Size partitioning of microbial and meiobenthic biomass and respiration on Brown's Bank, south-west Nova Scotia

Biomass and respiration (oxygen consumption) of bacteria, microfauna, and meiofauna were measured in coarse sand sediment from Brown's Bank (172 m) off Nova Scotia, Canada. Community biomass, excluding macrofauna, had a median value of 35 mg C m⁻², dominated by bacteria (51%), microfauna (25%), and a minor meiofauna component (2·5%). Protozoan microfauna were mostly microflagellates (colourless cryptomonads). The experimental design allowed partitioning of benthic metabolism without using subtraction from whole community rates. Addition-removal experiments with fauna separated into size categories were used to construct a respiration-biomass regression for all taxa. Respiration rates for faunal groups were then calculated from their biomass in the natural sediment. Total microbial and meiofaunal community respiration had a median rate of 0·55 ml O₂ m⁻² h⁻¹ which was partitioned into median proportions of bacteria (50%) microflagellates (27%), and metazoan meiofauna (4%). Correlations among faunal biomass values from incubated vials of sediment suggested that bacteria were important prey for protozoans. With added biomass of meiofauna, protozoans also became a potentially important source of prey. The results demonstrated the significance of microflagellate protozoans in these sediments and their metabolic and trophic importance relative to meiofauna and even bacteria.     

Water filtration through reflective microtidal beaches and shallow sublittoral sands and its implications for an inshore ecosystem in Western Australia

Volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in Western Australia. The filtered volumes were large, 19 m³ m^?1 day^?1 and 73 m³ m^?1 day^?1 on two ‘clean’ beaches but only 0·4 m³ m^?1 per tidal cycle on a beach covered in kelp and seagrass wrack. The mean residence times of this water in the interstitial system and its percolation paths were both short, 1–7 h and 2–5 m respectively. Water input was greater across a beach cusp horn than across a cusp embayment. Most input occurred in the upper swash zone where the water table was less than 20 cm deep. Tidal variations in input volumes were evident even with tide ranges of only 20 cm. The inshore zone off these beaches filters on average 0·07 m³ m^?2 day^?1 at an average depth of 5·5 m under 0·4 m waves of 6·5 s duration. The importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore ‘lagoon ecosystem’ is estimated and discused.     

Tourism impacts on benthic communities of sandy beaches

This study evaluated the effect of human trampling on the benthic macrofauna of two beaches in Southeast Brazil with different levels of intensity of tourism, Grussaí (more impacted) and Manguinhos (less impacted), during periods of high and low tourism activity. The macrofauna of urbanized (U) and non‐urbanized (NU) sectors of the inter‐tidal zone was sampled and the number of visitors was recorded. General linear models revealed a decreasing in abundance of macrofauna species in the urbanized sectors of analyzed beaches, which are exposed to higher trampling impact than in non‐urbanized areas. At Manguinhos Beach, trampling did not affect the macrofauna (<1 visitors ? m^?²), except for the polychaete Scolelepis sp., which was less abundant in the U sector. Considering the benthic community, Atlantorchestoidea brasiliensis, Hemipodia californiensis and Scolelepis sp. were more sensitive to human trampling pressure and may be used as potential bioindicators of tourism impact. Management plans should consider mitigation of the effects of tourism, such as the control of the visitor number and their decentralization.     

The colonization of macroalgal wrack by the meiofauna in the Arctic intertidal

A litter bag experiment was performed on a wrack-loaded beach in Hornsund (southern Spitsbergen) to study the decay rate of stranded macroalgae and their colonization by meiofauna. The average monthly loss of macroalgal dry mass was 45 ± 5%. The composition of the wrack-associated fauna was similar to those reported from other world regions. Nematodes composed of bacterivorous rhabditids and monhysterids were the numerically dominant taxon (>99% of the community). High nematode densities averaging 35,000 ind. per litter bag (6,500 ind g⁻¹ dwt) indicate their skills for rapid colonization and successful exploitation of the short-lived habitat established on an Arctic beach. We suggest that stranded macroalgae may play a role as a potential hotspot for nematodes and microbial processes in the Arctic coastal ecosystem. It is also suggested that wrack position on the beach profile which resulted in different wrack-age and moisture content may affect the composition and diversity of the wrack-associated meiofauna.     

The distribution and behaviour of tar balls along the Israeli coast

A fortnightly sampling of tar balls on six beaches along the Israeli coastline between 14 April 1975 and 25 June 1976 showed that the mean content of tar during that period was 3625 g m^?1 of beach front. The northern and central parts of the coast were significantly more polluted than the southern part. Between July 1975 and February 1976 the mean tar quantity decreased continuously from 5635 to 1344 g m^?1.A comparison of tar quantities on the Israeli beaches with those of other beaches in the world showed that the Israeli beaches are more polluted than those of the west Atlantic coast, are as polluted as other beaches on the eastern coast of the Mediterranean Sea, and are less polluted than the beaches of Alexandria, Egypt, and Paphos, Cyprus. It is suggested that the tar content on the beach is related to the degree of oil pollution in the sea. The closer a beach is to an oil shipping lane or an oil dumping site, the heavier it is polluted.During storms, beach tar balls are pushed by the waves to the back of the beach or, in the case of a cliffed coast, are carried along the shore by the longshore current. When the tar balls reach a gap in the cliff (such as an estuary), they are carried inland by the storm waves. There the tar may become buried or dry, shrink and break into small particles which are then dispersed by the wind.     

Macrobenthic zonation patterns along a morphodynamical continuum of macrotidal,low tide bar/rip and ultra-dissipative sandy beaches

The species composition, densities, biomass and zonation patterns of the macrobenthos of sandy beaches are greatly influenced by the morphodynamics and morphology of the beaches. Macrobenthic zonation patterns along a small-scale morphodynamic gradient, comprising eight Belgian beach sites, were investigated. By taking into account the dimensionless fall velocity (Ω) and the relative tidal range, the beach sites were ordered along the gradient from the ultra-dissipative beach type (UD) to the low tide bar/rip beach type (LTBR). The resulting beach state index varied between 1.8 and 4.2 and the beach profiles were related with the beaches' morphodynamic state.In total 35 macrobenthic species, mainly polychaetes and crustaceans, were encountered, varying between 19 and 23 species per beach site. The species composition was quite similar among beach sites, with Scolelepis squamata being abundant at all eight sites. Furthermore, the macrobenthic distribution patterns were mainly related to elevation at all beach sites. Some remarkable difference in metrics, largely related to the beach morphodynamics and the consequent hydrodynamics, were found. At the hydrodynamically benign and consequently macrobenthos-rich UD beaches, the highest macrobenthic densities and biomass occurred on the upper beach, while at the hydrodynamically harsh and thus macrobenthos-poor LTBR beaches, the maximum densities and biomass occurred lower on the beach. Species, typically occurring on the upper UD beaches, such as Eurydice pulchra, S. squamata, and Bathyporeia sarsi, were restricted to the sub-optimal middle and lower beach zone at LTBR beaches. Only Bathyporeia pilosa was found on the upper beach of both UD and LTBR beaches. The more robust polychaete Ophelia rathkei and the interstitial polychaete Hesionides arenaria were exclusively found in the hydrodynamically harsh conditions of the middle LTBR beach zone.     

Intraspecific diet shift in Talitrus saltator inhabiting exposed sandy beaches

Talitrid amphipods are the most abundant herbivores on exposed sandy beaches. Despite their important role as trophic intermediates between macrophytes and higher levels (i.e. insect and bird) of beach food webs, very little information is available on their feeding patterns. The main aim of this study was to investigate intraspecific differences in the feeding behaviour of Talitrus saltator. We tested the hypotheses that: (1) adult females and males showed different isotope signatures and therefore relied on different sources of food; and (2) patterns of variation of isotope signatures of juveniles differed from those of adult specimens, evidencing a diet shift during the development. We used stable isotope signatures and tested for differences upon the level on the shore, times of the year and beaches experiencing similar morpho-dynamic and environmental conditions. Finally, we investigated the trophic significance of macrophyte detritus in the diet of males, females and juveniles. Results showed that adult males had a more variable diet than females and juveniles (inferred from δ¹³C and δ¹⁵N values). Dual-isotope graphs suggested that Sargassum muticum and Cystoseira baccata wrack could be among the main food sources for both juvenile and adult stage.     

Meiobenthic diversity in space and time: The case of harpacticoid copepods in two Mediterranean microtidal sandy beaches

Meiobenthic data from two microtidal sandy beaches of the eastern Mediterranean (Crete, Greece) were used to investigate patterns of both alpha and beta diversity in space and time. Copepod assemblages and environmental variables related to sediment characteristics, morphodynamics and food were studied over a year at four distinct habitats at each beach; the retention, resurgence and saturation zones of Salvat's intertidal scheme (midlittoral zone), and the surf zone of the sublittoral. Αlpha diversity analysis indicated similar species richness at both beaches when the whole 13-month data set was considered but was higher at the sheltered site when each sampling period was examined separately. Both beaches supported higher diversity in the sublittoral zone. Species richness increased seawards at the midlittoral zone of the sheltered site whereas, no pattern was evident at the exposed site, where the intense hydrodynamic conditions homogenized the sediments. Beta diversity increased markedly towards the sublittoral, indicating greater differences in alpha diversity between the sublittoral and the midlittoral zone. Species turnover was more variable at the exposed beach and at the most landward stations, where environmental conditions change often between extremes. A proportion of the variation in alpha diversity was explained by food availability at both beaches and additionally by grain size at the sheltered site. However, no environmental variable explained beta diversity patterns. Although the results of our study support the hypothesis of Multicausal Environmental Severity proposed for sandy beach macrofauna, we believe the classic Intermediate Disturbance Hypothesis is a more appropriate framework for the meiofauna communities of the studied sites.     

The effect of the dominant polychaete Scolelepis squamata on nematode colonisation in sandy beach sediments: An experimental approach

The effect of an abundant sandy beach polychaete, Scolelepis squamata, on the colonisation of defaunated sediments by marine nematodes indicates that sandy beach fauna can be partially controlled by biological interactions within and across size groups. Experimental cores, equipped with windows allowing infaunal colonisation, were filled with defaunated sandy beach sediment containing two different treatments with and without S. squamata. These cores were inserted into microcosms filled with sediment with indigenous meiofauna collected from the field. The treatments were incubated in the laboratory at ambient temperature and salinity for 2, 7, 14 and 21 days, in order to follow the colonisation process of the defaunated sediments by the indigenous nematode fauna over time. Nematodes initially colonised both treatments, with abundances of up to 10% of the densities in the control; after 2 weeks, nematode densities in the cores without S. squamata surpassed the control densities. Nematode assemblages in both treatments were not species rich, and also differed in composition from the natural assemblages. The most successful colonising species, Enoplolaimus litoralis, was rare in the surrounding sediment, suggesting that colonisation was determined by species-specific characteristics such as body size, motility and feeding strategy. Initially the presence of macrofauna did not affect the nematode community composition, but after 2 weeks of the experiment, the presence of the polychaete seemed to facilitate the earlier establishment of non-opportunistic species.     

Relationship between oil pollution and psammolittoral meiofauna density of two South African beaches

The effects of stranded oil from a tanker collision off the South African coast on the meiofauna ratio and density have been monitored over a period of 1 year on two sandy beaches. The perturbation of two beaches was judged against reference beach meiofauna density behaviour. In the undisturbed beach, oil deposited in sediment depressed harpacticoid copepod numbers, while numbers of nematodes stayed similar to those of the reference levels. Removal of surface sand in the mechanically disturbed beach had a greater influence on the density of animals than oil. Both beaches showed recovery after six months, but evidence of pollution by oil of unknown origin was found.     

Across shore variability and trophodynamic features of meiofauna in a microtidal beach of the NW Mediterranean

The across shore variability and trophodynamics of meiofauna were studied in a microtidal beach of the Thyrrenian Sea (NW Mediterranean). Two sites were sampled at Collelungo beach (Maremma Park, Italy) subjected to different regimes of sediment erosion and deposition. At each site, four levels were sampled in November 2002 and May 2003 along a transect from the supralittoral zone to the surf zone. Sediment cores were taken down to a depth of 10 cm and meiofaunal abundance and community structure were analyzed and related to the principal trophic resources (quantity and quality of organic matter, chlorophyll a, bacteria density and biomass).Meiofaunal abundance ranged between 14 ind. 10 cm⁻² and 716 ind. 10 cm⁻² in the top 0–10 cm of sediment. Abundance was lower in the surface (0–2 cm) than in the deeper (5–10 cm) sediment layers but no significant differences were found between the two sites.Multivariate BIOENV analysis showed that dryness, grain size (related to physical processes) and bacterial biomass, were the main variables explaining meiofauna distribution in these beaches. Meiofaunal densities and number of taxa were always higher at the swash level, while lower abundances were observed at the dry sampling level (+5 m). This across shore trend was also observed for the quality of the organic matter (PRT/CHO) and bacterial densities. Nematode assemblage structure at the swash sampling level showed a dominance of non-selective deposit feeders (1B), with Xyalidae as the dominant family (56%), followed by Thoracostomopsidae (14%) and Selachnematidae (12%).According to the findings, physical and biological variables at the swash level create optimal living conditions for the meiobenthos, making the swash a key area within the beach ecosystem, with potential implications within basic and applied ecological studies.     

An assessment of the potential of major meiofauna groups for monitoring organic pollution

The numbers of six meiofauna groups (nematodes, copepods, turbellarians, archiannelids, oligochaetes and gastrotrichs) were estimated from 17 sandy beaches differing in their organic (sewage) pollution loadings. Nematodes were most abundant on polluted and fine sand beaches whilst copepods were more common on coarse sand and rare on polluted beaches. The ratio of nematodes to copepods may thus provide a useful index of beach quality. Archiannelids and oligochaetes seem restricted to particular habitat types and, with the turbellarians, have little potential for biomonitoring. Gastrotrichs occurred in large numbers on one polluted beach.     

Physical determinants of intertidal communities on dissipative beaches: Implications of sea-level rise

Sea-level rise is likely to cause significant changes in the morphodynamic state of beaches in the higher latitudes, resulting in steeper beaches with larger particle sizes. These physical changes have implications for beach invertebrate communities, which are determined largely by sediment particle size, and hence for ecosystem function. Previous studies have explored the relationships between invertebrate communities and environmental variables such as particle size, beach slope and exposure to wave action, and often these physical variables can be integrated in various indices of morphodynamic state. Most of these studies incorporated a full range of beach types that included wave-dominated surf beaches, where the wave action is harsh enough to enable reliable estimates of breaker height, a parameter included in several of the indices, and concluded that more dissipative beaches with gentler slopes and finer particle sizes often support a higher number of species and greater abundance than more reflective beaches. Whether these predictions remain valid for less wave-dominated beaches, where breaker height is more difficult to determine, is uncertain. In the present study, the abundance of meio- and macrofauna was quantified across a range of beaches in the UK, which are generally towards the lower energy end of the morphodynamic gradient, and their relationships with beach physical properties explored. No significant relationships were found between abundance and the standard morphodynamic indices, but significant relationships were found for both macro- and meiofaunal abundance when these indices were combined with an exposure index (derived from velocity, direction, duration and the effective fetch). All the relationships identified between abundance and combined morphodynamic indices indicated a higher abundance of both macro- and meiofauna on the more dissipative beaches. The reverse was however found for species richness. If predictions that accelerated sea-level rise will move beaches towards a more reflective morphodynamic state are correct, this could lead to declines in the abundance of meio- and macrofauna, with potential adverse consequences for ecosystem functioning.     

Exposed sandy beaches as semi-closed ecosystems

On the basis of various lines of evidence, mostly coming from exposed sandy beaches in Southern Africa, it is postulated that under certain conditions high energy sandy beaches and their adjacent surf zones may function as viable ecosystems. Where surf zones are reasonably broad and shallow, cellular circulation patterns predominate and these tend to retain nutrients generated by the macrofauna and interstitial fauna of the beach. These nutrients may then cause blooms of surf zone phytoplankton which in turn serve as food for macrofauna filter feeders. With the perimeter of the circulation cells of the surf zone forming its marine boundary, the beach and surf zone may together be considered an ecosystem with surf phytoplankton the primary producers, beach macrofauna the consumers and interstitial fauna the decomposers.     

Intertidal sand‐dwelling Peracarid fauna of North Island,New Zealand

Abstract

Substrate and infauna samples were taken at four tidal levels (mean high water springs, high mid beach, low mid beach, and mean low water neaps) with a 0.0625 m² quadrat at 14 North Island beaches in New Zealand. The distributions of Peracarida (Crustacea) were correlated with sediment type, tidal height, and degree of exposure; sampling began in March 1972 and was completed in November 1973.

Substrate samples were sieved and median diameter of the particles ranged from very coarse sand of — 0.60? to very fine sand of + 3.259?. Substrates were variously sorted: ? quartile deviation ranged from 0.14? to 0.66?, skewness from ‐ 0.08? to + 0.07?.

Peracarid fauna was moderately abundant; the maximum value was 720 animals per square metre on a fully exposed beach. Highest average abundance (303 per square metre) for the 14 beaches was recorded from the mean low water neap station. Amphipoda was the dominant group (54% of all Peracarida recorded), followed by Isopoda (33%) and Cumacea (13%). Frequency of occurrence at the 56 stations was headed by Amphipoda (64%), followed by Isopoda (46%), and Cumacea (20%).

The results are compared with data from Stewart Island beaches, and the biogeographical distributions of recorded Peracarida are discussed. An unexpectedly high degree of endemism exists for a warm‐temperate region, caused by the isolation of New Zealand, which has no direct shallow water contact with tropical or cold temperate regions.     

Meiofauna as descriptor of tourism-induced changes at sandy beaches

Tourism has long been considered as a 'clean industry' with almost no negative effects on the environment. This study demonstrated, in two different coastal systems (Mediterranean and Baltic), that tourism related activities are particularly affecting the sandy beach meio- and nematofauna in the upper beach zone, the specific ecotone in which many meiofauna species from both the marine and the terrestrial environment congregate. Tourist upper beaches are characterized by a lower % total organic matter (%TOM), lower densities, lower diversities (absence of Insecta, Harpacticoida, Oligochaeta, terrestrial nematodes and marine Ironidae nematodes) and higher community stress compared to nearby non-tourist locations. The %TOM was found to be the single most important factor for the observed differences in meiofauna assemblage structure at tourist versus non-tourist beaches in both the Mediterranean and the Baltic region. The free-living nematode assemblages from tourist upper zones depart significantly from expectations based on random selections from the regional nematode species pool. Furthermore upper zone assemblages are characterised by a low species diversity consisting of taxonomically closely related nematode species with r-strategist features. Generally, faunal differences between tourist and non-tourist beaches are decreasing towards the lower beach zones.     

Benthic responses to organic matter variation in a subtropical coastal area off SE Brazil

Organic matter quality, expressed as the proportion of chlorophyll a (Chl a) to degraded organic material (i.e. phaeopigments), is known to influence the structure of benthic associations and plays an important role in the functioning of the ecosystem. This study investigates the vertical distribution of microbial biomass, meiofauna and macrofauna with respect to organic matter variation in Ubatuba, Brazil, a southeastern, subtropical coastal area. On three occasions, samples were collected in exposed and sheltered stations, at high and low hydrodynamic conditions. We hypothesize that benthic assemblages will have high meio‐ and macrofaunal densities and high microbial biomass at the sediment surface at the sheltered site, and lower and vertically homogeneous microbial biomass and densities of meio‐ and macrofauna are expected at the exposed site. The accumulation of fresh organic matter at the sediment surface was observed at both stations over the three sampling dates, which contributed to the higher densities of meiofauna in the first layers of the sediment column. Macrofauna followed the same trend only at the exposed station, but changes in the number of species, biodiversity and feeding groups were registered for both stations. Microbial biomass increased at the sheltered station over the three sampling dates, whereas at the exposed station, microbial biomass was nearly constant. Physical exposure did not influence organic matter loading at the sites and therefore did not affect overall structure of benthic assemblages, which negates our original hypothesis. Most of the benthic system components reacted to organic matter quality and quantity, but relationships between different‐sized organisms (i.e. competition and/or predation) may explain the unchanged microbial profiles at the exposed site and homogeneous vertical distribution of macrofauna at the sheltered site. In conclusion, the high quality of organic matter was a crucial factor in sustaining and regulating the benthic system, but coupled results showed that interactions between micro‐, meio‐ and macrofauna can be highly complex.     

Intertidal sand‐dwelling Peracarid fauna of Stewart Island

Abstract

The distributions of infaunal Peracarida (Crustacea) and their correlation with sediment type, tidal height, and degree of exposure were studied in winter (June) at five beaches on Stewart Island, New Zealand. The beaches were selected lo cover a range of exposures to wind and wave action and substrate sorting. Substrate and infauna samples were taken at four tidal levels from each, with a 0.0625 m² quadrat.

Sieve separation and statistical analysis of the substrate samples indicated predominantly sand‐sized particles from all beaches, with median diameters in the range +1.52 to +2.92 ? (phi) units. Substrates were well sorted throughout the size range: ? quartile deviation ranged from 0.26 to 0.71, skewness from —0.18 to +0.07 ?.

Peracarid fauna was generally abundant, with a maximum of 29 136 per m²sampled in a more sheltered beach. Cumacea was the most abundant group, followed by Amphipoda, Isopoda, and Tanaidacea; dominance followed a similar sequence, being 78%, 19%, 2% and 1% respectively. Frequency of occurrence at the 19 stations was headed by Amphipoda (100%), with Isopoda 53%, Cumacea 32% and Tanaidacea 11%.