Experimental investigations of benthic reentry by migrating meiobenthic copepods

The resettlement behavior of meiobenthic copepods, which actively migrated from sediments in a seagrass bed, was investigated in a shallow subtidal area in Tampa Bay, Florida, U.S.A. Experimental studies were conducted to determine whether meiobenthic copepods after emerging from sediments at sunset reenter the sedimentary substratum or select other subhabitats, water and seagrass blades. Migrating copepods were collected with emergence traps and transferred to experimental aquaria in the field which contained sediment, seagrass-blade and water treatments. Settlement into each type of treatment was measured in separate 2-h and 9-h experiments. Differences in densities of copepod taxa retrieved from emergence traps and introduced into experimental aquaria were recorded as were differing relative proportions of each copepod species returning to the substratum treatments. Settlement patterns of total copepods and three dominant copepod species, Zausodes arenicolus, Halicyclops sp. and Robertsonia hamata, departed from those expected by chance. The populations of R. hamata and Halicyclops sp. which settled were generally skewed towards males and a close matching of males and copepodites within treatment dishes was evident. Similar to nighttime-emergence patterns, timing and magnitude of postmigration reentry differs among copepod taxa and such reentry may be linked to reproductive events. Complex behavioral processes previously noted for fish and macrofaunal organisms in seagrass beds may also be important in recruitment and reassortment of meiobenthic copepods.     

The role of meiofauna in the marine ecosystem: evolutionary considerations*

The meiobenthos are regarded as the first metazoans to appear on earth This paper considers some aspects of their role in the marine ecosystem over evolutionary time. It is speculatively suggested that they have had a profound influence on many structural and functional attributes of the marine ecosystem as we see it today, both in the benthic and pelagic realms. Certain features such as size spectra, the life-history characteristics of the macrobenthos, and the energetic balance between ecological compartments of the marine ecosystem are considered to result from evolution away from negative interactions with the meiobenthos.     

Meiobenthic distribution and nematode community structure in five European estuaries

Meiofauna from the intertidal zone of five European estuaries (Ems, Westerschelde, Somme, Gironde, Tagus) was investigated. Samples represented a cross section of various benthic habitats from near-freshwater to marine, from pure silts to fine-sandy bottoms. The meiobenthic community comprised everywhere a fauna strongly dominated by nematodes, with meiobenthic density increasing with increasing salinity. The Ems differed from the other estuaries due to the presence of a well developed community of Copepods, Gastrotrichs, large Ciliates and/or soft-shelled Foraminiferans in some sites. The Westerschelde stood out due to the near-absence of harpacticoid copepods and, as in the Tagus, the lower meiobenthic densities in the marine part of the estuary. For nematode community analysis, we also included data from the Tamar which were obtained from the literature (Warwick &; Gee, 1984). This resulted in the enumeration of 220 species, belonging to 102 genera, each with a characteristic distribution along the salinity, sedimentary and latitudinal gradients. Using the multivariate technique CANOCO, a zonation along these different physicochemical determinants was observed as well although salinity and sediment characteristic (scale of hundreds of meters to kilometers) proved to be more important in explaining community structure than latitudinal differences (scale of hundreds of kilometers). Nematode diversity was nearly entirely determined on the genus level and was positively related to salinity. Deviations from this general trend in the Gironde and the Tamar were attributed to sedimentary characteristics or to low macrobenthic predation. The presence of a typical opportunistic colonizing nematode species Pareurodiplogaster pararmatus in the low-salinity region of the Gironde could indicate (organic?) pollution or disturbance of the intertidal mud-flats.     

Micro-benthic crustacean communities in tundra lakes of North-East European Russia

We studied micro-benthic copepods and cladocerans in the bottom substrates of 12 lakes in the Bol’shezemel’skaya tundra in North-East European Russia during the summer. About 30 species of Cladocera and 28 species and subspecies of Copepoda were found. The majority of the micro-crustaceans are palaearctic or northern palaearctic. But the harpacticoid fauna of the western part of the studied region had specific European features, and three species of the harpacticoid fauna in the eastern part of the region were Siberian. It is therefore a boundary territory for two zoogeographical regions, the arctic and subarctic zones. Acidophilic (Arcticocamptus arcticus (Lilljeborg 1902)) and halophilic (Microsetella norvegica (Boeck 1864)) harpacticoid species were found in the lakes of the eastern part of Bol’shezemel’skaya tundra. On basis of their way of locomotion we distinguished five ecological groups and on basis of their feeding habits four ecological groups of micro-crustaceans. Groups with a similar way of locomotion were likely distributed over the studied water bodies. Habitat (inshore versus offshore), substrate particle size and substrate hardness were of paramount importance for the species distribution.     

The integral structure of a benthic infaunal assemblage

It has been suggested that the scaling relationships of many features of the physical environment and biological traits are fractal-like, but for the marine benthic infauna certain aspects of the environment clearly are not. These include temporal features such as the cycles of annual climate, primary production and tides, and also some spatial features such as sediment granulometry and the size of the primary producers that constitute the food supply. We explicitly addressed these issues by determining the degree to which infaunal assemblage structure (diversity, species composition, spatial pattern) varies with mesh size, sample size and sample dispersion within an apparently homogeneous area of coarse intertidal sand in the Isles of Scilly, UK. Samples were extracted using a standard range of 5 mesh sizes (63, 125, 250, 500, 1000 μm), with the sample areas and distances between samples scaled to the mesh size. All metazoans were identified to species level. Diversity and species composition did not show a gradual and even degree of change over the size range. Instead, they showed a dramatic stepwise change between the 250 and 500 μm mesh size samples, being relatively constant in the < 500 and > 500 μm categories, with diversity higher in the former. Higher proportions of species in the < 500 μm categories had values of an index of dispersion significantly different to 1 than among species in the > 500 μm categories. This suggests a fractal structure within but not between the < 500 and > 500 μm body size categories. The implications of this for rapid diversity assessment by extrapolation between size classes are discussed. Although the interplay between 3 and 2 dimensional processes in what is a essentially a 2-D study may account for some of the observations, comparative studies suggest that these patterns do not simply correspond to the physical scaling of habitat complexity, and they must therefore relate to some more universal scaling relationships that are not fractal-like. We suggest that the important relationships are those between body size and various biological characteristics such as feeding behaviour, reproductive mode and life history as they are affected by the spatial and temporal structure of the environment.     

An assessment of the meiobenthos from nine mountain lakes in Western Canada

The numbers and biomass of meiobenthic invertebrates of nine representative mountain lakes were assessed relative to the macrobenthic invertebrates retained on 0.425 mm mesh. The meiobenthos accounted for an average of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSGaaeaaca% aIXaaabaGaaG4maaaaaaa!3777!\[{\raise0.7ex\hbox{$1$} \!\mathord{\left/{\vphantom {1 3}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$3$}}\]of the total biomass and 97% of total numbers retained on 0.045 mm mesh. In general surveys in these lakes, the use of 0.250 mm mesh instead of 0.425 mm mesh would be unlikely to improve estimates of total numbers and biomass enough to justify the additional effort needed. Accepting the meiobenthic turnover rate to be three to five times that of the macrobenthos, meiobenthic production is probably close to or much higher than the macrobenthic production in these lakes.     

The use of meiofauna in marine pollution impact assessment*

The use of meiofaunal assemblages for the detection and quantification of perturbation of the marine environment by man is examined. The theoretical and practical advantages and drawbacks of meiofaunal monitoring are described and different methods of impact assessment described and evaluated. It is suggested that identification of meiofaunal material need not present a major obstacle to its use, as sensitive responses of meiofaunal assemblages to pollution can be recorded without the necessity for specific identifications. It is concluded that the great sensitivity to pollution of some meiofaunal groups (particularly copepods) offers the potential for better estimation of the real extent of pollution impact than is being achieved by sole reliance on examination of the macrofaunal assemblage. Meiofaunal monitoring should also be considered where there is difficulty in adequate sampling of the macrofauna, due to impoverishment or practical difficulties.     

A pedal corer for the quantitative sampling of sediments and benthic organisms in submerged areas accessible on foot

This paper presents a new device to collect quantitative samples of sediment and benthic organisms. The device is specially designed for sampling with the advantages of box-corer or Eckman dredges in submerged areas that are accessible on foot. The pedal corer is a simple, lightweight, user-friendly device that does not disturb the sediment structure and provides easy access to the sample contained inside the core. With this device, sampling in shallow water zones that are constantly submerged is made easy and sampling time is extended in intertidal zones. Handling editor: J. Saros     

Distribution of sub-littoral meiobenthos off Goa coast,India

Vertical and horizontal distribution of meiofauna was studied off Goa coast. Bottom deposit included mainly fine sand and silt. Total number of animals ranged from 250 to 2925/10 cm². Highest faunal density was in the top 6 cm layer. The fauna consisted of two main groups, nematodes and foraminiferans which together formed 60 to 80% of the total meiofauna. Fine sand supported a rich fauna. Interstitial water and organic content of the sediment was found to be the limiting factor in the distribution of meiobenthos.     

The influence of mangrove-derived tannins on intertidal meiobenthos in tropical estuaries

Summary Mangrove-derived tannins negatively effected laboratory-reared nematode populations and natural communities of meiobenthos in tropical mangrove forests along the northeastern coast of Australia. In the low and mid intertidal zones of five mangrove estuaries, nearly all of the dominant meiofaunal taxa correlated negatively with concentrations of sediment tannins. Only nematodes correlated with low tannin concentrations in the high intertidal zones. The negative exponential equation y=be ^-mx represented the best-fit for most of the meiofauna-tannin relationships. The mangrove-dwelling nematode, Terschellingia longicaudata did not grow (r=0.001) in the laboratory on fresh, tannin-rich leaves of the red mangrove, Rhizophora stylosa. Population growth of the nematode was significantly greater on fresh, tannin-poor leaves of the grey mangrove, Avicennia marina (r=0.081) with best growth (r=0.112) attained on a diet of tannin-free, mixed cereal. These preliminary field and laboratory results suggest that hydrolyzable tannins leached from mangrove roots and leaf litter are an important factor regulating intertidal meiobenthic communities in tropical mangrove forests along the northeastern Australian coast.