The ecology of marine microbenthos. 1. The quantitative importance of ciliates as cornpared with Metazoans in various types of sediments

ABSTRACT An investigation of the quantitative importance of protozoans -especially ciliates -has been undertaken in Scandinavian waters. Ciliates were found in numbers from 10 6 to 4 X 10 7 individuals per m' representing 0.03-2.3 grammes wet weight per m'. Highest numbers were found in fine sand and in localities with a rich growth of sulphur-bacteria. In these sediments ciliates are 10 to 100 times more numerous than the total number of metazoans, and their biomass is of the same order or sometimes larger than the biomass of the micro-metazoans (nematodes, turbellarians, gastrotrichs etc.). In coarser sand ciliates are fewer, and micro-metazoans play a larger quantitative role. This distribution is explained by the small size and other morphological adaptations making ciliates able to inhabit the small interstitia of fine sand, and also their ability to endure reducing and anaerobic conditions. In the detritus layers which cover clayey and muddy sediments ciliates are few in number and play a small role compared with metazoan groups, such as nematodes, which may sometimes be as numerous as ciliates. A comparison with the enumeration of the benthic metazoans in Niva Bay carried out by Muus (J 967) shows that 93 % of all animals in the bay are ciliates which, however, only comprise 0.4 % of the total animal biomass. Large dinofiagellates were found in numbers of 10 5 to 1.5 X 10 7 per m'. Euglenoids are less numerous, normally fewer than 5 X 10 5 per m'. Naked amoebae seem also to play a small quantitative role; more than 10 5 per m' were rarely found. Ciliates show a maximum population size in summer, but this maximum may be obscured by other factors in more exposed localities. Large populations of active animals are found throughout the year. The importance of ciliates in community respiration is discussed. It is concluded that in localities with fine sand and in sulphureta the ciliates account for a larger part than the rnicro-rnetazoa, and that the ciliates contribute significantly to the energetics of these communities

Cosmopolitan metapopulations?

A “metapopulation” is a group of populations of the same species separated by space but linked by dispersal and migration. Metapopulations of macroscopic organisms tend to have geographically-restricted distributions, but this does not seem to be the case in microbial eukaryotes due to their astronomical abundance. The term “metapopulation” was first applied to protists’ biogeography in the article Finlay and Fenchel (2004), published in PROTIST, which contributed to the popularity of the paper. The article considered protist species as consisting of a single, cosmopolitan population. Here, we recall this paper, and assess developments during the last 15 years with respect to the question of protist species distribution on the surface of the earth

Patterns of Diversity in Soft-Bodied Meiofauna: Dispersal Ability and Body Size Matter

Background: Biogeographical and macroecological principles are derived from patterns of distribution in large organisms, whereas microscopic ones have often been considered uninteresting, because of their supposed wide distribution. Here, after reporting the results of an intensive faunistic survey of marine microscopic animals (meiofauna) in Northern Sardinia, we test for the effect of body size, dispersal ability, and habitat features on the patterns of distribution of several groups.Methodology/Principal Findings: As a dataset we use the results of a workshop held at La Maddalena (Sardinia, Italy) in September 2010, aimed at studying selected taxa of soft-bodied meiofauna (Acoela, Annelida, Gastrotricha, Nemertodermatida, Platyhelminthes and Rotifera), in conjunction with data on the same taxa obtained during a previous workshop hosted at Tjärnö (Western Sweden) in September 2007. Using linear mixed effects models and model averaging while accounting for sampling bias and potential pseudoreplication, we found evidence that: (1) meiofaunal groups with more restricted distribution are the ones with low dispersal potential; (2) meiofaunal groups with higher probability of finding new species for science are the ones with low dispersal potential; (3) the proportion of the global species pool of each meiofaunal group present in each area at the regional scale is negatively related to body size, and positively related to their occurrence in the endobenthic habitat.Conclusion/Significance: Our macroecological analysis of meiofauna, in the framework of the ubiquity hypothesis for microscopic organisms, indicates that not only body size but mostly dispersal ability and also occurrence in the endobenthic habitat are important correlates of diversity for these understudied animals, with different importance at different spatial scales. Furthermore, since the Western Mediterranean is one of the best-studied areas in the world, the large number of undescribed species (37%) highlights that the census of marine meiofauna is still very far from being complete

Protozoa and Oxygen

Aerobic protozoa can maintain fully aerobic metabolic rates even at very low O2-tensions; this is related to their small sizes. Many – or perhaps all – protozoa show particular preferences for a given range of O2-tensions. The reasons for this and the role for their distribution in nature are discussed and examples of protozoan biota in O2-gradients in aquatic systems are presented. Facultative anaerobes capable of both aerobic and anaerobic growth are probably common within several protozoan taxa. It is concluded that further progress in this area is contingent on physiological studies of phenotypes