ISSN:0020-9309    

DOI:10.1002/iroh.19950800202

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19950800203

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractA photographic survey of the seafloor was conducted during RRSDiscoverycruise 204 in September/October 1993 at the oligotrophic site of the French EUMELI programme at c. 21° N: 31° W (4650 m) on the Cape Verde Abyssal Plain. Two systems were used, a wide angle system (WASP) obtaining usable photographs covering 10 to 30m2, and an epibenthic sledge mounted system obtaining photographs of about 2 m2.A total of more than 3000 usable frames were obtained, covering about 64000 m2of seafloor. The photographs indicated an epibenthic invertebrate megafaunal density of 5.2 hectare−1and a demersal fish density of 1.8 hectare−1.In contrast, the photographs were dominated bylebensspuren, particularly of the ‘spoke‐burrow’ type usually attributed to echiurans. Spoke‐burrow density, where related burrows and other features such as sediment mounds are considered unitary, is estimated at 871 hectare−1.We describe and quantify the five principal types of spoke burrow encountered in this study and, on the basis of these observations and some morphometric studies of thelebensspuren, discuss the possible behaviour of their producers.We have no direct knowledge of the production rate of, or longevity of,lebensspurenin the study area. However, based on a number of assumptions and limited data from other areas we suggest that trace producer (mainly echiurans) density is on the order of tens of individuals per hectare. These trace producers probably greatly outnumber the rest of the invertebrate megabenthos, and we can only guess at the role this potential large population of hidden benthos might have in the overall structure and function of the deep‐se

ISSN:0020-9309    

DOI:10.1002/iroh.19950800204

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractA flexible graphics simulation approach, combining graphics simulation with nonlinear parameter optimisation, is described for estimating likely growth and survivorship from size frequencies measured in samples of deep‐sea benthic invertebrates. Relationships between patterns in size structure, such as bimodal size distributions, are shown to result from limited combinations in values of growth and mortality parameters. Although it is possible to fit demographic models to such size data by optimising goodness‐of‐fit of model frequencies to those observed, the outcome may be dependent on assumptions of a stable age structure from year to year. Simulation studies show that populations with relatively low values of the von Bertalanffy growth‐rate constantKand of survivorship, which show year‐to‐year variability in level of recruitment, will display strongly varying adult size structure at an inter‐annual timescale. Those with highKand high adult surivorship. and which typically show a bimodal distribution of size frequencies, will be much more resilient to such changes. However, high adult survivorship in a relatively long‐lived species will result in relatively stable adult age structure even whenK, and the probability for any recruitment at all, is low. The implications of these findings are discussed in terms of contrasting models developed for populations of the deep‐sea ophiuroidsOphiura ljungmaniandOphiomusium lymani, and of the deep‐sea echiniodEchinus affinis.in samples from permanent stations in the Rockall Trough, no

ISSN:0020-9309    

DOI:10.1002/iroh.19950800205

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19950800206

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractFour putative species of the seapen genusUmbellula, U. lindahli, U. thomsonii, U. durissimaandU. monocephalus, are found at bathyal and abyssal depths in the Porcupine Seabight and Abyssal Plain in the NE Atlantic Ocean and at bathyal depths off the Bahamas. The most common species,U. lindahli, has a cosmopolitan distribution in the world ocean.In situobservations, from bathyal depths in the Bahamas, of the posture ofU. lindahlishow that the polyps are spread out to maximize particle capture from the water column. In addition, the individuals ofU. lindahlifrom the Bahamas suggest that the tentacles are cropped by a predator, but there is no evidence of predation in the NE Atlantic specimens. Reproduction inU. lindahliis typical of that previously observed in pennatulids. Fecundity is high, although most of the oocytes present are previtellogenic with only a few developing through to maximum size at any one time. Some specimens ofU. lindahliappear to be infested with a small flatworm.

ISSN:0020-9309    

DOI:10.1002/iroh.19950800207

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19950800208

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractRecords attributed toEurythenes gryllusare discussed in the light of described morphological variation, and the existence of a third species in the genus is postulated. The presence of five pairs of oostegites inE. gryllus, a character almost unique among the Amphipoda, is confirmed. Brooding females ofE. gryllusandE. obesus, captured in deep midwater hauls in the eastern North Atlantic Ocean, are reported for the first time. The 120 mmE. gryllusfemale carried 237 hatchlings (mean length 11.13 mm) and the 48 mmE. obesusfemale 47 hatchlings (mean length 7.99 mm). Hatchlings showed variability in size and bodily proportion, and measurements of individual body segments could not be used to predict overall length. Despite this variability, no evidence for more than one instar was found. The hatchlings ofE. gryllusare established as a hitherto unrecognized instar in this species. Egg size forE. gryllusandE. obesusis predicted. The biological consequences of the absolute and relative size of hatchling in the two species, and the depths of capture of theE. gryllusfemale, are discussed.

ISSN:0020-9309    

DOI:10.1002/iroh.19950800209

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractThe diets of 33 fish species from the southern Portuguese slope, at depths between 498 and 740 m were studied through the examination of stomach contents. Species of scyliorhinids, squalids, rajids, chimaerids, anguilliforms, notacanthids, macrourids, gadids and merluccids, with pelagic, benthope‐lagic and benthic modes of life were examined.Nezumia sclerorhynchusfeeding habits were studied in detail. Its diet its dominated by amphipods. No differences of prey preferences were recorded corresponding to predator size classes. The studied predators can exploit a wide range of prey, but they feed mainly on benthopelagic and epibenthic material. Consequently it is difficult to establish distinct feeding guilds, so confirming a generalist type of feeding for most of the upper slope dwelling fishe

ISSN:0020-9309    

DOI:10.1002/iroh.19950800210

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractSpecies diversity, faunal composition and abundance in the deep‐sea macrobenthos are investigated at two, adjoining deep‐sea areas off Portugal experiencing contrasting hydrodynamic conditions in order to test for the importance of disturbance in structuring the community. The first was located at 5,035 m depth on a presumably low current‐energy site on the Tagus Abyssal Plain (TAP) and the second was centered in the lower end of the Setubal Canyon (SC) at 3,400 m depth where high levels of hydrodynamic activity are inferred from ripple bedforms visible in sea bed photographs. Closely grouped, transponder‐mapped, “vegematic” box core samples were taken at each site. Agglutinated foraminifers numerically dominate the macrofauna (retained by 300 μm sieve) at both sites. Seagrass content in the SC cores indicates downslope detrital input from shallow water which is absent in the TAP samples. This must contribute, possibly with high levels of resuspended particles in near‐bed flow, to the almost tenfold difference in abundance of metazoan macrofauna at the two sites. Expected species diversity measured from rarefaction is highest at TAP, both for pooled data and when foraminifers. tanaids and bivalve are considered separately. Evenness (equitability) in species' abundances is also higher at TAP than at SC. These differences are compared with benthic community data from the hydrodynamically disturbed High Energy Benthic Boundary Layer (HEBBLE) site on the Nova Scotia continental rise, and from the Rockall Trough (N.E. Atlantic). In common with these sites, strong bed flow at SC is thought to result in relatively high abundances, lower species richness and greater unevenness by acting to periodically disturb and reduce populations. Differences in the degree to which different faunal groups seem to be affected might be related to differences in lifestyle, particularly b

ISSN:0020-9309    

DOI:10.1002/iroh.19950800211

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY