Early life stages of cephalopods in the Sargasso Sea: distribution and diversity relative to hydrographic conditions

The distribution of early life stages of cephalopods was studied during a cruise of the German R.V. "Poseidon" to the Sargasso Sea in March 1993, covering an area south-east of Bermuda from 24°N to 31°N and 61°W to 65°W. Hydrographic measurements were carried out by conductivity, temperature and depth casts and/or expendable bathythermographs. The subtropical convergence zone was detected at a latitude of approximately 27°20′N and divided the Sargasso Sea into a northern and a southern area. Zooplankton sampling with a 6 m2 Isaac–Kidd midwater trawl and Bongo nets yielded a total catch of 909 specimens of early life stages of cephalopods, representing at least 13 families and 20 mainly oceanic species. Multivariate statistical analyses were performed in order to compare the species composition and abundance of cephalopods. Two different assemblages were clearly identified, north and south of the front. According to the position of the front an analysis of similarity (ANOSIM) was applied, which confirmed the observed differences in species composition at a highly significant level. The Cranchiidae, mainly represented by the endemic species Leachia lemur, was the most abundant family, especially in the northern part of the Sargasso Sea, and was mainly responsible for the distinction between the cephalopod assemblages. In general, higher abundances of early life stages and a higher diversity was observed north of the subtropical convergence zone, which is assumed to form a faunal boundary

Cephalopods of the Sargasso Sea - Distribution patterns in relation to hydrographic conditions

A comprehensive collection of mainly early life cephalopods that were sampled during two research cruises to the Sargasso Sea with the FRV Walther Herwig III in April 2014, and the RV Maria S Merian in April 2015, is analysed in this work. In 2014, 714 specimens were collected by a pelagic midwater trawl, and further 1,349 specimens by an Isaacs-Kidd Midwater Trawl (IKMT). A total of 2,487 cephalopods were caught during the cruise in 2015. They belonged to 36 species (20 families). The most abundant family was represented by the Flying squids (Ommastrephidae). Identification of cephalopods was supported by DNA barcoding based on partial COI sequences. The subtropical convergence zone (STCZ) was found at approximately 27°N. This frontal system is characterised by a sharp near-surface temperature gradient and divides the Sargasso Sea into a northern and a southern area. This distinction was also reflected in the cephalopod community composition. For example, the cranchiid Leachia lemur prevailed in the northern part, while the cirrate octopod, Japetella diaphana was mainly distributed in the southern part of the study area. PCA and RDA analyses detected a significant correlation between species occurrence and sea surface temperature. Ordination analysis (MDS) showed significant differences in the cephalopod assemblages between day and night with midwater species (Enoploteuthidae, Pyroteuthidae) dominating the night catches, probably due to their upward migration into the top 200 m during the night

The status and importance of cephalopod systematics in southern Africa

A checklist of southern African cephalopods published in 1974 listed 94 species for the region 20–45°S, 10–40°E. Just 23 years later the number of known species has doubled to an estimated 195, represented in theSouth African Museum collection by 4 252 accessioned lots (15 434 specimens, excluding many paralarvae). In 1995, cephalopods constituted the sixth most valuable fisheries resource worldwide (after shrimps and tunas). Only one subspecies, Loligo vulgaris reynaudii, is targeted in South Africa at present, but it is important commercially because of the high prices it commands internationally. A number of other species constitute alternate resources of potential commercial interest, including at least 12 sepiids, 7 loliginids, 6 ommastrephids and 9 octopods. Cephalopods are also important in the trophic relations of marine fish, birds and mammals. Knowledge of the southern African cephalopod fauna is important not only for regional biodiversity studies but also from a wider perspective. The region is strategically placed between the Atlantic, Indian and Southern oceans and the faunal composition is complex. The southern African cephalopods include about 20–30% of the known world cephalopod species. Resolution of taxonomic problems in the southern African context goes a long way towards global resolution, particularly among the oceanic species. The size and complexity of the South African Museum’scephalopod collection prompted the holding of a systematics workshop to produce a guide to southern African cephalopods. This paper provided a basis for that Biodiversity Workshop. A provisional checklist for the region is provided, species constituting a potential resource for either artisanal or larger fisheries are identified and unresolved problems in the systematics (including an undescribed genus and at least 12, but probably more than 20, new species) are indicated

Distribution patterns of oceanic micronekton at seamounts and hydrographic fronts of the subtropical Atlantic Ocean

In the past the oceanic environment has often been compared with terrestrial deserts and until today relatively little is known about the ecology of the high seas. Within the present study pelagic oceanic communities of cephalopods and fish in the subtropical North Atlantic were investigated, and it was analysed at different spatial scales how these communities varied in response to physical gradients and hydrographic processes. First, the influence of the subtropical convergence zone in the Sargasso Sea on the distribution of early life stages of cephalopods was determined. This large-scale front turned out to represent a distinct faunal boundary, with higher diversity and abundance values in the northern part of the Sargasso Sea compared to the southern area. Second, mesoscale distribution patterns of paralarval cephalopods and larval fish were described at Great Meteor Seamount in relation to the specific hydrographic features, as e.g. the Taylor cap. Processes structuring the pelagic communities were identified and their impact evaluated by different multivariate statistical techniques. Fish and cephalopods were similarly influenced, although the retention potential at the seamount was much more pronounced for larval fish. Third, the diurnal vertical migration behaviour of juvenile and adult cephalopods was investigated from samples collected at three seamounts of different topographic morphology. A logistic regression model was developed to demonstrate the probability of occurrence in relation to daytime and catch depth. Because of the species-specific vertical distribution the seamounts represented a topographic obstacle, resulting in an impoverished fauna at shallower water depth

Species composition and distribution patterns of early life stages of cephalopods at Great Meteor Seamount (subtropical NE Atlantic)

The distribution of early life stages of cephalopods was studied during a cruise of RV Meteor in September 1998 at Great Meteor Seamount, an isolated flat-topped seamount in the subtropical eastern North Atlantic. Zooplankton sampling was conducted with a multi-opening-closing net (modified MOCNESS, 1 m² net opening, 335 µm mesh size) in seven depth strata between 290 m depth and the surface. 1180 early life stages of cephalopods were collected, representing at least 18 families and 31 mainly oceanic species. Most of the identified cephalopods comprised mesopelagic species (e. g., representatives of the families Enoploteuthidae and Pyroteuthidae) that showed diel vertical migration patterns. Hydrographic measurements parallel to zooplankton sampling revealed slow anticyclonic recirculation around the seamount forming a Taylor column and, thus, some retention potential for passive particles. Nevertheless, multivariate statistical analysis revealed no differences in the cephalopod community between the area in the proximity of the summit and the adjacent oceanic region. This was partly related to the depth of the plateau (< 300 m), which resulted in only slightly enhanced primary production, as well as to the low retention potential for active vertical migrators. However, reduced numbers of cephalopods were observed over the summit in night-time sampling, indicating gap formation above the seamount

Comparative captures of pelagic cephalopods by midwater trawls

The captures of pelagic cephalo pods by the 3 m Isaacs-Kidd midwater trawl (IKMT), the 8m2 reetangular midwater trawl (RMT 8), and the small (1400 mesh) Engeltrawl (E.MT) are compared. The sampling site was a one-degree square area in the North Atlantic Ocean east of Bermuda known as Ocean Acre. The IKMT and the RMT 8 were equipped with closing devices. Comparative samples were taken on the same cruise or at least during the same season of the year. The comparisons were made on net captures taken at 13 standardized depth increments from the surface to 1250m for both day-time and night-time. Comparisons were developed for catch rate (standardized to number of specimens captured per hour of trawling), species composition, size distribution, and co-occurrence of species. The comparison of IKMT and the RMT 8, nets with nearly equivalent mouth openings, indicates that the IKMT catches slightly larger specimens of the same species than the RMT 8. The RMT 8, however, catches more specimens per hour of a given species than the IKMT, and it tends to catch a greater diversity of species. The Engel trawl, a net with a much larger area of mouth opening than the other nets, catches a significantly greater number of species, more specimens of each species, and very much !arger specimens than either the IKMT or the RMT 8

Trophic interactions of Bathyraja trachura and sympatric fishes

Quantifying deep-sea food webs can be resource intensive due to the difficulties of sampling fishes from the deep sea. The diet of fishes is often quantified through stomach content analysis, through this method has many sampling constraints, and it can be difficult to obtain sufficient samples for an in-depth study. This study attempts to fill a critical data gap by determining the diet and trophic level of the deep-sea Roughtail Skate, Bathyraja trachura, using traditional stomach content analysis. This study also attempts to determine the validity and accuracy of stable isotope analysis in the continental slope fishes of the deep-sea of the eastern North Pacific, as an alternative method to determine trophic level in fishes. The Roughtail Skate is an abundant deep-sea skate in the eastern North Pacific. Little is known about the diet of this skate, which is landed as by-catch in commercial bottom trawls. Skates were collected between 2005 and 2008 from fishery-independent trawl surveys of the continental slope and outer shelf. Geometric Index of Importance (GII) values indicated that crustaceans (71.4%), fishes (17.8%), polychaetes (4.3%), and cephalopods (3.7%) were the most important prey groups in the diet. Diet differed significantly with total length, but not with sex. Larger individuals (by total length) had significantly higher trophic level values, and year and latitude explained variation in the diet for three prey categories. In this study, fishes and invertebrates collected from the continental slope (1,000 m depth) of the eastern North Pacific were analyzed using stable isotope analysis (SIA). The carbon and nitrogen stable isotope results were used to construct dual isotope plots to investigate the trophic relationships of this deep-sea community. The plots indicated a decoupling of the benthic and pelagic food webs, with the benthic food web being isotopically enriched. Stomach and isotope samples were collected from 32 Roughtail Skates (Bathyraja trachura) to determine the validity and accuracy of SIA in determining the trophic levels of the skates. A linear regression analysis indicated that nitrogen values from SIA and trophic levels calculated from stomach content analysis, when plotted against skate total length, exhibited similar variation and patterns, although only the stomach content analysis yielded significant results (stomach content: p=0.020, r2=0.168; stable isotope: p=0.077, r2=0.101)

Systematics, distribution, and abundance of the epiplanktonic squid (Cephalopoda, Decapoda) larvae of the California Current, April, 1954- March, 1957

Our knowledge of the biology of oceanic cephalopods is extremely limited. The population sizes, distribution patterns, breeding seasons, life histories, and growth rates are virtually unknown. In view of the fact that these organisms are undoubtedly abundant and ecologically important, both as predators and prey, this state of ignorance is unfortunate. Part of the reason for this lack is attributable to the great difficulty of adequately sampling the adults. The larvae and some juveniles, however, can be caught, in the types of plankton nets and trawls generally in use. Therefore the possibility exists that the times and places of spawning, and the developmental history of many species, may be determined from zooplankton surveys. Using this approach presupposes that a sufficiently extensive area is surveyed and that the sampling is intensive in both space and time. It is also necessary that enough specimens of the adults and intermediate-sized ranges be available for accurate identification of the larvae. This is best done by tracing the morphological changes through progressively smaller individuals. The Marine Life Research Group at Scripps Institution of Oceanography (SIO) has available a very large collection of zooplankton samples taken by the California Cooperative Oceanic Fisheries Investigations (CalCOFI) in the California Current. This program has surveyed a large portion of this current system by monthly cruises for a period of ten years. It is from these samples that the data in this report are derived

Pelagic deep-sea metazoan biodiversity and ecology revealed by environmental DNA analysis in combination with other censuses

The deep sea (> 200 m) not only represents the largest habitat on earth, but also has the highest faunal biomasses and greatest number of individual organisms. While the deep sea provides humans with substantial services, its ecosystems remain poorly studied. Logistical and technical challenges to sample deep-sea ecosystems as well as organisms’ avoidance behavior to underwater gear stress the need for alternative techniques. In this thesis, I focused on a relatively novel tool in deep-sea biology; environmental DNA (eDNA) analysis. Environmental DNA is genetic material that organisms shed into their environment. This eDNA can be assigned to a specific taxon and provides information on species presence, diversity and distribution without the need to encounter or capture the source animal. The first objective of this thesis was to develop a pipeline to collect diversity and distribution data on deep-sea cephalopods with eDNA analysis from water and sediment samples. The second objective was to establish biodiversity baselines and distribution patterns of key organisms in the deep sea and to put these patterns into an ecological context. The third objective of this thesis was to identify cephalopod and fish taxa that potentially contribute to the vertical transport of carbon. This thesis showed that eDNA can be used successfully in the assessment and monitoring of deep-sea pelagic metazoans in hotspots of diversity and climate change. Especially when eDNA analysis is analyzed in different kinds of samples and used in combination with other techniques, it can help to answer ecological questions and ultimately contribute to aid in conservation of deep-sea habitats