RATES OF METAZOAN MEIOFAUNAL MICROBIVORY : A REVIEW Paul Montagna To cite this version: Paul Montagna. RATES OF METAZOAN MEIOFAUNAL MICROBIVORY : A REVIEW. Vie et Milieu / Life & Environment, Observatoire Océanologique - Laboratoire Arago, 1995, pp.1-9. hal- 03051016 HAL Id: hal-03051016 https://hal.sorbonne-universite.fr/hal-03051016 Submitted on 10 Dec 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. VIE MILIEU, 1995, 45 (1): 1-9 RATES OF METAZOAN MEIOFAUNAL MICROBIVORY : A REVIEW PAUL A. MONTAGNA The University of Texas at Austin, Marine Science Institute, P.O. Box 1267, Port Aransas, Texas 78373 U.S.A. BACTERIES RÉSUMÉ - La méiofaune consomme des Bactéries, des microalgues, des Proto- MICROALGUES zoaires, du matériel détritique et d'autres méiobenthontes. Elle peut également ab- NUTRITION sorber de la matière organique dissoute. L'objet de cet article de synthèse concerne RÉPONSE FONCTIONNELLE la méiofaune microphage, et en particulier la prédation sur les Bactéries et les microalgues par les Nématodes et les Harpacticoïdes. La plupart des études utilisent les techniques radioisotopiques. Elles se divisent en deux catégories : celles qui envisagent d'élucider la biologie de la nutrition de la méiofaune, et celles qui cherchent à évaluer l'impact de l'importance de la méiofaune dans le recyclage du carbone. La méiofaune broute (sélectionne) les petites particules de la biomasse microbienne. Le taux de broutage de la méiofaune augmente lorsque l'abondance de la nourriture bactérienne disponible s'accroit. C'est une réponse fonctionnelle que les modèles d'optimisation prédisent. La méiofaune présente également des taux de consommation différents selon les sources de nourriture. Il existe des dif- férences ontogénétiques du taux de broutage et de sélection. Ces différences in- tragénériques sont faibles. Les modes de nutrition varient avec les diverses phases du cycle de vie. En dépis d'une forte variabilité d'un point à l'autre du globe, le taux moyen de broutage de la méiofaune est de 0,01 • h1, ce qui représente 1% par heure de la biomasse des hétérotrophes et des autotrophes. Ainsi, la méiofaune a un impact global significatif sur tous les processus faisant intervenir des micro- bionthes. BACTERIA ABSTRACT - Metazoan meiofauna eat bacteria, microalgae, protozoans, détritus, MICROALGAE and other meiofauna. They also have the ability to absorb dissolved organic matter. FEEDING The focus of this review is on meiofaunal microbivory, particularly the use of FUNCTIONAL RESPONSES bacteria and microalgae by nématodes and harpacticoids. Most of the studies utilize radioisotope techniques. The studies fall into two catégories : those done to elu- cidate meiofaunal feeding biology, and those done to assess the impact and im- portance of meiofauna in carbon cycling. Meiofauna graze on (i.e., select) small particles of microbial biomass. Meiofaunal grazing rates increase when offered increased abundances of microbial food. This is a functional response predicted by optimization models. Meiofauna also have différent grazing rates on différent species of food. Ontogenetic grazing rate and sélection différences exist. The évi- dence for intrageneric différences in grazing rates is weak. Différences of feeding modes exist with différent life history stages. There is much variability from site to site Worldwide, but on average meiofauna graze at a rate of 0.01 h ', or 1% of the standing stock of both heterotrophs and autotrophs per hour. Therefore, meiofauna have a significant global impact on microbially mediated processes. INTRODUCTION solid feeders that either eat or clean whole parti- cles (Marcotte, B.M. 1977, Ph.D. Thesis, Dalhousie University, 212 pp., described in Hicks During the 1970's, little was known about how, and Coull, 1983). There are also four nematode what, and how much meiofauna consumed feeding groups : deposit feeders, epistrate feeders, (Fenchel, 1978; Coull and Bell, 1979). A lot has scavengers and predators (Jensen, 1987). Al- changed. The kinematics of meiofaunal feeding though some nématodes (as well as meiofaunal has been defined. There are four harpacticoid sized annelids) are deposit feeders, most metazoan feeding groups : point feeders that are sélective meiofauna behavior is adapted to pick spécifie mi- epistrate pickers, line feeders that scrape edges of crobial food items, e.g., microalgae, bacteria, and particles, plane sweepers that sweep food into protozoans. Some workers have referred to this their mouths from two-dimensional surfaces, and feeding habit as «grazing,» and have measured 2 P.A. MONTAGNA how much microbial biomass is consumed by algae (Deco, 1988), and one study used fluores- meiofauna (Montagna, 1984; Decho, 1988; Blan- cence-labeled bacteria to measure grazing on bac- chard, 1991). Whereas macrofaunal (and pre- teria (Epstein and Shiaris, 1992). Both of thèse sumably meiofaunal) deposit feeders have fluorescence techniques are very powerful and adaptations to acquire food by ingesting large have advantages for studies spécifie to bacteria or volumes of sédiment (Lopez and Levinton, 1987), microalgae. The radioisotope approach has prob- meiofaunal grazers have adaptations to pick out lème, but it is currently the only way to measure spécifie microbial particles (Marcotte, 1977 in grazing on both bacteria and microalgae. There- Hicks and Coull, 1983; Jensen, 1987). fore, this review will mostly cover radioisotope One of the most successful areas of study tracer studies. There are two techniques for em- during the 1980's was to measure how much ploying radioactive tracers to measure the inverte- meiofauna eat in the field. It was found that meio- brate feeding via grazing. Microbial food is either fauna can vary their ingestion rates of microbes pre-labeled (Haney, 1971) or labeled while it is in response to changes in food quality or quantity being grazed (Daro, 1978). Both techniques have (Deco, 1988; Montagna and Yoon, 1991). Thèse advantages and disadvantages that limit their use results suggest that meiofaunal grazing rates are to either laboratory or field studies. The pre-label- a functional response to changes in the environ- ing technique requires growing microbes with a ment. I use this term in the same way that Taghon radioactive tracer, introducing the labeled microbe and Green (1990) defined functional response : to the existing microbial community and knowing «how any animal changes its feeding rate in re- the spécifie activity of the food source. Such con- sponse to changes in abundance of its food. » ditions are best achieved in laboratory studies. Meiofauna, particularly harpacticoids, can ex- The synoptic labeling technique is more amenable ponentially increase feeding rates as a function of to in situ studies, because only the radioactive increased microphytobenthos (Montagna, et al, tracer is introduced and microbial uptake of the 1995). More information is needed on how to tracer and meiofaunal grazing can be measured at apply models to meiofauna feeding, but we need the same time. a reliable and easy way to obtain feeding rate It is difficult to review the literature and dé- measurements. The current radioisotope tech- termine the comparative quantitative différences niques are neither well understood, nor easy to in meiofaunal microbivory, because of différences use (Montagna, 1993). in approach to measuring feeding rates and diffé- Together nématodes and harpacticoids usually rences in reporting the rates measured. In large make up 90-98 % of the meiofaunal community part, the différences exist because différent end- (Mclntyre, 1969; Coull and Bell, 1979; Dye and points are desired. Studies on carbon flow might Furstenburg, 1981; Platt, 1981). This paper fo- report rates on a biomass spécifie basis (e.g., |Xg 1 cuses on nématodes and harpacticoids because C • ind • h" ), whereas studies on the impact of they dominate the community. So, when I refer meiofauna grazing on microbial populations might 1 to metazoan meiofauna, I am referring to mainly report the flow rate (e.g., h )- The focus of this nématodes and harpacticoids and exclude benthic review is on assessing the latter issue, therefore microfauna (flagellâtes, ciliates and foraminifera). I have reported flow rates. This requires that the There is no doubt that microfauna are important, amount of food (e.g., carbon, chlorophyll, or num- but they may have différent behavior and meta- ber of cells) offered or available for eating is bolism than metazoan meiofauna (Rivkin and De known and reported. In this case it is simple to Laca, 1990). Meiofauna can utilize organic matter calculate the flow rate, i.e., the percent grazed per in diverse forms, but this review is focusing on unit time. An advantage to reporting the flow rate the utilization of the microflora : bacteria and mi- is that the inverse is the turnover time required crophytobenthos. The main purpose of this paper for the microbial population to maintain itself is to review the current literature on meiofaunal under the grazing pressure of meiofauna. Turnover