Effects on fiords of modified freshwater discharge due to hydroelectric power production

Natural freshwater discharge to Norwegian fjords is characterized by low runoff during winter when precipitation is stored as snow and ice, and a marked peak in the discharge due to snow melting in spring. Hydroelectric power production causes a modified runoff pattern with increasing freshwater discharge during winter and reduced flow in spring. The effects of runoff regulations on physical and biological properties of fjords are considered on basis of available litterature. Documented physical effects include changes in salinity, modified current systems and changes in temperature caused by altered mixing depth following a regulation. Oxygen levels of the deeper layers in fjords with shallow sills may be altered. The possibility of changes in the vertical transport of nutrients to the euphotic layer is discussed. Notes are made on changes in temperature, nutrient supply and material load from regulated rivers. In light of these physical changes, possible biological implications are discussed though biological data are insufficient. The differences in characteristics among fjords are stressed, with special emphasis on varying influence by the outer coastal waters

Systematics, functional morphology and distribution of a bivalve (Apachecorbula muriatica gen. et sp. nov.) from the rim of the ‘Valdivia Deep’ brine pool in the Red Sea

The deep brine pools of the Red Sea comprise extreme, inhospitable habitats yet house microbial communities that potentially may fuel adjacent fauna. We here describe a novel bivalve from a deep-sea (1525 m) brine pool in the Red Sea, where conditions of high salinity, lowered pH, partial anoxia and high temperatures are prevalent. Remotely operated vehicle (ROV) footage showed that the bivalves were present in a narrow (20 cm) band along the rim of the brine pool, suggesting that it is not only tolerant of such extreme conditions but is also limited to them. The bivalve is a member of the Corbulidae and named Apachecorbula muriatica gen. et sp. nov. The shell is atypical of the family in being modioliform and thin. The semi-infaunal habit is seen in ROV images and reflected in the anatomy by the lack of siphons. The ctenidia are large and typical of a suspension feeding bivalve, but the absence of guard cilia and the greatly reduced labial palps suggest that it is non-selective as a response to low food availability. It is proposed that the low body mass observed is a consequence of the extreme habitat and low food availability. It is postulated that the observed morphology of Apachecorbula is a result of paedomorphosis driven by the effects of the extreme environment on growth but is in part mitigated by the absence of high predation pressures.We are grateful to all help from the other Leg 4 Red Sea Expedition 2013 KAUST participants; Ioannis Georgakakis, Thor A. Klevjer, Perdana Karim Prihartato, Anders Rostad and Ingrid Solberg. Leonidas Manousakis and Manolis Kalergis from Hellenic Centre for Marine Research (HCMR) assisted in ROV operations. The captain and crew of RV 'Aegaeo' provided support during the entire cruise. Ohoud Mohammed Eid Alharbi assisted with the electron microscopy. The Red Sea Expedition 2013 was sponsored by KAUST. We also thank Ronald Janssen of the Senckenberg Institution for the loan of comparative material from the RV Meteor expeditions

Large mesopelagic fishes biomass and trophic efficiency in the open ocean

Xabier Irigoien et al.With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters.This research was conducted by the Malaspina 2010 Expedition project, funded by the Spanish Ministry of Economy and Competitiveness (Consolider-Ingenio 2010, CSD2008-00077). Additional financial support was provided by the Basque Country Government and by AZTI-TecnaliaPeer Reviewe

Simulation of optically conditioned retention and mass occurrences of Periphylla periphylla

Jellyfish blooms are of increasing concern in many parts of the world, and in Norwegian fjords an apparent increase in mass occurrences of the deep water jellyfish Periphylla periphylla has attracted attention. Here we investigate the hypothesis that changes in the water column light attenuation might cause local retention and thereby facilitate mass occurrences. We use a previously tested individual-based model of light-mediated vertical migration in P. periphylla to simulate how retention is affected by changes in light attenuation. Our results suggest that light attenuation, in combination with advection, has a two-sided effect on retention and that three fjord categories can be defined. In category 1, increased light attenuation turns fjords into dark “deep-sea” environments which increase the habitat and retention of P. periphylla. In category 2, an optimal light attenuation facilitates the maximum retention and likelihood for mass occurrences. In category 3, further increase in light attenuation, however, shoals the habitat so that individuals are increasingly exposed to advection and this results in loss of individuals and decreased retention. This classification requires accurate determinations of the organism's light preference, the water column light attenuation and topographical characteristics affecting advection

Vertical distribution of fish and krill beneath water of varying optical properties

The distribution of acoustical scattering layers of fish and krill changed markedly in concert with fluctuating fluorescence (chlorophyll a) in upper waters, possibly due to a varying 'shadow effect'. Beneath clear waters on the outer Norwegian shelf (about 300 m depth), mesopelagic fish (Maurolicus muelleri) were located at approximately 150 to 200 m by day. Krill (mainly Thysanoessa inermis) was primarily found below the mesopelagic fish and above planktivorous demersal fish (Norway pout Trisopterus esmarkii). The vertical distributions changed abruptly across a front into water with less Light penetration associated with increased fluorescence (chlorophyll a). Mesopelagic fish ascended by about 100 m accompanied by a rise of krill. Demersal fish left the benthic boundary zone, with ascending Norway pout foraging in the lower part of the krill layer. We suggest that the intermediate light conditions inside the front provided an 'antipredation window' (sensu Clark & Levy 1988: Am Nat 131:271-290) and thereby favorable feeding conditions for the planktivore. These results indicate that properties of upper layers may impact plankton and fish distributions and their predator-prey interactions throughout the water column on continental shelves

First reports of a mass mortality event across multiple life stages in a mesopelagic jellyfish in high latitude coastal waters

publishedVersionPaid Open Acces

Flexible behaviour in a mesopelagic fish (Maurolicus muelleri)

Variability of mesopelagic scattering layers is often attributed to environmental conditions or multi-species layer composition. Yet, little is known about variation in behaviour among the individuals forming scattering layers. Based on a 10 months high-resolution dataset from stationary echosounders in a Norwegian fjord, we here assess short-term and long-term behaviour of a single mesopelagic fish species, the pearlside Maurolicus muelleri. The daytime vertical extension of the monospecific pearlside scattering layers spanned four orders of magnitude ambient light in the autumn and winter and less than one order of magnitude in summer. While the main layers tracked relatively stable light levels over daytime, some individuals actively crossed light gradients of up to 1.5 orders of magnitude. This included individuals that moved between scattering layers, and apparently bold individuals that made regular upward excursions beyond the main population distribution. During the daytime, M. muelleri mitigated the risk of predation by forming tight groups in the upper scattering layer and, at light levels >10−6 µmol m−2 s−1, by instantly diving into deeper waters upon encounters with predators. Our observations suggest that individual, and probably state-dependent, decisions may extend the pearlsides’ vertical distribution, with implications for predator–prey interactions.publishedVersio

Vertical migration, feeding and colouration in the mesopelagic shrimp Sergestes arcticus

Intraspecific variation in vertical distribution, timing of vertical migration, and colouration of the mesopelagic shrimp Sergestes arcticus were studied in the >400 m deep part of Masfjorden, Norway. Very few individuals were caught in the upper strata during daytime, and larger individuals occurred deeper during the day than smaller ones. Vertical migration was prominent and no overall trend of increasing length with depth was found at night. Small individuals arrived in the upper layers earlier than larger ones. Animal colouration assessed by digital photography revealed significant variance in individual redness. Depth of capture was the most important factor explaining colouration, with increasing degree of redness with depth. Assessing the gut fullness of the transparent shrimps provided a rapid way of estimating feeding activity and showed that feeding took place mainly at night

Life in a warm deep sea: routine activity and burst swimming performance of the shrimp Acanthephyra eximia in the abyssal Mediterranean

Measurements of routine swimming speed, "tail-flip'' escape responses, and oxygen consumptions were made of the deep-sea shrimp Acanthephyra eximia using autonomous landers in the Rhodos Basin at depths of up to 4,400 m and temperatures of 13 - 14.5 degrees C. Routine swimming speeds at 4,200 m averaged 0.18 m s(-1) or 3.09 body lengths s(-1), approximately double those of functionally similar oceanic scavengers. During escape responses peak accelerations of 23 m s(-2) or 630.6 body lengths s(-2) were recorded, with animals reaching speeds of 1.61 m s(-1) or 34.8 body lengths s(-2). When compared to shallow-water decapods at similar temperatures these values are low for a lightly calcified shrimp such as A. eximia despite a maximum muscle mass specific power output of 90.0 W kg(-1). A preliminary oxygen consumption measurement indicated similar rates to those of oceanic crustacean scavengers and shallower-living Mediterranean crustaceans once size and temperature had been taken into account. These animals appear to have high routine swimming speeds but low burst muscle performances. This suite of traits can be accounted for by high competition for limited resources in the eastern Mediterranean, but low selective pressure for burst swimming due to reductions in predator pressure