Abstract
The present study focused on the dynamics of the phenology and life cycle of the Phaeophyceae invader Sargassum muticum at three sites on the Atlantic coast of Morocco over a period of two years (2013 and 2014). The results showed that S. muticum has two distinct growth phases; one with slower growth in winter followed by one with faster growth in spring-early summer, when the species exhibited high elongation and branching activities with thalli length ranging from 1 to more than 5 m depending on the study site. The site S1, with a rocky substratum covered by submerged sands, promotes thalli elongation, with maximum lengths of 643.33 11.10 cm recorded in July. At the rocky sites (S2 and S3), the maximum length of the seaweed depends on the pools’ depth. Although the elongation of thalli is enhanced by the water body depth, the settlements’ density (5-48 ind. m–2) seems to be mainly related to the nature of the substrate. The maturity index progressively increases from spring to early summer, when it reaches the highest values. S. muticum seems to be more abundant and more easily acclimated in shallow rockpools (sufficiently lighted and semi-exposed to wave action at the mid and lower tidal levels) than in protected sandy bottom sites with low hydrodynamic forces.
Highlights
Sargassum muticum (Yendo) Fensholt (Yendo 1907) is regarded as one of the most aggressive introduced marine macroalgae (Boudouresque and Verlaque 2002)
S. muticum was observed outside its original range for the first time on the North American Pacific coast of British Columbia, Canada (Scagel 1956)
Table 1. – Three-way ANOVA testing the effect of site (3 levels), month (12 levels) and year (2 levels) as fixed factors on the thalli length, density and maturity index of Sargassum muticum communities on the Moroccan Atlantic coasts
Summary
Sargassum muticum (Yendo) Fensholt (Yendo 1907) is regarded as one of the most aggressive introduced marine macroalgae (Boudouresque and Verlaque 2002). S. muticum was observed outside its original range for the first time on the North American Pacific coast of British Columbia, Canada (Scagel 1956) It reached northern California (USA) (Abbott and Hollenberg 1976) and Mexico (Devinny 1978). S. muticum is present on most of the European Atlantic coasts and continues to spread in particular on the southern coasts of the Iberian Peninsula (Bermejo et al 2012) and in the British Isles (Engelen et al 2015) It has reached the north Atlantic coast of Africa (Sabour et al 2013)
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