Regulacija vertikalnog fluksa i sastav planktona u jednostavnom ekološkom sistemu: “snapshots” iz malog slanog jezera Rogoznica (Hrvatska)

Vertical flux regulation was investigated in the small, shallow, marine and partly anoxic Lake Rogoznica (eastern coast of the Adriatic Sea) by studying plankton composition, zooplankton fecal pellet (FP) production and vertical carbon flux. The lake is naturally eutrophicated with high nutrient and particulate organic carbon (POC) concentrations and relatively low species diversity. However, the few species found can be highly abundant. Due to a simple ecological structure and low physical forcing, Lake Rogoznica may be regarded as a natural laboratory especially suitable for plankton studies. Only one copepod species, Acartia italica, was found in the lake and had a maximal abundance of 140 animals L-1. The mixotrophic dinoflagellate Ceratium furca and the diatom Chaetoceros curvisetus accounted for ~90% of the phytoplankton biomass. Phytoplankton made up 30% of the POC flux at 5 m and 10% at 10 m depth and was dominated by C. curvisetus and C. furca. Average export of POC was 730 ± 40 mg m-2d-1 at 5 m and 750 ± 90 mg m-2d-1 at 10 m depth, and detritus comprised 68 and 86 % at 5 and 10 m depth, respectively. Despite high copepod abundance and high suspended FP concentration, FP only contributed 4 – 5% of the vertical POC flux. The highest contribution to vertical carbon flux was in terms of detritus, and high retention was likely due to FP grazing or fragmentation by A. italica copepodites above 5 m depth. It is concluded that Lake Rogoznica is a productive system where organic material is rapidly transformed to detritus.Istraživan je vertikalni protok u malom, slanom, plitkom i djelomično anoksičnom jezeru Rogoznica (istočna obala Jadranskog mora) na temelju sastava planktona, produkcije zooplanktonskih fekalnih peleta i vertikalnog protoka ugljika. Jezero je prirodno eutroficirano s visokim koncentracijama hranjivih soli, a posebito čestičnim organskim ugljikom (POC) i relativno niskoj raznolikosti vrsta. Nekoliko pronađenih vrsta su pokazivale visoke brojnosti. Zbog svoje jednostavne ekološke strukture i slabih fizikalnih sila jezero Rogoznica se smatra prirodnim laboratorijem pogodnim za istraživanje planktona. Pronađena je samo jedna vrsta kopepoda, Acartia italica, s maksimalnom brojnošću od 140 jedinki L-1. Miksotrofni dinoflagelat Ceratium furca i diatomeja Chaetoceros curvisetus su bili zastupljeni s ~90% u fitoplanktonskoj biomasi. Fitoplankton predstavlja do 30% u dotoku čestičnog organskog ugljika na dubini od 5 m, te 10% na dubini od 10 m, a prevladavale su vrste C. curvisetus i C. furca. Prosječni dotok čestičnog organskog ugljika iznosio je 730 ± 40 mg m-2 d-1 na dubini od 5 m i 750 ± 90 mg m-2 d-1 na dubini od 10 m, dok je detritus obuhvaćao 68% odnosno 86% dotoka na dubinama od 5 i 10 m. Usprkos visokoj zastupljenosti kopepoda i koncentraciji suspendiranih fekalnih peleta, doprinos fekalnih peleta vertikalnom dotoku čestičnog organskog ugljika je bio samo 4 – 5 %. Najveći doprinos vertikalnom protoku ugljika predstavlja detritus i visoko zadržavanje je vjerojatno posljedica grazing-a fekalnih peleta ili njihove fragmentacije od strane kopepodita A. italica na dubini iznad 5 m. Ustanovljeno je da je jezero Rogoznica produktivni sistem u kojem se organski materijal brzo pretvara u detritus

High abundances of small copepods early developmental stages and nauplii strengthen the perception of a non-dormant Arctic winter

The traditional view is that the Arctic polar night is a quiescent period for marine life, but recent reports of high levels of feeding and reproduction in both pelagic and benthic taxa have challenged this. We examined the zooplankton community present in Svalbard fjords, coastal waters, and the shelf break north of Svalbard, during the polar night. We focused on the population structure of abundant copepods (Calanus finmarchicus, Calanus glacialis, Metridia longa, Oithona similis, Pseudocalanus spp., Microcalanus spp., and Microsetella norvegica) sampled using 64-µm mesh nets. Numerically, copepod nauplii (≥ 50%) and the young developmental stages of small copepods (< 2 mm prosome length as adult) dominated the samples. Three main patterns were identified: (1) large Calanus spp. were predominantly older copepodids CIV–CV, while (2) the small harpacticoid M. norvegica were adults. (3) For other species, all copepodid stages were present. Older copepodids and adults dominated populations of O. similis, Pseudocalanus spp. and M. longa. In Microcalanus spp., high proportion of young copepodids CI–CIII indicated active winter recruitment. We discuss the notion of winter as a developing and reproductive period for small copepods in light of observed age structures, presence of nauplii, and previous knowledge about the species. Lower predation risks during winter may, in part, explain why this season could be beneficial as a period for development. Winter may be a key season for development of small, omnivorous copepods in the Arctic, whereas large copepods such as Calanus spp. seems to be reliant on spring and summer for reproduction and development.publishedVersio

New insights into the Barents Sea Calanus glacialis population dynamics and distribution

Arctic copepods are major grazers and vital food for planktivores in polar ecosystems but challenging to observe due to remoteness and seasonal sea ice coverage. Models offer higher spatio-temporal resolution, and individual-based models (IBMs) are useful since they incorporate individual variability which characterizes most copepod populations. Here, we present an IBM of the Arctic copepod Calanus glacialis, a key secondary producer in polar regions of the Barents Sea. The model is coupled to a three-dimensional physical-biological model, and an IBM for the Atlantic congener C. finmarchicus. We use the model to fill seasonal “gaps” between discontinuous spatio-temporal sampling for studying the spatial and seasonal population dynamics. Our simulations suggest that, across the Atlantic and Arctic domains of this ecosystem, total population egg production peaks in July, and copepodid 3 is the main overwintering stage descending to deeper overwintering depths between July and September. Total population biomass peaks at 5 times higher carbon mass than the seasonal minimums and is driven by the seasonal build-up of biomass in stages C4, C5 and adults. Ocean currents spreads the population over a large area, though with a clear spatial separation between C. glacialis and C. finmarchicus in the northern and southern Barents Sea, respectively. There is a mixture between 1- and 2-years life cycles in the model population, and those who require two diapause phases to reach maturity have spent a larger part of their life north of 77°N, where temperatures are colder and the growth season shorter than further south. A remaining question is where the source population of C. glacialis in this ecosystem resides, and whether the population relies on local survival and reproduction or continuous supply from a source population outside the Barents Sea

New insights into the Barents Sea Calanus glacialis population dynamics and distribution

Arctic copepods are major grazers and vital food for planktivores in polar ecosystems but challenging to observe due to remoteness and seasonal sea ice coverage. Models offer higher spatio-temporal resolution, and individual-based models (IBMs) are useful since they incorporate individual variability which characterizes most copepod populations. Here, we present an IBM of the Arctic copepod Calanus glacialis, a key secondary producer in polar regions of the Barents Sea. The model is coupled to a three-dimensional physical-biological model, and an IBM for the Atlantic congener C. finmarchicus. We use the model to fill seasonal “gaps” between discontinuous spatio-temporal sampling for studying the spatial and seasonal population dynamics. Our simulations suggest that, across the Atlantic and Arctic domains of this ecosystem, total population egg production peaks in July, and copepodid 3 is the main overwintering stage descending to deeper overwintering depths between July and September. Total population biomass peaks at 5 times higher carbon mass than the seasonal minimums and is driven by the seasonal build-up of biomass in stages C4, C5 and adults. Ocean currents spreads the population over a large area, though with a clear spatial separation between C. glacialis and C. finmarchicus in the northern and southern Barents Sea, respectively. There is a mixture between 1- and 2-years life cycles in the model population, and those who require two diapause phases to reach maturity have spent a larger part of their life north of 77°N, where temperatures are colder and the growth season shorter than further south. A remaining question is where the source population of C. glacialis in this ecosystem resides, and whether the population relies on local survival and reproduction or continuous supply from a source population outside the Barents Sea.publishedVersio

Genetics redraws pelagic biogeography of Calanus

Planktonic copepods of the genus Calanus play a central role in North Atlantic/Arctic marine food webs. Here, using molecular markers, we redrew the distributional ranges of Calanus species inhabiting the North Atlantic and Arctic Oceans and revealed much wider and more broadly overlapping distributions than previously described. The Arctic shelf species, C. glacialis, dominated the zooplankton assemblage of many Norwegian fjords, where only C. finmarchicus has been reported previously. In these fjords, high occurrences of the Arctic species C. hyperboreus were also found. Molecular markers revealed that the most common method of species identification, prosome length, cannot reliably discriminate the species in Norwegian fjords. Differences in degree of genetic differentiation among fjord populations of the two species suggested that C. glacialis is a more permanent resident of the fjords than C. finmarchicus. We found no evidence of hybridization between the species. Our results indicate a critical need for the wider use of molecular markers to reliably identify and discriminate these morphologically similar copepod species, which serve as important indicators of climate responses.publishedVersionPaid Open Acces

Production of dissolved organic carbon by Oithona nana (Copepoda: Cyclopoida) grazing on two species of dinoflagellates

Spource:doi:10.1007/s00227-016-3005-9</a

First record of a rare species, Polyasterias problematica (Prasinophyceae), in Balsfjord, northern Norway

Polyasterias problematica is a poorly investigated prasinophyte species, practically known only from a few, primarily historical studies. Fragmentary information on the species indicates that P. problematica is mainly distributed in the euphotic zone of the Canadian and Russian Arctic, Atlantic Canada, the mid-Atlantic and some European seas. Here, we present the first record of this species in the Balsfjord waters, northern Norway. A detailed morphological description, with line drawings and microscopy-based photographs, as well as information on its up-to-date geographical distribution and possible explanations for its extraordinary scarcity are provided