Influence of Marine Protozoa on Nutrient Regeneration1

Abstract

Per unit weight, marine protozoa excrete dissolved phosphorus one to two orders of magnitude faster than marine microcrustaceans and several orders of magnitude faster than marine macrofauna.Protozoa may therefore be responsible for a major fraction of faunal nutrient excretion even though present only as a minor fraction of the faunal biomass.Regeneration of dissolved inorganic phosphate from organic detritus proceeds faster and more completely in the presence of bacteria and ciliates or colorless flagellates than in the presence of bacteria alone. An increased consumption of organic detritus in the presence of protozoa is performed by bacteria, which are kept in a prolonged state of "physiological youth" by grazing protozoa. Present results indicate that it is the protozoa that produce, via excretion, the greater regeneration of nutrients from organic detritus. By constituting a nutrient source for protozoa, bacteria are indirectly involved in this increased regeneration.

Nutrient cycling in a microflagellate food chain: III. Phosphorus dynamics

“…Our estimates of BEET (QPI Ep-') for Paraphysomonas imperforafa ranged from 0.6 to 2 d (Table 4), values which are considerably longer than the tens of minutes found by Johannes (1965) for several Protozoa excreting phosphorus. Taylor & Lean (1981) similarly found that phosphorus turnover times for a ciliate and a rotifer were on the order of tens of hours.…”

“…Taylor & Lean (1981) similarly found that phosphorus turnover times for a ciliate and a rotifer were on the order of tens of hours. These authors criticized the conclusion of Johannes (1965) that Protozoa regenerate a larger proportion of their ingested nutrients than do Metazoa. They pointed out that, even though Protozoa have greater weight-specific metabolic rates than do Metazoa, they also have extremely high gross growth efficiencies: in effect, Protozoa retain a large fraction of the nutrients they incorporate.…”

“…In particular, there has been much controversy over the relative roles of bacteria and Protozoa in this process (Johannes 1965, Barsdate et al 1974, Fenchel & Hamson 1976, Ammerman & Azam 1985. Johannes (1964Johannes ( , 1965 was the first to make a strong plea that Protozoa played an important role in recycling nutrients, based on his findings that the bodyequivalent excretion times (BEET) for excretion of phosphorus by some marine ciliates were as low as 14 to 20 min. By comparing these values with those of larger marine animals, he concluded that Protozoa must play an important role in nutrient cycling because their weight-specific regeneration rates and ' Contribution No.…”

“…These results were criticized by Barsdate et al (1974) and Fenchel & Harrison (1976) on the grounds that bacteria rather than Protozoa were the main regenerators of nutrients and that the prime function of Protozoa was to keep bacteria in a state of 'physiological youth'. Additionally, Taylor & Lean (1981) argued that phosphorus turnover times for ciliates were significantly greater than those attained by Johannes (1965) and Buechler & Dillon (1974), and that, in general, the efficiency of nutrient incorporation by Protozoa was greater than that of Metazoa. The recent evidence that bacteria play a key role in recycling phosphorus from dissolved nucleotides (Ammerman & Azam 1985) has added further uncertainty as to which group of microbes plays the major role in regenerating nutrients.…”

Primary production of particulate protein amino acids : algal protein metabolism and its relationship to the composition of particulate organic matter

“…Johannes (1965) demonstrated that remineralization 1a enhanced by the presence of both bacteria and protozoa, compared to just bacteria alone. Evidence aa to the importance of these microorganisms in organic matter cycling is steadily sccumulating (e.g .…”