NE Pacific Ocean Research Articles

High and highly variable cooling rates during pyroclastic eruptions on Axial Seamount, Juan de Fuca Ridge

We present a calorimetric analysis of pyroclastic glasses and glassy sheet lava flow crusts collected on Axial Seamount, Juan de Fuca Ridge, NE Pacific Ocean, at a water depth of about 1400m. The pyroclastic glasses, subdivided into thin limu o Pele fragments and angular, blocky clasts, were retrieved from various stratigraphic horizons of volcaniclastic deposits on the upper flanks of the volcanic edifice. Each analysed pyroclastic sample consists of a single type of fragment from one individual horizon. The heat capacity (cp) was measured via differential scanning calorimetry (DSC) and analysed using relaxation geospeedometry to obtain the natural cooling rate across the glass transition. The limu o Pele samples (1mm grain size fraction) and angular fragments (0.5mm grain size fraction) exhibit cooling rates of 104.3 to 106.0Ks−1 and 103.9 to 105.1Ks−1, respectively. A coarser grain size fraction, 2mm for limu o Pele and 1mm for the angular clasts yields cooling rates at the order of 103.7Ks−1. The range of cooling rates determined for the different pyroclastic deposits presumably relates to the size or intensity of the individual eruptions. The outer glassy crusts of the sheet lava flows were naturally quenched at rates between 63Ks−1 and 103Ks−1. By comparing our results with published data on the very slow quenching of lava flow crusts, we suggest that (1) fragmentation and cooling appear to be coupled dynamically and (2) ductile deformation upon the onset of cooling is restricted due to the rapid increase in viscosity. Lastly, we suggest that thermally buoyant plumes that may arise from rapid heat transfer efficiently separate clasts based on their capability to rise within the plume and as they subsequently settle from it.

The composition, origin and fate of complex mixtures in the maltene fractions of hydrothermal petroleum assessed by comprehensive two-dimensional gas chromatography

Sedimentary organic matter in hydrothermal systems can be altered by high temperature fluids to generate petroleum. The saturated and aromatic fractions of these hydrothermal oils are compositionally similar to conventional oil with the exception that they often contain higher concentrations of polycyclic aromatic hydrocarbons (PAH) as well as substantial mixtures of coeluting organic compounds that produce dramatically rising signal on the baseline of gas chromatograms termed unresolved complex mixtures (UCMs). Little is known about the compounds that compose UCMs and why or how they form. This is in part due to an inability to discriminate between in situ and migrated components that characterize the petroleum generated in hydrothermal systems. However, UCMs are also a product of the limitations imbedded in analytical separation techniques. With the advent of comprehensive two-dimensional gas chromatography (GC×GC), a revision of what should constitute molecular complexity needs to be considered. We address these problems by comparing the molecular compositions of the maltene fractions of three previously published hydrothermal petroleum samples using time of flight-mass spectrometry (GC×GC–ToF-MS) and 12 hydrothermal petroleum samples in cores from three locales using comprehensive two-dimensional gas chromatography with flame ionization detection (GC×GC–FID). The sediment cores were collected from Middle Valley, located off the axis of the Juan de Fuca Ridge, and the Escanaba Trough, along the Gorda Ridge, both in the NE Pacific Ocean, as well as from the Guaymas Basin in the Gulf of California. We define a UCM in GC×GC data to be a condition in which ⩾25% of the detected peaks within a chromatographic area coelute in either the first or second dimension. In turn, complex (CM) and simple mixtures (SM) are defined as having 5–24% and <5% coelution, respectively. All CM and UCMs were dominated by an array of configurational isomers, which becomes increasingly aromatic with higher molecular weight. We relate this to a multi-molecular complexity metric (MCM) by quantitatively comparing the difference in total peak variance and peak density for a GC×GC chromatogram. MCM values correlate with biomarker thermal maturity ratios for the Escanaba Trough and Guaymas Basin samples indicating that molecular complexity in these hydrothermal environments is in part a function of burial temperatures. Partial Least Squares (PLS) linear regression was applied to the total number of peak retention times as a proxy for the bulk molecular differences between each hydrothermal oil sample. Differences in the sample regressions correlate with the thermal maturity and the degree of PAH alkylation, indicating that this technique can be used to assess the degree of oxidative weathering due to dehydrogenation and hydrocarbon cracking. Subtracted chromatograms were then used to quantitatively track all of the individual molecular changes within the pyrolytic regime at Escanaba Trough. These subtracted chromatograms indicate that high molecular weight PAHs are highly mobile in hydrothermal fluids and may represent a phase partitioning that is occurring at greater depths. This phase condenses just below the seafloor to form an UCM in the near surface sediments. Saturated hydrocarbon biomarkers, such as hopanes, steranes and biphytanes are less mobile and more prone to being cracked and/or aromatized prior to migration toward the ocean floor. Together these techniques suggest that the molecular complexity of hydrothermal petroleum maximizes during the early stages of thermal maturation. The diversity of compounds forming these UCMs then decreases with increasing dehydrogenation, dealkylation and condensation reactions associated with elevated thermal stress and exposure to oxidants within the hydrothermal fluids.

314 Interglacial conditions during mid- to late Pleistocene in the NE and SW Pacific Ocean

314 Interglacial conditions during mid- to late Pleistocene in the NE and SW Pacific Ocean

PCB-Associated Changes in mRNA Expression in Killer Whales (Orcinus orca) from the NE Pacific Ocean

Killer whales in the NE Pacific Ocean are among the world's most PCB-contaminated marine mammals, raising concerns about implications for their health. Sixteen health-related killer whale mRNA transcripts were analyzed in blubber biopsies collected from 35 free-ranging killer whales in British Columbia using real-time quantitative polymerase chain reaction. We observed PCB-related increases in the expression of five gene targets, including the aryl hydrocarbon receptor (AhR; r(2) = 0.83; p < 0.001), thyroid hormone α receptor (TRα; r(2) = 0.64; p < 0.001), estrogen α receptor (ERα; r(2) = 0.70; p < 0.001), interleukin 10 (IL-10; r(2) = 0.74 and 0.68, males and females, respectively; p < 0.001), and metallothionein 1 (MT1; r(2) = 0.58; p < 0.001). Best-fit models indicated that population (dietary preference), age, and sex were not confounding factors, except for IL-10, where males differed from females. While the population-level consequences are unclear, the PCB-associated alterations in mRNA abundance of such pivotal end points provide compelling evidence of adverse physiological effects of persistent environmental contaminants in these endangered killer whales.

Cold seep and oxygen minimum zone associated sources of margin heterogeneity affect benthic assemblages, diversity and nutrition at the Cascadian margin (NE Pacific Ocean)

Hydrate Ridge (HR), located on the northeastern Pacific margin off Oregon, is characterized by the presence of outcropping hydrates and active methane seepage. Additionally, permanent low oxygen conditions overlay the benthic realm. This study evaluated the relative influence of both seepage and oxygen minima as sources of habitat heterogeneity and potential stress-inducing features on the bathyal metazoan benthos (primarily nematodes) at three different seep and non-seep HR locations, exposed to decreasing bottom-water oxygen concentrations with increasing water depth. The nematode seep communities at HR exhibited low diversity with dominance of only one or two genera (Daptonema and Metadesmolaimus), elevated average individual biomass and δ13C evidence for strong dependance on chemosynthesis-derived carbon, resembling deep-sea seeps worldwide. Although the HR seep habitats harbored a distinct nematode community like in other known seep communities, they differed from deep-sea seeps in well-oxygenated waters based on that they shared the dominant genera with the surrounding non-seep sediments overlain by oxygen-deficient bottom water. The homogenizing effect of the oxygen minimum zone on the seep nematode assemblages and surrounding sediments was constant with increasing water depth and concomitant greater oxygen-deficiency, resulting in a loss of habitat heterogeneity.

The specific gravity of mesopelagic fish from the northeastern Pacific Ocean and its implications for acoustic backscatter

Abstract Davison, P. 2011. The specific gravity of mesopelagic fish from the northeastern Pacific Ocean and its implications for acoustic backscatter. – ICES Journal of Marine Science, 68: . Knowledge of the species present, their morphology, and their size distribution is required to infer biomass from acoustic surveys of fish. The gas content and specific gravity of the body (with gas removed), ρf, was measured for 71 species of mesopelagic fish in the NE Pacific Ocean. Those species that have functional swimbladders when large maintain constant ρf with increasing body size. Species without functional swimbladders as adults show decreased ρf with increasing body size. The acoustic-backscattering cross-section, σbs, was modelled for all individuals collected from three fish species that differed in the presence of a gas-filled swimbladder. The change in σbs with increasing body size was markedly different between the three. The low body density of those mesopelagic fish without gas-filled swimbladders greatly reduces their σbs. In species of fish that possess a functional swimbladder as juveniles and in which the swimbladder regresses with growth, the σbs first decreases, then increases with increased body size. Knowledge of the ontogenetic changes in swimbladder inflation and body density in mesopelagic fish is critical for the construction of the backscattering models used to interpret acoustic surveys.

Dinoflagellate cyst-based reconstructions of mid to late Holocene winter sea-surface temperature and productivity from an anoxic fjord in the NE Pacific Ocean

Published contemporary dinoflagellate distributional data from the NE Pacific margin and estuarine environments ( n = 136) were re-analyzed using Canonical Correspondence Analysis (CCA) and partial Canonical Correspondence Analysis (pCCA). These analyses illustrated the dominant controls of winter temperature and productivity on the distribution of dinoflagellate cysts in this region. Dinoflagellate cyst-based predictive models for winter temperature and productivity were developed from the contemporary distributional data using the modern analogue technique and applied to subfossil data from two mid to late Holocene (∼5500 calendar years before present–present) cores; TUL99B03 and TUL99B11, collected from Effingham Inlet, a 15 km long anoxic fjord located on the southwest coast of Vancouver Island that directly opens to the Pacific Ocean through Barkley Sound. Sedimentation within these basins largely comprises annually deposited laminated couplets, each made up of a winter deposited terrigenous layer and spring to fall deposited diatomaceous layer. The Effingham Inlet dinoflagellate cyst record provides evidence of a mid-Holocene gradual decline in winter SST, ending with the initiation of neoglacial advances in the region by ∼3500 cal BP. A reconstructed Late Holocene increase in winter SST was initiated by a weakening of the California Current, which would have resulted in a warmer central gyre and more El Niño-like conditions.

Volcanic ash as fertiliser for the surface ocean

Abstract. Iron is a key limiting micro-nutrient for marine primary productivity. It can be supplied to the ocean by atmospheric dust deposition. Volcanic ash deposition into the ocean represents another external and so far largely neglected source of iron. This study demonstrates strong evidence for natural fertilisation in the iron-limited oceanic area of the NE Pacific, induced by volcanic ash from the eruption of Kasatochi volcano in August 2008. Atmospheric and oceanic conditions were favourable to generate a massive phytoplankton bloom in the NE Pacific Ocean which for the first time strongly suggests a connection between oceanic iron-fertilisation and volcanic ash supply.

Blue whale vocalizations and the seasonal variability of ambient noise levels at the Aloha Observatory.

In February, 2007 the Aloha Observatory added a cabled, bottom mounted hydrophone, which supplied a 20‐month continuous recording of ambient noise from 0.02 Hz to 11 kHz. This observatory is situated at a depth of 4700 m, 100 km north of Oahu. This site is known to be close to (possibly within) one of the primary habitats of NE Pacific and NW Pacific blues, and other whales during the winter. Numerous previously reported measurements throughout the NE Pacific Ocean have demonstrated that the fundamental frequencies of NE blues vocalizations have systematically decreased from about 22.5 Hz in 1958 to about 16.5 Hz in 2007 (the cause of the frequency shift is unknown). Limited measurements suggest that the fundamental frequencies of NW blues vocalizations have also decreased with time and were about 18 Hz in 2007. Ambient noise levels from the Aloha site were analyzed in 1‐Hz bands for 1 year to permit observation of the seasonal dependence of ambient noise levels as a function of frequency. The data reveal distinct peaks in noise levels at 16.5 and 18.5 Hz between November and March, consistent with observations of the fundamental frequencies of NE and NW blue whale vocalizations. Since blues and other whales repertoire of vocalizations cover a broad frequency range, the contributions of their vocalizations to noise levels at other frequencies will be considered.

Atmospheric distribution and removal of volcanic ash after the eruption of Kasatochi volcano: A regional model study

In August 2008, Kasatochi volcano on the Aleutian Islands erupted without much advance warning. Volcanic ash released during this eruption quickly settled out of the atmosphere, mainly into the NE Pacific Ocean. The amount of volcanic ash, as well as the ash fall area and volume into the NE Pacific Ocean, remains speculative, as only a limited number of measurements is available. We used a three‐dimensional atmosphere/chemistry‐aerosol model to determine the atmospheric distribution of SO2 and volcanic ash and its fallout after the eruption of Kasatochi volcano. In a first step, modeled atmospheric SO2 distributions are compared with satellite data, thereby evaluating the model capabilities to reasonably reproduce atmospheric transport patterns. For modeled volcanic ash mass a considerable reduction of the atmospheric content already occurred by 10 August, the second day after the eruption in accordance with satellite observations. Gravitational settling is the most efficient removal process for volcanic ash mass, exceeding dry and wet deposition by far. Assuming an ash volume of 0.3 km3 released during the eruption of Kasatochi volcano and a median ash particle diameter of 4 μm, the mass of volcanic ash removed at ground within the 0.1 mm isopach covers an area of 7.6 × 105 km2 over the NE Pacific Ocean and makes up 49% of the removed material out of the atmosphere. The amount of ash and that of iron attached to it is sufficient to explain measured seawater CO2 decrease at the ocean station Papa in August 2008 induced by iron fertilization and subsequent phytoplankton production.

Canadian west coast fjords and inlets of the NE Pacific Ocean as depositional archives

Abstract The west coast of Canada is one of the major fjord coastlines of the world, hosting about 150 fjords which are locally known as inlets. Much of the coastline remains remote without extensive research, and this paper summarizes what is known of the Canadian west coast fjord environments. Two fjord regimes are recognized along the British Columbia coastline. Mainland fjords drain high mountains and ice fields with sediment input from snowmelt and glacier runoff in spring and summer. By contrast, the inlets on Vancouver Island are in a milder marine climate, and sediment input occurs mostly during heavy rains of autumn and winter. Due to unique oceanographic conditions and shallow sills at the mouth of some Vancouver Island inlets, anoxic bottom waters exist which allow the preservation of annually laminated sediments. Studies of these annually laminated sediment archives over the past decade, including two international drill ship investigations, have characterized the deglacial, sea-level and palaeoenvironmental history of the British Columbia coastal area. These coastal depositional archives have also advanced our knowledge of the cyclical nature of the NE Pacific ocean and climate system, as well as given evidence of infrequent, yet significant abrupt changes that characterize it.

Do trans-Pacific air masses deliver PBDEs to coastal British Columbia, Canada?

In order to distinguish between ‘local’ and ‘background’ sources of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in coastal British Columbia (Canada) air, we collected samples from two sites: a remote site on western Vancouver Island, and a near-urban site in the Strait of Georgia. Seasonally-integrated samples of vapor, particulate, and rain were collected continuously during 365 days for analysis of 275 PCB and PBDE congeners. While deposition of the legacy PCBs was similar at both sampling sites, deposition of PBDEs at the remote site amounted to 42% (10.4 mg/ha/year) of that at the near-urban site. Additional research into atmospheric circulation in the NE Pacific Ocean will provide more insight into the transport and fate of priority pollutants in this region, but trans-Pacific delivery of PBDEs to the west coast of North America may underlie in part our observations. For example, approximately 40% of >12,000 ten-day back trajectories calculated for the remote site originated over Asia, compared to only 2% over North America.

Pyroclastic eruptions from Axial caldera, Juan de Fuca Ridge, NE Pacific Ocean

Unconsolidated volcaniclastic glass deposits on the flanks of Axial Seamount, a caldera system situated on the Juan de Fuca Ridge in the NE Pacific Ocean, demonstrate the occurrence of explosive events, in addition to effusive activity. The variety of produced glass fragments ranges from various angular forms to thin deep-sea limu o Pele, with dominantly moderately fractionated to occasionally primitive MOR basalt composition. A model involving the collapse of a magmatic foam layer may account for the observed spectrum of glass fragments.

The use of moored inverted echosounders for monitoring near‐surface processes

The near‐surface ocean is a difficult place to conduct measurements of physical and biological processes. High‐frequency inverted echo‐sounders (IES), moored a short distance below the surface, provide a simple means for sustained, high‐resolution monitoring. In particular, long duration deployments are useful in capturing transient events, such as storms or solitary wave trains, and placing their occurrence within the context of longer term trends. Lessons learned from use of these moored IES systems can be applied to modern ocean observatories. A number of long duration deployments of a self‐contained 200kHz IES were made in the late 1990's. Three specific examples will be discussed. Firstly, an investigation of calibrated volume scattering from near‐surface bubbles in the NE Pacific Ocean showed the frequent occurrence of vertical, plume‐like structures drawn downwards up to 25 m. Within the plumes, the backscatter cross‐section exhibited an exponential decay with depth, with e‐folding scale in the range 0.5 to 2.5 m. Secondly, imaging of near‐surface internal solitary waves was performed from a mooring near the Oregon coast, supplementing measurements made with nearby temperature sensors. These measurements showed some suggestion of scattering by turbulence. Thirdly, through the use of both backscatter intensity and echo statistics, a moored IES demonstrated quantitative monitoring of migratory zooplankton and fish populations.

The Long-range Ocean Acoustic Propagation EXperiment (LOAPEX): An overview

The Long-range Ocean Acoustic Propagation EXperiment (LOAPEX), conducted in the NE Pacific Ocean, provided acoustic transmissions from a ship-suspended source at eight widely separated stations, and from a cabled acoustic source near the Island of Kauai, HI. The transmissions were received on several bottom-mounted horizontal hydrophone arrays distributed about the NE Pacific Ocean Basin and two, nearly colocated, vertical hydrophone line arrays spanning roughly 3500 m of the water column. Ranges varied from 50 km to several Mm. The goals of the experiment are (i) to study the evolution, with distance (range), of the acoustic arrival pattern and in particular the dependence of the spatial and temporal coherence; (ii) to investigate the nature of the deep caustics and the associated arrivals well below their turning depths; (iii) to analyze the effects of the ocean bottom near the bottom-mounted acoustic source cabled to Kauai; and (iv) to produce a thermal snapshot of the NE Pacific Ocean. The experiment goals, design, and methods are described as well as preliminary data results. [Work supported by ONR.]

Moving ship thermometry

The long‐range ocean acoustic propagation experiment (LOAPEX), conducted in the NE Pacific Ocean, provided acoustic transmissions from a ship‐suspended source at seven stations spanning a near zonal path of 3200 km. The transmissions were received on several bottom‐mounted horizontal hydrophone arrays distributed about the NE Pacific Ocean Basin. The experiment and a simple inverse method are described and a preliminary thermal ‘‘snapshot’’ of the ocean basin is presented. [Work supported by ONR.]

Phytoplankton community response to Fe and temperature gradients in the NE (SERIES) and NW (SEEDS) subarctic Pacific Ocean

Abstract Ship-board iron enrichment bottle experiments were carried out with samples collected at the mesoscale iron fertilization experimental site (SERIES) in the subarctic NE Pacific in the summer of 2002. Samples were collected on Day 14 of the experiment outside the patch that was in a typical high nitrate and low chlorophyll (HNLC) condition. The iron concentration in the incubation bottles ranged from 0.1 to 2.0 nM by adding FeCl3 solution. The increase in chlorophyll-a (chl-a) in the micro (>10 μm) and nano-sized (2–10 μm) fraction was observed as a function of the added iron. Chl-a in the pico-sized fraction (0.7–2 μm) showed no increase with time. Nitrate and silicate were exhausted in the Fe-amended bottles, while those in the control bottle remained at the end of incubation. The relative consumption ratio of silicate to nitrate for the control bottles was significantly higher than that for the Fe-amended bottles. As a hyperbolic relation was found between iron concentration and the rate of increase in Chl-a (specific growth rate) for the micro and nano-sized fraction, the Monod equation was fit to obtain a maximum growth rate (μmax) and a half-saturation constant for iron (KFe). The μmax values were 0.72 and 0.48 d−1 for the micro and nano-sized fraction, respectively. The KFe values were 0.10 and 0.08 nM for the micro and nano-sized fraction, respectively. The μmax agreed with the rate of increase in Chl-a observed in situ for the mesoscale iron fertilization experiment. The μmax value for micro-sized fraction at 12 °C was half of that in the western subarctic Pacific Ocean (SEEDS experiment in 2001), indicating the Chl-a increase rate (potential growth rate) after iron enrichment was much higher in SEEDS than that in SERIES. The KFe values were much lower than that in SEEDS, suggesting that the phytoplankton community in the NE subarctic Pacific Ocean acclimates to a lower ambient Fe concentration. This difference in KFe between SERIES (NE) and SEEDS (NW) may reflect the previously suggested gradient in Fe flux to the subarctic Pacific Ocean. A temperature gradient was also applied to investigate the effect of temperature on the growth response of the phytoplankton community. No obvious effect of temperature increase to 16 °C was found in SERIES, while μmax and KFe changed significantly with temperature in SEEDS.

Modelling the ecosystem response to iron fertilization in the subarctic NE Pacific: The influence of grazing, and Si and N cycling on CO2 drawdown

Abstract We have employed a coupled one-dimensional mixed layer /ecosystem /carbon cycle model to simulate both the normal annual cycle and the iron-fertilization experiment in the subarctic NE Pacific Ocean near Ocean Station P (50°N, 145°W) during summer 2002. We considered two size classes of phytoplankton, the larger representing diatoms, where each size class has a different degree of iron limitation, and compartments for nitrate, ammonium, microzooplankton, sinking detritus, and a prescribed annual cycle in mesozooplankton. The base ecosystem model is formulated in terms of nitrogen, but is coupled to sub-models of silicon and carbon. Diatoms formed aggregates during blooms that sink rapidly from the surface ocean, and diatoms also can be grazed by microzooplankton, consistent with observations. Using the same parameter set as for the base ecosystem model, we reproduce the basic responses to fertilization: an initial bloom of small phytoplankton (including calcifying coccolithophorids), followed rapidly by an increase of microzooplankton biomass; a continuing increase in diatoms that peak as silicate becomes limiting; and a later rapid sinking event of both carbon and silica particulates. Generally this sequence proceeds more rapidly in simulations than in situ. Simulations of the fertilization response show little sensitivity to the assumed fraction of small phytoplankton that are calcifiers, but a strong sensitivity to the assumed diatom uptake ratio Si:N. With an uptake ratio of 2.5, silicate is rapidly exhausted after fertilization, and 8 months later the regional p CO 2 was 14 μatm higher than in the case with no fertilization (assuming no exchange with surrounding waters): for all other simulations the p CO 2 anomaly is negative (indicating increased CO 2 exchange from the atmosphere) but small, 2–5 μatm, suggesting a persistence for a single large-scale fertilization of less than 1 year. Simulated mixed layer Si:N drawdown ratios for different fixed diatom uptake ratios of Si:N illustrate the dangers of interpreting uptake ratios from drawdown ratios: (i) for a fixed uptake ratio the drawdown ratio varies with time as the ratio of small to large phytoplankton changes, and (ii) simulated drawdown ratios are always higher than uptake ratios because of the more rapid recycling (according to the model structure) of N relative to Si in the surface layer. Sensitivity simulations, with the diatom uptake ratio for Si:N varying as an inverse function of iron limitation and with a higher remineralization rate for detrital Si, delayed the onset of silica limitation after fertilization by several days. The magnitude and timing of the diatom peak was unchanged, indicating that in the model the (early) termination of the diatom bloom following fertilization resulted from formation and sinking of aggregates, and not Si limitation.

Catastrophe, recovery and range limitation in NE Pacific kelp forests: a large-scale perspective

The 1997-98 El Nino was one of the strongest on record and resulted in widespread losses of the giant kelp Macrocystis pyrifera (Agardh) along the west coast of North America. Draw- ing on a rich history of studies that have shown abnormally large waves and warm nutrient-poor water associated with El Ninos to negatively impact giant kelp populations at some locations in south- ern and Baja California, we examined (1) how these impacts scale up when considered across the species' geographic range in the NE Pacific Ocean and (2) if these impacts are generalizable over broad spatial scales. Working at 56 sites in 14 study locations over a 3 yr period (1997 to 2000), we examined how giant kelp populations were impacted by and recovered following the 1997-98 El Nino over a ~1500 km span along the west coast of North America. Our results indicate that while nearly all giant kelp disappeared from the southern one-third of the species' range along the coast of Baja California, Mexico, and heavy losses occurred throughout the central one-third of the species' range in southern California, USA, only minor impacts were observed throughout the northern one- third of the species' range in central California. Further, although highly variable among regions, these impacts were similar and generalizable among locations within each region. Our results also suggest that, as has been observed in local-scale studies, this large-scale variability in giant kelp mortality was driven by large-scale patterns in ocean temperature (nutrient concentration) and wave intensity. Recovery following El Nino, in contrast, was variable at multiple spatial scales and although not directly tested here, presumably influenced by numerous factors such as proximity to upwelling areas, competition with other algae, grazing, and propagule availability. Further, variability in the rates of recovery among locations resulted in a generally slow recovery of giant kelp throughout most of Baja California, and residual large-scale impacts of the El Nino were still evident 2 yr after the El Nino ended. As global climate change may lead to increases in the frequency and intensity of El Ninos, our findings have broad implications for the ways in which ecosystems might be expected to respond to them and provide a measure by which their impacts to giant kelp ecosystems may be compared among events.

Selective foraging by fish-eating killer whales Orcinus orca in British Columbia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 316:185-199 (2006) - doi:10.3354/meps316185 Selective foraging by fish-eating killer whales Orcinus orca in British Columbia John K. B. Ford*, Graeme M. Ellis Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, British Columbia V9T 6N7, Canada *Email: fordjo@pac.dfo-mpo.gc.ca ABSTRACT: As the apex non-human marine predator, the killer whale Orcinus orca feeds on a wide diversity of marine fauna. Different ecotypic forms of the species, which often exist in sympatry, may have distinct foraging specialisations. One form found in coastal waters of the temperate NE Pacific Ocean, known as the ‘resident’ ecotype, feeds predominantly on salmonid prey. An earlier study that used opportunistic collection of prey remains from kill sites as an indicator of predation rates suggested that resident killer whales may forage selectively for chinook salmon Oncorhynchus tshawytscha, the largest but one of the least abundant Pacific salmon species. Potential biases in the prey fragment sampling technique, however, made the validity of this finding uncertain. We undertook field studies of foraging behaviour of resident killer whales to resolve this uncertainty and to examine potential variation in prey selection by season, geographical area, group membership and prey availability. Foraging by resident killer whales was found to frequently involve sharing by 2 or more whales. Prey fragments left at kill sites resulted mostly from handling and breaking up of prey for sharing, and all species and sizes of salmonids were shared. Resident killer whale groups in all parts of the study area foraged selectively for chinook salmon, probably because of the species’ large size, high lipid content, and year-round availability in the whales’ range. Chum salmon Oncorhynchus keta, the second largest salmonid, were also taken when available, but smaller sockeye O. nerka and pink O. gorbuscha salmon were not significant prey despite far greater seasonal abundance. Strong selectivity for chinook salmon by resident killer whales probably has a significant influence on foraging tactics and seasonal movements, and also may have important implications for the conservation and management of both predator and prey. KEY WORDS: Prey choice · Food sharing · Foraging specialisation · Salmonid predation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 316. Online publication date: July 03, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.