An ecological and economic review of meiofauna as food for fish*

After briefly reviewing the evidence that meiofauna are an integral part of the complex food web of invertebrate infaunal and epifaunal organisms, it is shown that, at least in intertidal and shallow subtidal habitats, meiofauna are an important food for the small (30–60 mm) juveniles of some commercially important fishes (flatfish and salmonids) or for fish which are themselves food for commercial species. The evidence that fish feed preferentially on a few species of harpacticoid copepod rather than on the numerically dominant meiofaunal taxa is presented and discussed. It is argued that, in addition to benthic copepods being energetically efficient as food for fishes, it is differences in the activity and availability between major taxa of meiofauna as they relate to the feeding strategies of the fish which go a long way to explaining this apparent general preference of fish for harpacticoid copepods rather than nematodes. From literature estimates of consumption rates, it is concluded that the supply of meiofaunal food to juvenile fish is unlikely to be limiting although this may not be the case in some shallow subtidal muddy sand habitats. Whilst it is recognized that fish predation may influence the magnitude of the seasonal peaks in numbers, predation is not the principal cause of seasonal fluctuations in harpacticoid copepod species abundances. The effects of predation on other aspects of community structure is unknown. Finally, the possible role of meiofauna in mariculture systems is briefly discussed.     

Description of intertidal macro- and meiobenthic assemblages in Maxwell Bay, King George Island, South Shetland Islands, Southern Ocean

The intertidal benthic fauna of the Antarctic coastal areas is largely unknown and has long been thought to be absent or, at most, to be scarce. Since climate changes cause a progressive expansion of ice-free intertidal soft-bottom areas, the fauna of these areas could serve as essential criterion to evaluate the kind and dimension of such changes. We therefore investigated the faunal composition of the intertidal soft-bottom area of Maxwell Bay (King George Island, South Shetlands) in December 2006. Samples for quantitative analyses were taken from the soft-bottom during low tide using a plastic corer. We performed detailed analyses of the soft-bottom beneath a cobble layer, while hard-bottom and macrophytes were only sporadically investigated. Approximately 5,000 specimens were collected of which polychaetes (37.3 ± 7.6 (max. 44.7) ind. × 100 cm^?³) and harpacticoids (28.9 ± 28.5 (max. 104.0) ind. × 10 cm^?³) were the most abundant macro- and meiofauna taxa of the soft-bottom, followed by oligochaetes, nematodes, mollusks, and amphipods. A total of 58 macrofauna species were registered, of which 27 were identified only to a supraspecific level. The most species-rich macrofauna taxon was polychaetes with at least 24 species, followed by amphipods, gastropods, and oligochaetes with 6 species each. The harpacticoid copepods were represented by 15 families with more than 30 species. In summary, we show that the Antarctic intertidal soft-bottom is densely populated by macro- and meiofauna and that it deserves closer attention in the future to determine whether it can indeed serve as an indicator of the effect of climate changes on the Antarctic coastal areas.     

Variations in the intertidal and subtidal macrofauna and sediments along a salinity gradient in the upper forth estuary

The intertidal and subtidal soft-sediment macrofauna of the upper Forth estuary, eastern Scotland, UK has been examined. The intertidal fauna was sampled in 1977, and again in 1988/89, at up to twelve stations along the salinity gradient. The subtidal fauna was sampled in 1982 and in 1988/89 at up to 15 stations. The stations span the region of the freshwater-seawater interface, and area of the turbidity maximum. Large spatial and temporal variations in macrofaunal abundance and species composition were observed. Sites at the head of the estuary with low salinity were dominated by oligochaetes, but more saline areas were characterised by a depauparate estuarine fauna. The area has historically received large quantities of organic waste both from sewage and industrial discharges which supported very high abundances of oligochaetes of up to 500,000 m⁻² in the upper reaches of the estuary. Reductions in the organic inflow to the area since the early-1980's have begun to cause reductions in oligochaete populations and also allowed the further penetration intertidally of non-oligochaete species into the upper and middle reaches of the estuary. No comparable upstream penetration by the non-oligochaete subtidal fauna has been observed, possibly on account of the greater sediment instability in the estuary's main channel.     

Disturbance and organization of macroalgal assemblages in the Northwest Atlantic

Large seaweeds are often structurally dominant in subtidal and intertidal rocky shore benthic communities of the N.W. Atlantic. The mechanisms by which these algal assemblages are maintained are surprisingly different in the two habitats. In the subtidal community, kelps are dominant space competitors in the absence of strong grazing interactions. In contrast, the large perennial seaweeds of intertidal zones (fucoids and Chondrus crispus) are competitively inferior to both sessile filter feeders and ephemeral, pioneer algal species. Intertidal seaweed beds are maintained by carnivory of whelks, which reduces filter feeder populations, and by herbivorous periwinkles which reduce ephemeral algal populations. Through most of the intertidal zone, disturbance, both biological and physical, dictates which species shall compete and equilibrium conditions obtain subsequently.The roles of subtidal consumers are quite different. Sea urchins are the major algal herbivores and these voracious animals maintain an equilibrium state in which large tracts of subtidal coralline pavement are kept free of kelp forests. Urchins do not seem to play a successional facilitative role for kelps in the way that periwinkles do for fucoids in the intertidal. Control of herbivore populations is thus a key to the maintenance of subtidal foliose algal beds. It is clear that parasitic amoebas can decimate sea urchin populations so that kelp forest dominance is assured. However, the importance of carnivory in limiting urchins in the subtidal community is unclear in the absence of appropriate manipulation experiments. It is possible that carnivorous decapods and fin fish control sea urchin populations and hence foliose algal abundance, but this must remain speculative. The seaweed-dominated state of the subtidal system is an alternative equilibrium condition to the urchin/coralline alga configuration. The structure of the kelp beds is relatively uniform in responding to frequent small-scale, infrequent large-scale, or no, disturbance.     

The meiofauna and macrofauna of some tropical beaches

The fauna of a number of intertidal habitats ranging from estuarine mud to marine sand has been examined in the region of Porto Novo, south-east India. Quantitative estimates of meiofauna and macrofauna are given, and the distribution and relationships of these two size categories discussed. Comparison is made with intertidal areas in other parts of the world.     

Distribution,abundance and ecology of the meiofauna in a tropical estuary along the west coast of India

The distribution and abundance of subtidal meiofauna in Mandovi estuary of Goa were studied from June 1983 to June 1984. Monthly faunal abundance ranged from 491 to 2791/10 cm² and dry weight biomass from 0.16 to 2.80 mg 10 cm². Free living nematodes were the dominant group contributing over 75% of the total density and 30 to 42% of the total biomass. Among nematodes the deposit feeders were more abundant in fine muddy substratum while epigrowth feeders dominated in sandy substratum.Harpacticoids were next, comprising 6.9 to 8.7% of the total meiofauna number, followed by turbellaria (3.8–4.5%), polychaeta (2.8–3.2%) and ostracods (1.6–4.5%) The contribution of other groups to faunal density was 4.5–6.2%. In the biomass the ostracods contributed most (29.8–54.7%), followed by nematodes (23.8–34.6%). Over 60% of the fauna occurred in the top 2 cm of the sediment and the faunal density reduced significantly with increasing depth in the sediment. The vertical distribution of meiofauna was positively correlated to the vertical distribution of Eh, chlorophyll a and interstitial water. Seasonality was greatly influenced by the south-west monsoon and the fauna quickly repopulated after the monsoon. Salinity, temperature and food influenced the faunal abundance.     

Non-Linear Interactions Determine the Impact of Sea-Level Rise on Estuarine Benthic Biodiversity and Ecosystem Processes

Sea-level rise induced by climate change may have significant impacts on the ecosystem functions and ecosystem services provided by intertidal sediment ecosystems. Accelerated sea-level rise is expected to lead to steeper beach slopes, coarser particle sizes and increased wave exposure, with consequent impacts on intertidal ecosystems. We examined the relationships between abundance, biomass, and community metabolism of benthic fauna with beach slope, particle size and exposure, using samples across a range of conditions from three different locations in the UK, to determine the significance of sediment particle size beach slope and wave exposure in affecting benthic fauna and ecosystem function in different ecological contexts. Our results show that abundance, biomass and oxygen consumption of intertidal macrofauna and meiofauna are affected significantly by interactions among sediment particle size, beach slope and wave exposure. For macrofauna on less sloping beaches, the effect of these physical constraints is mediated by the local context, although for meiofauna and for macrofauna on intermediate and steeper beaches, the effects of physical constraints dominate. Steeper beach slopes, coarser particle sizes and increased wave exposure generally result in decreases in abundance, biomass and oxygen consumption, but these relationships are complex and non-linear. Sea-level rise is likely to lead to changes in ecosystem structure with generally negative impacts on ecosystem functions and ecosystem services. However, the impacts of sea-level rise will also be affected by local ecological context, especially for less sloping beaches.     

Intertidal meiofaunal biodiversity with respect to different algal habitats: a test using phytal ostracodes from Southern California

Rocky intertidal algae harbor a diverse invertebrate meiofauna of arthropods, nematodes and other invertebrates. Despite its ecological importance, relatively little is known about the diversity and composition of this important component of intertidal biodiversity. In this study, we quantified species composition, abundance and distribution of ostracodes, an important group of phytal meiofauna, at two different intertidal areas in southern California. In total, we recovered 22 ostracode species from three different orders (16 podocopids, five myodocopids and one platycopid), nearly a quarter of which could not be assigned to existing taxa. The abundance of ostracodes differed significantly among algal types, with structurally complex algae bearing many more ostracodes per gram of algae than simple forms (blade-like algae and the surfgrass Phyllospadix). Although most ostracode species were recovered from multiple kinds of algae, different algae harbored distinct assemblages that could be discriminated statistically on the basis of relative abundances of ostracode species. This segregation of the ostracode fauna according to algal species is evident even over very short spatial scales (<1 m). Finally, ostracode samples from turf-forming algae were more species rich than samples from other kinds of macroalgae. Since turf-forming algae are easily damaged by human trampling, this component of ostracode biodiversity may be particularly vulnerable to anthropogenic impacts on the intertidal habitat. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

The composition,structure, and distribution of benthic ostracod fauna (Ostracoda,Myodocopa) in Antarctic waters

The benthic fauna of ostracods of the order Myodocopida of Antarctic waters is characterized by high diversity, relative species abundance, and a complicated taxonomic and ecological structure, with a simplified biogeographical structure. This fauna, which is distinguished by a high level of endemicity, although at a low taxonomic rank, includes a great share of deep-sea and subtidal elements. Ostracod populations of High and Low-Antarctic subzones differ qualitatively and quantitatively. A distinct impoverishment of fauna is observed in the region of the Antarctic divergence compared to the more northern areas. The number of species increases with depth to reach its maximum in the lower subtidal zone and on the upper continental slope at depths of 200–500 m. The number of species decreases with increasing depth. Myodocopida have not been yet found in the Antarctic waters deeper than 5000 m.     

Microscopic species make the diversity: a checklist of marine flora and fauna around the Island of Sylt in the North Sea

Based on the past 150 years of research and ongoing time-series observations we give a comprehensive overview of marine species composition around the island of Sylt in the eastern North Sea. A total of 2758 species is listed according to the categories microplankton (591 species), zooplankton (137), nekton (118), benthic microflora (158), benthic macroflora (125), benthic micro-and meiofauna (1204), benthic macrofauna (509), birds and mammals (91), and neobiota (39). Plants account for a third of the species, most (85%) of them are microscopic Chromista. Among animals, 60% of the species are micro- and meiofauna though this faunal component is still insufficiently known. These figures are similar to records from the southern North Sea and therefore may by typical for temperate climate sedimentary coastal areas. A comparison with the total of marine species suggests that the small benthic fauna may be severely understudied over most of the world. Analysis of global change depends on sound baseline data and species inventories like this can assist in the detection of biodiversity changes. They emphasise rare species and the full range of local habitats while time-series measurements usually rely on a few selected habitats and biotic components to generate a very general picture of the state of an ecosystem.     

Spatial variability in structural and functional aspects of macrofauna communities and their environmental parameters in the Jade Bay (Wadden Sea Lower Saxony, southern North Sea)

Spatial distribution and functional structure of intertidal benthic macrofauna in relation to environmental variables in the Jade Bay (southern North Sea) were studied and compared with other intertidal areas of the Wadden Sea. A total of 128 stations covering the whole Jade Bay were sampled in summer 2009. A total of 114 taxa were found. Highest species numbers occurred in the subtidal areas, whereas highest mean abundances were found in the upper intertidal areas. Based on species abundance data, six significantly distinct macrofauna communities in the Jade Bay were identified and evaluated with multivariate statistics, univariate correlations and canonical correspondence analysis. Differences in these community patterns were caused by the response of the dominant species (Hydrobia ulvae, Tubificoides benedii, Pygospio elegans, Caulleriella killariensis, Scoloplos armiger, Urothoe poseidonis, Microprotopus maculatus) to prevailing environmental conditions along the gradient from the lower and exposed sandy intertidal areas via intermediate mixed sediments to the upper mudflat areas. Distribution patterns in relation to tidal zonation were best explained by variability in submergence time, Chlorophyll a (chl a) content and sediment composition (mud content), which are proxies for hydrodynamic conditions and food availability. Species inventory and species richness were comparable with other intertidal areas of the Wadden Sea, but the Jade Bay differs from these areas regarding dominant species. Differences in sediment composition and morphological characteristics (macrotidal versus mesotidal Wadden Sea areas) are discussed for comparison of regional differences.     

Historical changes in the benthos of the Wadden Sea around the island of Sylt in the North Sea

The situation regarding the distribution and abundance of seagrass, macroalgae and benthic fauna near the island of Sylt in the south-eastern North Sea during the period 1923 to 1940 is compared with that of the 1980s. Evidence of organic enrichment in recent times is provided by (1) massive growth of green algal mats on sheltered tidal flats, (2) a decline of red algae in the subtidal zone, (3) an expansion of mussel beds along low water line and down to 20 m depth, (4) increased abundance of polychaetes inhabiting intertidal and subtidal sandy bottoms. Seagrass beds have undergone complex changes which remain unexplained. Intensified erosion has contributed to the loss of habitats in the intertidal zone, and probably affected sessile epifauna in the deep channels. Here, direct removal and disturbance by the bottom-trawling fishery may also have contributed to the observed species impoverishment. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988)     

Linking Intertidal and Subtidal Food Webs: Consumer-Mediated Transport of Intertidal Benthic Microalgal Carbon

We examined stable carbon and nitrogen isotope ratios for a large variety of consumers in intertidal and subtidal habitats, and their potential primary food sources [i.e., microphytobenthos (MPB), phytoplankton, and Phragmites australis] in a coastal bay system, Yeoja Bay of Korea, to test the hypothesis that the transfer of intertidal MPB-derived organic carbon to the subtidal food web can be mediated by motile consumers. Compared to a narrow δ¹³C range (−18 to −16‰) of offshore consumers, a broad δ¹³C range (−18 to −12‰) of both intertidal and subtidal consumers indicated that ¹³C-enriched sources of organic matter are an important trophic source to coastal consumers. In the intertidal areas, δ¹³C of most consumers overlapped with or was ¹³C-enriched relative to MPB. Despite the scarcity of MPB in the subtidal, highly motile consumers in subtidal habitat had nearly identical δ¹³C range with many intertidal foragers (including crustaceans and fish), overlapping with the range of MPB. In contrast, δ¹³C values of many sedentary benthic invertebrates in the subtidal areas were similar to those of offshore consumers and more ¹³C-depleted than motile foragers, indicating high dependence on phytoplankton-derived carbon. The isotopic mixing model calculation confirms that the majority of motile consumers and also some of subtidal sedentary ones depend on intertidal MPB for more than a half of their tissue carbon. Finally, although further quantitative estimates are needed, these results suggest that direct foraging by motile consumers on intertidal areas, and thereby biological transport of MPB-derived organic carbon to the subtidal areas, may provide important trophic connection between intertidal production and the nearshore shallow subtidal food webs.     

Shallow benthic fauna communities of South Georgia Island

Benthic communities in several fjords and sheltered bays of the north coast of South Georgia Island were examined using SCUBA and shore sampling in November 2004. It is one of the most northerly islands within the Polar Front and its well studied, terrestrial biota is described as sub Antarctic. The intertidal and subtidal zones and their fauna are, by comparison, little known. We describe the composition of the substratum and benthic communities of sites in several northern bays, including an exceptional community in the extremely sheltered Moraine Fjord with a 2 m sill at its entrance. In this, like those in some other fjordic systems, some taxa occur shallower than elsewhere, and in this instance, get large and are probably old. Elsewhere, we found the coastal fauna was fairly similar to Antarctic shallow communities in the southern Scotia Arc and Peninsula region. Of the taxa we found, we identified 53 to genus and 41 to species. Most of these were typical Antarctic shallow benthic taxa. Certain flatworms, nemerteans, bivalve and gastropod molluscs, amphipod and isopod crustaceans, asteroid echinoderms and stalked ascidians were very abundant, but some normally common Antarctic higher taxa and species were notably absent or rare.     

Spatial and temporal distribution patterns of the macrozoobenthos assemblage in the salt marshes of Tejo estuary (Portugal)

The present study focuses on the spatial and temporal distribution of the macroinvertebrate community of the salt marsh areas of the Tejo estuary, based on surveys conducted from autumn 1998 to summer 2000. Samples were collected quarterly in five different intertidal areas along an elevation gradient in: mudflats, creek mouths, creeks, pioneer salt marsh areas and middle marsh areas. A total of 36 benthic invertebrate taxa were identified. Insect larvae were the most well represented group, with 10 taxa identified. Oligochaetes and ostracods were the most numerically abundant taxa, whereas bivalves dominated in biomass. Benthic macroinvertebrate assemblages were dominated, both in number and biomass, by deposit feeders. Three distinct macroinvertebrate assemblages were distinguished along the elevation gradient, based on species presence, density and biomass: the unvegetated muddy areas with a macrobenthic assemblage composed mostly by infauna; the salt marsh pioneer areas of Spartina maritima in which several epibenthic taxa were found, as well as endobenthic taxa characteristic of muddy sediment; and the creek margins, with epifauna taxa such as insect larvae and crustaceans and a low abundance of benthic infauna. Total biomass in the unvegetated and Spartina areas was higher during spring and summer mainly due to the increase in biomass of Scrobicularia plana and Hydrobia ulvae. No decreases in the salt marsh macroinvertebrate biomass values were observed during the highest densities of their potential nektonic predators (summer). This fact might indicate that macroinvertebrates are not a limiting resource for the nektonic species, and that the natural biomass increment of these invertebrate species could be masking the predation/disturbance caused by the nektonic species.     

Subtidal populations of the blue mussel <Emphasis Type="Italic">Mytilus edulis</Emphasis> as key determinants of waterfowl flocks in the southeastern Barents Sea

Ornithological surveys conducted over the Pechora Sea (the southeastern part of the Barents Sea) in the 1990 s revealed huge non-nesting flocks of marine ducks, the largest in the European North. Especially dense waterfowl aggregations are constantly observed at the shallows near Dolgij Island during molting period and migration to wintering places. All the marine ducks flocking there are specialized benthos feeders predominantly consuming mussels Mytilus edulis. At the same time, numerous previous benthic studies in the Pechora Sea did not reveal mussels near Dolgij Island where benthic biomass was somewhat lower than in the adjacent areas (Denisenko in Mar Ecol Prog Ser 258:109–123. 2003) which left the food source for these abundant bird flocks enigmatic. In the course of an expedition in summer 2007 we found subtidal populations of M. edulis in shallows to the southwest of Dolgij Island. These populations were confined to a coastal zone and were characterized by a highly disjunct distribution with the biomass reaching up to 4 kg m⁻². We describe these subtidal populations as well as an intertidal mussel population on the western shore of Dolgij Island.     

九龙江口底栖生物生态研究

本文研究了九龙江口底栖生物种类组成、数量分布、季节变化及其与环境因子的关系等生态特点。结果表明,九龙江口底栖生物种类丰富(计440种)。其分布具有三种生态类型:河口种、海水种和近岸广盐种。平均总生物量为56.17克/米~2,平均栖息密度为358个/米~2。底栖生物与环境因子的关系密切:河口区底栖生物种群和数量的分布趋势是随着盐度的增高而增多;局部区域的水动力特点以及不同的沉积物类型也影响底栖生物种类和数量的分布。     

Composition,distribution and biomass of meiobenthos in the Oosterschelde estuary (SW Netherlands)

Meiofauna composition, abundance, biomass, distribution and diversity were investigated for 31 stations in summer. The sampling covered the whole Oosterschelde and comparisons between the subtidal — intertidal and between the western-central — eastern compartment were made.Meiofauna had a community density ranging between 200 and 17 500 ind 10 cm^–2, corresponding to a dry weight of 0.2 and 8.4 gm^–2. Abundance ranged between 130 and 17 200 ind 10 cm^–2 for nematodes and between 10 and 1600 ind 10 cm^–2 for copepods. Dry weight biomass of these taxa was between 0.5–7.0 gm^–2 and 0.008–0.3 gm^–2 for nematodes and copepods respectively.The meiofauna was strongly dominated by the nematodes (36–99%), who's abundance, biomass and diversity were significantly higher intertidally than subtidally and significantly higher in the eastern part than in the western part. High numbers were positively correlated with the percentage silt and negatively with the median grain size of the sand fraction. The abundance and diversity of the copepods were highest in the subtidal, but their biomass showed an inverse trend being highest on the tidal flats.The taxa diversity of the meiofauna community and species diversity of both the nematodes and the copepods were higher in subtidal stations than on tidal flats. In the subtidal, the meiofauna and copepod diversity decreased from west to east, whereas nematode diversity increased.The vertical profile clearly reflected the sediment characteristics and could be explained by local hydrodynamic conditions.Seasonal variation was pronounced for the different taxa with peak abundance in spring, summer or autumn and minimum abundance in winter.Changes in tidal amplitude and current velocity enhanced by the storm-surge barrier will alter the meiofauna community structure. As a result meiofauna will become more important in terms of density and biomass, mainly due to increasing numbers of nematodes, increasing bioturbation, nutrient mineralisation and sustaining bacterial growth. A general decrease in meiofauna diversity is predicted. The number of copepods is expected to decrease and interstitial species will be replaced by epibenthic species, the latter being more important in terms of biomass and as food for the epibenthic macrofauna and fishes.