Macroinfaunal Community Research Articles

Benthic communities restructure quickly under shifting salinities: a reciprocal transplant experiment

Salinity regimes in estuarine habitats will shift pending sediment diversions, which will reconnect Louisiana, USA, coastal wetlands to the Mississippi River. The river has been hydrologically disconnected from fringing estuaries for over a century, but high local rates of relative sea-level rise have contributed to land loss, and sediment diversions will be built to prevent future loss. A reciprocal transplant experiment of benthic cores was used to determine how macrofaunal communities may be altered pending salinity regime shifts. A total of 147 benthic cores (3142 cm3) were excavated and transplanted within 3 salinity regimes in Barataria Bay, LA, for 2 or 5 mo. We observed a significant effect of salinity treatment on benthic macroinfaunal community composition in every transplant, regardless of origin or date sampled. Results show that communities recolonized in as little as 2 mo, and reveal the species assemblages responsible for the restructure. Species assemblage changes included dominance of generalist species (spionid and capitellid polychaetes) and shifts between deposit feeders and suspension feeders as freshwater flow varied. Lower-salinity treatment decreased species richness, while higher-salinity treatment increased both species richness and abundance. Benthic communities will likely restructure quickly under the sediment diversion scenarios and leave few founder effects in response to changes in salinity regimes across the estuary. Pulsed diversion operations may yield different results, but only springtime operations are likely to impact benthic recruitment. Comprehensive knowledge of how benthic communities restructure post-restoration will enable both appropriate regional planning as well as future predictions in coastal estuaries undergoing hydrologic alteration.

Macrofaunal diversity patterns in coastal marine sediments: re-examining common metrics and methods

Complex biodiversity patterns arise in marine systems due to overlapping ecological processes, including organism interactions, resource distribution, and environmental conditions. Despite the importance of documenting these patterns, describing diversity in natural ecosystems remains challenging. Here, we investigate 3 nearshore sub-Arctic sites to describe benthic macroinfaunal taxa and biological traits, with the ultimate aim of determining whether common diversity metrics and typical sampling efforts adequately capture community composition in these systems. First, we assess how diversity relates to sediment depth and examine relationships among commonly used taxonomic and functional diversity indices. Second, using a power analysis, we explore how sampling effort influences the interpretation of diversity patterns in coastal systems. We report significant variation in community composition among sites, even across small spatial scales of km, and find that taxonomically diverse communities do not necessarily correspond to high functional diversity. We further find that although environmental factors such as sediment depth consistently affect macroinfaunal diversity, the direction and magnitude of these relationships are site-dependent. Finally, we demonstrate that typical sampling effort for coastal benthic studies (for example, <5 push cores of ~7 cm diameter) may not capture macroinfaunal community composition adequately, potentially obscuring hotspots in common diversity metrics such as taxonomic or functional richness. However, indices such as Simpson’s diversity may be well-suited to resource-limited studies with restricted sampling capacity. Our results highlight the importance of adopting multi-pronged approaches to biodiversity assessment and determining optimal sample sizes for marine benthic systems, particularly in the context of biodiversity monitoring for conservation purposes.

Benthic macroinfaunal communities of the pockmark fields in the south-eastern Bay of Biscay

Pockmarks are concave depressions on the sea bottom produced by fluid escape from subaqueous sediments which can be found worldwide in muddy and silt/clay sediments. Due to their morphological and geochemical characteristics, certain pockmarks play an important role in structuring benthic communities, and consequently, they have been proposed to be protected. The present research provides a characterisation of the benthic macrofauna composition in pockmark fields in the southeaster Bay of Biscay. A total of 11 samples were acquired in and close to pockmarks covering a range of depths of 414–992 m. The survey strategy considered the acquisition of one sample inside of each of the selected pockmarks and another sample near, but out of them. Collected macrofaunal organisms were identified at lowest taxonomical level (species) when possible, structural parameters were calculated and a hierarchical cluster analysis carried out with species data. Species density, biomass, richness, diversity and evenness were found to be higher in samples collected inside pockmarks in comparison to samples obtained outside but not statistically significant. This could be explained by the inactivity of the studied pockmarks, which do not offer/generate a particular environment with unusual characteristics that limit or enhance the development of specific species/groups with special traits.

Macro-infaunal diversity and assemblage in the mangrove habitat of Lawas, Sarawak, Malaysia

The diversity and composition of macrofaunal communities are important components to understand the mangrove ecosystem structures and functions. To understand the seasonal distribution of macro-infaunal community and diversity, this study was conducted from July 2019 to February 2020 in the intertidal mangrove forest of Punang-Sari-River estuary, Lawas, Sarawak. Sampling was carried out during post-monsoon, intermediate-September, pre-monsoon, and monsoon. It was observed that, the seasonal physico-chemical parameters were significantly (P < 0.05) different, including the temperature, salinity, rainfall, pore water nitrogenous compounds (NO2, NO3 and NH3-N), phosphate and micro minerals. A total of 39 infaunal macrobenthos taxa from 27 families were recorded while the mean abundance of infaunal macro benthos was found higher in monsoon (997.29 individuals/m2). The most abundant, the highest important species index and percentage contribution species was Bivalvia Eurytellina lineata (W. Turton, 1819) due to year-round favorable ecological condition. Seasonal faunal grouping suggested post-monsoon, intermediate-September and pre-monsoon were comparable in species and individual abundance. The Simpson, and Shannon indices were found significantly (P < 0.0001) higher in monsoon, while Margalef richness was found higher in pre-monsoon. The soil was sandy loam with major portion of sand, and positively correlated with sand and infaunal abundance in all seasons. The ANOSIM and SIMPER analysis suggested that the highest species abundance similarity was observed between post-monsoon and pre-monsoon, while the highest dissimilarity was observed between intermediate-September and pre-monsoon. The Canonical Correspondence Analysis results suggested, a number of species were influenced by ecological factors, for instance, salinity, soil pH, PO4, micro–macro minerals, water pH, and nitrogenous compounds. The relationship within benthic infaunal abundance in the mangrove ecosystem with their seasonality, ecological variables, and soil properties were established and addressed in this study.

Distribution and Sediment Selection by the Mud Shrimp Upogebia noronhensis (Crustacea: Thalassinidea) and the Potential Effects on the Associated Macroinfaunal Community

Burrowers such as thalassinideans remobilize sediment in benthic ecosystems, altering granulometry, enhancing organic matter cycling and oxygenation. We characterized the distribution of the mud shrimp Upogebia noronhensis and the associated macroinfauna along a depth and granulometric gradient in a shallow subtidal area in the southern Brazilian coast. Mud shrimp densities were estimated by burrow opening count using 0.25 m2 quadrats in three sediment zones: sand, sand-mud transition and mud. Macroinfaunal community descriptors and sediment granulometric characteristics were assessed. U. noronhensis average density varied from 0.6 to 145 individuals m−2 and was highest in the transition zone and lowest in the sand zone. Macrofauna in the sand zone was at least three times more abundant and 1.2 times richer, averaging 436.3 organisms and 39 species, while the transition and mud zones were more even in species distribution (species evenness &gt; 0.7). The shrimp presence seems to be linked to a coarse sand content &lt;80% and clay and silt &lt;40% in the sediment, a compromise between gallery construction ability and filter-feeding suitability. High densities and aggregated distribution of mud shrimp, combined with alteration of sediment grain composition and organic matter, are likely to affect macroinfaunal abundance nearby the burrows.

Historical Shifts in Benthic Infaunal Diversity in the Northern Gulf of Mexico since the Appearance of Seasonally Severe Hypoxia

Severe and persistent bottom-water hypoxia (≤2 mg O2 L−1) occurs on the Louisiana/Texas continental shelf from mid-May through mid-September over a large area (up to 23,000 km2 in mid-summer). Benthic infauna are less mobile than demersal organisms and become stressed by the low dissolved oxygen; benthic community composition, abundance, diversity, and biomass become altered. From the 1950s to the early 1970s, when sediment core indicators identified the initiation and subsequent worsening of dissolved oxygen conditions, there were no hydrographic data or benthic infaunal studies within the current area of frequent bottom-water hypoxia. This study highlights the impacts of severe hypoxia on benthic macroinfaunal communities and how they may have changed from less-hypoxic periods. Polychaetes were and are the dominant taxa in the available studies, but polychaete species richness in summer is now curtailed severely beginning with our 1985–1986 data. Species richness of polychaetes in summer hypoxia (1985–1986 and 1990–1991) was about 60% less than comparable taxa in 1972–1973. Abundance of polychaetes was much less in summer than spring, and recent infaunal biomass in summer was only 15% of what was found in spring. The result is less prey for demersal penaeid shrimp and fishes. Over the period of our comparison, infaunal feeding modes shifted from subsurface deposit feeders and surface deposit feeders to primarily surface deposit feeders (i.e., 95.5% of all polychaetes). Most were opportunistic, hypoxia tolerant, and recruited in high numbers following hypoxia abatement, some in fall and winter but most in spring. As benthic communities succumb to the stress of severe and continued seasonal low oxygen, they occupy the few upper centimeters of the sediment profile above the redox discontinuity layer with negative feedbacks to the water column by way of altered biogeochemical processes.

Macroinfauna responses and recovery trajectories after an oil spill differ from those following saltmarsh restoration

Given the severity of injuries to biota in coastal wetlands from the Deepwater Horizon oil spill (DWH) and the resulting availability of funding for restoration, information on impacted salt marshes and biotic development of restored marshes may both help inform marsh restoration planning in the near term and for future spills. Accordingly, we performed a meta-analysis to model a restoration trajectory of total macroinfauna density in constructed marshes (studied for ~30 y), and with a previously published restoration trajectory for amphipods, we compared these to recovery curves for total macroinfauna and amphipods from DWH impacted marshes (over 8.5 y). Total macroinfauna and amphipod densities in constructed marshes did not consistently reach equivalency with reference sites before 20 y, yet in heavily oiled marshes recovery occurred by 4.5 y post spill (although it is unlikely that macroinfaunal community composition fully recovered). These differences were probably due to initial conditions (e.g., higher initial levels of belowground organic matter in oiled marshes) that were more conducive to recovery as compared to constructed marshes. Furthermore, we found that amphipod trajectories were distinctly different in constructed and oiled marshes as densities at oiled sites exceeded that of reference sites by as much as 20x during much of the recovery period. Amphipods may have responded to the rapid increase and high biomass of benthic microalgae following the spill. These results indicate that biotic responses after an oil spill may be quantitatively different than those following restoration, even for heavily oiled marshes that were initially denuded of vegetation. Our dual trajectories for oil spill recovery and restoration development for macroinfauna should help guide restoration planning and assessment following the DWH as well as for restoration scaling for future spills.

Dominant Bivalve in an Exposed Sandy Beach Regulates Community Structure Through Spatial Competition

Fluctuations in abundance of dominant species can cause competitive release of resources with consequences on community structure and functioning. In the present study, changes in the intertidal macroinfauna community of an exposed sandy beach were evaluated during two contrasting periods characterized by low and high densities of the yellow clam Amarilladesma mactroides. The increase in clam abundance and biomass was associated with a significant decrease in abundance of the rest of the community. In particular, a decline was observed for the pea crab Austinixa patagoniensis, a commensal species that lives in the burrows of the shrimp Sergio mirim. Our study demonstrates that fluctuations in clam abundance lead to long-term changes in community structure, suggesting the presence of competitive interactions. The environmental stability over the two periods strengthens the hypothesis that the competition between species is crucial for shaping the ecological community. Stable isotope analysis allows discarding trophic competition as mechanism of exclusion. Image maps reveal complementary distribution of species, showing the relevance of the spatial competition, which is mediated by changes in abundance of a third species. Indeed, high densities of A. mactroides reduce the available area for the establishment of the S. mirim burrows, limiting the foraging behavior of its commensal, the pea crab. Such an interaction drives density-dependent exclusion of the pea crab from the intertidal zone following the establishment of the yellow clam population. This study illustrates that spatial competition triggered by the increase of a bed-forming species can have community-wide consequences in exposed sandy beaches.

Influence of phytodetrital quality on macroinfaunal community structure and epifaunal response

Influence of phytodetrital quality on macroinfaunal community structure and epifaunal response

Potential impacts of finfish aquaculture on eelgrass (Zostera marina) beds and possible monitoring metrics for management: a case study in Atlantic Canada.

Eelgrass (Zostera marina) has been designated an Ecologically Significant Species in Atlantic Canada. The development and rapid expansion of netpen finfish aquaculture into sensitive coastal habitats has raised concerns about the impacts of finfish aquaculture on eelgrass habitats. To date, no studies have been done in Atlantic Canada to examine these impacts or to identify potential monitoring variables that would aid in the development of specific conservation and management objectives. As a first step in addressing this gap, we examined differences in environmental variables, eelgrass bed structure and macroinfauna communities at increasing distances from a finfish farm in Port Mouton Bay, a reference site in adjacent Port Joli Bay, and published survey results from other sites without finfish farms along the Atlantic Coast of Nova Scotia. Drawing on research done elsewhere and our results, we then identified possible metrics for assessing and monitoring local impacts of finfish aquaculture on eelgrass habitats. Our results suggest some nutrient and organic enrichment, higher epiphyte loads, lower eelgrass cover and biomass, and lower macroinfauna biomass closer to the farm. Moreover, community structure significantly differed between sites with some species increasing and others decreasing closer to the farm. Changes in the macroinfauna community could be linked to observed differences in environmental and eelgrass bed variables. These results provide new insights into the potential impacts of finfish aquaculture on eelgrass habitats in Atlantic Canada. We recommend a suite of measures for assessment and monitoring that take into account response time to disturbance and account for different levels of eelgrass organizational response (from physiological to community).

Environmental and sediment conditions, infaunal benthic communities and biodiversity in the Celtic Sea

While it is recognised that the nature of the sediment is a major driver of benthic macro-infaunal community structure, it is also true that diverse environmental factors determine the distribution and composition of sediments. Among those factors are depth, tidal stress and seasonal stratification of the water column. In the Celtic Sea an area of seabed approximately 20 km wide and 125 km long was selected in which variation in water depth, stratification, primary production and current velocity were minimised, but which contained sediments ranging from fine muds to coarse gravelly sands. 55 stations were sampled across the area using a box-corer. At each station a comprehensive suite of sediment and biogeochemical measurements were made. Macrofauna were identified and weighed. Of the stations sampled, four had been chosen as focal sites for a study of relationships between benthic biogeochemistry and sediment type. Relationships between variation in environmental and sediment variables and macrofaunal community structure were analysed using a range of non-parametric multivariate techniques. Environmental variables were discriminated into situational variables that broadly encapsulate potential drivers of spatial heterogeneity in the benthos such as depth and fishing effort, and in-situ variables that were measured at each site concurrently with the sampling of the macrobenthos, such as sediment properties and biogeochemical measurements. Among the former, analyses tended to identify the importance of average shear stress and depth in explaining observed variation in benthic community structure, even though the area had been chosen to minimise variation in those factors. Analyses using in-situ measurements of sedimentary conditions at each site identified very fine sand content (correlated with average shear stress) as the most important explanatory variable. Most of the measured biogeochemical variables varied with sediment structure, particularly reflecting differences between finer-grained sediments with higher organic content (generally from deeper areas) and coarser sediments with lower organic content. While clear spatial heterogeneity in sediments and associated biogeochemical variables could be demonstrated, spatial variation in benthic abundance and biomass was less clear. Benthic community structure varied significantly with sediment type, but did not vary closely with the in-situ environmental variables measured at the same sites. This may indicate that the samples collected were too small to accurately characterise the benthic assemblage at each site, or that most species inhabiting the area inhabit a range of sediment types, or that processes which are not reflected in sediment or biogeochemical measurements are also important determinants of benthic community structure.

Food quantity and quality in Barkley Canyon (NE Pacific) and its influence on macroinfaunal community structure

The highly heterogeneous nature of submarine canyon physical landscapes can influence organic matter spatial distribution and thus benthic community and food web structure. We therefore studied patterns in quantity and quality (i.e., nutritional value for benthic organisms) of sediment and bottom-water particulate organic matter and their influence on macroinfaunal community structure in Barkley Canyon (NE Pacific) at multiple spatial scales (10 s to 100 s of meters). At large scales (100 s of meters), we hypothesised that canyon heterogeneity would drive organic matter patterns: topographic features (slope, aspect, curvature, rugosity, and benthic positioning index) and other environmental variables (depth, dissolved oxygen concentration, surface primary productivity, and sediment type). Our multivariate distLM analysis identified mean grain size, surface primary productivity and benthic positioning index (concave/convex seafloor topography) as the primary drivers of organic distribution in sediments. Noting different degradation rates among food variables, we inferred that the freshest organic matter reaches bottom waters of Barkley Canyon at 400 m, where ambient currents at the canyon head region likely concentrate primary productivity from surface waters. Evidence of deposition (increased amounts of fresh food) first appeared at 600 – 800 m, coincident with finer sediments, convex topography, and convergence of canyon branches. Degraded organic matter accumulated at 1500 and 2000 m where the comparatively fine sediments adsorb a greater proportion of available organic material than at shallower depths but limited delivery of surface primary productivity reduces overall food quality. Despite clear differences in food quantity and quality among sites (100 s of m apart), dissolved oxygen primarily drove macrofaunal distribution, along with hydrocarbons, indicative of a chemosynthetic ecosystem. At smaller spatial scales (10 s of meters) we found greater food patchiness associated with the topographically complex upper canyon (≤ 800 m). We also found distinct communities at smaller spatial scales (10 s of m apart) at 200 m, where fatty acid biomarkers distinguished a food patch rich in zooplankton. Overall, canyon heterogeneity rather than depth primarily determines patterns of organic matter (quantity and quality) in Barkley Canyon, with greater food patchiness at sites ≤ 800 m depth. Organic matter distribution appears to influence macroinfaunal community structure more strongly at smaller spatial scales in contrast to major stressors (i.e., oxygen) that act over larger scales.

Correction to: Spatial Variation of Macroinfaunal Communities Associated with Zostera marina Beds Across Three Biogeographic Regions in Atlantic Canada

Seagrass beds and their associated species communities play key roles in coastal ecosystems. The importance of the ecological functions provided by eelgrass (Zostera marina) and macroinfauna are well understood; however, the spatial variation and linkage of the two are much less known. Here, we performed large-scale field surveys across three biogeographic regions in Atlantic Canada along the coasts of New Brunswick, Nova Scotia, and Newfoundland. First, we examined variation in eelgrass bed structure (shoot density, canopy height, biomass) and environmental parameters (tissue nitrogen and carbon, sediment organic content, microphytobenthos and annual algae) at 19 sites across the 3 regions. Next, we examined the variation in macroinfauna community composition and summary measures (species richness, diversity, total abundance, and biomass). We then linked the eelgrass bed structure and environmental variables to the macroinfauna community to determine what best explained observed patterns. Our results indicate that eelgrass bed structure and most environmental parameters varied at the site level, whereas most variation in the macroinfauna community was explained by region. Furthermore, the abundance of microphytobenthos was the best predictor of the macroinfauna community. We suggest that in moving forward with protecting and managing eelgrass habitats, eelgrass bed structure should be assessed on a site-by-site basis; however, benthic productivity (microphytobenthos) may be a useful tool in evaluating macroinfauna and ecosystem health on a region-scale.

Infralittoral-sublittoral (submerged zone) macroinfauna community structure of high-impact, medium-impact and non-impact beaches on the Gulf of Cádiz coast (SW Spain). Evaluation of anthropogenic alterations: Nourishments, human impact and urbanization

Beaches are dynamic transitional environments subject to numerous natural and anthropic alterations. In these ecosystems, the infralittoral-sublittoral macrofauna communities play a key role in the food web. The objective of this study was to compare macrofauna communities on six beaches on the Gulf of Cádiz coast, which were classified according to the anthropic alterations they support, and evaluate the influence of abiotic factors on the species distribution. Sampling was done in the infralittoral-sublittoral zone of each beach using a modified manual dredge. Five perpendicular transects of 25 m, each separated by 10 m, were performed per beach, with a total sample area of 43.75 m2 per beach. A total of 27 species were found, of which Donax trunculus, Diogenes pugilator, and Tritia grana were the most abundant. Anthropogenic effects are appreciable in the infralittoral-sublittoral although they are areas that are permanently submerged and less exposed than the intertidal. Beach nourishments carried out with large volumes of sand can alter the grain size, the most influential parameter on the distribution of the species, and consequently, affect the macrofauna community that inhabits these beaches.

Spatial Variation of Macroinfaunal Communities Associated with Zostera marina Beds Across Three Biogeographic Regions in Atlantic Canada

Spatial Variation of Macroinfaunal Communities Associated with Zostera marina Beds Across Three Biogeographic Regions in Atlantic Canada

Benthic macroinfaunal community structure, resource utilisation and trophic relationships in two Canadian Arctic Archipelago polynyas.

Climate change driven alterations to patterns of Arctic marine primary production, with increasing phytoplankton- and decreasing ice algal production, have the potential to change the resource utilisation and trophic structure of the benthic communities relying on the algae for food. To predict the benthic responses to dietary changes, we studied the macroinfaunal community compositions, and used the faunal δ13C and δ15N signatures to investigate their main food sources and trophic positions in North Water (NOW) and Lancaster Sound (LS) polynyas in the Canadian Arctic Archipelago. Macroinfaunal density (10 952 ind. m-2) and biomass (3190 mg C m-2) recorded in NOW were higher than previously found in the Arctic at depths >500m, and significantly higher than in LS (8355 ind. m-2 and 2110 mg C m-2). This was attributed to higher particulate organic matter fluxes to seafloor in NOW. Polychaetes were significant taxa at both sites in terms of density and biomass, and in addition crustacean density in NOW and bivalve density in LS were high. Facultative filter and surface deposit feeders were highly prevalent at both sites, suggesting feeding plasticity is a successful strategy for accessing different food sources. The macrofaunal δ13C signatures reflected the signatures of pelagic particulate organic matter at the sites, and an isotope mixing model confirmed phytoplankton as the main food source for most taxa and feeding guilds. The food web length in LS was longer than in NOW (3.2 vs. 2.8 trophic levels). This was attributed to a larger reliance on reworked organic matter by the benthic community in LS, whereas the high export fluxes at the highly productive NOW resulted in higher rates of selective consumption of fresh algal matter. Despite studies suggesting that loss of ice algae from consumer diets in the Arctic might have a negative impact on the benthos, this study suggests that Arctic macrobenthic communities thrive using phytoplankton as their main food source and should thus be able to cope or even benefit from predicted changes to patterns of primary production.

Estimating the effect of burrowing shrimp on deep-sea sediment community oxygen consumption.

Sediment community oxygen consumption (SCOC) is a proxy for organic matter processing and thus provides a useful proxy of benthic ecosystem function. Oxygen uptake in deep-sea sediments is mainly driven by bacteria, and the direct contribution of benthic macro- and mega-infauna respiration is thought to be relatively modest. However, the main contribution of infaunal organisms to benthic respiration, particularly large burrowing organisms, is likely to be indirect and mainly driven by processes such as feeding and bioturbation that stimulate bacterial metabolism and promote the chemical oxidation of reduced solutes. Here, we estimate the direct and indirect contributions of burrowing shrimp (Eucalastacus cf. torbeni) to sediment community oxygen consumption based on incubations of sediment cores from 490 m depth on the continental slope of New Zealand. Results indicate that the presence of one shrimp in the sediment is responsible for an oxygen uptake rate of about 40 µmol d−1, only 1% of which is estimated to be due to shrimp respiration. We estimate that the presence of ten burrowing shrimp m−2 of seabed would lead to an oxygen uptake comparable to current estimates of macro-infaunal community respiration on Chatham Rise based on allometric equations, and would increase total sediment community oxygen uptake by 14% compared to sediment without shrimp. Our findings suggest that oxygen consumption mediated by burrowing shrimp may be substantial in continental slope ecosystems.

Decomposition of jellyfish carrion in situ: Short-term impacts on infauna, benthic nutrient fluxes and sediment redox conditions

Jellyfish often form blooms that persist for weeks to months before they collapse en masse, resulting in the sudden release of large amounts of organic matter to the environment. This study investigated the biogeochemical and ecological effects of the decomposition of jellyfish in a shallow coastal lagoon in New South Wales, Australia. Catostylus mosaicus carrion was added to the surface of shallow sub-tidal sediments and biogeochemical parameters and macrofaunal abundance immediately below the jellyfish carrion were measured over three days. Sediment plots without jellyfish served as controls. Sediment oxygen demand and carbon and nitrogen efflux increased by up to 60-fold in the jellyfish plots, compared to control plots, and dissolved organic nutrient fluxes were more sustained than in previous studies due to the use of fresh rather than frozen biomass. The decomposing jellyfish progressively altered sediment redox conditions, indicated by an increase in porewater iron (II) and sulfide concentrations measured by high-resolution in situ diffusive samplers. Abundance of some macrofaunal taxa in the jellyfish plots decreased relative to controls, however, the abundance of a carnivorous gastropod, which was presumably feeding on the carrion, increased in the jellyfish plots. While jellyfish carrion may be a food source for some macrofauna, low oxygen conditions coupled with the accumulation of toxic dissolved sulfides in the near-surface sediments may explain the overall change in the macroinfaunal community.

Macroinfaunal Communities on mud Volcanoes in the Gulf of Cádiz (NE Atlantic): Preliminary Results

This study was carried out from a series of samples obtained from the diapiric mud volcano system of the Guadalquivir River (Gulf of Cadiz) during the ARSA 0307 campaign. Five stations were sampled over depths ranging between 490 and 717 m. The main objective of this study is to provide a preliminary description of the infaunal communities living in these environments, reaching the taxonomic rank of family. As a result of this study we conclude that the polychaetes were the most abundant faunistic group in all stations sampled, accounting for more than 50 % of the total infaunal abundance. Following in abundance were crustaceans, dominated by amphipods and the group called “others.” Molluscs and echinoderms are the infauna with the lowest abundance values. After a multivariate analysis, no defined groupings were found between the different stations.

Infaunal macrobenthos in the Porcupine Bank (NE Atlantic)

Infaunal macrobenthos in the Porcupine Bank (NE Atlantic)