title: Macroalgal blooms alter community structure and primary productivity in marine ecosystems.
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 programmes. They also have many detrimental effects on marine and estuarine ecosystems, including induction of hypoxia, release of toxic hydrogen sulphide 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 meta-analysis 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.
authors.affiliation: University College Dublin, Dublin, Ireland.
authors.forename: Devin A
authors.initials: DA
authors.lastname: Lyons
authors.forename: Christos
authors.initials: C
authors.lastname: Arvanitidis
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Blight
authors.forename: Eva
authors.initials: E
authors.lastname: Chatzinikolaou
authors.forename: Tamar
authors.initials: T
authors.lastname: Guy-Haim
authors.forename: Jonne
authors.initials: J
authors.lastname: Kotta
authors.forename: Helen
authors.initials: H
authors.lastname: Orav-Kotta
authors.forename: Ana M
authors.initials: AM
authors.lastname: Queirós
authors.forename: Gil
authors.initials: G
authors.lastname: Rilov
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Somerfield
authors.forename: Tasman P
authors.initials: TP
authors.lastname: Crowe
mesh_terms: D000818:Animals; D044822:Biodiversity; D058448:Biota / Q000502:physiology*; D017753:Ecosystem; D005068:Eutrophication / Q000502:physiology*; D057097:Harmful Algal Bloom / Q000502:physiology*; D007448:Invertebrates / Q000502:physiology*; D008386:Marine Biology; D009792:Oceans and Seas; D052817:Phototrophic Processes / Q000502:physiology*; D011157:Population Dynamics; D013045:Species Specificity
keywords: biodiversity; ecosystem functioning; green tide; harmful algal bloom; macroalgal bloom; macroalgal mat; species richness