Pelagic biomass and community structure over the mid-continental slope off southeastern Australia based upon acoustic and midwater trawl sampling

Ja, Koslow; Rj, Kloser; Williams, Alan

doi:10.3354/meps146021

Cited by 98 publications

(62 citation statements)

References 24 publications

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“…21. ADCP data provide continuous, depth-resolved views of migrating sound-scattering layers, which can be integrated with in situ net data to obtain a comprehensive picture of migrating animal communities (22)(23)(24). Our technique identifies the depth of the main DVM stationary depth, at which the strongest subeuphotic sound scattering layer is centered during the daytime.…”

Section: Dvm Association With Anoxic Watersmentioning

confidence: 99%

Enhancement of anammox by the excretion of diel vertical migrators

Bianchi

Babbin

Galbraith

2014

Proc. Natl. Acad. Sci. U.S.A.

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Measurements show that anaerobic ammonium oxidation with nitrite (anammox) is a major pathway of fixed nitrogen removal in the anoxic zones of the open ocean. Anammox requires a source of ammonium, which under anoxic conditions could be supplied by the breakdown of sinking organic matter via heterotrophic denitrification. However, at many locations where anammox is measured, denitrification rates are small or undetectable. Alternative sources of ammonium have been proposed to explain this paradox, for example through dissimilatory reduction of nitrate to ammonium and transport from anoxic sediments. However, the relevance of these sources in open-ocean anoxic zones is debated. Here, we bring to attention an additional source of ammonium, namely, the daytime excretion by zooplankton and micronekton migrating from the surface to anoxic waters. We use a synthesis of acoustic data to show that, where anoxic waters occur within the water column, most migrators spend the daytime within them. Although migrators export only a small fraction of primary production from the surface, they focus excretion within a confined depth range of anoxic water where particle input is small. Using a simple biogeochemical model, we suggest that, at those depths, the source of ammonium from organisms undergoing diel vertical migrations could exceed the release from particle remineralization, enhancing in situ anammox rates. The contribution of this previously overlooked process, and the numerous uncertainties surrounding it, call for further efforts to evaluate the role of animals in oxygen minimum zone biogeochemistry.anammox | denitrification | oxygen minimum zone | diel vertical migration W ater column oxygen minimum zones (OMZs), where oxygen concentrations plummet to submicromolar levels (1), are responsible for approximately one-third of the total removal of fixed nitrogen from the oceans (2, 3). Several processes mediated by specialized prokaryotes convert fixed inorganic nitrogen (NH 4 + , NO 2 − , and NO 3 − ) to N 2 in anoxic waters. Canonical denitrification, consisting of dissimilatory NO 3 − reduction to NO 2 − (DNRN) followed by the further oxidation of organic matter with NO 2 − (the denitrification step), was long considered the dominant fixed N removal pathway in anoxic waters. Over the last decade, anammox has gained attention as a major sink of fixed N in nearly anoxic waters (O 2 < 10 mmol·m −3 ) (4, 5).Stoichiometric considerations would suggest a close coupling between denitrification and anammox (6, 7). Under anoxic conditions, the NH 4 + liberated by the remineralization of organic matter through DNRN and denitrification should accumulate in the water column because conventional (aerobic) nitrification cannot proceed. However, this accumulation is not observed in the cores of anoxic waters, where observed NH 4 + concentrations are generally much less than 1 mmol·m −3 (8). In these regions, oxidation of NH 4 + with NO 2 − by anammox is thought to be the major sink of NH 4 + (9). Given that no significant NH 4 + acc...

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Section: Dvm Association With Anoxic Watersmentioning

confidence: 99%

Enhancement of anammox by the excretion of diel vertical migrators

Bianchi

Babbin

Galbraith

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…In both sampling seasons, 4 replicate trawls of 15 min duration were carried out at a boat speed of ~5 to 7 km h −1 in each water depth at each location during the slack-water phase of the tidal cycle, with each replicate trawl covering a distance of 1.1 to 1.7 km and being separated by a distance of at least 500 m from that of all other replicate trawls. Sampling did not commence until at least 1 h after sunrise and was completed at least 1 h before sunset (Koslow et al 1997). The area swept during each trawl was calculated from the width of the net's mouth and the distance trawled, the latter being determined from the latitudes and longitudes at the start and finish of each trawl.…”

Section: Sampling Regime and Environmental Datamentioning

confidence: 99%

Relationships between latitude and environmental conditions and the species richness, abundance and composition of tropical fish assemblages over soft substrata

Travers¹,

Potter²,

Clarke³

et al. 2012

Mar. Ecol. Prog. Ser.

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Large-scale studies are required to elucidate the environmental factors that structure faunal communities. The relationships between the characteristics of the coastal ichthyofaunas over the soft substrata of tropical north-western Australia and both latitude and environmental factors were thus explored by analysing trawl data obtained for deep and shallow inshore waters at 7 regularly spaced locations along this 1500 km coast during both the dry and wet seasons. In the dry season, species richness and density were greater in the Kimberley and Pilbara bioregions than in the intervening Canning bioregion, where, in contrast to particularly the Kimberley, rivers and mangroves are largely absent. Species richness and density were greatest in the most northern bioregion (Kimberley) during the wet season, when nutrient input from rivers and water temperatures were highest. The high species richness and density at 1 Canning location during the wet season was presumably related to increased productivity brought about by local cyclonic events. Ichthyofaunal compositions in the Kimberley differed markedly from those in the Canning and Pilbara, where tidal range was less and water clarity greater due, in particular, to far greater densities of leiognathids and terapontids. Compositions at all locations in the dry season differed from those in the wet, when chlorophyll a concentrations and/or water temperatures were greatest and large numbers of certain species were recruited. Ichthyofaunal composition at each location almost invariably differed markedly between water depths, reflecting, inter alia, the tendency for some species to use nearshore waters as nursery areas and for others to occupy particular habitats.

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“…The natural heterogeneity, both in space and time, of the distribution of a pelagic community also introduces errors into estimates of density derived from sampling with nets. The combined errors make it impossible for trawling studies to address the heterogeneous distribution of overall community abundance and density as well as its movement (Koslow et al 1997). Trawling studies are the best way to address questions related to species composition; however, other techniques are required to address questions of spatial and temporal patterns of the community.…”

Section: Introductionmentioning

confidence: 99%

“…Most importantly, there is an inherent bias associated with 'net avoidance' (see, for example, Holliday & Pieper 1995, Medwin & Clay 1998. In one study combining trawl sampling with acoustic methods, acoustic sampling estimates of biomass were 7 times greater than trawl estimates (Koslow et al 1997). Sampling with nets yields a highly biased assessment of overall biomass of marine pelagic communities (Kenchington 1989).…”

Section: Introductionmentioning

confidence: 99%

Diel horizontal migration of the Hawaiian mesopelagic boundary community observed acoustically

Benoit‐Bird¹,

Au²,

Brainard³

et al. 2001

Mar. Ecol. Prog. Ser.

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ABSTRACT:The mesopelagic boundary community off the leeward coasts of 2 Hawaiian Islands, Oahu and Hawaii, was investigated with an echosounder modified to read directly into a laptop computer. Acoustic sampling was conducted over a total distance of 12.6 km off the Waianae coast of Oahu and 46.3 km off the Kona coast of Hawaii. The density of organisms was determined using echo energy integration, and relative abundance was determined in a way analogous to catch-per-uniteffort. The vertical range of mesopelagic organisms expanded as the mesopelagic layer rose and then compressed as it descended. The vertical range of the layer off the Kona coast was larger than that off the Waianae coast, possibly because of the greater bottom depth off Kona. Near midnight, the boundary community 3 km from the shoreline was split into 2 distinct layers, one beginning approximately 25 m from the surface and one beginning approximately 90 m from the surface. The density and the relative abundance of mesopelagic organisms were consistently higher off the Waianae coast than the Kona coast. However, the density of organisms observed in both locations was high, reaching a maximum of 1800 organisms m -3 off Waianae and 700 organisms m -3 off Kona. The maximum relative abundance off Waianae neared 100%, while off Kona it never exceeded 70%. In both locations, organisms were found within 1 km of shore, in waters much shallower than their assumed daytime habitat. The temporal patterns of relative abundance and density of organisms in waters closest to the shores of each island resembled a bell curve, with a peak in relative abundance and density around midnight. In waters further from shore, the temporal patterns in relative abundance and density had a bimodal distribution, with peaks around both 21:00 and 03:00 h. These patterns in relative abundance and density are significantly affected by the distance of the sampling location from the shoreline, but not by the depth of the sampling site. The data suggest that the organisms of the mesopelagic boundary community undergo a diel horizontal migration that is reciprocal, 1.8 km in 2 h toward shore and then the same distance in approximately the same amount of time away from shore, in addition to their well-established vertical migration. The temporal patterns of the horizontal component of the migration are predictable and are conserved between days, phases of the moon, seasons, and islands.

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Pelagic biomass and community structure over the mid-continental slope off southeastern Australia based upon acoustic and midwater trawl sampling

Cited by 98 publications

References 24 publications

Enhancement of anammox by the excretion of diel vertical migrators

Enhancement of anammox by the excretion of diel vertical migrators

Relationships between latitude and environmental conditions and the species richness, abundance and composition of tropical fish assemblages over soft substrata

Diel horizontal migration of the Hawaiian mesopelagic boundary community observed acoustically

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