Browsing by Author "Holmer, Marianne"
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- A meta-analysis of seaweed impacts on seagrasses: generalities and knowledge gapsPublication . Thomsen, Mads S.; Wernberg, Thomas; Engelen, Aschwin; Tuya, Fernando; Vanderklift, Mat A.; Holmer, Marianne; McGlathery, Karen J.; Arenas, Francisco; Kotta, Jonne; Sillimann, Brian R.Seagrasses are important habitat-formers and ecosystem engineers that are under threat from bloom-forming seaweeds. These seaweeds have been suggested to outcompete the seagrasses, particularly when facilitated by eutrophication, causing regime shifts where green meadows and clear waters are replaced with unstable sediments, turbid waters, hypoxia, and poor habitat conditions for fishes and invertebrates. Understanding the situations under which seaweeds impact seagrasses on local patch scales can help proactive management and prevent losses at greater scales. Here, we provide a quantitative review of available published manipulative experiments (all conducted at the patch-scale), to test which attributes of seaweeds and seagrasses (e.g., their abundances, sizes, morphology, taxonomy, attachment type, or origin) influence impacts. Weighted and unweighted meta-analyses (Hedges d metric) of 59 experiments showed generally high variability in attribute-impact relationships. Our main significant findings were that (a) abundant seaweeds had stronger negative impacts on seagrasses than sparse seaweeds, (b) unattached and epiphytic seaweeds had stronger impacts than 'rooted' seaweeds, and (c) small seagrass species were more susceptible than larger species. Findings (a) and (c) were rather intuitive. It was more surprising that 'rooted' seaweeds had comparatively small impacts, particularly given that this category included the infamous invasive Caulerpa species. This result may reflect that seaweed biomass and/or shading and metabolic by-products like anoxia and sulphides could be lower for rooted seaweeds. In conclusion, our results represent simple and robust first-order generalities about seaweed impacts on seagrasses. This review also documented a limited number of primary studies. We therefore identified major knowledge gaps that need to be addressed before general predictive models on seaweed-seagrass interactions can be build, in order to effectively protect seagrass habitats from detrimental competition from seaweeds.
- An overview of ecological status, vulnerability and future perspectives of European large shallow, semi-enclosed coastal systems, lagoons and transitional watersPublication . Newton, Alice; Icely, John; Cristina, Sónia; Brito, Ana; Cardoso, Ana Cristina; Colijn, Franciscus; Riva, Simona Dalla; Gertz, Flemming; Hansen, Jens Würgler; Holmer, Marianne; Ivanova, Kateryna; Leppäkoski, Erkki; Canu, Donata Melaku; Mocenni, Chiara; Mudge, Stephen; Murray, Nicholas; Pejrup, Morten; Razinkovas, Arturas; Reizopoulou, Sofia; Pérez-Ruzafa, Angel; Schernewski, Gerard; Schubert, Hendrik; Carr, Laishalla; Solidoro, Cosimo; PierluigiViaroli, null; Zaldívar, José-ManuelThe paper gives an overview of some of the large, shallow, semi-enclosed coastal systems (SECS) in Europe, These SECS are important both from the ecological and the economic perspective (socioecological systems) and provide many valuable ecosystem goods and services. Although some of the systems are transitional waters under theWater Framework Directive, this is not the case for all of the systems. The paper adopts a Driver-Pressure-State-Impact-Response approach to analyse the ecological status, vulnerability and future perspectives of these systems in the context of global change.
- Eutrophication in transitional waters: an overviewPublication . Zaldívar, José-Manuel; Cardoso, Ana Cristina; Viaroli, Pierluigi; Newton, Alice; Wit, Rutger; Ibañez, Carles; Reizopoulou, Sofia; Somma, Francesca; Razinkovas, Arturas; Basset, Alberto; Holmer, Marianne; Murray, NicholasDespite their ecological and economic importance, Transitional Waters (TWs) have fallen behind all the other water categories in respect to the implementation of the Water Framework Directive (WFD) and further, pose some interpretation problems in other existing Water Directives. The problems faced by TWs concerning the implementation of WFD are mainly related to their characteristics, including: the high spatio-temporal variability, the fast response time to perturbations, their high productivity, the fact that primary production in these systems is normally not dominated by phytoplankton, their high socio-economic importance with a long historical tradition, and the strong anthropogenic pressures which exists in these systems. The present review attempts to bring together the main elements characterizing TWs and to identify the current understanding of the process of eutrophication and the problems this raises in establishing reference conditions, in view of the need of implementing the WFD. It is thus necessary to reach agreement on working definitions of TWs that can form the basis for the development of methodologies permitting the establishment of reference conditions; gain an understanding of the processes of eutrophication and the drivers and pressures that play a major role in their evolution; and investigate the use of indicators susceptible of accurately reflecting the ecological quality status of these types of water, as required by the WFD.