Environmental stability and seasonality of a harpacticoid copepod community

The southwest monsoon on the west coast of India brings about dynamic changes in estuaries and coastal waters. The response of the meiofauna to monsoonal rain is obvious, but the impact of such environmental changes on the community structure of harpacticoid copepod species and their seasonality in the estuaries influenced by the tropical monsoon is poorly understood. In this study the spatial and temporal variability in abundance and community structure of meiobenthic copepods was investigated over an annual cycle (June 1983 to June 1984), in an estuary influenced by the tropical monsoon. Total meiofaunal abundance showed wide variations in space and time. Minimum and maximum densities were observed in the monsoon and pre-monsoon seasons, respectively. Quick recovery of harpacticoid populations in the early post-monsoon season indicated their recuperative power under adverse conditions. Of the 25 species recorded from lower, middle and upper reaches, eight comprised over 70% of the total copepod population. The peak and low occurrence of dominant species displayed striking correlations with the summer and rainy seasons, respectively. While other species were restricted in distribution, Stenhelia longifurca was recorded from all salinity regimes. The harpacticoid community was greatly influenced by the onset of the monsoon period, and their spatial and temporal variabilities were related with physico-chemical parameters and the variability of these parameters in the estuary.     

Patterns of micro- and meiofaunal abundance in marine sediments,measured with the adenosine triphosphate assay

Adenosine triphosphate (ATP) measurements are used to determine vertical and seasonal distributions of microorganisms and meiofauna in sediments from a 14 m-deep mud bottom in central Long Island Sound on 12 sampling dates from April 1975 to October 1976. Below the topmost 1 cm of sediment, ATP measurements can be useful in estimating and comparing standing stocks of microorganisms and meiofauna. In the top 1 cm, however, large quantities of newly settled bivalves (Yoldia limatula, Nucula annulata, and Mulinia lateralis) and juvenile polychaetes (Owenia fusiformis) in summer and fall months account for total ATP concentrations. The ATP content of individual meiofauna ranges from 1.97 ng individual copepod nauplius^-1 to 190.7±60 ng individual M. lateralis ^-1. In general, the total ATP content of individual polychaetes and bivalves is much higher than that of individuals of other groups. However, on a mg ATP per g wet or dry tissue basis, the ATP content of micro- and meiofaunal taxa are not significantly different. In addition to providing a means for comparing micro- and meiofaunal standing stocks, ATP measurements permit examination of the relative contribution of different meiofauna to the total living biomass of meiofauna in sediments. Total sediment ATP concentrations are greatest in the top 1 cm at all seasons, and decrease with increasing depth in the sediment. Annual concentrations in the topmost centimeter average 4.22 g g dry sediment^-1 and range seasonally from 1.09 to 7.64 g g dry sediment^-1. At a depth of 10 cm, values average 0.16 and range from 0.019 to 0.35 g g dry sediment^-1. High ATP concentrations in surface sediment reflect high concentrations of microorganisms and meiofauna at the sediment-water interface. The top 2 cm of sediment contain 71% of all meiofauna, with 41% occurring in the topmost cm. In general, densities are lowest in the winter and highest during the spring and summer, averaging 490 individuals 10 cm^-2, and varying from 87 to 1366 individuals 10 cm^-2. Because of wide variation in recruitment patterns of the benthos in Long Island Sound, the extremes of the range in meiofaunal densities can be observed in the same month in two different years. In order to monitor and compare standing stocks of organisms less than 1 mm in size in sediments, the ATP assay can save hours of processing time compared with alternate methods such as direct counts.     

Impact of heavy metals of industrial plant wastewater on benthic communities of Bizerte Lagoon (Tunisia)

ABSTRACT

The aim of this study was to assess the consequences of human impact on the characteristics of sediments heavy metal concentration, grain size and its influence on the structure of the microbial and meiofaunal community assemblages. A survey was carried out in July 2013 within six sites located in the Bizerte Lagoon (Tunisia), both downstream and upstream of industrial effluents. The highest total sediment metal concentrations were detected in stations located close to the industrial sewage discharge points. In these stations, the lowest densities of the total meiofauna (33?±?13?ind/10?cm^?2) and conversely the highest densities of cultivable bacteria that are heavy metal resistant have been reported (16?±?80.34?CFU?g^?1). Univariate (ANOVA) and multivariate (MDS/CCA) analyses demonstrate high dissimilarity (0.06) in meiofaunal and bacterial community structures between downstream and upstream industrial sewages. Furthermore, canonical correspondence analysis CCA results indicated that heavy metal sediment contamination promoted bacteria that are resistant to heavy metals, while heterotrophic bacteria supported the development of meiofauna taxa. The results highlight the importance of bacteria/meiofauna interactions, as both meiofaunal and microbial communities give indications of the ecological impact of heavy metal contamination in sediment.     

Distribution quantitative de la méiofaune dans l'aire d'épandage de l'égout de Marseille

A quantitative analysis of meiofauna was carried out at ten sample stations distributed along a transect off Marseilles' (France) sewage outfall in November, 1981. The meiofauna was counted and average and total biomass of nematodes and copepods were calculated for each station. Comparison of data between stations or groups of stations was made using statistical tests. The results revealed three sectors in which effects of pollution on meiofauna differed: (1) A heavily polluted coastal zone (at a distance of 30 to 150 m from the outfall), relatively poor in meiofauna, which, however, was not completely absent-as were macrobenthic organisms; the meiofauna was composed mainly of nematodes and copepods, but acarians and naupliar larvae (probably copepods) were also numerous; the copepods were uncommonly large in size, and alone consituted most of the total benthic biomass in this zone. (2) An intermediate zone (400 to 1 150 m away from the coast), also polluted and much richer in meiofauna than the coastal zone; the meiofauna groups were more diversified, annelids (mainly polychaetes) increasing in number, while acarians became scarce and copepods decreased in size; at 400 m away from the outfall, where the sediment is strongly polluted, the nematode population consisted of large individuals which contributed greatly to the biomass; at 400 and 800 m, the distribution of both meiofauna and macrobenthos was heterogeneous; at 1 150 m away from the outfall, maximal meiofaunal densities were recorded, due primarily to an increase in nematode numbers; here, unlike all the stations nearer to the coast, total nematode biomass was greater than copepod biomass. (3) An off-shore zone (1.8 to 4 km distant from the coast), slightly polluted, where meiofauna densities were reduced and individuals decreased in size with increasing depth. Generally, an enrichment in the meiofauna was evident from the coastal to the intermediate zone. Enrichments induced by urban pollution have been recorded previously, but not, as in the present study, at a distance of 1 km away from the outfall, succeeding to a highly impoverished coastal zone. Thus, by supplying organic matter and nutrients, Marseilles' sewage can enrich sediments, but only to a certain distance away from the outfall, where the deleterious effects of pollutants are attenuated.     

A meiofaunal “thiobios” limited to the anaerobic sulfide system of marine sand does not exist

The spatial relationship of interstitial metazoans to sources of oxygen has been studied on a tidal flat in the Wadden Sea near Sylt (eastern part of the North Sea). Consistently, meiofauna remains in close proximity to oxygenated layers or pocket areas within the sediment. This is exemplified by the pattern of meiofaunal abundance and species composition alongside oxic burrows of the lugworm Arenicola marina L. A specific meiofauna confined to oxygen-deficient horizons of the sediment does not exist.     

The relative significance of bacteria,meio- and macrofauna on an exposed sandy beach

A survey of the intertidal biota of a sandy beach on the west coast of South Africa has shown standing stocks of macrofauna, meiofauna and bacteria of 241.23, 200.17 and 663.07 g dry wt m^-1 of shoreline respectively, an approximate biomass ratio of 1:1:3. The distribution of the macrofauna was the reverse of the usual pattern, with highest biomass occurring at the level of the current driftline. This appears to be related directly to the ready availability of food in the form of drift algae. Peak meiofaunal numbers were also found below the driftline and it is proposed that meiofaunal distribution is governed by dissolved organic matter (DOM) levels in the interstitial environment. Bacteria were abundant up to 1.2 m below the sediment surface, with the highest concentrations occurring at low tidal levels. The significance of the various biotic components in the energetics of the sandy intertidal is discussed. Turnover estimates suggest that bacteria may account for about 87% of annual production, with meiofauna and macrofauna making up 10 and 3% respectively. Despite this overwhelming importance of bacteria, the macro-and meiofauna probably play a vital role in making small organic particles available to bacteria for mineralization and in optimising conditions for microbial growth.     

Vertical profiles of bacterial abundance,productivity and growth rates in coastal sediments of the central Great Barrier Reef lagoon

Vertical patterns of bacterial densities, productivity and specific growth rates in coastal muds, quartz sands and muddy sands of the central Great Barrier Reef lagoon were examined in summer (February) and autumn (May) 1988. Variations in these parameters with station location, sediment depth and season were complex, exhibiting significant main and interaction effects in most instances. Some trends were apparent despite the large and complex variations. Bacterial densities did not vary seasonally, ranging from 2.9 to 38.1×10⁹ cells g^-1 dry wt, averaged over sediment depth (0 to 20 cm) and seasons. Trend analysis revealed that densities decreased with increasing sediment depth. Bacterial production (tritiated thymidine incorporation into DNA) was high, ranging from 0.4 to 5.7 gCm^-2 d^-1 (integrated over 10 cm depth), as were specific growth rates (grand mean, =0.25 d^-1; range=0.004 to 1.3 d^-1). Both were generally higher in summer than in autumn. Vertical profiles of productivity and specific growth rates revealed actively growing bacterial assemblages down to 20 cm depth. Factors which may account for these very abundant and productive communities are: (1) subsurface accumulations of detritus exported from adjacent mangrove forests, and (2) physical disturbance from tidal scouring and severe climate (e.g. cyclones, wet-season floods). Disturbance events occur frequently enough to inhibit the development of highly sulphidic conditions, but stimulate production of bacterial types (aerobes, fermenters) capable of incorporating labelled thymidine into their DNA.     

Predation on meiofaunal and macrofaunal invertebrates by western sandpipers (Calidris mauri): evidence for dual foraging modes

Western sandpiper (Calidris mauri) predation was examined by concurrent experiments and direct observations of foraging behaviour on high intertidal mudflats of the Fraser River estuary, British Columbia. Western sandpipers foraged by either “pecking” on the surface (64% of observational time) or probing into sediment (29%). The first experiment (probe-mark method) consisted of collecting small-volume cores (21.2 cm³) of probed (experimental) and non-probed (control) sediment on the tidal flat, following a 22.5-min feeding period. The second experiment (exclosure method) involved deploying exclosures immediately prior to the feeding period and subsequent collection of cores from inside (control) and outside (experimental) the exclosures. Sediment cores were analysed for both macrofaunal and meiofaunal size fractions. Comparisons between macro- and meiofaunal invertebrate densities in experimental and control sediments revealed significant differences, attributed to shorebird predation, for both experiments. The probe-mark experiment detected the removal of large infaunal polychaetes (∼ 20 mm), while the exclosure experiment showed depletion of epifaunal harpacticoid copepods (0.063–0.5 mm). Predation on macrofaunal cumaceans was detected in both experiments. Invertebrates selected by western sandpipers neither fell within traditional infaunal size classifications (macro- vs. meiofauna; 500 μm delineation) nor corresponded to the highest densities of taxa. Rather, inference from experimental results and observations is that western sandpipers forage in two modes, by: (1) surface gleaning of epibenthic copepods and cumaceans in the macro- and meiofaunal size ranges and (2) selective probing for larger infauna, such as polychaetes. These findings were facilitated by the combination of methodologies employed. Received: 29 December 1999 / Accepted: 11 September 2000     

A field colonization experiment with meiofauna and seagrass mimics: effect of time,distance and leaf surface area

From a conservation point of view, it is essential to know how fast an ecosystem can recover after physical disturbance. Meiofauna and especially harpacticoid copepods are abundant in seagrass beds and are therefore useful to study ecosystem recovery after disturbance. In the western Caribbean coast, a fragmented Thalassia testudinum seagrass bed was selected to conduct a colonization field experiment by means of plastic seagrass mimics. Meiofauna colonization, with special emphasis on harpacticoid copepods, was followed in relation to: (1) colonization time (2, 4, 6, 10, 14 and 21 days); (2) distance to source of colonizers (close and far series) and (3) leaf surface area to colonize (small, medium, large). Colonization was recorded after 2 days with average meiofauna densities of 480 ind/100 cm² (close) and 1350 ind/100 cm² (far) of leaf surface area, while on average 400 ind/100 cm² were collected from the natural seagrass plants. In this early phase, the meiofauna diversity was high, with on average 8 taxa. A longer period of colonization (21 days) showed an increased meiofaunal density and diversity (average density: 3220 ind/100 cm², 13 taxa). Increasing meiofauna colonization with time is probably related to the development of a biofilm making the leaf more attractive for meiofauna. The effect of distance was not so pronounced as that of time. Total absolute densities were highest in the far series (5 m away from natural seagrass patch), mainly because of nematode densities. Meiofauna diversity was lower in the far series than in the close series (at the border of the natural seagrass patch). A larger individual leaf surface area did not affect the overall meiofauna densities but had a significant positive effect on copepod densities. Larger surface areas promoted the presence of epiphytic copepod families such as Tegastidae and Dactylopusiidae. Overall, we found a rapid recovery of meiofauna in fragmented seagrass beds with primary colonizers (both nematodes and benthic opportunistic copepods) originating from the sediment and later colonizers as epiphytic copepods and their nauplii from the local seagrass regeneration pool.     

Investigations on epibenthic meiofauna I. Abundances on and repopulation of the tube-caps of Diopatra cuprea (Polychaeta: Onuphidae) in a subtropical system

Cryptic meiofauna populated the imbricate, shell-sediment matrix of the tube-caps produced by the polychaete Diopatra cuprea (Bose) in Tampa Bay, Florida, USA. Nematodes, copepods (adults and nauplii), polychaetes (adults and juveniles) and amphipods (adults and juveniles) were the most abundant taxa found on tube-caps. Meiofaunal densities on tube-caps were 4 to 19 times higher than equivalent volumes of sediment in cores taken adjacent to D. cuprea tubes. Recruitment onto tube structure occurred within 1 to 2 d after defaunated tube-caps were replanted into sediments in the field (February–November 1980). Repopulation of copepods (adults and nauplii) attained levels equal to or exceeding natural abundances on tube caps within 1 to 5 d; nematode recovery rates were inconsistent. Short-term experiments using a variety of defaunated tube treatments indicated that immigration onto above-sediment tube-caps proceeds via both water column and sediment pathways. Based on data on tube-cap longevity and construction as well as meiofaunal recruitment rates, we conclude that the generation of new tube-cap structure is exploited rapidly by meiofauna.     

Features of spatial distribution of benthic infauna in a Mediterranean shallow-water bay

The unique hydrography of the Western Mediterranean Sea does not favour the formation of typical estuaries, although it does favour that of other land-sea systems. However, in Els Alfacs, a shallow-water bay situated in the Ebre Delta (northeast Spain), where there are considerable continental inputs, the distribution patterns of the macrofauna and the meiofauna reflect a hydrographical regime very similar to that of an estuary. During July 1987, 23 stations were sampled in the Alfacs Bay using plastic cores. The distribution pattern of the meiofauna follows a gradient and presents a less marked zonation than the macrofauna. Nevertheless, in both cases the peak densities of both faunal components are spatially separated from the principal site of freshwater inflow. The average density of the macrofauna (10 430 individuals/m²) and the meiofauna (704 100 individuals/m²) occurs in the bay during the period of maximum flow (spring-summer), and as such this bay is one of the most productive areas of the Western Mediterranean.     

Physical factors controlling abundance of meiofauna on tidal and atidal beaches

Quantitative samples of interstitial sand beach meiofauna were collected from Morocco along the North African coast (Algeria and Tunisia) and northwards to Lebanon, Turkey and Cyprus. Data on the sediment median diameter, sorting coefficient and beach temperature were used to construct multiple-regression equations relating these factors to the total meiofaunal numbers. Curvilinear regression was found to give a significantly better fit than linear regression in all cases but one. Treating the whole Mediterranean data, the equation explained 9.3% of the variance in meiofaunal abundance. Within narrower geographical areas, however, the equations explained significantly more of the variance: 56.70% of Moroccan tidal beach data, 75.60% of South Tunisian tidal beach data, and 62.3% of South Tunisian atidal beach data. For the tidal beach equations sorting was the most important factor, followed by temperature and median diameter. It is suggested that the factors controlling meiofaunal abundance on these beaches are likely to be wave, tide and current action which also control sorting. The lack of fit of most atidal beach data suggests that here biological interactions such as competition and predation may control meiofaunal abundance. The detection of beaches affected by pollutants may also be possible using regression techniques. Beaches having a significantly enriched population (sewage-induced) or depleted population (pollutant-induced) can be readily detected.     

Effect of monsoonal climate on sulfate reduction in coastal sediments of the central Great Barrier Reef lagoon

Rates of sulfate reduction were measured during the spring dry and summer wet seasons of 1992 in shallow coastal sediments of the central Great Barrier Reef lagoon. In the dry season, sulfate reduction rates, integrated to 18–20 cm depth, ranged from 23.8 to 30.8 mmol S m^-2 d^-1. In the wet season, heavy monsoonal rains and wind-induced waves caused severe disturbance of sediments leading to less anoxic conditions, and to a 2- to 3-fold decline in rates of sulfate reduction (10.2 to 12.8 mmol S m^-2 d^-1). The percentage of reduced ³⁵S recovered as acid-volatile sulfide (% AVS_red) ranged from 15.8 to 44.9% in spring, and was significantly reduced at each station in summer (range 14.5 to 31.4%). An analysis of variance indicated that seasonality accounted for 31.5% of the total variance in total rates of sulfate reduction, with only 7.5% of the variance accounted for by depth into the sediment; there were no station differences. In both seasons, there were no clear patterns in the proportion of radiolabel incorporated into the AVS and chromium-reducible sulfur (CRS) pools with depth into the sediment. These results are contrary to the seasonal patterns and pathways of sulfate reduction in temperate coastal sediments.     

Meiofauna on the seagrass Thalassia testudinum: population characteristics of harpacticoid copepods and associations with algal epiphytes

The composition and abundance of bladedwelling meiofauna was determined over a 15 mo period (1983–1984) from a Thalassia testudinum Banks ex König meadow near Egmont Key, Florida, USA. Harpacticoid copepods, copepod nauplii, and nematodes were the most abundant meiofaunal taxa on T. testudinum blades. Temporal patterns in species composition and population life-history stages were determined for harpacticoid copepods, the numerically predominant taxon. Sixteen species or species complexes of harpacticoid copepods were identified. Harpacticus sp., the most abundant harpacticoid, comprised 47.8% of the total copepods collected, and was present throughout the study. Copepodites dominated the population structures of the blade-dwelling harpacticoid species on most collection dates. Ovigerous females and/or copepodites were always present, indicating continuous reproductive activity. Results suggest that epiphytic algae influence meiofaunal abundance on seagrass blades, as densities of most meiofaunal taxa at Egmont Key were positively associated with percent cover of epiphytic algae throughout the study. The majority of significant correlations between meiofaunal density and cover of epiphytic algae involved filamentous algae, although encrusting algae dominated the epiphytic community. It appears that resources provided by epiphytic algae to seagrass meiofauna (additional food, habitat, and/or shelter from predation) may be associated with algal morphology.     

Shifting abundance of the ctenophore Mnemiopsis leidyi and the implications for larval bivalve mortality

Along the mid-Atlantic coast of the US, the ctenophore Mnemiopsis leidyi (Agassiz) appears to be increasing in abundance and undergoing shifts in its historical seasonal distribution. We provide new data on shifting ctenophore abundance in Long Island estuaries and its implications for top-down control of the plankton community. Peak mean biovolume estimates of M. leidyi in Long Island estuaries in 2006 revealed ctenophore abundance values that were a factor of two to five times greater than previous studies conducted two decades ago. Furthermore, peak M. leidyi densities in 2006 occurred 2–3 months earlier than previously documented, suggesting a shift in the seasonal maxima of M. leidyi. Application of daily ingestion rates to zooplankton abundance indicates that, at its highest densities M. leidyi can remove an overall average of 20–89% per day of bivalve veligers and other zooplankton taxa, including adult copepods, nauplii, and tintinnids. Increasing ctenophore abundance, especially during a period when they were not historically abundant (i.e., June) may have significant consequences for species which spawn at this time. For example, current populations of M. leidyi represent a major source of larval mortality for bivalves which may inhibit recovery of shellfish populations and reinforce their low abundance state in Long Island estuaries.     

A comparison of macrofaunal and meiofaunal distribution and standing stock across a rocky shore,with an estimate of their productivities

In 1984 and 1985 algal, macrofaunal and meiofaunal standing stocks were estimated on a exposed rocky shore along the west coast of False Bay, South Africa, using comparable, area-based sampling techniques. The shore supported a rich growth of algae, particularly in summer, when a maximum standing crop of 403 g m^-2 was recorded in the low shore. In winter, the largest component of macrofaunal biomass comprised the filter-feeding barnacle Tetraclita serrata, which attained 75 g m^-2 in the middle balanoid; but as a result of late recruitment and high mortality of this species, the summer shore was dominated by herbivorous gastropods, particularly Patella cochlear, which attained a maximum biomass of 66 g m^-2 on the low shore. Meiofaunal numbers and biomass were closely correlated to the distribution of algal turfs and associated trapped sediments. Numerically, the most important components of the meiofauna were nematodes and copepods, while the biomass was more evenly shared among foraminifera, minute gastropods, copepods and insect larvae. Numbers and biomass peaked in the lower balanoid during winter (1.9×10⁶ individuals, or 8.5 g m^-2). Macrofauna:meiofauna numbers and biomass ratios are presented for each zone and the distribution patterns discussed in relation to the conditons in each. Numerically, meiofauna exceed macrofauna by an overall ratio of 1:391, with values ranging from 1:556 in the lower balanoid to 1:18 in the Littorina zone. Macrofaunal biomass exceeds that of meiofauna in all zones by an overall ratio of 10:1, but values range from 2.1:1 in the upper balanoid to 48:1 in the middle balanoid. By incorporating turnover ratios extrapolated from the literature, mean annual productivity ratios have been calculated. These indicate that macrofauna account for 75% of total secondary production and meiofauna for 25%. Failure to incorporate meiofauna in analyses of energy flow on rocky shore ecosystems would thus lead to considerable errors. The possible trophic role of meiofauna in such systems is discussed.     

Fiddler crab burrowing affects growth and production of the white mangrove (<Emphasis Type="Italic">Laguncularia racemosa</Emphasis>) in a restored Florida coastal marsh

Positive plant–animal interactions are important in community ecology, but relatively little attention has been paid to their effect on the production of mangroves, dominant halophytic trees in tropical coastal marshes. Here, the role of fiddler crab (Uca spp.) burrowing on the growth and production of the white mangrove, Laguncularia racemosa (<2 years old), was examined in a restored marsh in Tampa Bay, Florida (27°41.65 N, 82°30.34 W) with manipulative experiments from June 2006 to May 2007. Fiddler crab burrowing significantly increased mangrove height by 27%, trunk diameter by 25%, and leaf production by 15%, compared to mangroves in crab exclusion enclosures. Additionally, the exclusion of fiddler crabs significantly increased interstitial water salinity from 32.4 to 44.2, and decreased the oxidation–reduction potential of the low organic sediments, but did not affect soil pH or sulfide concentration. Mangrove height, trunk diameter, and leaf production along a transect that varied in crab burrow density were positively associated with the number of crab burrows. Further, the density of sympatric Spartina alterniflora shoots was positively correlated with crab burrow density along the transect. As in temperate marshes, fiddler crabs can have significant ecological effects on mangrove communities, serving as ecological engineers by modulating the amount of resources available to marsh plants, and by altering the physical, chemical, and biological state of these soft sediment communities. In restored coastal systems that typically have very poor sediment quality, techniques such as soil amendment could be used to facilitate a more natural interaction between crabs and mangroves in ecosystem development.     

Contribution à l'étude écologique de quelques zoanthaires tempérés et tropicaux

Within the framework of an ecological investigation on zoanthids, 3 genera and 6 species have been studied from the vicinity of Marseilles, and 5 genera including 11 species analysed from near Tulear, southwest coast of Madagascar. The tropical forms are mainly distributed throughout the intertidal zone. These zoanthids require vigorously moving waters and a high level of salinity. Sensibility to pollution differs according to species. Distribution is based upon the degree of dampness and upon the nature of the bottom. In intertidal zoanthids, the degree of desicoation determines the vertical zonation of species occurring on the reef. Light is an important distributional factor in species which are mostly submerged, especially when they are associated with symbiotic algal cells. Another major factor is the composition of the sediment, although this is less important for the tropical species studied (except for Isaurus spongiosus Andre, 1877). A model is proposed for comparison of species in terms of sensibility to environmental factors. In temperate areas, zoanthids appear to be “mixticoles”, but the formation of the incrustation present in many zoanthids is not connected with the composition of the substrate. From an ethological point of view, temperate zoanthids differ from tropical species. The differences manifest themselves in morphological features and in behaviour. Since the macrocnemic zoanthids mainly dwell in temperate waters and brachycnemic zoanthids in tropical waters, it may be possible to extend these differences to macrocnemic and brachycnemic groups.     

Distribution patterns of meiofauna associated with a sublittoral<Emphasis Type="Italic"> Laminaria</Emphasis> bed in the Cantabrian Sea (north-eastern Atlantic)

This study deals with meiofauna associated with a sublittoral population of the kelp Laminaria ochroleuca located on the northern coast of Spain. By sampling once a year over a 4-year period, we examined patterns of faunal distribution as a function of some environmental factors at the meso-scale level (depth, and exposure to waves and surge). We also examined the relationship between L. ochroleuca abundance (as dry weight biomass and number of plants per sampling quadrat) and abundance and diversity of meiofauna. Finally, we investigated patterns of within-plant distribution (algal frond vs. algal holdfast), using also the meiofauna of the adjacent bottom as a referent to estimate the level of "phytal dependence" of the meiofauna collected on L. ochroleuca. We found that the bulk of permanent meiofauna consisted of nematodes, copepods, mites, polychaetes, tanaids and ostracods, with copepods being predominant on the fronds of the alga and nematodes in the holdfasts. The temporary meiofauna consisted of juvenile amphipods, bivalves and gastropods, together with barnacle nauplii and cyprids. Abundance and major composition of meiofaunal taxa were unrelated to both depth and hydrodynamic exposure of the sampling quadrats. However, we detected significant qualitative and quantitative faunal differences as a function of microhabitat. All meiofaunal groups were more abundant in holdfast samples than in frond and bottom samples. The gross taxonomic composition of meiofauna in bottom samples was similar to that in holdfast samples, but substantially different from that of meiofauna associated with the fronds. The L. ochroleuca holdfasts, in which dense aggregations of meiofauna can occur, appear to function as ecotone between phytal and rocky-bottom microhabitats. All together, our results suggest that the distribution of meiofauna within the Laminaria bed is mostly affected by factors operating at the microhabitat level rather than the meso-scale level.Communicated by L. Hagerman, Helsingør