Marine Research Findings of the VECTORS Project

This website provides access to the research results of the VECTORS project, which can be used to support marine management decisions, policies and governance as well as future research and investment. VECTORS was a large scale project that brought together more than 200 expert researchers from 16 different countries. It examined the significant changes taking place in European seas, their causes, and the impacts they will have on society.


All of the publications created as part of the VECTORS project are listed below (latest first).
Please use the search box below to find a publication by title, author(s), year or keyword; the most relevant results will be displayed at the top of the page.

  • Nurkse, K., J. Kotta, H. Orav-Kotta, M. Pärnoja and I. Kuprijanov. (2015). Laboratory experiment on the habitat occupance of the crab Rhithropanopeus harrisii (Gould) in an invaded ecosystem: The north-eastern Baltic Sea. Estuarine, Coastal and Shelf Science 154(5), 152-157. doi:10.1016/j.ecss.2014.12.046
    View abstract The Harris mud crab (Rhithropanopeus harrisii) arrived to the Baltic Sea in 1936. It was not until the late 2000s when the species considerably expanded its distribution area towards the northern Baltic Sea and formed a viable and expanding population. This introduction represents an appearance of a completely new function, as such larger epibenthic predators were previously missing from north-eastern Baltic Sea. In order to assess potential impacts of the crab to the invaded ecosystem, knowledge of the crab habitat preferences is required. This study experimentally evaluated the habitat occupancy of the Harris mud crab. The crab stayed more in vegetated boulders compared to unvegetated boulders or sandy habitats. There was an interactive effect between the presence of prey and crab population density with prey availability increasing the crab's affinity towards less favored habitats when population densities were low. Increased aggression between crab individuals increased their affinity towards otherwise less occupied habitats. Less favored habitats were typically inhabited by smaller individuals and presence of prey increased occupancy of some habitats for larger crabs. The experiment demonstrated that the crab may inhabit a large variety of habitats with stronger affinity towards boulder fields covered with the brown macroalga Fucus vesiculosus. This implies stronger impact of crab in such habitats in the invaded ecosystem.
  • Girardin, R., Y. Vermard, O. Thébaud, A. Tidd and P. Marchal. (2015). Predicting fisher response to competition for space and resources in a mixed demersal fishery. Ocean & Coastal Management 106, 124-135. doi:10.1016/j.ocecoaman.2015.01.017
    View abstract Understanding and modelling fleet dynamics and their response to spatial constraints is a prerequisite to anticipating the performance of marine ecosystem management plans. A major challenge for fisheries managers is to be able to anticipate how fishing effort is re-allocated following any permanent or seasonal closure of fishing grounds, given the competition for space with other active maritime sectors. In this study, a Random Utility Model (RUM) was applied to determine how fishing effort is allocated spatially and temporally by the French demersal mixed fleet fishing in the Eastern English Channel. The explanatory variables chosen were past effort i.e. experience or habit, previous catch to represent previous success, % of area occupied by spatial regulation, and by other competing maritime sectors. Results showed that fishers tended to adhere to past annual fishing practices, except the fleet targeting molluscs which exhibited within year behaviour influenced by seasonality. Furthermore, results indicated French and English scallop fishers share the same fishing grounds, and maritime traffic may impact on fishing decision. Finally, the model was validated by comparing predicted re-allocation of effort against observed effort, for which there was a close correlation.
  • Boyes, S.J. and M. Elliott. (2015). The excessive complexity of national marine governance systems – Has this decreased in England since the introduction of the Marine and Coastal Access Act 2009? Marine Policy 51, 57-65. doi:10.1016/j.marpol.2014.07.019
    View abstract With successive Government restructuring and the introduction of the Marine and Coastal Access Act in 2009, this paper revisits a previous set of organograms created in 2006 indicating the government departments with responsibilities relating to the marine and coastal environment in England in 2014. The 2009 Act presented an opportunity to harmonise marine management by simplifying the complexity in England through a radical restructuring of marine governance; however this is apparently not the case with many overlapping responsibilities still existing. This paper provides an overview of the 2009 Act, discussing some of the significant changes like the creation of the Marine Management Organisation (MMO), examines the current structure of marine management in England following its enactment and highlights the continued overlaps in jurisdiction, responsibilities and complexity of the government agencies with a marine remit.
  • Keyl, F., A.J. Kempf and A.F. Sell. (2015). Sexual size dimorphism in three North Sea gadoids. Journal of Fish Biology 86(1), 261-275. doi:10.1111/jfb.12579
    View abstract Existing biological data on whiting Merlangius merlangus, cod Gadus morhua and haddock Melanogrammus aeglefinus from a long-term international survey were analysed to address sexual size dimorphism (SSD) and its effect on their ecology and management. Results show that SSD, with larger females of the same age as males, is a result of higher growth rates in females. A direct consequence of SSD is the pronounced length-dependent female ratio that was found in all three gadoids in the North Sea. Female ratios of the three species changed from equality to female dominance at specific dominance transition lengths of c. 30, 35 and 60 cm for M. merlangus, G. morhua and M. aeglefinus, respectively. An analysis by area for M. merlangus also revealed length dependence of female ratios. SSD and length-dependent female ratios under most circumstances are inseparable. Higher overall energy demand as well as a higher energy uptake rate must result from the observed SSD and dimorphism in growth rates. Potential processes related to feeding, locomotion and physiology are proposed that could balance the increased energy investment of females. Potential consequences of SSD and length dependency of female ratios are the reduction of the reproductive potential of a stock due to size-selective fishing and biased assessment of the true size of the female spawning stock that could distort decisions in fisheries management.
  • Ojaveer, H., B.S. Galil, M.L. Campbell, J.T. Carlton, J. Canning-Clode, E.J. Cook, A.D. Davidson, C.L. Hewitt, A. Jelmert, A. Marchini, C.H. McKenzie, D. Minchin, A. Occhipinti Ambrogi, S. Olenin and G.M. Ruiz. (2015). Classification of non-indigenous species based on their impacts: considerations for application in marine management. PLOS Biology 13(4), e1002130. doi:10.1371/journal.pbio.1002130
    View abstract Assessment of the ecological and economic/societal impacts of the introduction of non-indigenous species (NIS) is one of the primary focus areas of bioinvasion science in terrestrial and aquatic environments, and is considered essential to management. A classification system of NIS, based on the magnitude of their environmental impacts, was recently proposed to assist management. Here, we consider the potential application of this classification scheme to the marine environment, and offer a complementary framework focussing on value sets in order to explicitly address marine management concerns. Since existing data on marine NIS impacts are scarce and successful marine removals are rare, we propose that management of marine NIS adopt a precautionary approach, which not only would emphasise preventing new incursions through pre-border and at-border controls but also should influence the categorisation of impacts. The study of marine invasion impacts requires urgent attention and significant investment, since we lack the luxury of waiting for the knowledge base to be acquired before the window of opportunity closes for feasible management.
  • Nunes, P.A.L.D., M.L. Loureiro, L. Piñol, S. Sastre, L. Voltaire and A. Canepa. (2015). Analyzing beach recreationist’s preferences for the reduction of jellyfish blooms: economic results from a stated-choice experiment in Catalonia, Spain. Plos One 10(6), e0126681. doi:10.1371/journal.pone.0126681
    View abstract

    Jellyfish outbreaks and their consequences appear to be on the increase around the world, and are becoming particularly relevant in the Mediterranean. No previous studies have quantified tourism losses caused by jellyfish outbreaks. We used a stated-choice questionnaire and a Random Utility Model to estimate the amount of time respondents would be willing to add to their journey, in terms of reported extra travel time, in order to reduce the risk of encountering jellyfish blooms in the Catalan coast. The estimation results indicated that the respondents were willing to spend on average an additional 23.8% of their travel time to enjoy beach recreation in areas with a lower risk of jellyfish blooms. Using as a reference the opportunity cost of time, we found that the subsample of individuals who made a trade-off between the disutility generated by travelling longer in order to lower the risk of jellyfish blooms, and the utility gained from reducing this risk, are willing to pay on average €3.20 per beach visit. This estimate, combined with the respondents’ mean income, yielded annual economic gains associated with reduction of jellyfish blooms on the Catalan coast around €422.57 million, or about 11.95% of the tourism expenditures in 2012. From a policy-making perspective, this study confirms the importance of the economic impacts of jellyfish blooms and the need for mitigation strategies. In particular, providing daily information using social media applications or other technical devices may reduce these social costs. The current lack of knowledge about jellyfish suggests that providing this information to beach recreationists may be a substantially effective policy instrument for minimising the impact of jellyfish blooms.

  • Molla, E., G. Cimino and M.T. Ghiselin.$  (2015). Alien biomolecules: a new challenge for natural product chemists. Biological Invasions 17(3), 941-950. doi:10.1007/s10530-014-0835-6
    View abstract Among natural products there are molecules well known to influence the abundance and distribution of marine organisms and to play important roles in their interactions with one another. Recently, chemical ecologists have also started to consider how research on natural products might be useful in understanding marine biological invasions, assessing their impact in the invaded areas, and considering how to deal with them. Their efforts especially focused on the Mediterranean Sea, which is one of the major hotspots of marine biological invasions on earth, showing in what way marine natural products (MNPs) may influence (1) the ability of exotic marine organisms to invade and to get established, (2) how they affect the invaded biota, and (3) public health and the economy. In all cases, the study of such chemical warfare between alien and native species started with the isolation of the pure chemicals required for chemical structure elucidation and subsequent biological testing, implying a central role of natural product chemistry in approaching critical issues in invasion biology. In this position paper we also introduce a theme of possible interest for managing marine invasive species, based on the exploitation of available chemical and biological information on MNPs. We show how a kind of chemical data originally gathered for other objectives—such as obtaining drugs from the sea—might also offer valid alternatives to unrealistic eradication campaigns, becoming the basis for a desirable commercial use of the bioactive compounds obtainable from marine pests, thus paving the way for making the control of invasions profitable. The pests might then be harvested, reducing their impact on marine ecosystems.
  • Dawson, M.N., K. Cieciel, M.B. Decker, G.C. Hays, C.H. Lucas and K.A. Pitt. (2015). Population-level perspectives on global change: genetic and demographic analyses indicate various scales, timing, and causes of scyphozoan jellyfish blooms. Biological Invasions 17(3), 851-867. doi:10.1007/s10530-014-0732-z
    View abstract Whether a perceived increase in the abundance of jellyfishes is related to changing marine environments has been considered primarily using large-scale analyses of multi-species assemblages. Yet jellyfish blooms—rapid increases in the biomass of pelagic coelenterate species—are single-species demographic events. Using published and new genetic analyses and population surveys, we investigate whether there may be a critical knowledge gap between the scales of recent analyses and the scales of natural phenomena. We find that scyphomedusae may show population genetic structure over scales of tens to hundreds of kilometers, that environments vary regionally and locally, and that populations of medusae can display uncorrelated dynamics on these scales. These findings suggest genetic differences between populations and/or environmental differences between sites are important determinants of population dynamics in these jellyfishes. Moreover, the local abundance of medusae may be most strongly correlated with preceding rather than current local environmental conditions, indicating there is a cumulative timecourse to the formation of ‘blooms’. Broad-scale macro-ecological analyses will need to build from coordinated, long-term, fine-grained studies to synthesize, rather than mask, population-level phenomena in larger-scale analyses.
  • Darling, J.A. (2015). Genetic studies of aquatic biological invasions: closing the gap between research and management. Biological Invasions 17(3), 951-971. doi:10.1007/s10530-014-0726-x
    View abstract Recent years have seen a dramatic rise in the application of genetic methods to understand aquatic biological invasions. In part these methods have been adopted to address fundamental questions in biogeography, evolutionary biology, population ecology, and other fields. But it is also commonly suggested that genetic information has the potential to directly inform the management of aquatic invasions. Here I explore the potential promise of genetic approaches for informing management of aquatic invasive species, the degree to which that promise has been realized in terms of utilization of genetic information by managers and other decision-makers, and the likely limitations to the value of genetic methods (both in principle and in practice) and ways in which these limitations might be overcome. I consider a range of possible applications of genetic tools for management, including molecular detection and identification of cryptic invaders, source tracking and reconstruction of invasion history, and inference of population demographics. Retrospective assessment of the utility of such applications is based on both literature review and solicitation of expert opinion, and suggests that a number of hurdles likely often prevent genetic information from effectively informing decision-making. These include (1) limitations or misunderstandings of the resolution and certainty afforded by genetic analysis; (2) failure to engage decision-makers in problem formulation, research design and research implementation; and (3) complex relationships between basic research and management actions. While some of the obstacles considered are rooted in theoretical and practical limitations of genetic analysis, others are clearly associated with poor communication and insufficient engagement of potential end-users of genetic information. I consider possible avenues for overcoming these obstacles and for improving the applicability of genetic information for supporting management decisions.
  • Comtet, T., A. Sandionigi, F. Viard and M. Casiraghi. (2015). DNA (meta)barcoding of biological invasions: a powerful tool to elucidate invasion processes and help managing aliens. Biological Invasions 17(3), 905-922. doi:10.1007/s10530-015-0854-y
    View abstract Biological invasions are a major threat to the world’s biodiversity with consequences on ecosystem structure and functioning, species evolution, and human well-being (through ecosystem services). Conservation of biological diversity and management of biological resources require multi-level management strategies on non-native species, in order to (1) prevent biological introductions, (2) detect non-native species at an early stage of the introduction, and (3) eradicate or maintain at a low level of population density non-native species that were successfully introduced. A pre-requisite to any control measures on non-native species is the ability to rapidly and accurately identify the putative threatening alien species. DNA barcoding, and its recent extension, DNA metabarcoding are complementary tools that have proved their value in the identification of living beings. Here we review their use in the identification of non-native species at several steps of the introduction processes, and how they can be applied in the control and management of biological introductions. Through examples covering various taxa and ecosystems (terrestrial, freshwater, marine), we highlight the strengths and weaknesses of approaches that we foresee as crucial in the implementation of early warning strategies.
  • Bayha, K.M., M.H. Chang, C.L. Mariani, J.L. Richardson, D.L. Edwards, T.S. DeBoer, C. Moseley, E. Aksoy, M.B. Decker, P.M. Gaffney, G.R. Harbison, J.H. McDonald and A. Caccone. (2015). Worldwide phylogeography of the invasive ctenophore Mnemiopsis leidyi (Ctenophora) based on nuclear and mitochondrial DNA data. Biological Invasions 17(3), 827-850. doi:10.1007/s10530-014-0770-6
    View abstract The ctenophore Mnemiopsis leidyi is one of the most successful marine bioinvaders on record. Native to the Atlantic coast of the Americas, M. leidyi invaded the Black Sea, Caspian and Mediterranean Seas beginning the in late 1980s, followed by the North and Baltic Seas starting in 2006, with major concomitant alterations in pelagic ecology, including fishery collapses in some cases. Using extensive native range sampling (21 sites), along with 11 invasive sites in the Black, Caspian, Mediterranean, North and Baltic Seas, we examined M. leidyi worldwide phylogeographic patterns using data from mitochondrial cytochrome b (cytb) and six nuclear microsatellite loci. Cytb and microsatellite data sets showed different levels of genetic differentiation in the native range. Analyses of cytb data revealed considerable genetic differentiation, recovering three major clusters (northwestern Atlantic, Caribbean, and South America) and further divided northwestern Atlantic sampling sites into three groups, separated approximately at Cape Hatteras on the US Atlantic coast and at the Floridian peninsula, separating the Gulf of Mexico and Atlantic coasts. In contrast, microsatellite data only distinguished samples north and south of Cape Hatteras, and suggested considerable gene flow among native samples with clear evidence of isolation by distance. Both cytb and microsatellite data sets indicated that the northern invaders (North/Baltic Seas) originated from north of Cape Hatteras, with cytb data pointing to Delaware and north. Microsatellite data indicated a source for the southern invaders (Black, Caspian and Mediterranean Seas) to be south of Cape Hatteras, while cytb data narrowed the source location to the Gulf of Mexico region. Both cytb and microsatellite data sets suggested that the southern invasion was associated with genetic bottlenecks while evidence was equivocal for the northern invasion. By increasing the native range spatial sampling, our dataset was able to sufficiently characterize patterns and levels of genetic differentiation in the native range of M. leidyi and identify likely biogeographic boundaries, allowing for the most complete characterization of M. leidyi’s invasion histories and most realistic estimates of its source region(s) to date.
  • Darling, J.A. and S. Piraino. (2015). MOLTOOLS: a workshop on ‘‘Molecular tools for monitoring marine invasive species’’. Biological Invasions. doi:10.1007/s10530-015-0855-x
    View abstract The 2011–2014 European Community project VECTORS (‘‘Vectors of Change in Oceans and Seas-Marine Life, Impact on Economic Sectors’’) was an integrated, multidisciplinary European project which aimed to improve our understanding of how environmental anthropogenic drivers are impacting European marine ecosystems now and in the future.  VECTORS investigated how these changes may affect marine biodiversity and ecosystem functioning, the range of goods and services provided by the oceans, the resulting socio-economic impacts and some possible future scenarios for mitigation and adaptation.
  • Marras, S., A. Cucco, F. Antognarelli, E. Azzurro, M. Milazzo, M. Bariche, M. Butenschön, S. Kay, M. Di Bitetto, G. Quattrocchi, M. Sinerchia and P. Domenici. (2015). Predicting future thermal habitat suitability of competing native and invasive fish species: from metabolic scope to oceanographic modelling. Conservation Physiology 3(1), cou059. doi:10.1093/conphys/cou059
    View abstract Global increase in sea temperatures has been suggested to facilitate the incoming and spread of tropical invaders. The increasing success of these species may be related to their higher physiological performance compared with indigenous ones. Here, we determined the effect of temperature on the aerobic metabolic scope (MS) of two herbivorous fish species that occupy a similar ecological niche in the Mediterranean Sea: the native salema (Sarpa salpa) and the invasive marbled spinefoot (Siganus rivulatus). Our results demonstrate a large difference in the optimal temperature for aerobic scope between the salema (21.8°C) and the marbled spinefoot (29.1°C), highlighting the importance of temperature in determining the energy availability and, potentially, the distribution patterns of the two species. A modelling approach based on a present-day projection and a future scenario for oceanographic conditions was used to make predictions about the thermal habitat suitability (THS, an index based on the relationship between MS and temperature) of the two species, both at the basin level (the whole Mediterranean Sea) and at the regional level (the Sicilian Channel, a key area for the inflow of invasive species from the Eastern to the Western Mediterranean Sea). For the present-day projection, our basin-scale model shows higher THS of the marbled spinefoot than the salema in the Eastern compared with the Western Mediterranean Sea. However, by 2050, the THS of the marbled spinefoot is predicted to increase throughout the whole Mediterranean Sea, causing its westward expansion. Nevertheless, the regional-scale model suggests that the future thermal conditions of Western Sicily will remain relatively unsuitable for the invasive species and could act as a barrier for its spread westward. We suggest that metabolic scope can be used as a tool to evaluate the potential invasiveness of alien species and the resilience to global warming of native species. 
  • Tidd, A.N., Y. Vermard, P. Marchal, J.K. Pinnegar, J.L. Blanchard and E.J. Milner-Gulland. (2015). Fishing for space: fine-scale multi-sector maritime activities influence fisher location choice. Plos One 10(1), e0116335. doi:10.1371/journal.pone.0116335
    View abstract The European Union and other states are moving towards Ecosystem Based Fisheries Management to balance food production and security with wider ecosystem concerns. Fishing is only one of several sectors operating within the ocean environment, competing for renewable and non-renewable resources that overlap in a limited space. Other sectors include marine mining, energy generation, recreation, transport and conservation. Trade-offs of these competing sectors are already part of the process but attempts to detail how the seas are being utilised have been primarily based on compilations of data on human activity at large spatial scales. Advances including satellite and shipping automatic tracking enable investigation of factors influencing fishers’ choice of fishing grounds at spatial scales relevant to decision-making, including the presence or avoidance of activities by other sectors. We analyse the determinants of English and Welsh scallop-dredging fleet behaviour, including competing sectors, operating in the eastern English Channel. Results indicate aggregate mining activity, maritime traffic, increased fishing costs, and the English inshore 6 and French 12 nautical mile limits negatively impact fishers’ likelihood of fishing in otherwise suitable areas. Past success, net-benefits and fishing within the 12 NM predispose fishers to use areas. Systematic conservation planning has yet to be widely applied in marine systems, and the dynamics of spatial overlap of fishing with other activities have not been studied at scales relevant to fisher decision-making. This study demonstrates fisher decision-making is indeed affected by the real-time presence of other sectors in an area, and therefore trade-offs which need to be accounted for in marine planning. As marine resource extraction demands intensify, governments will need to take a more proactive approach to resolving these trade-offs, and studies such as this will be required as the evidential foundation for future seascape planning.
  • Kristensen, K., U.H. Thygesen, K.H. Andersen, J.E. Beyer and J.M. Jech. (2014). Estimating spatio-temporal dynamics of size-structured populations. Canadian Journal of Fisheries and Aquatic Sciences 71(2), 326-336. doi:10.1139/cjfas-2013-0151
    View abstract Spatial distributions of structured populations are usually estimated by fitting abundance surfaces for each stage and at each point of time separately, ignoring correlations that emerge from growth of individuals. Here, we present a statistical model that combines spatio-temporal correlations with simple stock dynamics to estimate simultaneously how size distributions and spatial distributions develop in time. We demonstrate the method for a cod (Gadus morhua) population sampled by trawl surveys. Particular attention is paid to correlation between size classes within each trawl haul due to clustering of individuals with similar size. The model estimates growth, mortality, and reproduction, after which any aspect of size structure, spatio-temporal population dynamics, as well as the sampling process can be probed. This is illustrated by two applications: (i) tracking the spatial movements of a single cohort through time and (ii) predicting the risk of bycatch of undersized individuals. The method demonstrates that it is possible to combine stock assessment and spatio-temporal dynamics; however, this comes at a high computational cost. The model can be extended by increasing its ecological fidelity, although computational feasibility eventually becomes limiting.
  • Laur, K., H. Ojaveer, M. Simm and R. Klais. (2014). Multidecadal dynamics of larval gobies Pomatoschistus spp. in response to environmental variability in a shallow temperate bay. Estuarine, Coastal and Shelf Science 136, 112-118. doi:10.1016/j.ecss.2013.11.011
    View abstract Compared to commercial fish, there is relatively limited information available about the dynamics of non-commercial fish that very often play important structural and functional roles in marine ecosystems. Long-term investigations that provide quantitative estimates of the population dynamics as a function of environmental variability are needed to understand the ecology and role of the non-commercial fish in the ecosystem, and assist the ecosystem management where relevant. Here we analyze the inter-annual variability and long-term trends of the abundance of the larval non-commercial gobies Pomatoschistus spp. in a shallow coastal bay (Pärnu Bay, northeastern Baltic Sea) in 1959-2010, in relation to climate and prey field related variables. The abundance of larval Pomatoschistus spp. decreased over the last 50 years along with the concomitant decrease in the water transparency. The first appearance of larvae has shifted for about two weeks earlier and is mostly related to the timing of ice cover breakdown. However, some of the effects of the environmental forcing on larval fish may be obscured by the uncertainty of species identification of individuals of the genus Pomatoschistus at larval stage, and the investigated population of Pomatoschistus spp. consists of at least two species with slightly different ecologies and also environmental preferences.
  • Kalaus, M. and H. Ojaveer. (2014). Over one decade of invasion: the non-indigenous cladoceran Evadne anonyx G.O. Sars, 1897 in a low-salinity environment. Aquatic Invasions 9(4), 499-506. doi:10.3391/ai.2014.9.4.08
    View abstract Invasive species are often in focus in the non-indigenous species (NIS) research while low-abundance species receive relatively little attention. However, tracking NIS dynamics since the early stages of an invasion provides valuable information on the ecology of invasions. In the current paper, we investigated the invasion history and population dynamics of the small-bodied cladoceran Evadne anonyx G. O. Sars, 1897 in the Gulf of Riga (Baltic Sea) almost since its first detection in 2000. The species already was widespread the Gulf of Riga in 2001 and has been found in nearly every subsequent sample collected during summer months. However, the abundance of the species remained low, seldom 100 individuals m-3 . Both, salinity and water temperature affected the spatial distribution and population abundance of E. anonyx. The species was found to occur only sporadically at salinities below ca. 6. To obtain reliable presence/absence and density estimates on this small-bodied cladoceran, the entire zooplankton sample needed to be analysed.
  • Lyons, D.A., C. Arvanitidis, A.J. Blight, E. Chatzinikolaou, T. Guy-Haim, I. Kotta, H. Orav-Kotta, A.M. Queiros, G. Rilov, P.J. Somerfield and T.P. Crowe. (2014). Macroalgal blooms alter community structure and primary productivity in marine ecosystems. Global Change Biology 20(9), 2712-2724. doi:10.1111/gcb.12644
    View abstract Eutrophication, coupled with loss of herbivory due to habitat degradation and overharvesting, has increased the frequency and severity of macroalgal blooms worldwide. Macroalgal blooms interfere with human activities in coastal areas, and sometimes necessitate costly algal removal programs. They also have many detrimental effects on marine and estuarine ecosystems, including induction of hypoxia, release of toxic hydrogen sulfide into the sediments and atmosphere, and the loss of ecologically and economically important species. However, macroalgal blooms can also increase habitat complexity, provide organisms with food and shelter, and reduce other problems associated with eutrophication. These contrasting effects make their overall ecological impacts unclear. We conducted a systematic review and metaanalysis to estimate the overall effects of macroalgal blooms on several key measures of ecosystem structure and functioning in marine ecosystems. We also evaluated some of the ecological and methodological factors that might explain the highly variable effects observed in different studies. Averaged across all studies, macroalgal blooms had negative effects on the abundance and species richness of marine organisms, but blooms by different algal taxa had different consequences, ranging from strong negative to strong positive effects. Blooms' effects on species richness also depended on the habitat where they occurred, with the strongest negative effects seen in sandy or muddy subtidal habitats and in the rocky intertidal. Invertebrate communities also appeared to be particularly sensitive to blooms, suffering reductions in their abundance, species richness, and diversity. The total net primary productivity, gross primary productivity, and respiration of benthic ecosystems were higher during macroalgal blooms, but blooms had negative effects on the productivity and respiration of other organisms. These results suggest that, in addition to their direct social and economic costs, macroalgal blooms have ecological effects that may alter their capacity to deliver important ecosystem services.
  • Archambault, B., O. Le Pape, N. Bousquet and E. Rivot. (2014). Density-dependence can be revealed by modelling the variance in the stock-recruitment process: an application to flatfish. ICES Journal of Marine Science 71(8), 2127-2140. doi:doi:10.1093/icesjms/fst203
    View abstract Recruitment success in marine species is mostly driven by the high and variable mortality of first life stages, and the relationships between stock and recruitment are then largely dominated by residual variability. We show that analysing the residual variability may provide insights on the density-dependence process occurring during the recruitment. Following the seminal formulation of Mintoetal. (Survival variability and population density in fish populations. Nature, 2008), we show that when recruitment is considered as a sequence of a pelagic stage with stochastic density-independent mortality followed by a second stage with stochastic density-dependent mortality, then the variability of the recruitment rate per spawning biomass (RPSB) should be a decreasing function of the spawning biomass. Using stock-recruit data of 148 stocks from the RAM legacy database,we provide a test of this hypothesis by showing that the variability of RPSB is lower for fish species with the higher concentration during juvenile stages. Second, a hierarchical Bayesian model (HBM) is built to derive a meta-analysis of stock-recruit data for 39 flatfish stocks, characterized by a high concentration of juveniles in coastal nursery habitats. Results of the HBM show that the variance of the RPSB decreases with the spawning biomass for almost all stocks,thus providing strong evidence of density-dependence during the recruitment process. Finally, we attempt to relate patterns in recruitment variance to relevant life-history traits of flatfish species.
  • Arula, T., H. Ojaveer and R. Klais. (2014). Impact of extreme climate and bioinvasion on temporal coupling of spring herring (Clupea harengus m.) larvae and their prey. Marine Environmental Research 102, 102-109.
    View abstract We used weekly observational data from mid-May to end of July in 1958-2012 in Gulf of Riga to investigate temporal coupling between spring herring larvae and their first prey copepod nauplii, under the extreme hydroclimatic conditions. We focused on a small shallow estuary that is important nursery ground for larvae of the Gulf of Riga (Baltic Sea) herring population. We quantified the effect of extreme values of the winter air temperatures, time of ice retreat and spring water temperatures on the timing of peak abundance of herring larvae and copepod nauplii. We also assessed whether the invasion of the non-native cladoceran Cercopagis pengoi had notable effect on timing and abundance of copepod nauplii during the peak occurrence of herring larvae. In the years of earliest ice retreat the peak abundance of herring larvae was five weeks earlier than in the years of latest ice retreat, while the timing of nauplii remained unchanged. Abundant presence of the C. pengoi affected neither timing nor maximum abundance of copepod nauplii during the herring larvae first feeding period. Thus, we conclude that processes induced by climate variability are superior to invasion of C. pengoi in determining the timing and coupling of larval herring and copepod nauplii.
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