Ciliate community in the oligotrophic Gulf of Aqaba, Red Sea

Abstract

Ciliate data were gathered along a 600 m deepwater column in central waters of the Gulf of Aqaba, Israel. Samples were taken during winter mixing, the onset of stratification in spring and during summer stratification (2003 to 2005). The phytoplankton community strongly differed in these 3 periods, from highest abundances of eukaryotic algae during mixing, followed by a Synechococcus bloom right after the onset of stratification and a Prochlorococcus-dominated community in summer. Ciliate abundance and biomass were high compared to chlorophyll standing stock, with maximal values of 3534 cells l -1 and 3554 ng C l -1 , respectively. Abundances were at times 5-fold higher than those found in comparable studies on nutrient-poor pelagic systems and approached those observed in coastal waters. Ciliate carbon:chlorophyll ratios of up to 26 were astonishingly high, as compared to values of 2 to 5 normally observed. This indicates a high efficiency of the ciliates in utilizing the available food. The phytoplankton community in the Gulf is dominated by picocyanobacteria, and by repacking the algal prey into accessible particles, protozoans might be an important intermediate link in the pathway between phytoplankton and metazoan grazers. Oligotrichs and nanociliates contributed up to 98 and 88% of ciliate total abundance, respectively. Small oligotrich species appeared to be the superior competitors in this oligotrophic marine system, being able to utilize the dominant picoautotrophs efficiently.KEY WORDS: Nanociliates · Nutrient limitation · Ocean · Oligotrichia · QPS · Strombidium · Strobilidium · TintinnidsResale or republication not permitted without written consent of the publisher

Threats to Ultraoligotrophic Marine Ecosystems

“…Larger cells (>8 μm) are dominated by dinoflagellates and ciliates (Berninger & Wickham, 2005). The ciliates prey on the dominant picoautotrophs so that this primary production then becomes available to metazoan grazers (Claessens et al, 2008). Stable isotope analyses revealed a complex and diverse planktonic community that included herbivores and a large variety of omnivores (e.g.…”

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“…However, despite the oligotrophic status of the Gulf of Aqaba, which was supported by very low densities of autotrophic nanoflagellates, ciliate density was unexpectedly high. This was the case not only during nutrient-replete conditions in spring, but also in summer, when nutrients were strongly depleted (Claessens et al, 2008). This suggests that the ciliate community in the Gulf of Aqaba is much more efficient in utilizing nanophytoplankton as a food source during all seasons, and that the degree of topdown control (predation) of the ciliate community is relatively low in the gulf (although alternative food sources could be heterotrophic bacteria and heterotrophic nanoflagellates).…”

“…The lower ciliate population density at Abu Galoum (site 3), for example, was still two times higher than that found at the northern part of the Gulf of Aqaba (3534 cells L -1 ) in the earlier study by Claessens et al (2008). Moreover, the densities of ciliate populations in the Gulf of Aqaba were up to eight-fold higher than abundances in other comparable studies in nutrient poor systems (Revelante and Gilmartin 1990;James and Hall, 1995;Pitta et al, 2001) and were comparable with maximum values found in coastal waters or in more productive open ocean systems (Stoecker et al, 1989;Leakey et al, 1996).…”

“…Evaporation is exceptionally intense (average 200 cm / year) (Godeaux, 1986) and thus the water is saline. The gulf has been described as highly oligotrophic on the basis of the chlorophyll a values and primary productivity measurements carried out by several investigators (Kimor, 1990;Claessens et al, 2008Claessens et al, , 2010.…”

Community structure and trophic role of ciliates and heterotrophic nanoflagellates in Rhone River diluted mesoscale structures (NW Mediterranean Sea)

“…The ratio of ciliate carbon to chl a in open MW has been reported to range from 2 to 5 (Dolan & Marasé 1995, Dolan et al 1999. Claessens et al (2008) have recently reported values from 2 to 26 in the oligotrophic Red Sea. According to these authors, the higher this ratio, the higher the efficiency of ciliates in using algae as a food source.…”