Subsurface Deposit Feeders Research Articles

Adaptation of benthic invertebrates to food sources along marine-terrestrial boundaries as indicated by carbon and nitrogen stable isotopes

Frequent environmental changes and abiotic gradients of the Wadden Sea require appropriate adaptations of the local organisms and make it suitable for investigations on functional structure of macrozoobenthic communities from marine to terrestrial boundaries. To investigate community patterns and food use of the macrozoobenthos, a transect of 11 stations was sampled for species number, abundance and stable isotope values (δ13C and δ15N) of macrozoobenthos and for stable isotope values of potential food resources. The transect was located in the back-barrier system of the island of Spiekeroog (southern North Sea, Germany). Our results show that surface and subsurface deposit feeders, such as Peringia ulvae and different oligochaete species, dominated the community, which was poor in species, while species present at the transect stations reached high abundance. The only exception was the upper salt marsh with low abundances but higher species richness because of the presence of specialized semi-terrestrial and terrestrial taxa. The macrozoobenthos relied predominantly on marine resources irrespective of the locality in the intertidal zone, although δ13C values of the consumers decreased from −14.1±1.6‰ (tidal flats) to −21.5±2.4‰ (salt marsh). However, the ubiquitous polychaete Hediste diversicolor showed a δ15N enrichment of 2.8‰ (an increase of about one trophic level) from bare sediments to the first vegetated transect station, presumably due to switching from suspension or deposit feeding to predation on smaller invertebrates. Hence, we conclude that changes in feeding mode represent an important mechanism of adaptation to different Wadden Sea habitats.

Taxonomic and functional patterns of macrobenthic communities on a high-Arctic shelf: A case study from the Laptev Sea

The studies of functional structure of high-Arctic Ecosystems are scarce. We used data on benthic macrofauna from 500-km latitudinal transect in the eastern Laptev Sea, from the Lena delta to the continental shelf break, to describe spatial patterns in species composition, taxonomic and functional structure in relation to environmental factors. Both taxonomy-based approach and Biological Trait analysis yielded similar results and showed general depth-related gradient in benthic diversity and composition. This congruence between taxonomical and functional dimensions of community organization suggests that the same environmental factors (primarily riverine input and regime of sedimentation) have similar effect on both community structure and functioning. BTA also revealed a distinct functional structure of stations situated at the Eastern Lena valley, with dominance of motile, burrowing sub-surface deposit-feeders and absence of sedentary tube-dwelling forms. The overall spatial distribution of benthic assemblages corresponds well to that described there in preceding decades, evidencing the long-term stability of bottom ecosystem. Strong linear relationship between species and traits diversity, however, indicates low functional redundancy, which potentially makes the ecosystem susceptible to a species loss or structural shifts.

Tracing sea ice algae into various benthic feeding types on the Chukchi Sea shelf

Climate change in the Arctic is expected to have drastic effects on marine primary production sources by shifting ice-associated primary production to an overall greater contribution from pelagic primary production. This shift could influence the timing, amount, and quality of algal material reaching the benthos. We determined the contribution of sea ice particulate organic matter (iPOM) to benthic-feeding invertebrates by examining concentrations and stable carbon isotope values (expressed as δ13C values) of three fatty acids (FAs) prominent in diatoms: 16:4(n-1), 16:1(n-7), and 20:5(n-3). Our underlying assumption was that diatoms make up the majority in sea ice algal communities compared with phytoplankton communities. According to the FA concentrations, subsurface deposit feeders consumed the most iPOM and suspension feeders the least. Conversely, there were little differences in δ13C values of FAs between deposit and suspension feeders, but the higher δ13C values of 16:1(n-7) in omnivores indicated greater consumption of iPOM. We suggest that omnivores accumulate the ice algal FA biomarker from their benthic prey, which in turn may feed on ice algae from a deposited sediment pool. The dissimilar results between FA concentrations and isotope values suggest that the FAs used here may not be sufficiently source specific and that other unaccounted production sources, such as bacteria, may also contribute to the FA pool. We propose that FA isotope values are a more indicative biomarker than FA concentrations, with a further need for more specific ice algal biomarkers to resolve the question of ice algal contributions to the Arctic benthic food web.

Internal tides affect benthic community structure in an energetic submarine canyon off SW Taiwan

Submarine canyons are major conduits of terrestrial and shelf organic matter, potentially benefiting the seafloor communities in the food-deprived deep sea; however, strong bottom currents driven by internal tides and the potentially frequent turbidity currents triggered by storm surges, river flooding, and earthquakes may negatively impact the benthos. In this study, we investigated the upper Gaoping Submarine Canyon (GPSC), a high-sediment-yield canyon connected to a small mountain river (SMR) off southwest (SW) Taiwan. By contrasting the benthic meiofaunal and macrofaunal communities within and outside the GPSC, we examined how food supplies and disturbance influenced the benthic community assemblages.The benthic communities in the upper GPSC were mainly a nested subset of the adjacent slope assemblages. Several meiofaunal (e.g. ostracods) and macrofaunal taxa (e.g. peracarid crustaceans and mollusks) that typically occurred on the slope were lost from the canyon. The polychaete families switched from diverse feeding guilds on the slope to motile subsurface deposit feeders dominant in the canyon. The diminishing of epibenthic peracarids and proliferation of deep burrowing polychaetes in the GPSC resulted in macrofauna occurring largely within deeper sediment horizons in the canyon than on the slope. The densities and numbers of taxa were depressed with distinct and more variable composition in the canyon than on the adjacent slope. Both the densities and numbers of taxa were negatively influenced by internal tide flushing and positively influenced by food availability; however, the internal tides also negatively influenced the food supplies. While the meiofauna and macrofauna densities were both depressed by the extreme physical conditions in the GPSC, only the macrofaunal densities increased with depth in the canyon, presumably related to increased frequency and intensity of disturbance toward the canyon head. The population densities of meiofauna, on the other hand, rebounded more rapidly due to their fast growth rate and short generation time and thus did not display bathymetric pattern in the canyon.To our knowledge, this is the first benthic ecological study in a submarine canyon connected to a high-sediment-yield SMR. The biological responses to extreme physical conditions in the GPSC could have broad implications on understanding the anthropogenic and climate change impacts in the deep-sea ecosystems.

Breadth and composition of polychaete diets and the importance of diatoms to species and trophic guilds

Polychaetes are important components of trophic webs in sandy beaches, mainly due to their abundance and diversity of feeding modes, acting as detritivores or primary/secondary consumers. We characterized diets of several polychaete species from intertidal sandy beaches by gut content evaluation. Diet breadth (Levins Index) was calculated for each species to evaluate the influence of different feeding strategies on this metric. Diatom composition was also assessed to verify the relevance of microphtyobenthic primary production to macrobenthic feeding on sandy beaches and its relationship with feeding strategies. A total of 2583 guts from 17 species were evaluated. Diet information is compared with literature, and added to taxa with previously unknown feeding habit. Diet breadths were generally low, but surface deposit feeders had the highest values. Scolelepis squamata guts were dominated by foraminfera, which may either be an specialization or local conditions. Subsurface deposit feeders usually had few items and lower breadths, highlighting the importance of organic matter to this guild. Diatoms were frequently found, and benthic were more frequently consumed than planktonic ones. The high numbers of benthic diatoms found for some species highlight the importance local food sources to sandy beach food webs.

Effects of an invasive mussel, Arcuatula senhousia, on local benthic consumers: a laboratory 13C‐labeling study

Filter-feeding bivalves play an important ecological role in aquatic systems through benthic–pelagic coupling. However, the mechanisms by which invasive mussels influence the food uptake by local consumers are little known. We tested the interactive effects of the invasive mussel Arcuatulasenhousia and the native clam Ruditapes decussatus on the uptake of 13C-enriched microalgae, Isochrysis sp., by two polychaetes, the surface deposit feeder Cirriformia tentaculata and the sub-surface deposit feeder Phylo foetida. Polychaetes were exposed to two different densities of A.senhousia and R. decussatus used alone or together. In each treatment, the 13C-concentration throughout the sediment horizon (0–0.5, 0.5–2.5 and 2.5–5 cm) was also quantified. Results showed that, irrespective of bivalve densities, the 13C-uptake by C. tentaculata was lower in the presence of the two bivalves together than in the presence of one bivalve species (either A. senhousia or R. decussatus). This was consistent with decreased 13C-concentrations in the 0–0.5 cm sediment layer in the treatment with the two bivalves together. Contrary to C. tentaculata, no changes were observed among treatments in the 13C-uptake by P. foetida. This possibly reflected a limited 13C-enrichment of the lower sediment layers. Our main findings are: (1) A.senhousia reduces the 13C-uptake by R. decussatus, and (2) A.senhousia reduces the availability of phytoplankton-derived C for deposit feeders by impairing the feeding, incorporation and bio-deposition of R. decussatus. We conclude that the interaction of A.senhousia with native bivalves needs to be taken into consideration in future food web studies.

Polychaete distribution on the southwestern Atlantic continental shelf

ABSTRACTDiversity and distribution of polychaetes on the southeastern Brazilian Shelf (SBS) adjacent to the city of Santos were studied. The study area is situated in the vicinity of Santos Bay with its estuarine complex and other small rivers along the coast. A total of 16,274 specimens belonging to 214 polychaete species were found at 21 sampling stations during two different periods. Two communities occur along the shelf and were related firstly to sediment characteristics. Prionospio dayi (Spionidae) was dominant in the inner shelf community that was characterized by well-sorted, very fine sand. The outer shelf community was found in muddy sediments with high organic matter content and was dominated by subsurface deposit feeders, like Petersenaspis capillata (Sternaspidae) and Leitoscoloplos kerguelensis (Orbiniidae), and by large carnivores such as Aglaophamus sp. (Nephtyidae) and Sigambra sp. (Pilargidae). A transition zone of mixed sediments presenting high diversity and richness was found between these communities. The characteristics of bottom water and food quality in the sediment were important to divide the inner shelf into two sub-areas. Nearshore sampling stations (A group) were more influenced by freshwater input, mainly during summer. This influence is not conspicuous at stations close to 30 m depth (B group). However the effect of South Atlantic Central Water mass (SACW) intrusion on the benthic system was observed on the inner shelf – B group during the summer. The summer intrusion of SACW onto the inner shelf may explain the higher quality of organic matter that resulted in an increase in polychaete abundance and richness.

SPATIAL AND TEMPORAL CHARACTERIZATION OF SOFT BOTTOM POLYCHAETES IN A SHALLOW TROPICAL BAY (COLOMBIAN CARIBBEAN)

The spatial and temporal variations of the polychaete assemblages were studied within and off a shallow (10-25 m) tropical bay (Bahía de Portete). The polychaete abundances at family level and their trophic mechanisms were used for this purpose. Sediment samples were collected at six stations in this bay during the wet and dry seasons. Multivariate analysis indicated that off- Bay polychaete assemblages were different from the bay ones; this spatial variation was related to sedimentary characteristics, depth and turbid-water conditions. On the other hand, these assemblages did not show significant differences between the dry and wet seasons. The differences between these two assemblages were given specially by the Syllidae, Gonidadidae, Nephtyidae, Dorvilleidae, Ampharetidae, Sabellidae, Glyceridae, Lumbrineridae, Opheliidae and Maldanidae families, being more abundant and frequent off the bay, while Magelonidae, Cirratulidae, Cossuridae and Eulephetidae were more abundant and frequent within the bay. The first ten families were related to a higher sand content, lower organic matter content and lower turbid-water conditions; while the last four were related to higher mud percentages, higher organic matter content and higher turbid-water conditions. Trophic guilds data showed similar assemblages as described above, which differ in their feeding mechanisms; the bay stations were dominated by surface and subsurface deposit feeders showing the importance of detritus; while off-bay stations the carnivores were the dominant organisms, reflecting the high predation. In these assemblages, the trophic and taxonomic structure is more affected by the spatial variation in the physical characteristics of the water column and sediment than by the seasonal variation.

The good, the bad and the Ulva: the density dependent role of macroalgal subsidies in influencing diversity and trophic structure of an estuarine community

Worldwide, ecological subsidies enhance ecosystem productivity and therefore trophic support for greater biodiversity of taxa. While studies in terrestrial and aquatic ecosystems demonstrate that the magnitude of subsidies into ecosystems differs widely, the thresholds where subsidies may switch from exerting positive to negative effects are poorly understood. In estuaries, eutrophication promotes drift macroalgae that deposit on the benthos, cover intertidal flats for months and serve as pressed resource subsidies for benthic consumers. We hypothesized there would be a critical threshold of macroalgal biomass where ecosystem‐level effects would turn from positive to negative. We used manipulative field experiments varying macroalgal mat thickness (0.5, 1.5 and 4 cm) over eight weeks and quantified effects on macrofauna on a lagoon mudflat in California. We documented that plots with mat depths of 0.5 and 1.5 cm had higher diversity by supporting both surface feeding and burrowing detritivores. Non‐metric multidimensional scaling showed that the benthic community diverged with mat depth over the course of the experiment. After eight weeks, surface deposit feeders were associated mainly with 0.5 cm macroalgal subsidies, whereas subsurface deposit feeding capitellids were closely linked with 4 cm mats. Depth profiles of pore water sulfide concentration collected from 4 cm mats were 7622 ± 5294 μM, mean ± SE, (mean of means across depth profiles), whereas 0.5 cm treatments resulted in sulfide concentrations that were 0.25% of the 4 cm treatments. This suggests that the mechanism of negative effects for elevated macroalgal subsidies was development of anoxic conditions promoting sulfide accumulation. Thus, our study was the first to find a critical threshold, or ecological tipping point, beyond which the effects of anthropogenically enhanced subsidies to estuarine mudflat communities switched from positive to negative and to describe the mechanism by which elevated subsides altered the abiotic environment and likely reduced ecosystem functioning.

The fatty-acid composition and nutrition of deep-sea holothurians from the Sea of Okhotsk

The results of a comparative study of the fatty-acid composition in eight species of holothurians that were collected in the Sea of Okhotsk in the area of the Kuril Islands (depths of 90–560 m) are presented. It is shown that interspecific differences in the fatty-acid compositions of the holothurians were consistent with the isotope composition (δ13C and δ15N) and the structural features of the tentacles and the lifestyle of holothurians, as indicators of trophic resources used by these holothurians. According to the results of the cluster analysis, the holothurians were divided into three groups. The first group included suspension-feeding dendrochirotides Eupentacta pusilla and Pseudocnus fallax with a high content of the fatty acid 20:5(n-3), which is a marker of diatoms, and with the δ15N values that are typical of consumers of suspended organic matter. The second group consisted of the dendrochirotides Psolus chitonoides and Psolidium sp. with a much lower content of 20:5 (n-3) and higher contents of 20:4 (n-6) and 22:6 (n-3), as well as high values of δ15N, which are typical of surface deposit-feeders. The third group consisted of surface and subsurface depositfeeders, Chiridota sp., Molpadia orientalis, Pseudostichopus mollis, and Synallactes nozawai. Very high contents of 20: 4 (n-6) and 21: 4 (n-7) were typical of the third group and the highest values of δ15N, indicating feeding on repeatedly recycled organic matter.

Macrofaunal recolonization of copper-contaminated sediments in San Diego Bay

Effects of Cu-loading on macrofaunal recolonization were examined in Shelter Island Yacht Basin (San Diego Bay, California). Sediments with high and low Cu levels were defaunated and Cu-spiked, translocated, and then placed back into the environment. These demonstrated that the alteration observed in benthic communities associated with Cu contamination occurs during initial recolonization. After a 3-month exposure to sediments with varying Cu levels, two primary colonizing communities were identified: (1) a “mouth assemblage” resembling adjacent background fauna associated with low-Cu levels that was more diverse and predominantly dominated by surface- and subsurface-deposit feeders, burrowers, and tube builders, and (2) a “head assemblage” resembling adjacent background fauna associated with high-Cu concentrations, with few dominant species and an increasing importance of carnivores and mobile epifauna. Cu loading can cause reduced biodiversity and lower structural complexity that may last several months if high concentrations persist, with a direct effect on community functioning.

Large-scale effects of green tides on macrotidal sandy beaches: Habitat-specific responses of zoobenthos

Sandy beaches are highly dynamic ecosystems mainly driven by physical variables, such as tidal regime. These ecosystems support numerous essential ecological functions and contain a distinctive biodiversity, but are threatened by increasing direct or indirect anthropogenic pressures, among which are green tides composed of free living Ulva spp. Studies that have been conducted to understand the effects of macroalgal mats on coastal sediment communities have mostly addressed responses in atidal or microtidal systems, and are often single-site assessments. Using large-scale field surveys across 13 macrotidal sandy beaches of two types (exposed and semi-exposed) distributed along 2700 km of coast for 7 years (REBENT program, Brittany, France), we analysed responses of zoobenthos to the presence of green tides in relation to tidal range, exposure, sediment characteristics, air and seawater temperature, precipitations, wind and salinity. Despite the high variability existing between two distinct categories of sandy habitats and also between macrotidal beaches within the study area, differences in macrofaunal community structure arose from the presence of green tides: mean abundance and species richness of macrozoobenthic invertebrates were higher where green tides occurred. Moreover, macrobenthic assemblages in the two beach-categories respond differently to eutrophication seen as green tides. Surprisingly, the effects of the presence of Ulva mats were stronger at exposed sandy beaches than at semi-exposed beaches. Our study also highlights species-specific responses: herbivorous marine invertebrates and suspension feeders were favoured by the presence of Ulva mats, whereas large sub-surface deposit feeders and bivalve drifters which surf up and down the shore with the tides were negatively affected by green tides.

Influence of estuarine dynamics on macrobenthos spatial variability along the southeast continental shelf of Brazil

Along the southeast continental shelf of Brazil, the Paraiba do Sul River (PSR) plays a fundamental role in sediment and nutrient transport. This study focuses on the contribution of the PSR and its effect on the benthic macrofauna. Physical and chemical analyses of the sediment were conducted, and the macrofauna were identified and counted. Multivariate analyses were used to compare the distribution patterns of the benthic assemblages related to the depth gradient over two sampling periods. The principal component analysis showed that shallow waters assemblages are mostly influenced by the environmental descriptors temperature, salinity and chlorophyll a, whereas pheophytin, degree of sediment sorting, total carbonate and organic carbon were correlated with benthic assemblages at greater depths. The high organic enrichment reflected an increase in surface and sub-surface deposit feeders such as the polychaetes Spiophanes sp. and Prionospio cristata and the crustacean Phtisica marinain the deeper stations, with a corresponding decrease in other trophic groups. This study provides evidence of differences in organic matter sources, from primary production in shallow waters to detritus in deep waters. These sources provide different niches for the corresponding macrofaunal assemblages along the continental shelf adjacent to the PSR, with species richness and abundance of benthic populations related to the river output.

How much is too much? Identifying benchmarks of adverse effects of macroalgae on the macrofauna in intertidal flats

Eutrophication, defined as the accumulation of organic matter typically in response to anthropogenically enhanced nutrient inputs, often takes the form of macroalgal blooms in shallow estuaries and causes a cascade of adverse ecosystem effects. Confidence in the use of macroalgae as an indicator of eutrophication in estuaries is limited by the lack of quantitative data on thresholds of adverse effects. Field experiments can provide "benchmarks" of no effect or adverse effects that can be used to validate thresholds derived statistically from field data. To determine a benchmark of adverse effects of macroalgal abundance on macrobenthic faunal communities in intertidal flats, experiments were conducted in two sites in Bodega Harbor (BOD) and two sites in Upper Newport Bay (UNB), California, USA. At each site, 24 cages maintained six treatments of macroalgae for eight weeks, with mat depths of 0, 1.0, 1.5, 2.5, 3.5, and 5.0 cm composed mostly of bloom-forming green macroalgae in the genus Ulva. Every two weeks, cores of sediment (10 cm deep) were collected, and macrofauna were quantified. Mats 1 cm deep, equivalent to a biomass of 110-120 g dry mass (dm)/m2 or 840-930 g wet mass/m2, resulted in the reduction of macrofaunal abundance by at least 67% and species richness by at least 19% within two weeks at three of four sites. Loss was attributed to the decline of key functional groups. Surface-deposit feeders were eliminated from one site at BOD within four weeks and at one site in UNB within six weeks, while 1-cm mats negatively affected suspension feeders and herbivores in the second site at BOD. In contrast, the other site at UNB was not affected by macroalgal treatment, likely due to an initial community composed of a high proportion of subsurface-deposit feeders tolerant of stressful environments. Macroalgal abundances as low as 110-120 g dm/m2 had significant and rapid negative effects on macrobenthic invertebrates, providing a clear benchmark of adverse effects of macroalgal blooms on macrofaunal abundance and community structure, two indicators of ecosystem health. This information can inform the establishment of appropriate metrics for macroalgal abundance in eutrophic estuaries.

Trophic resource use by macrozoobenthic primary consumers within a semi-enclosed coastal ecosystem: Stable isotope and fatty acid assessment

The diet of different macrozoobenthic trophic groups was investigated in the Arcachon Bay—a semi-enclosed macrotidal ecosystem that shelters the largest Zostera noltei seagrass meadow in Europe—in early spring and late summer 2009, using stable isotopes and fatty acids. Fatty acid profiles and literature information about the biology and physiology of benthic consumers were combined to identify the main organic matter sources for the benthic primary consumers. An isotope mixing model was then run to evaluate the contribution of each organic matter source to each identified trophic group (suspension feeders, sub-surface deposit feeders, micro-and macrograzers, suspension-oriented interface feeders and deposit-oriented interface feeders). Variations in organism' diets with respect to both habitats (intertidal seagrass meadows, intertidal bare sediments and subtidal bare sediments) and study periods were also investigated. At the scale of this study, it appeared that the diet of macrozoobenthos primary consumers was based exclusively on autochthonous material (no use of terrestrial organic matter): mainly microphytobenthos, seagrasses and their epiphytes, and phytoplankton. In addition, the different trophic groups relied on different organic matter pools: for instance, suspension feeders mainly fed on microphytobenthos and phytoplankton, whereas subsurface deposit feeders fed on microphytobenthos, decayed seagrasses and bacteria, and grazers mainly fed on microphytobenthos, and seagrasses and their epiphytes. The same pattern was observed in both early spring and late summer, indicating a stability of the benthic system at a six-month time scale. Finally our results showed that, in Arcachon Bay, the seagrass meadow directly or indirectly (through detritus) plays a significant role in the diet of most benthic consumers.

Response of Trophic Groups of Macrobenthos to Organically Enriched Sediments: A Comparative Study between Temperate and Tropical Regions

This study is aimed to detect the level of environmental disturbance caused by farming activities using trophic groups of macrobenthic assemblages, with emphasizes the difference between temperate and tropical regions. The samples of macrobenthic assemblages were taken from 2 (two) farm sites, i.e. Southern Spencer Gulf, South Australia, where farming of southern bluefin tuna ( Thunnus maccoyii ) takes place, representing as a temperate region (Site I) and milk fish ( Chanos chanos ) farms and mangrove area at coastal region of Mngkang Kulon, Semarang, Central Java, Indonesia, representing as a tropical region (Site II). Macrobenthic abundance was categorised based on six major trophic groups. Macrobenthic assemblages dominated by all polychaetes, they are Capitellidae, Cirratullidae, Lumbrineridae, Nephtyidae, and Spionidae at Site I (temperate region), owing to their relatively tolerance to organic enrichment, both at the farm sites and at control sites. Surface deposit feeders (SDF) dominated in abundance at both control and fish farm sites at Site I, whilst subsurface deposit feeders (SSDF) exhibited highest in proportion at Site II over the study period, in particular species of Capittelidae, indicating that both sites has been influenced by fish farm activities. The abundance of deposit feeders was significantly higher at the farm sites than at the reference sites. Organic carbon in the sediment surface is likely to correlate with deposit feeding and sub-surface deposit feeding species richness, whereas total and food particulate matter correlate with species diversity. The result of this comparative study implies that response of trophic groups of macrobenthos to environmental disturbance are considerably similar at both tropical and temperate regions.

Invasive mangrove removal and recovery: Food web effects across a chronosequence

Red mangrove (Rhizophora mangle) was introduced to Hawai'i in 1902 and has since overgrown many coastal areas in Hawai'i, transforming nearshore sandy habitat into heavily vegetated areas with low water velocity, high sedimentation rates, and anoxic sediments. Introduced mangrove forests provide habitat for exotic species, including burrowing predators, which can exert top-down effects on benthic communities. Removal of mangrove overstory is a popular management technique, and, here, we study community change over a chronosequence of mangrove removals from 2007 to 2011, investigating infaunal community structure, crab abundance, and response to predator exclusion in the presence of mangrove overstory and along the chronosequence of removals. Overstory removal results in gradual changes in community composition concurrent with slow decomposition of sedimentary mangrove biomass (k=0.36±0.06×10−3d−1). Changes over time after removal include an increase in total infaunal abundance, a decrease in sub-surface deposit feeders, and an increase in suspension-feeding worms. Burrowing crab densities are uniform across mangrove and removal sites, and, unlike in native mangroves, their effects on infaunal communities are similarly negligible in both mangrove and removal areas. These results show that recovery from invasion and removal occurs gradually and is not governed by top-down effects.

Gain of palps within a lineage of ancestrally burrowing annelids (Scalibregmatidae)

AbstractScalibregmatidae is a small annelid family of subsurface deposit feeders in sand or mud, which are generally well adapted to infaunal burrowing. The overall morphology of Scalibregmatidae is very similar, with thick bodies, small parapodia, and no prostomial appendages or short horns. The only exception is members of the genera Axiokebuita and Speleobregma that most frequently inhabit crevices or gravel and possess extensive ventral ciliated palps and globular adhesive pygidium. Character reconstruction using maximum likelihood and Bayesian methods show that ciliated palps and adhesive pygidium are synapomorphies of the Axiokebuita–Speleobregma clade. The most likely transformation series is from horns to ciliated palps, the origin of which correlates with the occurrence of Axiokebuita and Speleobregma in crevices or gravel. The wide spaces among rocks or granules yield high permeability and inertial water flow, preventing deposition of organic matter. Under these flow conditions that differ significantly from those of sand or mud bottom, ciliated palps aid to the collection of suspended particles and an adhesive pygidium provides attachment. With palps being a highly debated character in annelid evolution, it is remarkable that prominent ciliated palps are gained within a lineage of ancestrally nonpalpate annelids, most likely increasing their fitness when colonizing a new environment.

Effects of cold winters and regime shifts on macrofauna communities in shallow coastal regions

Several ecosystem components in the North Sea have undergone fundamental changes following climatic change and this paper aims to establish if these changes also have affected macrofauna communities in the southern North Sea. From 1978 to 2005, the macrofauna communities were sampled seasonally in the sublittoral zone off the island of Norderney, one of the East Frisian barrier islands. Abundance, biomass and species numbers of single species or larger taxonomic groups showed differences in long-term variability and eurytherm species dominated in the study area. After the cold winter of 1978/79 until the mid 1980s a higher percentage of arctic-boreal species were found, while after 1988 the percentage of species with a southern distribution in the North Sea increased in connection with a smooth biological regime shift and a positive North Atlantic Oscillation (NAO) index. Interface-feeders dominated the communities, followed by sand lickers and subsurface deposit-feeders. The latter were more abundant after cold winters, probably due to their ability to utilise dead buried faunal organic matter. Multivariate analyses revealed that cold winters affected the community structure more briefly, while a smooth biological regime shift in 1989/1990 and a climate regime shift induced abrupt biological regime shift in 2001/2002 caused longer-term progressive change in the macrofauna community structure. The significant correlation between macrofauna abundance, biomass and species number and the NAO index failed until 2001 due to a change in climate systems over the northern Atlantic hemisphere.

Inter-annual dynamics of abyssal polychaete communities in the North East Pacific and North East Atlantic—A family-level study

Characterising how deep-sea communities change on contemporary time-scales and understanding underlying ecosystem processes has become important under changing climate and the rise in the exploitation of deep-sea resources. However, little is known about these dynamics and processes. Long-term observations from which inter-annual variations can be detected are scarce in the deep sea. This study examines inter-annual changes in density, family richness and evenness, family and functional group rank abundance distributions of infaunal polychaetes at two abyssal stations in the North East Pacific (Station M, 1991 to 2005) and in the North East Atlantic (Porcupine Abyssal Plain, 1991 to 1999). The two long-term data sets were used to investigate not only if polychaete community structure and composition varied at inter-annual scales in terms of diversity and rank abundance distributions but also if any changes were related to previous observations in megafauna and environmental factors at each locality. The polychaete community structure at each locality was analysed using univariate statistics as well as multivariate ordination techniques based on Bray-Curtis similarity of the yearly family density. Sub-surface deposit feeders, such as Paraonidae, dominated the North East Pacific, whereas surface deposit feeders, such as Cirratulidae, dominated the North East Atlantic. Both stations showed inter-annual variations in density, family evenness and rank abundance distributions. The greatest changes occurred in 1998 in both time series when polychaete densities peaked, and switches in the rank abundance of the most abundant families and functional groups took place. Inter-annual variations in the polychaete community were correlated with a limited number of holothurian species changes, but no correlation was found with particulate organic matter flux or climate indices. Ecological and environmental factors behind the family-level changes remain elusive. Overall, changes in the dominance of functional groups imply changes in abyssal ecosystem functioning with potential consequences on carbon cycling at the seabed.