Benthic Macrofaunal Communities Research Articles

Biodiversity patterns of the benthic macrofaunal communities across the intertidal sedimentary shores of two Antarctic islands

Antarctic benthic ecosystems support a unique fauna characterized by high levels of diversity and endemism. However, our knowledge of the macrofauna communities across the Antarctic intertidal sedimentary shore is limited, and their fundamental ecological features, including spatial variability, remain poorly understood. This study aimed to investigate the abundance, community structure (i.e. taxa-specific abundance), and biodiversity patterns (α-, β-, and λ-diversity) of benthic macrofauna communities on intertidal sedimentary shores of two Antarctic islands (South Shetland archipelago, N of Antarctic Peninsula): Livingston and Deception. We conducted a quantitative sampling during two Austral summer campaigns (2004 and 2005), studying eleven intertidal sites, with five sites located on Livingston and six on Deception. Our results demonstrated a significantly higher abundance of intertidal benthic macrofauna communities on Livingston than on Deception. Furthermore, significant differences in community structure were observed between the two islands. In terms of biodiversity patterns, there were no significant differences in the number of taxa within communities (α-diversity) between the two islands. However, significant differences in the variation of community composition (determined by the number and identity of taxa) between intertidal sites (β-diversity) were observed, shedding light on the higher total taxa count (λ-diversity) on Livingston compared to Deception. We suggest that the island-specific characteristics (e.g., granulometric characteristics, ice disturbance, sedimentation rates, and geothermal activity) determine the differences observed in macrofauna communities. However, other ecological processes and factors are operating on different spatial and temporal scales (e.g., population dynamics, biotic interactions, oceanographic conditions, and climate change) that influence the occurrence and abundance of macrofaunal taxa. Our findings contribute to the fundamental understanding of the spatial variability of these communities and provide essential information for better management decisions and conservation practices in Antarctic coastal ecosystems.

Benthic macrofauna communities reflect eutrophic condition in a low-inflow estuary

Nutrient enrichment drives potentially severe changes in low-inflow and temporarily closed estuaries where tidal mixing and freshwater flushing is limited, and bottom-water anoxia occurs frequently. Our research assesses the influence of nutrient enrichment by comparing macrobenthos community metrics in a persistently hypereutrophic South African estuary. This is then compared to published literature for an estuary with a similar catchment size and mean annual runoff, but which experiences limited anthropogenic nutrient input. Macroinvertebrate abundance and richness were higher in an estuary with limited anthropogenic nutrient loading, and this varied seasonally for both estuaries. Oxygen saturation had a significant influence on taxonomic level abundances, with lower oxygen levels in the polluted estuary reducing macroinvertebrate abundances. Macroinvertebrates tolerant of organic pollution (e.g., Oligochaeta) were also more abundant in the polluted estuary. This study highlights the effects of increased nutrient loading in low-inflow estuaries and confirms the supposition from several previous studies that macrozoobenthos could be used as a responsive tool from a bioindicator perspective to monitor eutrophication.

Methane diffusion affects characteristics of benthic communities in and around microbial mat-covered sediments in the northeastern Japan sea

We investigated relationships between features of benthic macrofaunal communities and geochemical parameters in and around microbial mat-covered sediments associated with a methane seepage on Sakata Knoll in the eastern Japan Sea. A depression on top of the knoll corresponds to a gas-hydrate-bearing area with seepage of methane-rich fluid, and microbial mats cover the seafloor sediments. Sediment cores were collected at three sites for this study: one within a microbial mat, a second a few meters outside of the microbial mat, and a third from a reference site outside the gas-hydrate-bearing areas. Morphological analysis showed that the site inside the microbial mat had higher macrofaunal density and biomass compared with the other sites. 18S rRNA gene analysis showed that annelids were dominant in the surface sediment inside the microbial mat with the possible occurrence of microbial anaerobic oxidation of methane (AOM), whereas in the surface sediments outside the microbial mat and at the reference site the predominant species belonged to phylum Cercozoa. Morphological analysis also showed that the surface sediment inside the microbial mat noticeably favored annelids, with dorvilleid Ophryotrocha sp. and ampharetid Neosabellides sp. identified as major constituents. Statistical analysis showed that sulfidic sediment conditions with concentrations of H2S up to 121 μM resulting from AOM likely resulted in the predominance of annelids with tolerance to sulfide. Both the 18S rRNA genes and macrofaunal characteristics showed that benthic biodiversity among the three sites was greatest outside the microbial mat. The site outside the microbial mat may represent geochemical transition conditions, including a lower rate of upward methane gas-flow compared with the site inside the microbial mat. The high biodiversity there might result from the presence of species specifically suited to the transition zone as well as species also found in photosynthesis-based communities of the background environment.

Effects of Spartina alterniflora invasion on macrobenthic faunal community in different habitats of a mangrove wetland in Zhanjiang, South China

Mangroves are indispensable for maintaining biodiversity and human well-being in local or global, and their structure and functioning highly depend on the macrobenthos Although exotic cordgrass, Spartina alterniflora Loisel, is an increasing threat to the mangrove wetlands (including the associated unvegetated shoals) of China, its effects on the macrobenthic fauna in such wetlands is poorly understood. The macrobenthic faunal communities were compared in (1) an Avicennia marina monoculture vs. an S. alterniflora-invaded A. marina stand (a mixture of A. marina and S. alterniflora) and in (2) an unvegetated shoal vs. an S. alterniflora-invaded shoal that had rapidly become an S. alterniflora monoculture in Zhanjiang, China. The presence of S. alterniflora had little influence on indices of the macrobenthic faunal community in the A. marina monoculture, but significantly decreased the density and biomass of macrobenthic faunal community in the unvegetated shoal. The composition of the macrobenthic faunal community was more similar between the invaded and non-invaded A. marina stand than between the invaded and non-invaded unvegetated shoal. Compared the four habitats, the presence of vegetation significantly decreased the density and biomass of macrobenthic faunal community. Further analysis showed that differences in the macrobenthic faunal community between invaded and non-invaded habitats were associated with increases in the sediment organic matter content and plant density. These results indicate that the effects of S. alterniflora on the macrobenthic faunal community depend on habitat type of mangrove wetland is invaded, whereas additional research is needed to confirm and clarify these findings.

Seafloor warm water temperature anomalies impact benthic macrofauna communities of a high-Arctic cold-water fjord

Amid the alarming atmospheric and oceanic warming rates taking place in the Arctic, western fjords around the Svalbard archipelago are experiencing an increased frequency of warm water intrusions in recent decades, causing ecological shifts in their ecosystems. However, hardly anything is known about their potential impacts on the until recently considered stable and colder northern fjords. We analyzed macrobenthic fauna from four locations in Rijpfjorden (a high-Arctic fjord in the north of Svalbard) along its axis, sampled intermittently in the years 2003, 2007, 2010, 2013 and 2017. After a strong seafloor warm water temperature anomaly (SfWWTA) in 2006, the abundance of individuals and species richness dropped significantly across the entire fjord in 2007, together with diversity declines at the outer parts (reflected in Shannon index drops) and increases in beta diversity between inner and outer parts of the fjord. After a period of three years with stable water temperatures and higher sea-ice cover, communities recovered through recolonization processes by 2010, leading to homogenization in community composition across the fjord and less beta diversity. For the last two periods (2010-2013 and 2013-2017), beta diversity between the inner and outer parts gradually increased again, and both the inner and outer sites started to re-assemble in different directions. A few taxa began to dominate the fjord from 2010 onwards at the outer parts, translating into evenness and diversity drops. The inner basin, however, although experiencing strong shifts in abundances, was partially protected by a fjordic sill from impacts of these temperature anomalies and remained comparatively more stable regarding community diversity after the disturbance event. Our results indicate that although shifts in abundances were behind important spatio-temporal community fluctuations, beta diversity variations were also driven by the occurrence-based macrofauna data, suggesting an important role of rare taxa. This is the first multidecadal time series of soft-bottom macrobenthic communities for a high-Arctic fjord, indicating that potential periodic marine heatwaves might drive shifts in community structure, either through direct effects from thermal stress on the communities or through changes in environmental regimes led by temperature fluctuations (i.e. sea ice cover and glacial runoff, which could lead to shifts in primary production and food supply to the benthos). Although high-Arctic macrobenthic communities might be resilient to some extent, sustained warm water anomalies could lead to permanent changes in cold-water fjordic benthic systems.

Contrasting benthic ecological functions in deep-sea canyon and non-canyon habitats: Macrofaunal diversity and nutrient cycling

Understanding ecosystem functioning and stability of continental slope environments requires assessing the effects of habitat heterogeneity (canyon and non-canyon habitats) on benthic macrofaunal communities and ecosystem functioning. We evaluated the importance of habitat heterogeneity and phytodetrital enrichment in canyon, channel, and inter-canyon habitats of the Gulf of Maine, Northwest Atlantic. Using an ROV, we collected sediment cores at five seafloor sites in the Gulf of Maine (663–969 m depth). Over ∼24 h, we incubated ∼6 cores per site, three of which were enriched with the diatom Chaetoceros muelleri. For all core treatments, we measured macrofaunal composition, functional diversity indices (functional richness, evenness, and divergence), and benthic nutrient fluxes (ammonium, nitrate, phosphate, and silicate), as well as oxygen consumption. We also dedicated two non-incubated cores to quantifying sedimentary and chemical-physical characteristics. We found that benthic communities differed among the three habitats, but these differences and our phytodetrital additions did not translate to significant differences in rates of benthic fluxes among habitats., expect for nitrate and phosphate fluxes. Total organic carbon and chlorophyll-a explained most of the variation in oxygen consumption, which was similar in enriched and control cores. We conclude that large-scale habitat heterogeneity contributes to variation in benthic community composition, but with no consistent effect on nutrient fluxes. These results also suggest that phytodetrital deposition influences oxygen consumption but plays a lesser role in short-term nutrient cycling in deep-sea heterogeneous habitats, perhaps masked by other environmental variables. Moreover, sediments with high functional richness and relatively high functional divergence may sometimes lack the specific trait types that rapidly enhance nutrient regeneration and thus contribute to ecosystem functioning of deep-sea sediments.

The interplay between terrestrial organic matter and benthic macrofauna: Framework, synthesis, and perspectives

AbstractEcosystems are shaped by physical, chemical, and biological drivers, which affect the quality and quantity of basal energy sources, with impacts that cascade to higher trophic levels. In coastal, shelf, and marine habitats, terrestrial‐derived organic matter (ter‐OM) can be a key driver of ecosystem structure and function. Climate change is expected to alter land–ocean connectivity in many regions, with a broad range of potential consequences for impacted ecosystems, particularly in the coastal zone. The benthic compartment is an important link between the large organic carbon pools stored on land and the marine environment. At the same time, the macrofauna plays a key role in the processing, biological uptake, and fate of ter‐OM in the aquatic environment, with implications for coastal ecosystem functioning, benthic–pelagic coupling, carbon burial, and biogeochemical cycles. However, information about relationships between land–ocean connectivity (including ter‐OM loads) and coastal benthic community responses remains spread across disciplines, and a broad perspective on the potential impacts of a changing climate is still missing. Here, we explore the interplay between benthic macrofaunal communities and ter‐OM through a paired narrative and research weaving analysis, which combines systematic mapping and bibliometric analysis. The review describes the past development and status of the research field as well as the lack of information in some geographical regions and habitats worldwide. We highlight the role of macrofauna in carbon cycling and the growing evidence that ter‐OM plays a key role in the structure and function of benthic communities, not strictly limited to estuarine habitats. Climate change poses challenges for the prediction of future ter‐OM fluxes and potential macrofauna responses to this additional stressor, thus requiring new methodological approaches (e.g., multimarker approaches for OM characterization) and long‐term monitoring programs across different habitats and spatiotemporal scales.

Distribution of benthic macrofaunal communities in intertidal flat under hydrodynamic influence: a case study of Jiangsu coast, East China

Distribution of benthic macrofaunal communities in intertidal flat under hydrodynamic influence: a case study of Jiangsu coast, East China

Simulating fish farm enrichment and fallowing impacts reveals unequal biogeochemical recovery of benthic variables

Finfish aquaculture is playing an increasing role in global food provision, with accompanying increases in benthic impacts under intensive pen production systems. Deposited faeces under and near fish pens affect the seafloor environment and biogeochemical functioning. To maintain healthy coastal environments, many fish farms operate by alternating input and fallowing periods to allow benthic coastal receiving environments to recover from excess organic matter inputs. Here, we used flow-through annular flume mesocosms to simulate sustained organic matter inputs to the benthos with a subsequent fallowing period of no inputs. To quantify the effects of excess organic matter loading on benthic receiving environments, we carried out repeated closed-system flux studies to quantify the benthic carbon mineralisation processes, with a focus on benthic oxygen, inorganic and organic carbon, nitrogen, phosphate, and sulphide fluxes, along with the redox state throughout the input and recovery period. We found that recovery periods were input-dependent, with parameters requiring longer fallowing periods to recover following larger inputs. While some benthic parameter fluxes such as dissolved organic carbon, sulphide, and ammonium returned to their pre-input state relatively rapidly (1-2 mo) following cessation of inputs, others such as sediment oxygen demand, ammonium, and redox required longer (>7 mo) to recover. Our results suggest that in situations where the benthic macrofaunal community has been severely impaired, extended fallowing periods may be required in order to permit the biogeochemical composition of the seabed to return to a more natural state, with implications for farm-consenting permits and planning as well as operational fallowing practices.

Recolonization and recovery of an Arctic benthic community subject to mine-tailings deposits

Deposition of large volumes of mine tailings takes place in several Norwegian fjords, but the impacts on marine ecosystems have received relatively little scientific attention. At a 40 + −year old tailing deposition area for a copper mine in the Arctic fjord Repparfjorden, we investigated both short-term colonization of mine tailings-contaminated sediments through a field experiment, and the present faunal state in the old deposit area. Copper-concentrations at the old deposition site were still high (up to 291 mg/kg dry weight (dw)), and exceeded the Norwegian environmental-quality threshold (84 mg/kg dw). Furthermore, copper was identified as a significant structuring factor for the fauna in the fjord, although faunal diversity was relatively high and the community not severely disturbed. In the colonization experiment, experimental boxes filled with defaunated sediment capped with mine tailings were subject to colonization for 15 months. Benthic macrofaunal communities were successfully established in all boxes, but the boxes with tailings showed lower species richness, abundance and biomass than the controls. Mine tailings continue to have local impacts on seafloor communities decades after deposition, and even low levels of metal-rich sediments can affect faunal recruitment. These results have implications for submarine deposition of mining waste and the impacts they have on coastal ecosystems.

Effect of Temporarily Opening and Closing the Marine Connection of a River Estuary

The lower Rio Grande is a river-dominated estuary that serves as the border between Texas, USA, and Tamaulipas, Mexico. River estuaries encompass the section of the river influenced by tidal exchange with the Gulf of Mexico, but the connection with the Rio Grande is intermittent and can be temporarily open or closed. During the 4.8-year study period, the river mouth was closed 30% of the time, mostly during average or dry climatic conditions, with the temporary closing of the river mouth being linked to hydrology. When the Rio Grande estuary is closed, salinity is low (1.5 psu compared to 4.8 psu when open), nitrate plus nitrite are low (4.4 μM compared to 31.5 μM when open), and ammonium is high (9.6 μM compared to 4.3 μM when open), but chlorophyll is similar (20 μg/L compared to 21 μg/L when open). Benthic macrofaunal abundance and biomass are higher when the river mouth is closed: 16,700 individuals m−2 and 3.3 g m−2 compared to 8800 individuals m−2 and 2.4 g m−2 when the Rio Grande river mouth is open. Benthic macrofaunal community structure is divided into two groups: chironomid larvae and Oligochaeta dominated when the river mouth was closed, whereas polychaetes Mediomastus ambiseta and Streblospio benedicti dominated when the river mouth was open. The implications of these results for managing freshwater flows are that the open and closed conditions each have a characteristic benthic macrofaunal community that is strongly influenced by system hydrology.

Species and genetic diversity relationships in benthic macroinvertebrate communities along a salinity gradient

BackgroundSpecies- and genetic diversity can change in parallel, resulting in a species-genetic diversity correlation (SGDC) and raising the question if the same drivers influence both biological levels of diversity. The SGDC can be either positive or negative, depending on whether the species diversity and the genetic diversity of the measured species respond in the same or opposite way to drivers. Using a traditional species diversity approach together with ultra-conserved elements and high throughput sequencing, we evaluated the SGDCs in benthic macrofauna communities in the Baltic Sea, a geologically young brackish water sea characterised by its steep salinity gradient and low species richness. Assessing SGDCs from six focal marine invertebrate species from different taxonomic groups and with differing life histories and ecological functions on both a spatial and temporal scale gives a more comprehensive insight into the community dynamics of this young ecosystem and the extrinsic factors that might drive the SGDCs.ResultsNo significant correlations between species diversity and genetic diversity were found for any of the focal species. However, both negative and positive trends of SGDCs for the individual focal species were observed. When examining the environmental drivers, no common trends between the species were found, even when restricting the analysis to specific taxonomic classes. Additionally, there were no common environmental factors driving the diversity relationships for species sharing the same SGDC trend (positive or negative). Local population dynamics, together with the invasion history of the individual species and their unique adaptation to the distinctive environment of the Baltic Sea, are expected to be of major influence on the outcome of the SGDCs.ConclusionsThe present results highlight the importance of assessing SGDCs using multiple species, not just a single indicator species. This emphasises a need to pay attention to the ecology and life history of the focal species. This study also provides insight into the large differences in both patterns and drivers of genetic diversity, which is important when including genetic biodiversity in conservation plans. We conclude that the effects of environmental and biological factors and processes that affects diversity patterns at both the community and genetic levels are likely species dependent, even in an environment such as the Baltic Sea with strong environmental gradients.

Benthic Macrofauna Community Bioirrigation Potential (BIPc): Regional Map and Utility Validation for the South-Western Baltic Sea.

Benthic community bioirrigation potential (BIPc), an index developed to quantify the anticipated capacity of macrofauna to influence the solute exchange at the sediment-water interface, was calculated for the south-western Baltic Sea. This index can be regarded as an effect trait that is useful for predicting ecosystem processes impacted by animal burrow ventilation. The special feature, and presumably an advantage, of BIPc, compared to alternative recently developed benthic macrofauna-based bioirrigation indices, lies in its ability to distinguish the taxa-specific score values between diffusion- and advection-dominated sediment systems. The usefulness of the BIPc index was compared against the estimates of the well-established community bioturbation potential index (BPc). The BIPc index displayed a moderately but significantly stronger correlation with estimates of irrigation rates derived from tracer experiments. Using a random forest machine learning approach and a number of available relevant environmental predictor layers, we have modelled and mapped the spatial differences in this ecosystem functioning expression. The key species contributing to bioirrigation potential in the study area were identified. The interannual variation in BIPc was assessed on a small exemplary dataset. The scores required to calculate the index, that were assigned to 120 taxa dominating abundance and biomass in the region, are provided for reuse. The utility, temporal variability and uncertainty of the distribution estimate are discussed.

Community Structure of Benthic Macrofauna and the Ecological Quality of Mangrove Wetlands in Hainan, China

Few studies have systematically assessed the ecological status of mangrove wetlands following the stress of anthropogenic activities in China. This study investigated the spatial and seasonal distribution of benthic macroinvertebrate communities and assessed the ecological quality of mangrove habitats on an island scale in Hainan, China (containing the third largest mangrove area of China and the highest mangrove species richness). For the benthic macrofauna community structure, a total of 102 macrobenthic taxa belonging to 50 families were identified, with Crustaceans, Molluscs, Polychaetes, and Oligochaeta having relative abundances of 52.3%, 36.1%, 10.8%, and 0.8%, respectively. Decapoda and Gastropoda dominated the benthic community abundance. Non-metric multidimensional scaling and an analysis of similarities revealed significantly different macroinvertebrate assemblages among the regions during the two seasons. The South mangroves had the lowest macrofauna species numbers, biodiversity, richness, and abundance. The macrofaunal species richness, Shannon index, Margalef index, abundance, and biomass markedly affected by region and season. As indicated by the biotic indices AMBI (AZTI’s Marine Biotic Index) and M-AMBI, more than half of the mangrove habitats on Hainan Island were slightly to heavily disturbed and had poor to moderate ecological quality. Our results recommend long-term monitoring for evaluating the quality status of mangrove wetlands and avoiding extensive land-use conversion of mangroves. Holistic approaches considering ecological characteristics and combining information on both floral and faunal functionality would contribute to the effective management and conservation of mangroves in disturbed areas.

Effects of Meteorological Factors on Waterbird Functional Diversity and Community Composition in Liaohe Estuary, China.

Functional trait diversity represents ecological differences among species, and the structure of waterbird communities is an important aspect of biodiversity. To understand the effect of meteorological changes on the waterbird functional diversity and provide suggestions for management and conservation, we selected a study area (726 km2) in Liaohe Estuary, located in northeast China. We explored the trends of the waterbird functional diversity changes in response to meteorological factors using fourth corner analysis. Our study demonstrated that temperature was a key factor that impacted waterbird functional diversity in spring, while precipitation had a greater impact in autumn. The population size of goose and duck was positively associated with temperature and negatively with precipitation, while that of the waders (Charadriiformes) showed opposite association trends. Herbivores and species nesting on the bare ground exhibited responses to meteorological factors similar to those of geese and ducks, while benthivores and waterbirds nesting under grass/shrubs exhibited trends similar to those of waterbirds. Waterbirds with smaller bodies, shorter feathers, and lower reproductive rates preferred higher temperatures and less precipitation than other waterbirds. In addition, we observed seasonal variations in waterbird functional diversity. In spring, we should pay attention to waders, herbivores, and waterbirds nesting on the bare ground when the temperature is low. In autumn, waders, benthivores, and omnivores need more attention under extreme precipitation. As the global climate warms in this study area, waterbird functional diversity is expected to decline, and community composition would become simpler, with overlapping niches. Biodiversity management should involve protecting intertidal habitats, supporting benthic macrofaunal communities, preparing bare breeding fields for waterbirds favoring high temperatures to meet their requirements for population increase, and preventing the population decline of geese and ducks, herbivores, and species nesting under grass/shrubs. The findings of our study can aid in developing accurate guidelines for waterbird biodiversity management and conservation.

Multiple effects of a typhoon strike and wastewater effluent on benthic macrofaunal communities in a mangrove estuary

Multiple effects of a typhoon strike and wastewater effluent on benthic macrofaunal communities in a mangrove estuary

Seasonal trends in benthic macrofauna communities and their relationship with environmental factors in an Atlantic lagoonal system

Seasonal trends in benthic macrofauna communities and their relationship with environmental factors in an Atlantic lagoonal system

Patterns of Benthic Communities in Arctic Fjords (Novaya Zemlya Archipelago, Kara Sea): Resilience vs. Fragility

Despite a large number of studies, a detailed overall picture of benthic communities zonation in the Arctic fjords is currently lacking. Our study aimed to find out whether there is a universal model for the distribution of benthic communities based on the structural features of the fjords. We examined benthic macrofaunal communities in fjords with various environmental settings on the eastern coast of Novaya Zemlya Archipelago, Kara Sea. The material was collected during five cruises undertaken from 2013 to 2016. A total of 50 stations located in the five fjords were taken. In all five fjords, macrofauna had a similar composition assembled from a regional species pool, with a predominance of species tolerant to glacial sedimentation and fluctuations in temperature and salinity. Benthic communities changed consistently along the axis of the bay from the outer slope to the inner parts. Biodiversity and quantitative characteristics of the macrofauna decreased along the environmental gradient related to terrigenous and glacial runoff, consistent with patterns reported in other studies of Arctic glacial fjords. The most impoverished communities were dominated by bivalvePortlandia arcticaand isopodSaduria sabini. At the same time, fjord walls and sills, characterized by low sedimentation rates, strong currents and the presence of ice-rafted debris, were inhabited by patchy distributed benthic communities dominated by species confined to hard substrates. In general, the distribution of communities corresponded to five zones: depleted inner periglacial areas, the upper subtidal belt with stony substrates, deep inner semi-isolated basin, outer non-isolated basins and upper slope transitioning to lower slope. Our study can provide a reference point for monitoring changes in fjord ecosystems in response to climate change and the potential impact of human activities.

Taxonomic and functional diversity of benthic macrofauna associated with rhodolith beds in SE Brazil.

Rhodoliths are free-living and morphologically diverse marine calcareous algae commonly distributed over the continental shelf seafloor. They increase the seabed structural complexity and are of potential value as feeding and reproductive grounds for a myriad of marine fauna. The higher structural seabed complexity within rhodolith beds may also increase benthic diversity by creating microhabitats, but this relationship has been rarely explored within rhodolith beds worldwide. Here we compared benthic macrofaunal (>500 µm) structure on rhodolith beds (nodule epifauna) and within unconsolidated sediments (sediment infauna) under high and low-density beds to test whether rhodolith bed density and nodule morphology influenced macrofaunal assemblages. We observed that macrofaunal density on nodules (2538 ± 288.7 ind·m−2) was 15-fold higher when compared to sediments under those beds (166 ± 38.8 ind·m−2). Rhodolith bed density was positively related to macrofaunal density, composition, and functional diversity on the rhodoliths. Low-density beds (61 ± 27.1 nodules·m−2) with discoid-shape nodules were dominated by peracarid crustaceans whereas high-density beds (204 ± 18.7 nodules·m−2) with spheroidal nodules were dominated by Annelid polychaetes. The sediment macrofauna was also positively influenced by the density of rhodolith nodules, which increased sediment carbonate and organic quality (protein and lipids) under high-density beds. Macrofaunal functional diversity was generally higher on rhodoliths, with low similarity (low nestedness) and high taxa turnover between macrofaunal assemblages of rhodoliths and sediments. These findings indicate that rhodolith beds provide an unique habitat for benthic macrofaunal communities, with exclusive functional and taxonomic richness that are likely not typical in the unconsolidated sediment below these beds in SE Brazil. This study highlights the importance of protecting rhodolith beds from multiple sources of anthropogenic disturbance and exploration on continental shelves.

Macrofaunal assemblage in the intertidal area of Saudi Arabian Gulf Coast

The Saudi Arabian Gulf coast is witnessing many industrial, recreational and other developmental activities. Impact of these activities on the intertidal macrofaunal communities of this region has not been documented well. Thirty four stations falling under four zones along this coast were sampled to study the benthic macrofaunal community. A total of 81 taxa were recorded and the species richness varied between the zones. Among the 48 polychaetespecies found, Exogone heterosetosa, Dialychone collaris, Ophelina longicaudata, Paraprionospio pinnata, Perinereis falsovariegata and Scololepis squamata were dominant. Species such as Littoraria scabra, Bullia vittata, Incatella cingulata, Meretrix meretrix, Donax sp. and Maoricardium setosum were dominant among the twelve gastropod species. The thirteen species of macrofauna identified to occur in all the zones comprised eight species of gastropods besides two species each of amphipods and isopods and one species of cumacean. ANOSIM showed significant differences in assemblage overall among the four zones and in pairwise comparison. Distance based linear modeling (DISTLM) showed the environmental parameters to explain 55.67% of the variability in macrofauna with variables such as pH, salinity, temperature, pebble and gravel showing significant relationship with macrofauna and explained higher variability. The alpha diversity values were comparatively lower in zone 3 which had high anthropogenic pressure. Shannon–Wiener​ diversity, Margalef richness and more importantly the M-AMBI showed the healthy nature of the study area. The findings of the present study are helpful in tracing the future changes in the intertidal habitat due to anthropogenic activities in this fast developing geographical area.