1986;Youngbluth et al 1988), so the measurements of Borodkin and Korzhikova (1991) for Mnemiopsis leidyi might be considered unusual and not reflect a general pattern in ctenophores. Virtually no information exists on the nutrient stoichiometry and physiology of ctenophores, and of P. pileus in particular.…”