157 research outputs found
Characteristics of survivors: growth and nutritional condition of early stages of the hake species <i>Merluccius paradoxus</i> and <i>M. capensis</i> in the southern Benguela ecosystem
Larval mortality in marine fish is strongly linked to characteristic traits such as growth and condition, but the variability in these traits is poorly understood. We tried to identify the variability in growth in relation to conditions leading to greater survival chances for early stages of Cape hake, Merluccius paradoxus and M. capensis, in the Benguela upwelling ecosystem. During two cruises in 2007 and one cruise in 2008, hake larvae and juveniles were caught. Otolith microstructures revealed a larval age ranging from 2 to 29 days post-hatching (dph), whereas juvenile age was 67–152 dph. RNA:DNA ratios, used to evaluate nutritional condition, were above the relevant threshold level for growth. No strong coupling between growth and condition was detected, indicating a complex relationship between these factors in the southern Benguela ecosystem. Merluccius paradoxus juveniles caught in 2007 (the surviving larvae of 2006) had significantly higher larval growth rates than larvae hatched in 2007 and 2008, possibly indicating selection for fast growth in 2006. High selection pressure on growth could be linked to predation avoidance, including cannibalism
Characteristics of survivors: growth and nutritional condition of early stages of the hake species Merluccius paradoxus and M. capensis in the southern Benguela ecosystem
Larval mortality in marine fish is strongly linked to characteristic traits such as growth and condition, but the variability in these traits is poorly understood. We tried to identify the variability in growth in relation to conditions leading to greater survival chances for early stages of Cape hake, Merluccius paradoxus and M. capensis, in the Benguela upwelling ecosystem. During two cruises in 2007 and one cruise in 2008, hake larvae and juveniles were caught. Otolith microstructures revealed a larval age ranging from 2 to 29 days post-hatching (dph), whereas juvenile age was 67–152 dph. RNA:DNA ratios, used to evaluate nutritional condition, were above the relevant threshold level for growth. No strong coupling between growth and condition was detected, indicating a complex relationship between these factors in the southern Benguela ecosystem. Merluccius paradoxus juveniles caught in 2007 (the surviving larvae of 2006) had significantly higher larval growth rates than larvae hatched in 2007 and 2008, possibly indicating selection for fast growth in 2006. High selection pressure on growth could be linked to predation avoidance, including cannibalism
The submarine volcano eruption at the island of El Hierro: physical-chemical perturbation and biological response
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Oxygen: A Fundamental Property Regulating Pelagic Ecosystem Structure in the Coastal Southeastern Tropical Pacific
Background: In the southeastern tropical Pacific anchovy (Engraulis ringens) and sardine (Sardinops sagax) abundance have recently fluctuated on multidecadal scales and food and temperature have been proposed as the key parameters explaining these changes. However, ecological and paleoecological studies, and the fact that anchovies and sardines are favored differently in other regions, raise questions about the role of temperature. Here we investigate the role of oxygen in structuring fish populations in the Peruvian upwelling ecosystem that has evolved over anoxic conditions and is one of the world's most productive ecosystems in terms of forage fish. This study is particularly relevant given that the distribution of oxygen in the ocean is changing with uncertain consequences. Methodology/Principal Findings: A comprehensive data set is used to show how oxygen concentration and oxycline depth affect the abundance and distribution of pelagic fish. We show that the effects of oxygen on anchovy and sardine are opposite. Anchovy flourishes under relatively low oxygen conditions while sardine avoid periods/areas with low oxygen concentration and restricted habitat. Oxygen consumption, trophic structure and habitat compression play a fundamental role in fish dynamics in this important ecosystem. Conclusions/Significance: For the ocean off Peru we suggest that a key process, the need to breathe, has been neglected previously. Inclusion of this missing piece allows the development of a comprehensive conceptual model of pelagic fish populations and change in an ocean ecosystem impacted by low oxygen. Should current trends in oxygen in the ocean continue similar effects may be evident in other coastal upwelling ecosystems
Expansion of oxygen minimum zones may reduce available habitat for tropical pelagic fishes
Climate model predictions1, 2 and observations3, 4 reveal regional declines in oceanic dissolved oxygen, which are probably influenced by global warming5. Studies indicate ongoing dissolved oxygen depletion and vertical expansion of the oxygen minimum zone (OMZ) in the tropical northeast Atlantic Ocean6, 7. OMZ shoaling may restrict the usable habitat of billfishes and tunas to a narrow surface layer8, 9. We report a decrease in the upper ocean layer exceeding 3.5 ml l−1 dissolved oxygen at a rate of ≤1 m yr−1 in the tropical northeast Atlantic (0–25° N, 12–30° W), amounting to an annual habitat loss of ~5.95×1013 m3, or 15% for the period 1960–2010. Habitat compression and associated potential habitat loss was validated using electronic tagging data from 47 blue marlin. This phenomenon increases vulnerability to surface fishing gear for billfishes and tunas8, 9, and may be associated with a 10–50% worldwide decline of pelagic predator diversity10. Further expansion of the Atlantic OMZ along with overfishing may threaten the sustainability of these valuable pelagic fisheries and marine ecosystems
Distribution and diel vertical movements of mesopelagic scattering layers in the Red Sea
© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Biology 159 (2012): 1833-1841, doi:10.1007/s00227-012-1973-y.The mesopelagic zone of the Red Sea represents
an extreme environment due to low food concentrations,
high temperatures and low oxygen waters. Nevertheless, a
38 kHz echosounder identified at least four distinct scattering
layers during the daytime, of which the 2 deepest
layers resided entirely within the mesopelagic zone. Two of
the acoustic layers were found above a mesopelagic oxygen
minimum zone (OMZ), one layer overlapped with the
OMZ, and one layer was found below the OMZ. Almost all
organisms in the deep layers migrated to the near-surface
waters during the night. Backscatter from a 300 kHz lowered
Acoustic Doppler Current Profiler indicated a layer of
zooplankton within the OMZ. They carried out DVM, yet a
portion remained at mesopelagic depths during the night.
Our acoustic measurements showed that the bulk of the
acoustic backscatter was restricted to waters shallower than
800 m, suggesting that most of the biomass in the Red Sea
resides above this depth.This research is based in part on work
supported by Award Nos. USA 00002, KSA 00011 and KSA 00011/02
made by KAUST to the Woods Hole Oceanographic Institution
The Submarine Volcano Eruption off El Hierro Island: Effects on the Scattering Migrant Biota and the Evolution of the Pelagic Communities
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World Ocean Review 2015 : living with the oceans 5. Coasts - a vital habitat under pressure
The fifth World Ocean Review (WOR) explores the coastal habitat and the diverse expectations upon this habitat. It provides a glimpse into millions of years of history, elucidates the theory of continental drift and discusses the many ways in which coasts have changed. It also illustrates how the diverse ecosystem services rendered by the coasts are being subjected to increasing pressure, and profiles measures that will be necessary in the future to respond effectively to the threats from both climate change and natural disasters
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