Bathyal Depths Research Articles

Depth-related shift in life history strategies of a brooding and broadcasting deep-sea asteroid

Combining field and laboratory work, this study investigated the reproductive cycle, aggregative behavior, spawning periodicity, development and early growth of the sea star Henricia lisa living at bathyal depths off eastern Canada. Marked differences were found between individuals from ~1,300 and ~600 m deep. The former had a male biased sex ratio and an aperiodic reproductive cycle, whereas the latter displayed an equal sex ratio and a biannual breeding pattern. Furthermore, the maximum size was larger and female fecundity roughly five times higher in shallower compared to deeper populations. In the tanks, aggregative behavior was recorded twice a year during the summer and winter breeding periods. The onset of aggregations and spawning coincided with a temperature of 3–4°C. Males spawned first and females typically responded inside 30–60 min. Between 12 and 20 eggs were retained to be brooded under the arched arms of the female, whereas the remainder were broadcasted and developed without parental care. The fertilized eggs underwent a first cleavage after 12 h, reached the brachiolaria stage in 1 month, became juveniles within 3–4 months and reached ~ 4 mm in diameter after 14–17 months of growth. The embryos and juveniles developed at the same rate whether brooded or not, and development of winter cohorts was typically slower due to lower prevailing temperatures. This study of H. lisa provides the first evidence of lecithotrophy in a seasonally breeding deep-sea echinoderm and of brooding in a deep-sea asteroid.

FORAMINIFERA USED IN THE CONSTRUCTION OF MIOCENE POLYCHAETE WORM TUBES, MONTEREY FORMATION, CALIFORNIA, USA

Unusual concentrations of foraminiferal tests interpreted to be the remnants of worm tubes occur in the Miocene Monterey Formation near Carmel and Mission Viejo, California. Lithostratigraphic and biostratigraphic correlations firmly establish their ages as late middle Miocene near Carmel and early late Miocene at Mission Viejo. The foraminifera indicate deposition occurred at bathyal depths. Surrounding strata are fine-grained, thin bedded and lack heavy bioturbation, features typical of the siliceous facies of the upper Monterey Formation and indicative of disaerobic conditions. The foraminiferal concentrations are arranged in tube-like shapes similar to those constructed by some modern marine worms. Because agglutinated worm tubes readily disaggregate after the worm’s death, very few tubes have been found in the fossil record. In addition, although some modern worms construct their tubes using foraminiferal tests, the fossil record of this phenomenon to date is represented by a single specimen from the Lias (Lower Jurassic). The fossil tubes from the Miocene of California have closest affinity with the polychaete worm genus Pectinaria , which includes Recent species living at littoral to abyssal depths. Foraminiferal tests were likely the predominant sand-sized particles available to worms in the Miocene environments, thus the worms likely did not purposefully select foraminiferal tests. Low-oxygen conditions might have enhanced the potential for tube preservation, but subsequent leaching at the Carmel localities removed most calcareous test material from the sediment.

First Record of a living Platycopida (Crustacea, Ostracoda) from Antarcticwaters and a Discussion on Cytherella serratula (Brady, 1880)

Previous records of Platycopida (Ostracoda) from the Antarctic region of the Southern Ocean include only a few fossil species from the Late Cretaceous to the Palaeocene: Cytherelloidea megaspirocostata Majoran & Widmark, 1998, [sic] Cytherella serratula (Brady, 1880), plus seven species left in open nomenclature. The present study documents the first record of a living platycopid from the Antarctic region and describes Cytherella rwhatleyi sp. nov. as new. Comparison among specimens collected at stations 60° longitude and 10° of latitude apart from each other show that very little intraspecific variation in outline and ornamentation of the valves, as well as on the hemipenis is presented by this new species. Otherwise, clear differences on valve and hemipenis are observed between different species (herein, Jellinek & Swanson 2003). Review of the literature indicates that several species (with great differences in valve outline and ornamentation) have been erroneously assigned to Cytherella serratula (Brady, 1880) demonstrating that this so-called cosmopolitan taxon is in truth most probably restricted to bathyal depths of the Northwestern Atlantic. Finally, the abundances of Cytherella rwhatleyi sp. nov. in the samples studied herein (considering O2 concentration measurements) contradict the proposed relationship between Platycopida and O2 concentration in water masses (Whatley et al. 2003).

Effects of the Oligocene climatic events on the foraminiferal record from Fuente Caldera section (Spain, western Tethys)

An expanded succession of upper Priabonian (upper Eocene) to Chattian (upper Oligocene) hemipelagic marls interbedded with turbiditic sandstone layers is present in the Spanish Fuente Caldera section (Subbetic Zone, western Tethys). We analyzed foraminifera from this section quantitatively, with emphasis on biostratigraphy and paleoecology. Benthic foraminifera indicate an upper to possibly upper–middle bathyal depth of deposition for most of the studied section, with paleobathymetric analysis made difficult because of the common presence of shallow-water taxa, some reworked by turbidites and others epiphytic taxa, which may have been transported by turbidites or by floating plant material. We identified three major biotic and paleoenvironmental events. 1) The major planktonic foraminiferal turnover across the Eocene/Oligocene boundary, which includes several first and last occurrences as well as a decrease in the percentage of surface water-dwellers, possibly linked to global cooling. 2) A dramatic sea-level drop indicated by the presence of a 37-m-thick sequence of calcarenites (lower half of planktonic foraminiferal Zone O2, ~ 31.5 Ma) with abundant trace fossils and allochthonous foraminifera. This sea-level fall, which triggered erosion of material in shallow marine settings and transport by turbidity currents into the basin, apparently post-dated the major glacial expansion on the Antarctic continent (Oi1, 33.7 Ma), and predated the later major expansion (Oi2 through Oi2b, 27–30.5 Ma), thus may have been tectonically controlled. 3) A warming event starting in the Chattian (lowermost part of Zone O6, ~ 27.1 Ma), which could be correlated to the globally recognised Late Oligocene Warming Event, but apparently started somewhat earlier (~ 27.1 Ma as compared to 26.5 Ma).

A Fossil Skull of the Extant Blue Marlin (Makaira nigricans Lacepède, 1802) from the Late Miocene of Orange County, California

A nearly complete fossil skull, including the rostrum, of blue marlin, Makaira nigricans Lacepède, 1802 (Perciformes: Xiphioidei: Istiophoridae), was collected from the Oso Member (latest Miocene) of the Capistrano Formation, Mission Viejo, Orange County, California. The specimen is compared with extant and fossil istiophorids, and 19 of its 20 morphological variables are within the range of values observed for extant M. nigricans, whereas only 13 or less variables are within the observed range of other extant istiophorids. Because extant M. nigricans usually inhabits a water column with a height of about 200 m or more and is the most tropical of all xiphioid species, its presence supports the hypotheses that the Oso Member was deposited at upper bathyal depths or greater and that the coastal paleoclimate of southern California was warmer during the late Miocene than at present.

Rosselia Ichnofabric in the Miocene Pullen Formation, Northwestern California: Implications for the Interpretation of Regional Tectonics

The occurrence of the Rosselia ichnofabric in the basal sandstone beds of the late Miocene Pullen Formation (basal Wildcat Group) provides strong evidence that supports our interpretation of a littoral-to-inner-shelf depositional setting for the lowest division of this formation. These sediments were deposited on a wave-cut platform developed along a steep coastline. Our study reconfirms the utility of the Rosselia ichnofabric in the identification of inner-shelf depositional settings having high net deposition rates, represented by the basal Pullen sandstone beds. We demonstrate how recognition of this unique ichnofabric can inform larger-scale tectonic interpretations. The correct interpretation of paleoenvironment in the case of the lowest Pullen beds confirms the view that rapid regional subsidence occurred shortly after their deposition. This allows us to eliminate a previously published alternate hypothesis that the initial accumulation of Pullen sediments occurred at bathyal depths on an inner trench slope.

Effect of commercial trawling on the deep sedimentation in a Mediterranean submarine canyon

In order to study sediment accumulation rates in the Palamós submarine canyon (Northwestern Mediterranean) during the last century, three sediment cores were extracted from the canyon axis at depths of 450, 1200 and 1750 m respectively, where instrumented moorings were previously located. Estimated sedimentation rates based on 210Pb and 137Cs profiles suggest that the contemporary trends of sediment transfer and accumulation in the canyon may be different from secular trends. During the seventies, a two-fold increase of the sediment accumulation rate took place at the 1750 m depth site. This change has been associated to trawling activities and is attributed to the rapid technical development that the local trawling fleet underwent during the seventies. The surroundings and rims of submarine canyons are frequently targeted by commercial trawling fisheries, an activity that may enhance the input of resuspended particles into canyons, and eventually trigger sediment gravity flows. Our results suggest that the effects of trawling over the dynamics of the seafloor may extend further and deeper from the fishing grounds, eventually extending to bathyal depths. Hence the anthropogenic influence on the sedimentary budget of some deep submarine environments may be more important than previously thought.

Nature and role of newly described symbiotic associations between a sea anemone and gastropods at bathyal depths in the NW Atlantic

The hormathiid sea anemone Allantactis parasitica was found living as an epibiont on numerous species of gastropods at depths of 725–1100 m along the continental slope of eastern Canada. The proportion of bathyal gastropods hosting 1–6 sea anemones reached 72.5% in a single trawl. Although A. parasitica was occasionally found on other substrata (i.e. empty shells, pebbles), laboratory trials confirmed that they preferably associate with living gastropods. Settlement of planula larvae occurred significantly more often on the shells of live bathyal gastropods than on all other substrata present in the tanks. Juvenile sea anemones (∼ 1 mm diameter) readily moved from the mud or other inert substrata onto shells of burrowed bathyal gastropods. Conversely, larvae, juveniles and adults of A. parasitica never associated with any shallow-water gastropods when given the opportunity. Trials exposing predatory sea stars ( Leptasterias polaris) from shallow and bathyal depths to bathyal gastropods ( Buccinum undatum) with epibiotic A. parasitica, and to asymbiotic bathyal and shallow-water B. undatum, revealed adaptive behaviours in both prey and predator. Shallow-water gastropods (devoid of epibionts) reacted defensively to L. polaris, whereas bathyal gastropods relied mostly on their epibionts to protect them, thus falling prey to L. polaris when the epibionts were removed. L. polaris from bathyal depths typically ignored symbiotic gastropods, but they consistently preyed on asymbiotic ones, while L. polaris from shallow areas initially attempted to prey on all gastropods, but learned to avoid those harbouring sea anemones. Furthermore, living as epibionts afforded sea anemones a means to escape one of their own predators, the sea star Crossaster papposus. The mutualistic relationship between hormathiid sea anemones and bathyal gastropods from the NW Atlantic may have evolved in response to predation pressure.

Turbidites deposited on Southern Central Chilean seamounts: Evidence for energetic turbidity currents

Gravity cores obtained from isolated seamounts located within, and rising up to 300 m from the sediment-filled Peru–Chile Trench off Southern Central Chile (36°S–39°S) contain numerous turbidite layers which are much coarser than the hemipelagic background sedimentation. The mineralogical composition of some of the beds indicates a mixed origin from various source terrains while the faunal assemblage of benthic foraminifera in one of the turbidite layers shows a mixed origin from upper shelfal to middle-lower bathyal depths which could indicate a multi-source origin and therefore indicate an earthquake triggering of the causing turbidity currents. The bathymetric setting and the grain size distribution of the sampled layers, together with swath echosounder and sediment echosounder data which monitor the distribution of turbidites on the elevated Nazca Plate allow some estimates on the flow direction, flow velocity and height of the causing turbidity currents. We discuss two alternative models of deposition, both of which imply high (175–450 m) turbidity currents and we suggest a channelized transport process as the general mode of turbidite deposition. Whether these turbidites are suspension fallout products of thick turbiditic flows or bedload deposits from sheet-like turbidity currents overwhelming elevated structures cannot be decided upon using our sedimentological data, but the specific morphology of the seamounts rather argues for the first option. Oxygen isotope stratigraphy of one of the cores indicates that the turbiditic sequences were deposited during the last Glacial period and during the following transition period and turbiditic deposition stopped during the Holocene. This climatic coupling seems to be dominant, while the occurrence of megathrust earthquakes provides a trigger mechanism. This seismic triggering takes effect only during times of very high sediment supply to the shelf and slope.

In situ stalk growth rates in tropical western Atlantic sea lilies (Echinodermata: Crinoidea)

Despite their greater familiarity as fossils, stalked crinoids, or sea lilies, remain important components of hard-substrate assemblages at bathyal depths in both tropical western Atlantic and Pacific regions. To determine stalk growth rates, specimens collected along the western margin of Little Bahama Bank using the submersibles Johnson Sea Link I and II were measured, tagged with color-coded cable ties, returned to the sea floor either to the site at which they were collected or to different habitats or depths, and recovered several months to over a year later. This paper examines stalk growth rates in Neocrinus decorus, Cenocrinus asterius, and the subspecies of Endoxocrinus parrae ( E. parrae parrae, E. parrae prionodes and E. parrae carolinae) and their variations relative to depth and current flow. Studies were carried out at three different depth sites: 249 m, 372–435 m and 540–576 m. N. decorus produces substantially more stalk per year than any subspecies of E. parrae or C. asterius (10–17 cm y − 1 versus no more than 3.6 cm y − 1 ) but contributes no more than twice as much skeletal volume to the sediment because of its more slender stalk. To examine environmental control of growth, E. parrae parrae was transplanted beyond its local depth range to the habitat at which deeper-dwelling E. parrae prionodes occurs (572 m). E. parrae parrae grew at 0.6 ± 0.4 cm y − 1 ( n = 6) here, significantly more slowly than in 404 m and more slowly than E. parrae prionodes (2.1 ± 0.6 cm y − 1 ; n = 4), supporting the hypothesis that these two morphs exhibit distinct growth strategies. Growth rates for E. parrae parrae and N. decorus do not differ significantly between adjacent high and lower current–velocity habitats at the same depth, although both exhibit significantly shorter stalk lengths and crown elevations on raised topography apparently subject to stronger flow.

Dynamics of suprabenthos-zooplankton communities around the Balearic Islands (western Mediterranean): Influence of environmental variables and effects on the biological cycle of Aristeus antennatus

Dynamics of suprabenthos and zooplankton were analyzed in two areas located in the NW (off Sóller harbour) and S (off Cabrera Archipelago) of Mallorca (Balearic Islands, western Mediterranean) at depths ranging between 135–780 m. Four stations situated respectively at 150 m (shelf-slope break), and at bathyal depths of 350, 650 and 750 m were sampled at bi-monthly intervals during six cruises performed between August 2003 and June 2004. Suprabenthos showed maximum biomass in both areas from late spring to summer (April to August), while minimum biomass was found in autumn (September–November). Though variable, temporal dynamics of zooplankton showed peaks of biomass in late winter and summer (February and June), while minimals occurred in autumn (August–September) and, at bathyal depths, in April. Suprabenthos (abundance; MDS analyses) showed a sample aggregation as a function of depth (3 groups corresponding to the shelf-slope break, upper slope — over 350 m; and the middle, deeper part of the slope — over 650–750 m), without any separation of hauls by season. By contrast, zooplankton samples were separated by season and not by depth. There was evidence of three seasonal groups corresponding to summer (June 2004–August 2003), autumn–winter (September and November 2003, February 2004), and spring (April 2004), being especially well established off Sóller. In general, suprabenthos was significantly correlated with the sediment variables (e.g. total organic matter content (% OM), potential REDOX), whereas zooplankton was almost exclusively dependent on Chl a at the surface, which suggests two different food sources for suprabenthos and zooplankton. The increase of suprabenthos abundance in April–June was paralleled by a sharp increase ( ca. 2.8 times) in the %OM on sediment during the same period, coupled ca. 1–2 months of delay with the peak of surface Chl a recorded in February–March (from satellite imagery data). Suprabenthos biomass was also correlated with salinity close to the bottom, suggesting a link between suprabenthos abundance and changes in the oceanographic condition of water masses close to the bottom. It is suggested that a higher suprabenthos biomass recorded off Sóller in comparison to that off Cabrera in June could, in turn, be related to a seasonal inflow of Levantine Intermediate Water (LIW) in April–June in this area at mid bathyal depths (350–650 m). This trend would be based on: 1) it was evident only at mid-slope depths between 350–750 m, coinciding with the LIW distribution, and 2) it was not recorded among zooplankton (collected throughout the water column). The possible effect of the fluctuations of suprabenthos and zooplankton on higher trophic levels has been explored studying the diet and food consumption rates of the red shrimp Aristeus antennatus, as indicator species by its dominance in bathyal communities. A. antennatus increased its food consumption from February to April–June 2004 off Sóller, which in the case of large (CL > 40 mm) specimens was found in both areas. In addition, there was a shift of diet from winter to spring–early summer. In this last period, A. antennatus preyed upon euphausiids and mesopelagic decapods and fish, while benthos (e.g. polychaetes and bivalves) decreased in the diet. This indicates an increase in the food consumption and probably in the caloric content of the diet in pre-spawning females in April–June 2004, which is synchronized with the period when gonad development begins in A. antennatus females (May–June). Anyway, macrozooplankton, and not suprabenthos, is crucial as a high energetic food source in the coupling between food intake and reproduction in the red shrimp.

Poorly known Ascidiacea collected in the vicinity of the Commander Islands and East Kamchatka, NW Pacific

Deep-water Ascidia escabanae known previously only from Escabana Trough, NE Pacific and Ciona pomponiae, originally described from Galapagos Islands are recorded at abyssal and bathyal depths in the region of Commander Islands and East Kamchatka in NW Pacific. Ciona gefesti is a junior synonym of C. pomponiae. The northern Atlantic species C. gelatinosa Bonnevie, 1896 (previously thought to be a subspecies of C. intestinalis and related to the Pacific Ocean C. mollis) is redescribed here and shown to be a distinct species. Also discussed are several littoral and bathyal Molgula spp. considered previously as closely related or possibly conspecific that are shown here to be separate species readily distinguished by their gonads. Molgula beringense sp.n. is described from the vicinity of the Bering Island.

Eggs of Rossia mollicella (Cephalopoda: Sepiolidae) deposited in a deep-sea sponge

Eggs of Rossia mollicella (Cephalopoda: Sepiolidae) deposited in a deep-sea sponge

Geology and petroleum potential of the Fairway Basin in the Tasman Sea

The Fairway Basin is a large, generally north – south-trending, sediment-filled structure in water 1500 – 3000 m deep, on the eastern slope of the Lord Howe Rise in the Tasman Sea, and is partly within Australian jurisdiction. It was poorly known until a few years ago, when seismic profiling and piston coring cruises were carried out. The basin, about 1100 km long and 120 – 200 km wide, can be divided into three segments—north, central and south—that trend northwest, north and north-northwest, respectively. All three segments probably formed by thinning of continental crust during breakup of Lord Howe Rise and surrounding aseismic continental ridges in the Late Cretaceous and Paleocene. Normal faulting, large inputs of terrigenous sediment and subsidence to bathyal marine depths occurred during that time. A period of compression, perhaps related to overthrusting on New Caledonia, occurred in the Eocene, leading to uplift (and in parts, erosion) of northern Lord Howe Rise, and reversal of faulting in the basin. By the Oligocene, the area was again in bathyal depths, and pelagic ooze and some turbidites accumulated. The basinal sequence is generally 2000 – 4000 m thick, with 1200 – 3200 m of Cretaceous to Eocene sediment concentrated in depocentres, capped by 500 – 800 m of Oligocene and younger sediment. In the depocentres, numerous sedimentary diapirs pierce sedimentary sequences. The sedimentary diapirs appear to be fed by Cretaceous muds deposited during rifting. Often, these diapirs are overlain by faults extending to the seafloor, and hummocky bathymetry is possibly caused by fluid escape. The overall geology suggests that the Fairway Basin may be a large frontier hydrocarbon province. Seismic profiles display a bottom-simulating reflector above many depocentres, 500 – 700 m below the seafloor. The bottom-simulating reflector has positive polarity, which could result from a diagenetic phase transformation, a thin gas hydrate layer with a sharp top, or from the sharp base of a gas layer (probably beneath gas hydrates). Standard piston cores taken above diapirs and apparent fluid-escape features have recovered little gas. Other than drilling, the next steps in assessing petroleum potential are to clearly document fluid-escape structures, and to sample any fluids emitted for hydrocarbons.

The response of benthic foraminifera to the K–Pg boundary biotic crisis at Elles (northwestern Tunisia)

The high-resolution quantitative study of benthic foraminifera from the Elles section (NW Tunisia) that contains one of the most complete Cretaceous–Paleogene (K–Pg) boundary transition and spans about 357 kyr provides detailed data on the palaeoenvironmental turnover across the K–Pg boundary. Benthic foraminifera indicate outer neritic-uppermost bathyal depths without perceivable bathymetrical changes throughout. Uppermost Maastrichtian assemblages are well preserved and highly diversified, indicating stable environment and mesotrophic to weakly eutrophic conditions during the latest Cretaceous. Benthic foraminifera underwent a major faunal turnover in coincidence with the K–Pg boundary, where a dramatic and sudden decrease in the percentage of both infaunal morphogroups and buliminids, as well as in diversity, heterogeneity, and genus and species richness of the assemblages, are recorded indicating overall oligotrophic conditions. Benthic foraminifera do not show significant extinction at the end of the Cretaceous, with only about 3% of the species clearly becoming extinct together with the temporary disappearance of some taxa. A stepped pattern of faunal recovery and restructuring is recognizable during the lowermost Danian reflecting the gradual restabilization of the environmental conditions after the K–Pg boundary event. The nature and the abundance of food supply to the sea floor conditioned the faunal turnover in the earliest Paleogene which reflects not only a sudden collapse of the food web due to the extinction of calcareous primary producers, but also a major, rapid change in composition and abundance of food supply just after the K–Pg boundary. Short-term blooms of some opportunistic species within the G. cretacea Zone and the lowermost part of the Ps. pseudobulloides Zone would reflect instability in the benthic assemblages that might be related to the transfer to the sea floor of food supply not easily used by the benthos through short-term, large blooms or changes in abundance of opportunistic, various phytoplankton groups. The major environmental instability at the sea floor that just follows the K–Pg boundary event may have been thus related to changes in the phytoplankton composition and abundance and would have taken place over a period of about 25 kyr. Benthic foraminiferal assemblages appear to stabilize in the lowermost part of Zone Ps. pseudobulloides (∼ 65 kyr after the K–Pg boundary event). The sea floor ecosystem, at least at outer neritic-uppermost bathyal depths, may have recovered over a considerably shorter period than commonly suggested, even if the food delivery to the sea floor had not fully recovered the pre-K–Pg levels as indicated by the lower percentages of infaunal morphogroups and buliminids. This would be also in agreement with the rapid recovery of terrestrial ecosystems following the biotic crisis at the K–Pg boundary. The drastic change of benthic foraminiferal assemblages coincident with the K–Pg boundary at Elles and their staggered reorganization during the lowermost Paleogene are largely compatible with the catastrophic effects of a huge asteroid impact on Earth at the K–Pg boundary that severely destabilized the oceanic phytoplankton-based food web.

Mode and tempo of the Paleocene-Eocene thermal maximum in an expanded section from the Venetian pre-Alps

Mode and tempo of an expanded Paleocene Eocene Thermal Maximum section in the Venetian Pre-Alps

Biodiversity and biogeographic relationships of the polychaete fauna in French Atlantic and Mediterranean waters

A survey of the literature, including the recent systematic reviews, reveals that 934 polychaete species have been recorded in French Atlantic (including the English Channel) and Mediterranean marine waters, including 818 species living on the continental shelf and 116 species that are strictly bathyal. These 934 species belong to 71 families, among which the Syllidae is the most diverse (97 species), followed by the Serpulidae (69 species), Spionidae and Phyllodocidae, each with more than 40 species. Forty-four families have fewer than 10 species recorded in each. The total number of species is spread over 11 continental shelf areas as well as the Atlantic and Mediterranean bathyal depths. In terms of species diversity, the richest areas are the Mediterranean coasts of Provence-Cote d’Azur (507 species) and Languedoc-Roussillon (483 species), the western part of the English Channel (402 species), and the southern part of the Bay of Biscay (343 species). The lowest numbers of species were recorded in the eastern English Channel, due to an impoverishment of all the fauna in this part of the Channel. Other areas—for example, the Iroise Sea, the coast of Corsica and Mediterranean bathyal depths—also show low numbers, but this may only reflect the fact that insufficient information about these areas is available. A similarity analysis of 13 areas distinguishes four distinct faunal groups, each specific to one of four general locations: (1) the bathyal Atlantic and Mediterranean zones, including the coast of Corsica, (2) the two Mediterranean coastal areas (Provence-Cote d’Azur and Languedoc-Roussillon), (3) the four zones of the Atlantic continental shelf, and (4) the English Channel. The combined species can be separated into 17 different biogeographic groups.

Depth related trends in proximate composition of demersal fishes in the eastern North Pacific

The proximate chemistry of the white muscle and liver of 18 species of demersal fish from the eastern North Pacific was studied to determine trends with depth, locomotory mode and buoyancy mechanism, foraging strategy and to elucidate energetic strategies. Data for 24 species from shallow water were taken from the literature and included for analysis of muscle water content. Benthopelagic species, primarily gadiforms, have significantly larger lipid-rich livers than benthic species. The benthopelagic species may use this lipid to add buoyancy, but it is also used as energy storage. Buoyancy mechanism was directly related to proximate composition. Fishes using gasbladders had normal muscle composition. The two species of benthopelagic fishes without gasbladders have either very high muscle lipid content ( Anoplopoma fimbria) or gelatinous muscle ( Alepocephalus tenobrosus) to aid in achieving neutral buoyancy. The macrourid, Albatrossia pectoralis, has a very small gasbladder and also has gelatinous muscle. Both of these benthopelagic fishes with gelatinous muscle feed on pelagic organisms. Gelatinous muscle was also found in two flatfishes that inhabit the oxygen minimum zone. For these fishes, high water content may serve to lower metabolic costs while maintaining large body size. Scavengers such as Coryphaenoides armatus and Coryphaenoides acrolepis have lipid rich livers and others such as A. fimbria and Pachycara sp. have high and variable muscle lipid content. Thus foraging mode also acts to influence proximate composition. Several depth-related trends in proximate composition were found. White muscle water content increased significantly with depth, and all four gelatinous species occurred at bathyal depths. This adds evidence in support of the hypothesis that decreasing light levels shorten reactive distances and relax the selective pressure for high locomotory capacity. In addition significant declines in liver protein content were observed, suggesting that the rates of metabolism in this organ also decline with depth. There was little evidence for food availability affecting proximate composition. There were no significant changes in either muscle or liver lipid or caloric density with depth. Total lipid stores actually increased significantly, but they were driven primarily by the abyssal scavenger C. armatus suggesting that foraging strategy rather than depth may be the most important factor determining total lipid stores.

Consumption of large bathyal food fall, a six month study in the NE Atlantic

We deployed 2 porpoise (Phocoena phocoena) carcasses at bathyal depth (2555 to 2710 m) in the Porcupine Seabight, NE Atlantic for periods of 1 wk and 6 mo respectively. Consumption rates of 0.085 and 0.078 kg h–1 were similar to those observed at abyssal depths in the Atlantic, and 1 order of magnitude slower than at bathyal depth in the Pacific. A distinct succession of scavenging species was observed at both carcasses: the abyssal grenadier Coryphaenoides armatus and the cusk eel Spectrunculus grandis numerically dominated the initial phase of carcass consumption and, once the bulk of the soft tissue had been removed (by Day 15), were succeeded by the squat lobster Munidopsis crassa. The blue hake Antimora rostrata and amphipod numbers were unexpectedly low, and consumption was attributed largely to direct feeding by C. armatus. The interaction of a crustacean prey species (M. crassa) and cephalopod predator (Benthoctopus sp.) was observed for the first time, revealing that large food falls also attract secondary predators that do not utilise the food fall directly. The staying time of a single parasitised C. armatus (18 h) greatly exceeded previous estimates (≤8 h). This study describes the first large food fall to be monitored at high frequency over a 6 mo period, and the first observations of a large food fall at bathyal depth in the NE Atlantic. It enables direct comparison with similarly sized food falls at abyssal depth, much larger megacarrion falls, and similar studies differing in geographic location, in particular those carried out under Pacific whale migration corridors.

Resolving the calibration problem in Cretaceous benthic foraminifera paleoecological interpretation: Cenomanian to Coniacian assemblages from the Benue Trough analyzed by conventional methods and correspondence analysis

Paleoecologic interpretation of Cretaceous benthic foraminiferal assemblages is frequently problematic because of the lack of modern indicator species. Late Cretaceous (Cenomanian to Coniacian) assemblages of the Nkalagu area in southern Nigeria (Lower Benue Trough) were analyzed paleoecologically and compared with isochronous assemblages of the Upper Benue Trough (Futuk and Ashaka). The analyzed sections are forming a transect from near shore to oceanic environments and therefore represent paleocological gradients. Late Cenomanian assemblages of the Nkalagu area are continuously dominated by Ammobaculites spp. Diversity is constantly low and a dysoxic to suboxic, normal marine, inner shelf environment can be assumed for this section. The Middle Turonian to Coniacian Sections at Nkalagu yielded various arenaceous and calcareous species. The most common genera are: Ammobaculites, Flabellammina, Gabonita, Gavelinella, Haplophragmoides, Nonionella, Planulina, Praebulimina and Trochammina. Middle to early Late Turonian sediments at Nkalagu were deposited at paleo-waterdepths of about 600 m, latest Turonian sediments at c. 250 m and Coniacian sediments at c. 600 m. Latest Turonian assemblages indicate unstable, alternating oxygen-rich and oxygen depleted conditions (suboxic to low oxic), changing to more stable conditions in the Coniacian at Nkalagu. The successive deepening indicated by the foraminiferal assemblages documents a change of the depositional environment from inner shelf to upper bathyal in the lower portion of the Benue Trough during the Cenomanian to Coniacian interval. Inner shelf assemblages from the Upper Benue Trough (Futuk and Ashaka localities) vary between brackish and normal marine conditions. Ammobaculites , Haplophragmoides and Gavelinella are the most frequent genera at Futuk, while additional occurrences of Ammotium, Reophax and Saccammina are indicative for brackish conditions at Ashaka. The application of a canonical correspondence analysis (CCA), embracing assemblages from the entire Benue Trough, enables the separation of different depositional environments with partly similar species content. In the present case, CCA is able to distinguish between brackish and normal marine conditions among shallow water assemblages, and between shelf and bathyal depths among normal marine depositional environments. CCA might therefore be used in settings with largely endemic associations and/or without modern species for calibration of assemblages, such as the Cretaceous Benue Trough.