Mesozooplankton grazing during the Phaeocystis globosa bloom

Abstract During spring blooms 1998 and 1999, three complementary methods were used to evaluate the in situ feeding activities of the dominant copepod species of the Belgian coastal zone: gut pigment content analysis using HPLC, the 14 C tracer method, and cell count experiments. The results obtained by all three methods consistently showed that Phaeocystis globosa is not an adequate food source for the spring copepods in the Belgian coastal zone. Our results demonstrated that, among the potential prey, copepods strongly selected diatoms and microzooplankton, and that these types of prey accounted for the major part of the ingested carbon. However, diatoms and microzooplankton ingestion did not always seem sufficient in terms of carbon to avoid food limitation. Comparison of clearance rates exerted on different potential prey types during the P. globosa peak with those before and after the P. globosa peak showed that the copepods' feeding pressure on diatoms was reduced during the P. globosa peak while that on microzooplankton was not. The low grazing pressure on P. globosa, together with the preferential grazing on diatoms, which reduces the competition for nutrients, and the predation on microzooplankton organisms, which reduces the microzooplankton grazing pressure on P. globosa cells, are likely to favour the P. globosa bloom in the Southern Bight of the North Sea.

Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia

Aim: Invasive species are of increasing global concern. Nevertheless, the mechanisms driving furtherdistribution after the initial establishment of non-native species remain largely unresolved, especiallyin marine systems. Ocean currents can be a major driver governing range occupancy, but this hasnot been accounted for in most invasion ecology studies so far. We investigate how well initialestablishment areas are interconnected to later occupancy regions to test for the potential role ofocean currents driving secondary spread dynamics in order to infer invasion corridors and thesource–sink dynamics of a non-native holoplanktonic biological probe species on a continental scale.Location: Western Eurasia.Time period: 1980s–2016.Major taxa studied: ‘Comb jelly’ Mnemiopsis leidyi.Methods: Based on 12,400 geo-referenced occurrence data, we reconstruct the invasion historyof M. leidyi in western Eurasia. We model ocean currents and calculate their stability to match thetemporal and spatial spread dynamics with large-scale connectivity patterns via ocean currents.Additionally, genetic markers are used to test the predicted connectivity between subpopulations.Results: Ocean currents can explain secondary spread dynamics, matching observed range expansionsand the timing of first occurrence of our holoplanktonic non-native biological probe species,leading to invasion corridors in western Eurasia. In northern Europe, regional extinctions after coldwinters were followed by rapid recolonizations at a speed of up to 2,000 km per season. SourceJASPERS ET AL. | 815areas hosting year-round populations in highly interconnected regions can re-seed genotypes overlarge distances after local extinctions.Main conclusions: Although the release of ballast water from container ships may contribute tothe dispersal of non-native species, our results highlight the importance of ocean currents drivingsecondary spread dynamics. Highly interconnected areas hosting invasive species are crucial forsecondary spread dynamics on a continental scale. Invasion risk assessments should considerlarge-scale connectivity patterns and the potential source regions of non-native marine species

Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia

Publication history: Accepted - 15 February 2018; Published - 16 May 2018.Aim: Invasive species are of increasing global concern. Nevertheless, the mechanisms driving further distribution after the initial establishment of non-native species remain largely unresolved, especially in marine systems. Ocean currents can be a major driver governing range occupancy, but this has not been accounted for in most invasion ecology studies so far. We investigate how well initial establishment areas are interconnected to later occupancy regions to test for the potential role of ocean currents driving secondary spread dynamics in order to infer invasion corridors and the source–sink dynamics of a non-native holoplanktonic biological probe species on a continental scale. Location: Western Eurasia. Time period: 1980s–2016. Major taxa studied: ‘Comb jelly’ Mnemiopsis leidyi. Methods: Based on 12,400 geo-referenced occurrence data, we reconstruct the invasion history of M. leidyi in western Eurasia. We model ocean currents and calculate their stability to match the temporal and spatial spread dynamics with large-scale connectivity patterns via ocean currents. Additionally, genetic markers are used to test the predicted connectivity between subpopulations. Results: Ocean currents can explain secondary spread dynamics, matching observed range expansions and the timing of first occurrence of our holoplanktonic non-native biological probe species, leading to invasion corridors in western Eurasia. In northern Europe, regional extinctions after cold winters were followed by rapid recolonizations at a speed of up to 2,000 km per season. Source areas hosting year-round populations in highly interconnected regions can re-seed genotypes over large distances after local extinctions. Main conclusions: Although the release of ballast water from container ships may contribute to the dispersal of non-native species, our results highlight the importance of ocean currents driving secondary spread dynamics. Highly interconnected areas hosting invasive species are crucial for secondary spread dynamics on a continental scale. Invasion risk assessments should consider large-scale connectivity patterns and the potential source regions of non-native marine species.Danish Council for Independent Research; Grant/Award Number: DFF-1325-00102B; FP7 People: Marie-Curie Actions, Grant/Award Number: MOBILEX, DFF - 1325-00025; EU, BONUS, BMBF, Grant/ Award Number: 03F0682; Excellence Cluster “Future Ocean”, Grant/Award Number: CP153

Assessment of Cryptophyceae ingestion by copepods using alloxanthin pigment: a caution

The accessory pigment alloxanthin is a well-known taxonomic marker for Cryptophyceae in natural seawater. The use of alloxanthin to estimate in situ zooplankton grazing and selectivity on Cryptophyceae was studied using 2 dominant copepods of the southern North Sea, Temora longicornis and Centropages hamatus. High-performance liquid chromatography (HPLC) analyses of water samples and of freshly caught copepods, starvation experiments, and feeding experiments (shipboard bottle-incubations) were carried out. Although alloxanthin was always detected in copepod extracts, (1) no correlation was found with alloxanthin in seawater, and (2) no significant grazing on Cryptophyceae was observed. Results of our gut-evacuation experiments showed that at least 78% of the initial alloxanthin content of T. longicornis and C. hamatus remained after 90 min, whereas fucoxanthin and chloropigments decreased rapidly with time. Alloxanthin and astaxanthin esters were the only pigments remaining in the body of T. longicornis after several hours¹ starvation. It is concluded that most of the detected alloxanthin did not originate from the gut but from the body tissues. Our results suggest that alloxanthin is not suitable as a biomarker for quantitative or qualitative estimates of copepod grazing on Cryptophyceae

First record of the Asian copepod Pseudodiaptomus marinus Sato, 1913 (Copepoda: Calanoida: Pseudodiaptomidae) in the southern bight of the North Sea along the coast of France

International audienceThe presence of the demersal Asian copepod Pseudodiaptomus marinus is reported for the first time in the southern bight of the North Sea, in both Calais harbour and the coastal waters off Gravelines, France. This is the first record of P. marinus in the Atlantic Ocean sector and the North Sea area. The species was collected in January and October 2010, and in January, February and April 2011. The very low number of collected individuals (0.2 to 4.0 ind.m-3) and the capture of only two ovigerous females and of a few numbers of copepodid CV stages suggest that the species survives and actually reproduces in both sites but does not manage to develop an abundant population. The presence of P. marinus in Calais harbour and coastal waters of the southern North Sea supports recent observations of other Asian species in the same area and suggests a passive transport via ship's ballast water

Do Phaeocystis colony blooms affect zooplankton in the Belgian coastal zone?

The ability of herbivorous zooplankton to control phytoplankton blooms, and to efficiently transfer primary production towards higher trophic levels such as invertebrates, fish larvae and planktivorous fish, is considered as a sign of equilibrium in marine ecosystems. This is not the case in the Southern Bight of the North Sea where massive Phaeocystis colony spring blooms sustained by anthropogenic nitrates, are suggested to be the consequence of a high resistance to losses, in particular grazing (Lancelot et al. 1994; 2002). To which extent Phaeocystis colony blooms are negatively impacting zooplankton dynamic is investigated in this chapter, based on available information on zooplankton in the Belgian coastal zone (BCZ).info:eu-repo/semantics/publishe

19'-hexanoyloxyfucoxanthin may not be the appropriate pigment to trace occurrence and fate of<i> Phaeocystis</i>: the case of <i>P. globosa</i> in Belgian coastal waters

Two haptophycean strains were isolated from field samples collected in 2001 in Belgian coastal waters (southern North Sea) during the Phaeocystis monitoring program of the AMORE Project. The morphology and pigment composition of these two strains, one identified as Phaeocystis globosa and the other as Imantonia rotunda, were carefully examined. The comparative analysis of their pigment signature revealed the presence of two fucoxanthin derivatives, 19'-butanoyloxyfucoxanthin and 19'-hexanoyloxyfucoxanthin (but-fuco and hex-fuco) in I. rotunda, which were undetectable in P. globosa. A further comparison of pigments and phytoplankton from field samples showed no significant correlation between hex-fuco concentration and P. globosa biomass in the water column. Low concentrations of this pigment were, however, detectable before and at the end of the Phaeocystis bloom. The presence of I. rotunda in the area, overlooked by light microscopy, but isolated in pure culture from field samples, might explain the presence of this pigment. We conclude that hex-fuco is not the appropriate pigment to estimate Phaeocystis abundance and trace its trophic fate in Belgian coastal waters. These results also indicate that pigment analysis should be coupled with a precise identification of phytoplankton taxa present in field samples