Multiple scale assessment of habitat, landscape, and geographic-specific attributes driving decapod assemblages in Posidonia oceanica seagrass meadows.

Seagrass meadows are biodiversity hotspots for invertebrate species including decapods. Understanding the drivers of species abundance, richness and diversity of decapod assemblages is crucial for the conservation of such hotspots, but how drivers act across multiple spatial scales remains unexplored. Here we describe the decapod assemblages of Posidonia oceanica seagrass meadows and assess the influence of attributes from three increasing spatial scales (habitat, landscape, and geographical levels) on the assemblages' structure and composition, as well as the variability partitioning among each one of these levels. Overall, geographical level attributes (i.e., inlet aperture, confinement) affected the most the decapod assemblages, while we only found a modest contribution from habitat (e.g., detritus biomass, sediment organic matter) and landscape attributes (e.g., fragmentation). We suggest that decapod assemblages are driven by the interaction of multiple processes occurring at different scales and other highly stochastic phenomena such as larval dispersion and recruitment.

DNA barcoding and morphology revealed the existence of seven new species of squat lobsters in the family Munididae (Decapoda, Galatheoidea) in the southwestern Pacific.

Specimens of squat lobsters belonging to the family MunididaeAhyong et al., 2010, representing the genera Garymunida Macpherson & Baba, 2022, Trapezionida Macpherson & Baba, 2022 and Typhlonida Macpherson & Baba, 2022, were collected during several cruises around New Caledonia and Papua New Guinea, Southwest Pacific. The integrative study of these specimens revealed the presence of one new species in Garymunida, five in Trapezionida and one in Typhlonida. We describe and illustrate these new species, providing some new data on the taxonomy of several rare or scarcely studied species of Trapezionida. Molecular data from different markers (mitochondrial and nuclear) was also included, based on data availability, to support the taxonomic status of different species. Finally, a key to species for each genus is also provided.

Genomic basis for early-life mortality in sharpsnout seabream.

Mortality at early life stages of fishes is common in nature and can be shaped by stochastic and selective processes. Selective mortality has rarely been assessed in natural conditions but can now be studied by combining genomic data with information on different life stages that realates to fitness. Here we investigate selective mortality between settlers and six-month survivors of the sharpsnout seabream by genotype-phenotype/environmental association studies in three localities along a geographic gradient. We gathered information on 105 individuals at 85,031 SNPs, obtained from individual based 2b-RAD libraries, as well as 9 phenotypic and environmental variables derived from individual otolith readings. We found common signals across localities for potential selection, such as lower survival rates for individuals hatching earlier, growing faster and experiencing higher temperatures during their planktonic phase. We identified 122 loci with parallel significant association to phenotypic and environmental variables. Importantly, one of these loci mapped to the exonic region of the il20rb, a gene involved in immune response, in the phylogenetically closest reference genome, showing parallel frequency changes in non-synonymous mutations in the three studied populations. Further temporal assessments are needed to understand how polymorphisms that are key to selective mortality are maintained.

Munidopsis geyeri and M. exuta (Crustacea: Munidopsidae): A study of two deep-sea, amphi-Atlantic species that co-occur in the southern Gulf of Mexico.

The history of colonization and dispersal of fauna among deep-sea chemosynthetic ecosystems remains enigmatic and poorly understood. The distribution of squat lobsters of the genus Munidopsis Whiteaves, 1874 can be influenced by the rich organic matter and associated organism communities of chemosynthetic ecosystems. The present work analyzed the molecular relationships and morphology of individuals from different populations of Munidopsis exuta Macpherson & Segonzac, 2005 and M. geyeri Pequegnat & Pequegnat, 1970 in such ecosystems along the Atlantic Equatorial Belt, including the Chapopote Knoll, in the southern Gulf of Mexico. Munidopsis geyeri is re-described based on the present findings and reference to the literature. This analysis documented the genetic distances, as well as range of variation in the diagnostic characters that support the separation of M. exuta and M. geyeri. Our results confirm that the two species coexist in seep ecosystems and have an amphi-Atlantic distribution.

Revision of the squat lobsters of the genus Phylladiorhynchus Baba, 1969 (Crustacea, Decapoda, Galatheidae) with the description of 41 new species.

The genus Phylladiorhynchus Baba, 1969 currently contains 11 species, all occurring in the shallow waters and on the continental shelf of the Indian and Pacific oceans. Recent expeditions in these oceans have resulted in the collection of numerous new specimens in need of analysis. We have studied this material using an integrative approach analysing both morphological and molecular (COI and 16S) characters. We describe 41 new species and resurrect three old names: P. integrus (Benedict, 1902) and P. lenzi (Rathbun, 1907), previously synonymized with P. pusillus (Henderson, 1885), and P. serrirostris (Melin, 1939), previously synonymized with P. integrirostris (Dana, 1852). Most species of the genus are described and illustrated. Some species are barely discernible on the basis of morphological characters but are highly divergent genetically. Species of Phylladiorhynchus are mainly distinguishable by the number of epigastric spines and lateral spines of the carapace, the shape and the armature of the rostrum, the number and pattern of the ridges on the carapace and pleon, the shape of thoracic sternite 3 and the armature of the P24 dactyli. A dichotomous identification key to all species is provided.

Megafauna of the German exploration licence area for seafloor massive sulphides along the Central and South East Indian Ridge (Indian Ocean).

BACKGROUND: The growing interest in mineral resources of the deep sea, such as seafloor massive sulphide deposits, has led to an increasing number of exploration licences issued by the International Seabed Authority. In the Indian Ocean, four licence areas exist, resulting in an increasing number of new hydrothermal vent fields and the discovery of new species. Most studies focus on active venting areas including their ecology, but the non-vent megafauna of the Central Indian Ridge and South East Indian Ridge remains poorly known.In the framework of the Indian Ocean Exploration project in the German license area for seafloor massive sulphides, baseline imagery and sampling surveys were conducted yearly during research expeditions from 2013 to 2018, using video sledges and Remotely Operated Vehicles. NEW INFORMATION: This is the first report of an imagery collection of megafauna from the southern Central Indian- and South East Indian Ridge, reporting the taxonomic richness and their distribution. A total of 218 taxa were recorded and identified, based on imagery, with additional morphological and molecular confirmed identifications of 20 taxa from 89 sampled specimens. The compiled fauna catalogue is a synthesis of megafauna occurrences aiming at a consistent morphological identification of taxa and showing their regional distribution. The imagery data were collected during multiple research cruises in different exploration clusters of the German licence area, located 500 km north of the Rodriguez Triple Junction along the Central Indian Ridge and 500 km southeast of it along the Southeast Indian Ridge.

A new species of Munida Leach, 1820 (Crustacea: Decapoda: Anomura: Munididae) from seamounts of the Nazca-Desventuradas Marine Park.

Munida diritas sp. nov. is described for the seamounts near Desventuradas Islands, in the intersection of the Salas & Gómez and Nazca Ridges, Chile. Specimens of the new species were collected in the summit (∼200 m depth) of one seamount and observed by ROV at two nearby ones. This species is characterized by the presence of distinct carinae on the thoracic sternites 6 and 7. Furthermore, it is not related with any species from the continental shelf nor the slope of America, while it is closely related to species of Munida from French Polynesia and the West-Pacific Ocean (i.e., M. ommata, M. psylla and M. rufiantennulata). In situ observations indicate that the species lives among the tentacles of ceriantarid anemones and preys on small crustaceans. The discovery of this new species adds to the knowledge of the highly endemic benthic fauna of seamounts of the newly created Nazca-Desventuradas Marine Park, emphasizing the relevance of this area for marine conservation.

Temperature reduces fish dispersal as larvae grow faster to their settlement size.

As species struggle to cope with rising ocean temperatures, temperate marine assemblages are facing major reorganization. Many benthic species have a brief but critical period dispersing through the plankton, when they are particularly susceptible to variations in temperature. Impacts of rising temperatures can thus ripple through the population with community-wide consequences. However, responses are highly species-specific, making it difficult to discern assemblage-wide patterns in the life histories of different fish species. Here, we evaluate the responses to temperature in the early life histories of several fish species using otolith reconstructive techniques. We also assess the consequences of future warming scenarios to this assemblage. We sampled recent settlers of nine common species across a temperature gradient in the Mediterranean Sea and obtained environmental data for each individual. Using otolith microstructure, we measured early life traits including pelagic larval duration (PLD), growth rate, settlement size, hatching and settlement dates. We used a GLM framework to examine how environmental variables influenced early life-history parameters. We show that increasing temperature results in considerable reduction in the dispersal potential of temperate fish. We find a nearly universal, assemblage-wide decline in pelagic larval duration (PLD) of between 10% and 25%. This was because, with increasing temperature, larvae grew quicker to their settlement size. Settlement size itself was less affected by temperature and appears to be an ontogenetically fixed process. Given current estimates of ocean warming, there could be an assemblage-wide reduction in larval dispersal of up to 50 km across the Mediterranean, reducing connectivity and potentially isolating populations as waters warm.

Warming intensifies the interaction between the temperate seagrass Posidonia oceanica and its dominant fish herbivore Sarpa salpa.

Apart from directly influencing individual life histories of species, climate change is altering key biotic interactions as well, causing community processes to unravel. With rising temperatures, disruptions to producer-consumer relationships can have major knock-on effects, particularly when the producer is a habitat-forming species. We studied how sea surface temperature (SST) modifies multiple pathways influencing the interaction between the foundational seagrass species, Posidonia oceanica, and its main consumer, the fish Sarpa salpa in the Mediterranean Sea. We used a combination of a field-based temperature gradient approaches and experimental manipulations to assess the effect of temperature on seagrass performance (growth) and fish early life history (larval development) as well as on the interaction itself (seagrass palatability and fish foraging activity). Within the range of temperatures assessed, S. salpa larvae grew slightly faster at warmer conditions but maintained their settlement size, resulting in a relatively small reduction in pelagic larval duration (PLD) and potentially reducing dispersion. Under warmer conditions (>24 °C), P. oceanica reduced its growth rate considerably and seemed to display fewer deterring mechanisms as indicated by a disproportionate consumption in choice experiments. However, our field-based observations along the temperature gradient showed no change in fish foraging time, or in other aspects of feeding behaviour. As oceans warm, our results indicate that, while S. salpa may show little change in early life history, its preference towards P. oceanica might increase, which, together with reduced seagrass growth, could considerably intensify the strength of herbivory. It is unclear if P. oceanica meadows can sustain such an intensification, but it will clearly add to the raft of pressures this threatened ecosystem already faces from global and local environmental change.

New occurrences of squat lobsters of the genus Eumunida Smith, 1883 (Decapoda, Eumunididae) in New Caledonia, the Solomon Islands and Papua-New Guinea, with the description of a new species.

Examination of numerous specimens of squat lobsters of the genus Eumunida Smith, 1883 collected by French cruises along the coasts of New Caledonia, the Solomon Islands and Papua-New Guinea revealed the presence of six species, including a new species. The collection data of all of these species are recorded. The new species, E. turbulenta n. sp., is described and illustrated from New Caledonia and Chesterfield Islands.

On some squat lobsters from India (Decapoda, Anomura, Munididae), with description of a new species of Paramunida Baba, 1988.

Squat lobster specimens belonging to the family Munididae were recently collected along the southwestern coast of the mainland of India and in the Andaman Islands. The specimens belong to two known species, Agononida prolixa (Alcock, 1894) and Munida compacta Macpherson, 1997, and a new species, Paramunida bineeshi sp. nov. We here redescribe A. prolixa and describe and figure the new species. Munida compacta is newly recorded from India, and we figure the live coloration. In addition, molecular and phylogenetic analyses of two mitochondrial markers (16S rRNA and COI) revealed the phylogenetic relationships of M. compacta and P. bineeshi sp. nov. with their most closely related congeners. The genetic similarity among the individuals of M. compacta from different locations is also addressed.

Individual-based population genomics reveal different drivers of adaptation in sympatric fish.

Connectivity and local adaptation are two contrasting evolutionary forces highly influencing population structure. To evaluate the impact of early-life traits and environmental conditions on genetic structuring and adaptation, we studied two sympatric fish species in the Western Mediterranean Sea: Symphodus tinca and S. ocellatus. We followed an individual-based approach and measured early-life history traits from otolith readings, gathered information on environmental variables and obtained genome-wide markers from genotyping-by-sequencing (GBS). The two species presented contrasting population structure across the same geographic gradient, with high and significant population differentiation in S. ocellatus, mostly determined by oceanographic fronts, and low differentiation and no front effect in S. tinca. Despite their different levels of genetic differentiation, we identified in both species candidate regions for local adaptation by combining outlier analysis with environmental and phenotypic association analyses. Most candidate loci were associated to temperature and productivity in S. ocellatus and to temperature and turbulence in S. tinca suggesting that different drivers may determine genomic diversity and differentiation in each species. Globally, our study highlights that individual-based approach combining genomic, environmental and phenotypic information is key to identify signals of selection and the processes mediating them.

A new species of squat lobster of the genus Hendersonida (Crustacea, Decapoda, Munididae) from Papua New Guinea.

Hendersonida parvirostris sp. nov. is described from Papua New Guinea. The new species can be distinguished from the only other species of the genus, H. granulata (Henderson, 1885), by the fewer spines on the dorsal carapace surface, the shape of the rostrum and supraocular spines, the antennal peduncles, and the length of the walking legs. Pairwise genetic distances estimated using the 16S rRNA and COI DNA gene fragments indicated high levels of sequence divergence between the new species and H. granulata. Phylogenetic analyses, however, recovered both species as sister species, supporting monophyly of the genus.

Helping decision making for reliable and cost-effective 2b-RAD sequencing and genotyping analyses in non-model species.

High-throughput sequencing has revolutionized population and conservation genetics. RAD sequencing methods, such as 2b-RAD, can be used on species lacking a reference genome. However, transferring protocols across taxa can potentially lead to poor results. We tested two different IIB enzymes (AlfI and CspCI) on two species with different genome sizes (the loggerhead turtle Caretta caretta and the sharpsnout seabream Diplodus puntazzo) to build a set of guidelines to improve 2b-RAD protocols on non-model organisms while optimising costs. Good results were obtained even with degraded samples, showing the value of 2b-RAD in studies with poor DNA quality. However, library quality was found to be a critical parameter on the number of reads and loci obtained for genotyping. Resampling analyses with different number of reads per individual showed a trade-off between number of loci and number of reads per sample. The resulting accumulation curves can be used as a tool to calculate the number of sequences per individual needed to reach a mean depth ≥20 reads to acquire good genotyping results. Finally, we demonstrated that selective-base ligation does not affect genomic differentiation between individuals, indicating that this technique can be used in species with large genome sizes to adjust the number of loci to the study scope, to reduce sequencing costs and to maintain suitable sequencing depth for a reliable genotyping without compromising the results. Here, we provide a set of guidelines to improve 2b-RAD protocols on non-model organisms with different genome sizes, helping decision-making for a reliable and cost-effective genotyping.

Revision of the squat lobsters of the genus Leiogalathea Baba, 1969 (Crustacea, Decapoda, Munidopsidae) with the description of 15 new species.

The genus Leiogalathea Baba, 1969 currently contains only two benthic species both occurring on the continental shelves and slope: L. laevirostris (Balss, 1913), widely reported in the Indo-Pacific region, and L. agassizii (A. Milne Edwards, 1880), from both sides of the Central Atlantic. A certain degree of morphological variability linked to their geographic distributions was previously noticed, mostly in L. laevirostris. In the present study, we revise numerous specimens collected from the Atlantic, Indian and Pacific Oceans, analysing morphological and molecular characters (COI and 16S rRNA). We found 15 new species; all of them are distinguished from L. laevirostris and L. agassizii by subtle but constant morphological differences and show clear genetic separation. Furthermore, L. imperialis (Miyake Baba, 1967), previously synonymized with L. laevirostris, was found to be a valid species. All species are described and illustrated. Species of the genus Leiogalathea are morphologically distinguishable on the basis of the spinulation of the carapace, the shape and the armature of the rostrum, the shape of the propodi of the walking legs, and the pattern of the setae covering on rostrum, carapace and chelae. Some species are barely discernible on the basis of these characters but are highly divergent genetically.

Three new species of squat lobsters of the genus Munidopsis Whiteaves, 1874, from Guadeloupe Island, Caribbean Sea (Crustacea, Decapoda, Munidopsidae).

The genus Munidopsis is one of the most diverse genera within squat lobsters. Here, three new species of Munidopsis, M. cornuata n. sp., M. senticosa n. sp., and M. turgida n. sp., from <500 m off Guadeloupe Island (Caribbean Sea), are fully described and illustrated. Among the Atlantic species of the genus, M. cornuata n. sp. belongs to the group of species having the dorsal surface of the carapace with spines and is most similar to M. robusta (A. Milne-Edwards, 1880), from the Gulf of Mexico and Caribbean Sea. Munidopsis senticosa n. sp. resembles M. barbarae (Boone, 1927) from the Bahamas and the Gulf of Mexico and M. penescabra Pequegnat Williams 1995, from off Georgia and Gulf of Mexico; the three species belong to the group having the carapace covered with sharp spines. Finally, M. turgida n. sp. is characterized by having the dorsal surface of the carapace, abdomen and pereiopods covered by granules; and resembles M. granulens Mayo, 1972, from NW Caribbean Sea. Apart from the morphological evidence, the analysis of mitochondrial genes (COI and 16S) supports establishing these new species, showing very high genetic divergences compared to their congeners (from 14.5 to 17% for COI, and 7.7 to 12.8% for 16S data).

The richness of small pockets: Decapod species peak in small seagrass patches where fish predators are absent.

Patchy landscapes behave differently from continuous ones. Patch size can influence species behaviour, movement, feeding and predation rates, with flow-on consequences for the diversity of species that inhabit these patches. To understand the importance of patchiness on regional species pools, we measured decapod richness and abundance in several seagrass patches with contrasting sizes. Additionally, we evaluated potential drivers of patch-specific species distribution including resource abundance, predator habitat use and the structural complexity of patches. Our results showed a non-random distribution of decapod species: small patches were clear hotspots of diversity and abundance, particularly of larger-bodied epifaunal decapods. Interestingly, these hotspots were characterized by lower nutrient resources, lower canopy height, but also lower predator use. Small fish invertivores such as Coris julis and several species of Symphodus were mostly restricted to large patches. These resident predators may be critical in clumping predation in large patches with consequences for how biodiversity of their prey is distributed across the seascape. Our results highlight the idea that a habitat mosaic with both large and small seagrass patches would potentially bolster biodiversity because preys and predators may seek refuge in patches of different sizes.