Flexible filter feeders:The gelatinous zooplankton community in the Netherlands after the invasion of the ctenophore <i>Mnemiopsis leidyi</i>

Of kwallen wereldwijd steeds meer voorkomen is een onderwerp van discussie, maar ze zorgen steeds vaker voor problemen zoals verstopte visnetten, verstopte koelwaterinlaten of wegblijvende toeristen. In Nederlandse kustwateren zorgde de vondst van de invasieve Amerikaanse ribkwal Mnemiopsis leidyi voor hernieuwde interesse in deze diverse diergroep. In 2010 startte Lodewijk van Walraven een onderzoek aan kwalachtigen in Nederlandse wateren, in een samenwerkingsverband tussen NIOZ Koninklijk Instituut voor Zeeonderzoek en Deltares, waarop hij 18 november promoveert.Vijftig jaar kwallenvangsten in een visfuik op Texel laten zien dat schijfkwallen na warmere winters vroeger in het jaar verschijnen. Het aantal gevangen kwallen was afgenomen. Ook naar poliepen (bodemstadia van kwallen) is er gezocht op veel plekken in de Nederlandse kustwateren: op de bodem, op wrakken en in havens. Helaas zijn alleen poliepen van de oorkwal gevonden. Kennis van het voorkomen van de poliepen kan zorgen voor een betere voorspelling van kwallenproblemen in de toekomst. De Amerikaanse ribkwal is nu de algemeenste kwalachtige in Nederlandse. Experimenten toonden aan dat deze soort zich ook in zeer brak water kan voortplanten. Computermodellen van verspreiding, overleving, voortplanting en groei van de ribkwallen bij verschillende temperaturen en voedselbeschikbaarheid voorspellen dat de Amerikaanse ribkwal zich vanuit Nederlandse wateren naar andere Europese wateren kan verspreiden. Als de Nederlandse kustwateren warmer worden zou de ribkwal zich meer en eerder kunnen voortplanten en veel dierlijk plankton weg kunnen eten, met gevolgen voor voedselbeschikbaarheid voor andere kwalachtigen en vissen als haring, sprot en ansjovis.Whether jellyfish numbers are increasing worldwide is an ongoing debate, but it is a fact that jellyfish-related problems such as clogged fishing gear and cooling water intakes, and tourists avoiding beaches, are increasing. In Dutch coastal waters the introduction of the invasive comb jellyfish Mnemiopsis leidyi triggered a renewed interest in this diverse group of anumals. In 2010 Lodewijk van Walraven started a study on gelatinous zooplankton in Dutch coastal waters, in a collaboration between the NIOZ Royal Netherlands Institute for Sea Research and Deltares, which he will defend on November 18.Fifty years of jellyfish catches in a fish fyke on Texel show that jellyfish are appearing earlier in the year following warmer winters. The number of jellyfish caught had decreased. Polyps (bottom-living stages of jellyfish) were also studied and searched for on the bottom, on wrecks and in harbours and ports. Only polyps of the moon jellyfish were found. Knowledge of the distribution of polyps can lead tob etter forecasting of jellyfish problems in the future.The American comb jellyfish is now the most common gelatinous species in Dutch waters. Experiments showed that the species can survive in very brackish waters. Computer models of distribution, survival, reproduction and growth of the species predict that Dutch waters act as a source of comb jellies for other European waters. When coastal waters get warmer, spawning of the invasive species could increase and shift to earlier months. This can have consequences for food availability of other gelatinous species and fish such as anchovy, sprat and herring

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

Sleutelaspect zoöplankton : analysedocument voor de basismonitoring Wadden

Dit document is opgesteld conform het format voor de analysedocumenten basismonitoring. Het doel van het analysedocument is: Vaststellen of we datgene monitoren wat we nodig hebben om te kunnen beoordelen of we met het gevoerde beheer de overeengekomen beleidsdoelen bereiken. Adviseren over de monitoring die gewenst is, maar nog ontbreekt. Het analysedocument beschrijft waar de monitoring niet toereikend is voor het analyseren van de doelen

Voorstel voor monitoring van zoöplankton in de Noordzee : monitoringplan zoöplankton MONS ID14

In this report, a draft plan for monitoring and supporting research of zooplankton in the Dutch part of the North Sea has been drawn up. The aim is to draw up a zooplankton monitoring plan that can provide answers to the following questions in due course: What is the composition and distribution of zooplankton in space and time? And also: what are the trends (years and decades) (in composition and distribution of zooplankton in space and time) and what are the effects of new human use? The results from the monitoring should enable to understand and predict changes in zooplankton in the North Sea, so that validated scenario studies can be performed. All this in order to be able to assess the ecological capacity and the effects of individual and cumulative use thereon. The monitoring plan consists of two phases, a 1-year inventory study and a 4-year monitoring to test whether the results can be used to answer the questions. First of all, an overview was drawn up of the available knowledge about the policy frameworks and goals for zooplankton monitoring, an overview was given of monitoring activities in the Netherlands and other North Sea countries and a description was made of conventional and innovative techniques that are used for zooplankton monitoring. Internationally (e.g. OSPAR) the focus is currently mainly on indicators that indicate the role of zooplankton in the food chain. The density and size distribution of the mesozooplankton (0.2 – 20 mm) is used as an indicator for the food availability of fish. Biodiversity is also important. These indicators can be measured in different ways. In addition to classical methods, in which net samples are analyzed under the microscope, more and more innovative methods are being used. Phase 1: The plan for the first phase concerns a 1-year study aimed at determining the required resolution for identifying trends in space and time and the feasibility of innovative techniques to be used in the monitoring of zooplankton. The plan includes which classical and innovative techniques can be used and how these can contribute to answering the knowledge questions. This concerns the collection of zooplankton with net samples and the analysis thereof, such as by means of microscopy, image analysis or DNA metabarcoding, and the application of in situ techniques, such as dragging a video plankton recorder, acoustic measurements and the use of scanners. Three sailing trips have been proposed for this and measurements at fixed measuring stations. Phase 2: The plan for phase 2 is still surrounded by uncertainties, because it is being implemented on the basis of the findings of phase 1. In this project, only a preliminary plan can be drawn up for a 4- year program and budgeted on the basis of the number of measurement locations and times. These will be smaller compared to the monitoring of phase 1. It is also unclear at the start of phase 2 which techniques will ultimately be selected, so that a specification must also be made for this

A synthesis of the distribution of Mnemiopsis leidyi in European waters

Jaspers, Cornelia ... et. al.-- International Council for the Exploration of the Sea Annual Science Conference (ICES ASC 2014), Sustainability in a changing ocean, 15-19 September 2014, La Coruña.-- 2 pagesWe synthesize the distribution of M. leidyi throughout European waters and show that it has established populations through northern and southern Europe reaching as far north as 63.5⁰NPeer Reviewe

Can guild- or site-specific contrasts in trends or phenology explain the changed role of the Dutch Wadden Sea for fish?

The Wadden Sea bordering the Dutch, German and Danish coast, is traditionally a region with important functions for many fish species: as a nursery area for juveniles (marine juveniles), as a feeding area, as a transit to and from fresh water, and resident species complete their whole life cycle there. Because of indications that the importance of the Dutch Wadden Sea has changed drastically for many species during the past decades, we analysed and classified trends of 24 common fish species in the last 45 years, whichwere assigned to 5 differentecological guilds. Trends were examined for threeWadden Sea regions and compared to trends in the adjacent two North Sea coastal regions. For these analyses we made a combined use of two longterm time series: an annual beamtrawl survey, the Demeral Fish Survey (DFS) with a high spatial but poor seasonal resolution and a fyke serieswith a high seasonal but poor spatial resolution.Weinvestigated forwhich species the DFS surveywas appropriate for trend analysis, and we evaluated whether a change in timing may contribute to patterns in DFS time trends. Total fish biomass showed a similar pattern in all tidal basins with an increase from 1970 to 1980, a peak in the mid-1980s and a strong decline from 1980 to 2000, with a subsequent stable trend. The pattern in the coastal region deviated especially in the past 10 years, with a further decline along the Dutch Wadden coast and an increase along the mainland coast. Most dramatic declines throughout the Wadden Sea occurred in speciesbelonging to the marine juvenile guild, notably plaice, sole and dab. A declining trend in marine juveniles is on-going in the western part, while it recently stabilised or even increased in the central and eastern part and in the coastal regions. Resident species showed more variable trends in the Wadden Sea with less pronounced directions: both increases and decreases occurred. In the coastal regions, several resident species have increased considerably in the last 15 years, a pattern not observed in the Wadden Sea. Also the size structure of the fish community changed in all regions,with generally the strongest declines in the largest size classes. The combined use of the two surveys showed that for some species the DFS was not timed in the period of peak occurrence. Althoughthe phenology of several species has changed, the DFS survey period still encompasses the peak period of most species