Invasion of Sargassum muticum in Limfjorden (Denmark) and its possible impact on the indigenous macroalgal community

Abstract

Attached Sargassum muticum (Yendo) Fensholt was first observed in the westernmost part of Limfjorden (Denmark) in 1984, and it has since colonized Limfjorden from west to east at a rate of 15 to 17 km yr -1. By 1997, S. muticum had become the most dominant macroalga, covering more than 6% of the bottom between 0 and 6 m depth, corresponding to ca 35% cover of the hard substrate. In 1990, the cover of S. muticum was strongly correlated with distance from the original source area in the westernmost part of the estuary, suggesting that colonization was still in progress. By 1997, the cover of S. muticum was less correlated with distance from the original source area and more strongly correlated with the amount of hard substrate, indicating that colonization was reaching its climax. The absence of S. muticum from certain parts of Limfjorden by 1997 is therefore best explained by lack of hard substrate in these areas, and not by insufficient colonization time. The increased abundance of S. muticum between 1990 and 1997 affected species richness and diversity of the macroalgal community only marginally. However, multivariate community analysis revealed significant changes in the macroalgal community structure that were closely related to the increased abundance of S. muticum. Not only did the dominance of S. muticum increase significantly from 1990 to 1997, but the cover of several indigenous species belonging to the genera Laminaria, Fucus, and Codium decreased during the same period, indicating competitive displacement through competition for hard substrate and light.KEY WORDS: Sargassum muticum · Macroalgae · Invasion · Macroalgal community structure Resale or republication not permitted without written consent of the publisher

Native pipefish Entelurus aequoreus are promoted by the introduced seaweed Sargassum muticum in the northern Wadden Sea, North Sea

“…Since S. muticum stocks are increasing in European waters (e.g. Critchley et al 1987, Karlsson & Loo 1999, Staehr et al 2000, a subject of further research should be whether these stocks could potentially trigger the high abundances of snake pipefish currently found in the northeast Atlantic Ocean.…”

“…After establishment, densities of S. muticum have strongly increased along European coasts (e.g. Critchley et al 1987, Karlsson & Loo 1999, Staehr et al 2000.…”

Epibiota communities of the introduced and indigenous macroalgal relatives Sargassum muticum and Halidrys siliquosa in Limfjorden (Denmark)

“…Several studies have indicated negative impacts by S. muticum on indigenous algal assemblages (Fletcher and Fletcher 1975;Ambrose and Nelson 1982;Viejo 1997;Cosson 1999;Staehr et al 2000) but only a limited number of studies have addressed the possible consequences for macroalgal epibiota. Those that have, have suggested few adverse effects, apparently due to a low degree of habitat specificity among the epibiota (Withers et al 1975;Jephson and Gray 1977;Viejo 1999).…”

Large-scale facilitation of a sessile community by an invasive habitat-forming snail

“…When non-indigenous species invade new communities, they interact with and have effects on many resident species (Staehr et al 2000;Crooks 2009;Altieri et al 2010). Similar to any other ecological network of interactions, this leads to some residents being adversely affected while others benefit.…”