pelagic ecosystem
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2021 ◽  
pp. 37-44
Author(s):  
Assia Henda-Benrekaa ◽  
Riadh Moulaï

Data on cetaceans within the pelagic ecosystem remains scarce in the Algerian basin. This is linked to a lack of investigations stemming from the difficulty of quantitative population evaluation through oceanographic surveys and/or strandings statistics. In this context, we considered that it is appropriate to focus on data acquisition from offshore observations as well as setting up a network for monitoring strandings on sites scattered along the Algerian coast. During 10 oceanographic surveys conducted in two Algerian coasts sectors (eastern and central) we observed a total of 245 delphinids corresponding to 8 species that had an irregular distribution. We also identified 83 individuals belonging to five species that stranded between 2007 and 2017.


2021 ◽  
Vol 168 (9) ◽  
Author(s):  
Katrin Quiring ◽  
G. Carroll ◽  
C. Champion ◽  
E. W. Heymann ◽  
R. Harcourt

AbstractMonitoring seabird diet can provide insights into marine ecosystems that are logistically difficult or costly to observe with traditional fisheries survey methods. Using digital photography, we described the diet of greater crested terns (Thalasseus bergii) breeding on Montague Island (36°15′ S, 150°13′ E), a colony located in an oceanographically dynamic region of southeast Australia. We investigated how the type and size of prey brought back to the colony changed in relation to both breeding stage and variation in local environmental conditions. 2469 prey items were identified to species or family level over 35 consecutive days of photo-sampling in 2018. Australian anchovy (Engraulis australis), a surface-schooling clupeid fish, was the most abundant prey returned to the colony during all breeding stages (84.5%). The proportion of anchovy increased from 77.0% when birds were provisioning their adult partners during incubation, to 92.4% when they were provisioning chicks, suggesting selective foraging behaviour on this energy-rich species to facilitate rapid chick growth. Anchovy size was significantly larger during incubation (91.1 ± 14.9 mm), smaller during early chick provisioning (71.8 ± 11.0 mm), and increased slightly during mid provisioning (79.6 ± 11.9 mm), indicating adaptive prey selection that is matched to the physical requirements of different breeding stages. The proportion of anchovy prey was also influenced by sea surface temperature (SST), with anchovy becoming more dominant with increasing local SSTs, up to ~ 17.5 °C. This study gives new insight into the types of prey that are seasonally available to predators in this region. The strong specialisation by greater crested terns for one energy-rich species of schooling fish (anchovy) suggests that variation in the size and composition of their prey may serve as an indicator of change in the pelagic ecosystem off southeast Australia.


Water ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 1881
Author(s):  
Astra Labuce ◽  
Anda Ikauniece ◽  
Iveta Jurgensone ◽  
Juris Aigars

Zooplankton as an essential component in the pelagic food web are directly linked to pelagic ecosystem functioning. Therefore, comprehension of zooplankton functional diversity (FD) and its responses to environmental changes is crucial for ecosystem-based view. To identify FD responses to environmental drivers, we analysed 25 years of summer data on the brackish mesozooplankton community (including rotifers, cladocerans, copepods, and meroplankton) from the eutrophied, shallow Gulf of Riga (Baltic Sea). We established that within the Gulf of Riga, open waters are notably different from coastal regions based on the dynamics of hydrological conditions (temperature, salinity), cyanobacterial dominance, abundance of mesozooplankton functional groups, and mesozooplankton FD indices. Competition over resources in combination with hydrodynamic features and predation by adult herring were seemingly the central structuring mechanism behind the dynamics of FD metrics (richness, evenness, divergence, and dispersion) within coastal mesozooplankton communities. Whereas predation by young herring was an important driver only for the mesozooplankton communities in the open waters. Cyanobacterial dominance, used as a proxy for food quality and availability, had no effect on summer mesozooplankton FD metrics.


2021 ◽  
Vol 499 (1) ◽  
pp. 590-594
Author(s):  
L. A. Pautova ◽  
V. A. Silkin ◽  
M. D. Kravchishina ◽  
V. G. Yakubenko ◽  
E. A. Kudryavtseva ◽  
...  

2021 ◽  
Vol 8 ◽  
Author(s):  
Tracey T. Sutton ◽  
Kevin M. Boswell ◽  
Heather D. Bracken-Grissom ◽  
Jose V. Lopez ◽  
Michael Vecchione ◽  
...  

Author(s):  
George L Hunt ◽  
Ellen M Yasumiishi ◽  
Lisa B Eisner ◽  
Phyllis J Stabeno ◽  
Mary Beth Decker

Abstract We investigated relationships among three metrics of sea-ice cover in eight regions of the eastern Bering Sea and the abundance of Calanus copepods, jellyfish medusae, and year-class strength of walleye pollock (Gadus chalcogrammus). In summer, Calanus spp. were more abundant over the middle shelf when sea ice lingered late into spring, and, to a lesser extent, when February sea-ice cover was heavy. Between 1982 and 1999, there were no significant (p ≤ 0.05) relationships between the amount or timing of sea-ice cover and pollock recruitment. However, between 2000 and 2015, pollock year-class strength was positively correlated with sea ice in the outer and middle shelves, with 17 of 24 regressions significant. Pollock year-class strength was best predicted by days with sea-ice cover after February. Pollock recruitment was positively influenced by copepod numbers, particularly in the middle shelf, with r2 values from 0.36 to 0.47. We hypothesize that the Calanus spp. present in the southeastern Bering Sea are primarily Calanus glacialis that have been advected south in association with sea ice. None of our sea-ice metrics explained the variance in jellyfish biomass. Jellyfish biomass in our study area in the pollock age-0 year was not correlated with pollock recruitment 3 years later.


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