Amphipod Assemblages Research Articles

“Hidden” biodiversity: a new amphipod genus dominates epifauna in association with a mesophotic black coral forest

AbstractBlack corals are important components of mesophotic and deep-water marine habitats. Their presence at great depths (e.g., 50 to 200 m) makes accessibility difficult, limiting our understanding of the associated biodiversity. Amphipods dominate vagile epifauna in marine habitats around the world, fulfilling important ecosystem functions. However, there are no studies on amphipods exclusively associated with black corals, including relationships between their ecological patterns (e.g., abundances) and the size of coral colonies. We investigated the epifaunal composition and abundance associated with black coral colonies of Antipathella wollastoni in the subtropical eastern Atlantic Ocean. In total, 1,736 epifaunal individuals were identified, of which 1,706 (98.27%) were amphipods, belonging to 6 taxa. We identified and described a new amphipod genus and species within the Stenothoidae family, Wollastenothoe minuta gen. nov., sp. nov., which outnumbered the amphipod assemblage (86.15%) and provided a complete taxonomic key of Stenothoidae family including this new finding. For the first time, the association between an amphipod species and a black coral was described, including a strong correlation between coral colony size and amphipod abundances. This study demonstrates that epifauna associated with mesophotic black corals remains largely undescribed.

An annotated checklist of the Amphipoda (Crustacea) of Kuwait, north-western Arabian Gulf

Kuwait’s intertidal and subtidal habitats were surveyed from 2013 to 2016 for amphipods, and earlier records from Kuwait and the rest of the Gulf were compared to provide the first annotated checklist of Amphipoda in Kuwait. A total of 82 sites in mainland and islands were surveyed including intertidal and subtidal zones. The resulting data identified 86 amphipod taxa belonging to 54 genera, 32 families and 3 suborders, including 20 new records to science that are currently being described. A total of 46 amphipod species, 34 genera and 19 families constituted new regional records either for Kuwait or the entire Gulf area. Information on local distribution, occurrence, and habitat are provided for each species. Within the tidal zonation, 50 species inhabited both the intertidal and subtidal areas, 19 were intertidal, 12 subtidal, and 3 species were found in the supratidal zone. Sandy and rocky shores supported the most diverse amphipod assemblages. A gradient of increasing amphipod species richness from north to south along Kuwait’s mainland coastline was revealed. The high level of regional endemism supported notable taxonomic distinction of the amphipod fauna of Kuwait from the other Gulf areas. Compositional dissimilarity among amphipod faunas increased with distance within a wide longitudinal gradient across the Gulf, Sea of Oman, and north-western Arabian Sea.

The remarkable Ponto-Caspian amphipod diversity of the lower Durso River (SW Caucasus) with the description of Litorogammarus dursi gen. et sp. nov.

The first insight into the unexpectedly diverse amphipod assemblage of the Durso River (Novorossiysk area) in the SW mountainous pre-Caucasian area is presented. The presence of six species is revealed, including three new records for the area and one species new to science. The phylogenetic relationships of all studied species and their relatives were examined based on the divergence of the COI mtDNA gene marker (barcoding). The conducted research clearly showed that the coastal part of the Black Sea and the adjacent pre-Caucasian river/land areas harbors a significant undescribed diversity, and that the transitional sea/river brackish biotopes are important reservoirs of the endemicity. A new genus, Litorogammarus gen. nov. is proposed for native pebble-dwelling species, namely Echinogammarus karadagiensis Grintsov, 2009, Echinogammarus mazestiensis Marin & Palatov, 2021 and the newly discovered Litorogammarus dursi sp. nov., from the lower (estuarine) part of the Durso River and adjacent coastal areas. These three species form a strongly supported molecular clade and share a number of characters such as smooth body without carinae and setae, antenna II armed with dense curled setae, lacking calceoli, pereopods III-VII with sparse, short setation, epimeral plates armed with spines only, telson lobes longer than broad, gradually tapering, bearing only spines. Pectenogammarus oliviiformis (Greze, 1985) comb. nov. is also discovered in the area and is re-described herein. Although this is probably one of the most abundant and common coastal pebble-dwelling species along the northeastern coasts of the Black Sea, it was previously poorly described and thus overlooked by researchers.

Spatiotemporal dynamics in freshwater amphipod assemblages are associated with surrounding terrestrial land use type

AbstractBiological assemblages are the result of dynamic processes that have explicit temporal and spatial dimensions. Although biodiversity patterns can be directly inferred from the structure of these assemblages, an assessment of changes through time and space is needed to understand how organisms initially assembled and how they are responding to local environmental and biotic factors. Small freshwater streams are particularly affected by contemporary anthropogenic activities and biological invasions, yet they are commonly less studied, as studies often focus on lakes and large streams. Here, we conducted a spatially explicit analysis of keystone shredder assemblages across eight years in 12 replicated small tributary streams. In each stream, we monitored multiple sites per kilometer of stream length. By assessing temporal beta diversity dynamics, defined by the gain or loss of species or abundance per species at individual sites, we show that changes in amphipod assemblages occur within the context of the surrounding terrestrial matrix and reflect recent amphipod colonization history. While amphipod composition was mostly constant in streams located in forested catchments, streams embedded in catchments with more extensive agricultural land use displayed more pronounced temporal changes, either driven by colonization of unoccupied upstream locations or by more pronounced but undirected fluctuations in gains and losses of species or abundance per species. Our study thus suggests that agricultural landscapes might destabilize aquatic amphipod assemblages, causing higher temporal changes in community structures and highlighting the vulnerability of aquatic ecosystems to terrestrial land use drivers.

The Effect of Environmental Dredging of Muck on an Assemblage of Benthic Amphipods

To yield environmental benefits, fine sediments with ~10% organic matter, termed muck, were dredged from a tributary to the Indian River Lagoon. Key changes were documented by sampling amphipods, sediments, and the water column near the bottom before dredging, and approximately one month and one year after dredging. Overall, muck yielded the fewest taxa, muck or sediments in creeks that were dredged yielded a moderate number of taxa, and undisturbed sediments in the lagoon yielded the highest number of taxa. Amphipods did not appear in areas with muck until one month and one year after dredging. In contrast, amphipods in sediments that were not muck decreased after dredging. Increases in the occurrence of amphipods paralleled increases in concentrations of dissolved oxygen and decreases in the water, silt/clay, and organic content of sediments. Overall, results indicated that conditions for amphipods were improved by removing muck, and that dredging sandier sediment led to decreased taxonomic richness and numbers of amphipods, which resembled the effects of navigational dredging. Thus, this study suggested that managers should consider the type of sediment to be dredged when permitting projects.

Drivers of variation in seagrass-associated amphipods across biogeographical areas

Amphipods are one of the dominant epifaunal groups in seagrass meadows. However, our understanding of the biogeographical patterns in the distribution of these small crustaceans is limited. In this study, we investigated such patterns and the potential drivers in twelve Cymodocea nodosa meadows within four distinctive biogeographical areas across 2000 Km and 13° of latitude in two ocean basins (Mediterranean Sea and Atlantic Ocean). We found that species abundances in the assemblage of seagrass-associated amphipods differed among areas following a pattern largely explained by seagrass leaf area and epiphyte biomass, while the variation pattern in species presence/absence was determined by seagrass density and epiphyte biomass. Seagrass leaf area was also the most important determinant of greater amphipod total density and species richness, while amphipod density also increased with algal cover. Overall, our results evidenced that biogeographical patterns of variation in amphipod assemblages are mainly influenced by components of the habitat structure, which covary with environmental conditions, finding that structurally more complex meadows harboring higher abundance and richness of amphipods associated.

Diversity and Zonation of Benthic Amphipod Crustaceans Affected by the Mississippi Submarine Canyon in the Northern Gulf of Mexico

Amphipod crustacean diversity and zonation are described from the large Mississippi Canyon that extends from the continental shelf across the entire continental margin. Benthic amphipods were sampled on four cruises from 2000 to 2004 from six locations in the Mississippi Canyon from depths of 480 through 2,750 m, and compared with five locations in a second transect on the open continental slope approximately 100 km west of the canyon to assess the canyon effect on the structure and composition of amphipod assemblages. Five replicates were collected from each location using 0.2 m–2 GOMEX box corer. Amphipods amounted to 40% of the total faunal abundance within the canyon compared to only 4% in the non-canyon samples. Of the seventy-two species (19 families) collected, 61 were encountered in the canyon compared to 38 on the non-canyon transect. The trough-like head of the canyon (480 m) supported high densities (4,446–26,933 ind./m2) of the filter feeding, tube dwelling ampeliscid amphipod (Ampelisca mississippiana), the highest densities sampled compared to any other single species, at any other location, either within or outside the canyon, reflecting extreme flux of organic detritus from the continental shelf. The dominance by this single species suppressed the within – habitat (alpha) diversity and evenness, compared to relatively high diversity within the 1,000–1,500 m depths interval both in and outside the canyon. The species richness and alpha diversity exhibited mid-depth maxima at ca. 1,100 m both in and out of the canyon. High species richness (61) over the entire length of the canyon is presumed to be a function of greater topographic complexity and intermittent mass wasting of sediment down the canyon axis. The absence of nestedness is attributed to the amphipod reproductive pattern that lacks dispersive larval stages and brooding comparatively small numbers of eggs in this taxon. Despite depressed diversity at the head of the canyon, the fact that the number of amphipod species in the Mississippi Canyon was 1.5 times their numbers on the adjacent slope suggests that this physiographic feature enriches geographic-scale species diversity.

Influence of environmental factors and sessile biota on vagile epibionts: The case of amphipods in marinas across a regional scale

Marinas are highly anthropized environments, with singular ecological characteristics. In the present study the spatial variability of the amphipod assemblage associated to floating pontoons was analyzed. Moreover, the influence of the environmental data and the sessile biota on the amphipod assemblage structure were assessed. Six marinas were selected along the Southern Iberian Peninsula, three in the Atlantic and three in the Mediterranean, and three floating pontoons were sampled at each marina. Four-teen amphipod species were identified, most of them corresponded to detritivores and generalist species. Statistical analyses considering amphipod composition and abundance did not show significant differences between the Atlantic and the Mediterranean, but there were significant differences among marinas. Copper had a significant correlation with the amphipod assemblage. The sessile species Bugula neritina and Ellisolandia elongata also showed a significant influence on the spatial patterns of the amphipod assemblages. Therefore, environmental conditions and sessile composition seem to affect, simultaneously, the spatial variability of amphipod assemblage associated to floating pontoons in marinas. Both factors are key to understand the singularity of marinas. This fact should be taken into consideration to prevent the use of a single management program in these environments.

Amphipod assemblages associated with native habitat-forming seaweeds of the Alboran Sea: influence by environmental protection and biogeographical patterns

Context Despite the key ecological role played by epifaunal communities associated with macroalgae in temperate coastal rocky shores worldwide, biodiversity and ecological patterns of their associated invertebrate communities are still poorly known. Aims The present study aims to compare the amphipod assemblages associated with the dominant canopy-forming macroalgae in shallow subtidal habitats of the Alboran Sea, as well as to explore its biogeographical patterns and the influence of protection measures. Methods Replicate samples of both Ericaria selaginoides (=Cystoseira tamariscifolia) and Halopteris scoparia were collected at two different bioregions within the Alboran Sea and both inside and outside marine protected areas. Key results Amphipoda was the dominant taxon within the mobile epifaunal community, both in terms of number of species (47 different species were recorded) and individuals (>70% of the total abundance). Assemblages associated with E. selaginoides and H. scoparia differed and showed a marked response to the Mediterranean–Atlantic gradient in this region; species related to warmer waters become increasingly dominant towards the east. However, there were no significant differences in amphipod assemblage composition, abundance or species richness between protected and non-protected areas. Conclusions Obtained results highlighted the relevance of these native macroalgae as habitat for epifauna, as well as the influence of macroalgal identity and regional biogeographical patterns on amphipod distribution. Implications This study provides valuable baseline information to monitor human-induced changes such as coastal pollution, invasive species, and climate change. It also draws attention about the uncertain response of epifaunal communities to management strategies (such as marine protected areas) and ecological processes (e.g. increasing predation pressure).

Which structural traits in Sargassum species really matter for caprellid assemblages?

Algal complexity is an important driver of the benthos in coastal marine ecosystems. Distinct algal architectures host communities with different structures. To assess how amphipod assemblages relate to algal complexity, we studied caprellids in four Sargassum species (S. cymosum, S. filipendula, S. furcatum, S. stenophyllum). Ten fronds from each algae species were collected from rocky shores in the coast of São Paulo (southeastern Brazil) in December 2009 and March 2010. In each frond, caprellids were identified and counted, and algal traits (length, number of branches, and epiphytic algae and hydroid cover) were measured. Sargassum architecture clearly differed among species. Caprellid density and richness significantly varied among Sargassum species and sampling dates, and amphipods showed a clear preference for specific algal traits. Preference for specific structures within the same habitat generates higher caprellid diversity, since it decreases competition for space in different microhabitats created by the structural complexity of algae. Presence of hydroids is the main driver of caprellid assemblage structure, with the former functioning as biogenic sources and influencing qualitative aspects of the habitat.

Soft-bottom exploration of assemblage patterns of the Red Sea amphipods at multiple spatial and vertical scales

We described here the assemblage patterns accompanying the soft-bottom amphipods on both spatial and vertical scales. During winter 2020, 6820 individuals were collected from Hurghada and Shalateen, the Red Sea coast from five different depths ranging from 0.5 to 35 m. Twenty two amphipod species were recorded of which 18 (82 %) and 9 (41%) species were from Hurghada and Shalateen, respectively. Perioculodes aequimanus was the most abundant sand amphipod amounting to 17% and 39% in Hurghada and Shalateen, respectively, followed byCeradocus rubromaculatus (27%) in Shalateen, and Metaphoxus sp. and Bemlos sp. (15%) in Hurghada. Depth influenced the total amphipod abundance in Hurghada, while, in Shalateen it showed an opposite assemblage pattern. The multivariate approach based on Non-Metric Multi-Dimensional Scaling (MDS) was helpful to detect differences between the study sites against depths.Sandy bottom composition, temperature, and depth variations were the main factors that influenced the amphipod assemblages according to the PCA and ANOSIM outputs. The SIMPER analysis showed that the amphipod Lysianassa ceratina and Lembos sp. were the most contributing species to the dissimilarity between the two study sites, whileGuernea petalocera was the most contributing species to the similarity between Hurghada and Shalateen.

Biogeography, diversity and environmental relationships of shelf and deep-sea benthic Amphipoda around Iceland.

The waters around Iceland, bounding the Northern North Atlantic and the Nordic seas, are a region characterized by complex hydrography and seabed topography. This and the presence of the Greenland-Iceland-Faroe-Scotland ridge (GIFR) are likely to have a major impact on the diversity and distribution of the benthic fauna there. Biodiversity in this region is also under increasing threat from climate-induced changes, ocean warming and acidification in particular, affecting the marine realm. The aim of the present study was to investigate the biodiversity and distributional patterns of amphipod crustaceans in Icelandic waters and how it relates to environmental variables and depth. A comprehensive data set from the literature and recent expeditions was compiled constituting distributional records for 355 amphipod species across a major depth gradient (18–3,700 m). Using a 1° hexagonal grid to map amphipod distributions and a set of environmental factors (depth, pH, phytobiomass, velocity, dissolved oxygen, dissolved iron, salinity and temperature) we could identify four distinct amphipod assemblages: A Deep-North, Deep-South, and a Coastal cluster as well as one restricted to the GIFR. In addition to depth, salinity and temperature were the main parameters that determined the distribution of amphipods. Diversity differed greatly between the depth clusters and was significantly higher in coastal and GIFR assemblages compared to the deep-sea clusters north and south of the GIFR. A variety of factors and processes are likely to be responsible for the perceived biodiversity patterns, which, however, appear to vary according to region and depth. Low diversity of amphipod communities in the Nordic basins can be interpreted as a reflection of the prevailing harsh environmental conditions in combination with a barrier effect of the GIFR. By contrast, low diversity of the deep North Atlantic assemblages might be linked to the variable nature of the oceanographic environment in the region over multiple spatio-temporal scales. Overall, our study highlights the importance of amphipods as a constituent part of Icelandic benthos. The strong responses of amphipod communities to certain water mass variables raise the question of whether and how their distribution will change due to climate alteration, which should be a focus of future studies.

Biogeography and Connectivity Across Habitat Types and Geographical Scales in Pacific Abyssal Scavenging Amphipods

Recently, there has been a resurgent interest in the exploration of deep-sea mineral deposits, particularly polymetallic nodules in the Clarion-Clipperton Zone (CCZ), central Pacific. Accurate environmental impact assessment is critical to the effective management of a new industry and depends on a sound understanding of species taxonomy, biogeography, and connectivity across a range of scales. Connectivity is a particularly important parameter in determining ecosystem resilience, as it helps to define the ability of a system to recover post-impact. Scavenging amphipods in the superfamilies Alicelloidea Lowry and De Broyer, 2008 and Lysianassoidea Dana, 1849 contribute to a unique and abundant scavenging community in abyssal ecosystems. They are relatively easy to sample and in recent years have become the target of several molecular and taxonomic studies, but are poorly studied in the CCZ. Here, a molecular approach is used to identify and delimit species, and to investigate evolutionary relationships of scavenging amphipods from both abyssal plain and deep (>3000 m) seamount habitats in three APEIs (Areas of Particular Environmental Interest, i.e., designated conservation areas) in the western CCZ. A total of 17 different morphospecies of scavenging amphipods were identified, which include at least 30 genetic species delimited by a fragment of the cytochrome c oxidase subunit I (COI) barcode gene. The scavenging communities sampled in the western CCZ included the most common species (Abyssorchomene gerulicorbis (Shulenberger and Barnard, 1976), A. chevreuxi (Stebbing, 1906), Paralicella caperesca Shulenberger and Barnard, 1976, and P. tenuipes Chevreux, 1908) reported for other ocean basins. Only four morphospecies, representing five genetic species, were shared between APEIs 1, 4, and 7. The two abyssal plain sites at APEIs 4 and 7 were dominated by two and three of the most common scavenging species, respectively, while the APEI 1 seamount site was dominated by two species potentially new to science that appeared to be endemic to the site. The presence of common species in all sites and high genetic diversity, yet little geographic structuring, indicate connectivity over evolutionary time scales between the areas, which span about 1500 km. Similar to recent studies, the differences in amphipod assemblages found between the seamount and abyssal sites suggest that ecological conditions on seamounts generate distinct community compositions.

Biodiversity and biogeographic affinity of benthic amphipods from the Yucatan Shelf: an analysis across the warm Northwest Atlantic ecoregions

The biodiversity and biogeographic affinity of benthic amphipods from the Yucatan continental shelf with the warm Northwest Atlantic ecoregions were analysed using species occurrence data from benthic marine habitats of the continental shelf (< 200 m). A comprehensive collection of distributional data (presence-only) was obtained from different sources and newly-sampled material and sorted according to 12 ecoregions from the Northwest Atlantic. Distribution of species richness, taxonomic distinctness, endemism, and spatial replacement was analysed across ecoregions. The faunal relationships among ecoregions were explored using a clustering analysis based on the Sørensen dissimilarity index, and a cladistic analysis of distributions and endemism based on parsimony. Results from the Yucatan shelf showed a representative species pool from the highly diverse Northwest Atlantic amphipod fauna (202 spp.), with intermediate levels of endemism and taxonomic distinctness. Results from dissimilarity and parsimony showed two groups of amphipod assemblages consistent with two of the main biogeographic provinces in the Northwest Atlantic: Carolinian and Caribbean. The incorporation of the Yucatan shelf species assemblage, as an ecoregion into the used classification scheme, had implications on the amphipods biogeographic affinity identification. The Yucatan ecoregion led to a latitudinal spatial replacement of amphipod species across ecoregions and provinces, revealing that the Yucatan ecoregion has a higher biogeographic affinity with tropical ecoregions of the Caribbean province. The spatial replacement of amphipods suggests that the Southern Gulf of Mexico ecoregion has a higher affinity with warm-temperate ecoregions of the Carolinian province and is proposed as a transitional zone between the identified provinces.

The Hyalella species flock of Lake Titicaca (Crustacea: Amphipoda): perspectives and drawbacks of dna-based identification

Abstract Lake Titicaca, in the High Andes of Perú and Bolivia, harbours the world’s third most speciose ancient-lake amphipod radiation on record. A minimum of nineteen species of Hyalella derived from at least five independent colonization episodes concentrate in this high altitude water body, although the actual species number present has not yet been established and could be much higher. Herein, we take advantage of the description of three new species (H. krolli, H. gonzalezi, and H. hirsuta) and the re-description of other two (H. solida and H. nefrens) to assess the feasibility of adopting a dna-based identification approach to resolve the magnitude of this highly speciose amphipod assemblage. A Bayesian phylogenetic analysis of the evolutionary relationships among South American Hyalella cox1 haplotypes, including those of four out of the five species dealt with herein, shows a great disagreement between taxonomic units delimited under morphological and genetic data, hampering species identification exclusively based on cox1 dna barcode sequences.

Sargassum-associated gastropod and amphipod assemblages in relation to metal pollution in a semi-enclosed bay

Anthropogenic impacts cause habitat losses and reduce biodiversity in marine coastal habitats. Coastal macroalgae beds and their associate invertebrates are highly susceptible to environmental contamination. This study evaluated the differences in diversity parameters of Sargassum-associated gastropod and amphipod assemblages in areas located at different distances from a pollution source in a semi-enclosed, highly impacted bay, with the concentration of heavy metals in benthic Sargassum spp. as a contamination parameter. The Sargassum collected from sites closer to the source of contamination had higher concentrations of Cu, Zn and Fe. Rarefaction curves demonstrated that gastropod assemblages had significantly lower species richness and diversity at sites closest to the pollution source and regression analysis showed that lower diversity indexes and lower abundance of the main species were correlated with higher levels of most heavy metal concentrations in Sargassum. Amphipod did not present a clear pattern of diversity differentiation, and no correlation of the most abundant species with metal concentrations, even though these animals are known to be sensitive to metal contamination. This study highlights the importance of simultaneously studying different taxonomic groups in order to better understand anthropogenic impacts in marine environments and shows that macroalgae-associated gastropod assemblages are a potential indicator of marine pollution in semi-enclosed areas.

Distribution pattern of the brackish Apocorophium lacustre (Vanhoffen, 1911) (Amphipoda: Corophiidae) and the structure of the amphipod assemblages in the upper Oder River catchment

Abstract Apocorophium lacustre (Vanhoffen, 1911), which is a native brackish amphipod species of the North Atlantic and Baltic coasts, was recorded in the upper Oder River for the first time in 2017. Before that, only alien amphipod species had been found in this area. The aims of the study were to describe the distribution pattern of A. lacustre in the upper Oder River catchment, to investigate the composition and structure of the amphipod assemblages against the background of the habitat conditions and to provide a genetic identification of the species using DNA barcodes. In total, 16 sites were studied. A. lacustre was recorded in 14 of them. It was not found at one site in the Oder River and at one location in the lower Klodnica River. A. lacustre outnumbered the other amphipods in the Oder, in the mouth section of the Klodnica and at one site in the Gliwice Canal. The alien species Gammarus tigrinus (Sexton, 1939) was dominant in the amphipod communities at the southernmost site in the Oder River, in the Klodnica Canal, and at most sites along the Gliwice Canal. In the Klodnica River, another alien species, Dikerogammarus villosus (Sovinsky, 1894), was dominant in the amphipod fauna at two sites. Though the density of A. lacustre was high in the Oder River, it was much lower in both the canals and the Klodnica River. In our study, the depth and river velocity both contributed to the distribution of this species.

Near-shore distribution of alien Ponto-Caspian amphipods in a European dam reservoir in relation to substratum type and occurrence of macroinvertebrate taxa

Knowledge of habitat requirements and interspecific interactions of invasive species helps predict their impact and spread. We determined the relationships within the invasive freshwater Ponto-Caspian amphipod assemblage, and their associations with macroinvertebrates in the near-shore zone of a central European lowland dam reservoir. We sampled five habitat types: bare sand at the water line, bare sand (0.2 m depth), bare sand (0.5 m depth), macrophyte-overgrown sand (1 m depth), stones (0.3 m depth) on four dates (October 2015–October 2016).Pontogammarus robustoidesoccurred in all habitats,Dikerogammarus villosusandEchinogammarus ischnuswere limited to the stony bottom. Amphipod densities were positively associated with one another exceptDikerogammarusjuveniles, negatively correlated with adults. The occurrence ofD. villosus,juvenileDikerogammarusandE. ischnuswas positively related to the presence of the shelter-forming bivalveDreissena polymorpha.Pontogammarus robustoideswas positively associated with sphaeriid clams and gastropods (shelters), as well as oligochaetes and chironomids (potential prey items).DikerogammarusvillosusandE. ischnuswere positively related to chironomids and oligochaetes, respectively. Coexistence of various alien amphipods in the studied area, indicated by prevailing positive relationships in their assemblage, may be enabled by the abundance of shelters and rich food sources allowing habitat partitioning.

Scavenging amphipods from the Wallaby-Zenith Fracture Zone: Extending the hadal paradigm beyond subduction trenches

Our understanding of the ecology of the hadal zone (> 6000 m depth) is based solely on subduction trenches, leaving other geomorphological features, such as fracture zones, troughs, and basins, understudied. To address this knowledge gap, the Wallaby-Zenith Fracture Zone, Indian Ocean (WZFZ; ~ 22°S, 102°E; maximum depth 6625 m measured during Expedition SO258) was studied using free-fall baited landers. We assessed the amphipod distribution and community assemblage of this non-subduction hadal feature and compared it to subduction hadal features. Eleven species were identified across the abyssal-hadal transition zone using a paired morphological and DNA barcoding approach. The community composition was found to change gradually from abyssal to hadal depths, which contrasts with the ecotone shift characteristic of subduction trenches. A large population of Bathycallisoma schellenbergi (Birstein & Vinogradov, 1958), a quintessential hadal amphipod, was present at the flat bottom of the WZFZ. Further, an mtDNA phylogeny resolved a degree of phylogeographic structure between the B. schellenbergi WZFZ population and four previously sampled Pacific Ocean subduction trench populations, indicating these features are not interconnected through ongoing gene flow. Combined, these data indicate that some amphipods have far broader distributions than previously understood, with some species present in both hadal subduction trenches and non-subduction fracture zones and basins interspersed across the abyssal plains. This initial exploration highlights that whilst non-subduction features are an overlooked minor fraction of the total hadal area, they are essential to our understanding of the ecological and evolutionary dynamics across the hadal zone.

Diversity and Functional Patterns of Benthic Amphipods in the Coralline Intertidal Zones of a Marine National Park, India

Coralline intertidal habitats of marine protected areas, are important model systems to investigate species diversity and ecological functioning of benthic communities. Spatial variability of amphipod species composition and functional traits were studied over a three year period during the summer season at five intertidal transects of the Gulf of Kachchh Marine Protected Area, India. A total of 22,706 individuals, comprising 71 species belonging to 40 genera and 23 families were identified. Aoridae, Dexaminidae, Eriopisidae, Lysianassidae and Maeridae were the best represented families (68.2% of total abundance). Distinct spatial patterns in the amphipod assemblage structure and functional traits were observed along the horizontal and vertical axes. The results demonstrated that the amphipod assemblage functioning was greatly influenced by the vertical gradient, with generally higher functional diversity in the lower intertidal zones suggesting increased diversity in resource use strategies, whereas the upper zones showed very little functional diversity possibly due to the prevalence of environmental filtering. As higher species and functional diversities promote better resource partitioning and resilience of the ecosystem, these results are important for the management of marine protected areas facing the dual challenges of global climate change and anthropogenic pressures.