Gui Menezes

Does Presence of a Mid-Ocean Ridge Enhance Biomass and Biodiversity?

In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers, trawls, traps, and a remotely operated vehicle to survey habitat, biomass, and biodiversity. Satellite remote sensing provided information on flow patterns, thermal fronts, and primary production, while sediment traps measured export flux during 2007–2010. The MAR, 3,704,404 km2 in area, accounts for 44.7% lower bathyal habitat (800–3500 m depth) in the North Atlantic and is dominated by fine soft sediment substrate (95% of area) on a series of flat terraces with intervening slopes either side of the ridge axis contributing to habitat heterogeneity. The MAR fauna comprises mainly species known from continental margins with no evidence of greater biodiversity. Primary production and export flux over the MAR were not enhanced compared with a nearby reference station over the Porcupine Abyssal Plain. Biomasses of benthic macrofauna and megafauna were similar to global averages at the same depths totalling an estimated 258.9 kt C over the entire lower bathyal north MAR. A hypothetical flat plain at 3500 m depth in place of the MAR would contain 85.6 kt C, implying an increase of 173.3 kt C attributable to the presence of the Ridge. This is approximately equal to 167 kt C of estimated pelagic biomass displaced by the volume of the MAR. There is no enhancement of biological productivity over the MAR; oceanic bathypelagic species are replaced by benthic fauna otherwise unable to survive in the mid ocean. We propose that globally sea floor elevation has no effect on deep sea biomass; pelagic plus benthic biomass is constant within a given surface productivity regime.

Genetic structure and history of populations of the deep-sea fish Helicolenus dactylopterus (Delaroche, 1809) inferred from mtDNA sequence analysis

Helicolenus dactylopterus is an Atlantic benthopelagic fish species inhabiting high‐energy habitats on continental slopes, seamounts and islands. Partial sequences of the mitochondrial control region (D‐loop) and cytochrome b (cyt b) were used to test the hypothesis that H. dactylopterus disperses between continental margin, island and seamount habitats on intraregional, regional and oceanic scales in the North Atlantic. Individuals were collected from five different geographical areas: Azores, Madeira, Portugal (Peniche), Cape Verde and the northwest Atlantic. D‐loop (415 bp) and cyt b (423 bp) regions were partially sequenced for 208 and 212 individuals, respectively. Analysis of variation among mitochondrial DNA sequences based on pairwise F‐statistics and amova demonstrated marked genetic differentiation between populations in different geographical regions specifically the Mid‐Atlantic Ridge (Azores)/northeast Atlantic (Portugal, Madeira) compared to populations around the Cape Verde Islands and in the northwest Atlantic. Some evidence of intraregional genetic differentiation between populations was found. Minimum‐spanning network analysis revealed star‐shaped patterns suggesting that populations had undergone expansion following bottlenecks and/or they have been colonized by jump dispersal events across large geographical distances along pathways of major ocean currents. Mismatch distribution analysis indicated that Azores and northwest Atlantic populations fitted a model of historical population expansion following a bottleneck/founder event estimated to be between 0.64 and 1.2 million years ago (Ma).

Mapping Condor Seamount Seafloor Environment and Associated Biological Assemblages (Azores, NE Atlantic)

Publisher Summary Seamounts are among the most common topographic features in the world ocean. Depending on their particular morphological traits, they can also be referred to as banks, knolls, guyots, mounds, or hills. Condor seamount is a linear volcano located in the Azores (northeast Atlantic), 35 km in length, 2–6 km wide, and of varied seafloor morphology. A scientific observatory devoted to research on seamount ecosystem structure and functioning has been established on Condor, secured by a temporary fishing closure. Multiple projects have contributed to this observatory by targeting the seamount with snapshots and long-term deployments of moored, satellite-based, and shipborne technologies. This chapter presents a brief characterization of the seamounts seafloor environment by focusing on the multibeam bathymetry data and a series of video, oceanographic, and fishery surveys. A classification based upon the bathymetric position index is presented to characterize the landscape composition of the seamount. Habitats of conservation importance, such as coral gardens and deep-sea sponge aggregations, are documented. A qualitative zonation of the benthic assemblages based on the video surveys is presented along with dominant fish and crustacean catch data for comparable depth strata. Understanding how deep-sea habitat-building species like corals and sponges distribute at fine scales over the complex topography of individual seamounts is therefore critical information to design usage zonation schemes.

Deep-water longline fishing has reduced impact on Vulnerable Marine Ecosystems

Bottom trawl fishing threatens deep-sea ecosystems, modifying the seafloor morphology and its physical properties, with dramatic consequences on benthic communities. Therefore, the future of deep-sea fishing relies on alternative techniques that maintain the health of deep-sea ecosystems and tolerate appropriate human uses of the marine environment. In this study, we demonstrate that deep-sea bottom longline fishing has little impact on vulnerable marine ecosystems, reducing bycatch of cold-water corals and limiting additional damage to benthic communities. We found that slow-growing vulnerable species are still common in areas subject to more than 20 years of longlining activity and estimate that one deep-sea bottom trawl will have a similar impact to 296–1,719 longlines, depending on the morphological complexity of the impacted species. Given the pronounced differences in the magnitude of disturbances coupled with its selectivity and low fuel consumption, we suggest that regulated deep-sea longlining can be an alternative to deep-sea bottom trawling.

The Pillars of Hercules as a bathymetric barrier to gene flow promoting isolation in a global deep‐sea shark (Centroscymnus coelolepis)

Knowledge of the mechanisms limiting connectivity and gene flow in deep‐sea ecosystems is scarce, especially for deep‐sea sharks. The Portuguese dogfish (Centroscymnus coelolepis) is a globally distributed and near threatened deep‐sea shark. C. coelolepis population structure was studied using 11 nuclear microsatellite markers and a 497‐bp fragment from the mtDNA control region. High levels of genetic homogeneity across the Atlantic (ΦST = −0.0091, FST = 0.0024, P > 0.05) were found suggesting one large population unit at this basin. The low levels of genetic divergence between Atlantic and Australia (ΦST = 0.0744, P < 0.01; FST = 0.0015, P > 0.05) further suggested that this species may be able to maintain some degree of genetic connectivity even across ocean basins. In contrast, sharks from the Mediterranean Sea exhibited marked genetic differentiation from all other localities studied (ΦST = 0.3808, FST = 0.1149, P < 0.001). This finding suggests that the shallow depth of the Strait of Gibraltar acts as a barrier to dispersal and that isolation and genetic drift may have had an important role shaping the Mediterranean shark population over time. Analyses of life history traits allowed the direct comparison among regions providing a complete characterization of this sharks populations. Sharks from the Mediterranean had markedly smaller adult body size and size at maturity compared to Atlantic and Pacific individuals. Together, these results suggest the existence of an isolated and unique population of C. coelolepis inhabiting the Mediterranean that most likely became separated from the Atlantic in the late Pleistocene.

Vertical migrations of a deep-sea fish and its prey.

It has been speculated that some deep-sea fishes can display large vertical migrations and likely doing so to explore the full suite of benthopelagic food resources, especially the pelagic organisms of the deep scattering layer (DSL). This would help explain the success of fishes residing at seamounts and the increased biodiversity found in these features of the open ocean. We combined active plus passive acoustic telemetry of blackspot seabream with in situ environmental and biological (backscattering) data collection at a seamount to verify if its behaviour is dominated by vertical movements as a response to temporal changes in environmental conditions and pelagic prey availability. We found that seabream extensively migrate up and down the water column, that these patterns are cyclic both in short-term (tidal, diel) as well as long-term (seasonal) scales, and that they partially match the availability of potential DSL prey components. Furthermore, the emerging pattern points to a more complex spatial behaviour than previously anticipated, suggesting a seasonal switch in the diel behaviour mode (benthic vs. pelagic) of seabream, which may reflect an adaptation to differences in prey availability. This study is the first to document the fine scale three-dimensional behaviour of a deep-sea fish residing at seamounts.

Rapid polymerase chain reaction–restriction fragment length polymorphism method for discrimination of the two Atlantic cryptic deep-sea species of scabbardfish

The present investigation provides an efficient diagnostic method based on polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis to discriminate between two cryptic species of scabbardfish, Aphanopus carbo and A. intermedius, with commercial relevance in several European fish markets. Two DNA fragments from the mtDNA, including control region and partial cytochrome oxidase subunit I genes of about 1100 bp and 700 bp, respectively, were isolated by PCR amplification. Digestion of the amplicon including the control region with HaeII and the amplicon including the COI gene with Sau3AI restriction enzymes allowed an unequivocal discrimination between the two scabbardfish species. This PCR–RFLP method allowed a clear and rapid discrimination of the trichiurid species studied.

Resolving taxonomic uncertainty in vulnerable elasmobranchs: are the Madeira skate (Raja maderensis) and the thornback ray (Raja clavata) distinct species?

Skates and rays constitute the most speciose group of chondrichthyan fishes, yet are characterised by remarkable levels of morphological and ecological conservatism. They can be challenging to identify, which makes monitoring species compositions for fisheries management purposes problematic. Owing to their slow growth and low fecundity, skates are vulnerable to exploitation and species exhibiting endemism or limited ranges are considered to be the most at risk. The Madeira skate Raja maderensis is endemic and classified as ‘Data Deficient’ by the IUCN, yet its taxonomic distinctiveness from the morphologically similar and more wide-ranging thornback ray Raja clavata is unresolved. This study evaluated the sequence divergence of both the variable control region and cytochrome oxidase I ‘DNA barcode’ gene of the mitochondrial genome to elucidate the genetic differentiation of specimens identified as R. maderensis and R. clavata collected across much of their geographic ranges. Genetic evidence was insufficient to support the different species designations. However regardless of putative species identification, individuals occupying waters around the Azores and North African Seamounts represent an evolutionarily significant unit worthy of special consideration for conservation management.

A global perspective on the trophic geography of sharks

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.Carbon isotopic analysis reveals global biogeographic traits in shark trophic interactions, and sheds light on the diverse foraging behaviour of sharks.

Annotated list of demersal fishes occurring at Sedlo Seamount, Azores north-east central Atlantic Ocean

Several fish surveys were carried out in recent years at Sedlo Seamount, Azores, north-eastern central Atlantic Ocean. An objective of the surveys was to determine the species composition of the demersal fish species living in the area. Four types of sampling gears (bottom trawl and three types of longline) were used at Sedlo Seamount resulting in very different species composition by gear and a very complete coverage of the fish fauna of the area. A list of fishes caught with these sampling methods is presented, along with other specific auxiliary information. Altogether 78 species from 43 families were listed for Sedlo Seamount, and as far as is known, 15 species were recorded for the first time for Azorean waters.