1. Propagule pressure is acknowledged as a key determinant of invasion success. Nonetheless, the role of morphological or physiological attributes of propagules (i.e., their quality) in regulating invader establishment has been little explored. In particular, no study has investigated how the presence of propagules differing in quality within an inoculum influences establishment across heterogeneous landscapes.

2. We experimentally tested the hypothesis that the quality (+Fronds+Rhizoids; +Fronds–Rhizoids; –Fronds+Rhizoids) and the diversity (1, 2, 3 fragment types) of vegetative fragments of the seaweed Caulerpa taxifolia determine their establishment success across seascapes consisting of bare sediments and patches of the seagrass Zostera muelleri exposed to different disturbance intensities (control, seagrass canopy clipping and total removal).

3. After 6 weeks, seaweed biomass, stolon and frond length, frond and rhizoid number were generally greater in unvegetated habitats (bare sediments and total seagrass removal) than full or reduced seagrass canopies. The type and the diversity of types of fragments inoculated had significant effects on the final biomass and morphological features of C. taxifolia only in vegetated habitats. In control plots, inocula of fragments retaining both fronds and rhizoids achieved higher biomass, developed longer stolons and more fronds. In canopy clipping plots, mixed inocula of +Fronds+Rhizoids and –Fronds+Rhizoids fragments had the greatest biomass and stolon length.

4. Synthesis. Assessing how propagules differing in quality perform in different habitats might be not sufficient to draw a comprehensive picture of invasion risk, as their establishment can be modulated by both negative and positive interactions among them. Propagule composition should be, therefore, considered as a further dimension of propagule pressure. Our results also suggest that the relevance of specific propagule traits for invader establishment decreases from intact to degraded habitats. Considering propagule size in terms of amount of competent propagules, rather than an absolute measure, would refine our ability of predicting invasion risk across habitats differing in biotic or abiotic conditions.

This dataset was generated by a field experiment. Data have been analyzed by means of ANOVA techniques.

The dataset is composed by two Excel worksheets. Data on the Total dry weight of Caulerpa taxifolia are reported in the first sheet (named Total dry weight). Data on Total stolon length, Rhizoid number, Leaf number and Mean frond length are reported in the second sheet (named Morphometric measures). Missing values (see paper for details) are omitted from the dataset.

The different types of fragments of Caulerpa taxifolia are coded as follows under the column "Fragment Type":

A = fragments with both fronds and rhizoids (+F +R)

B = fragments with fronds and without rhizoids  (+F -R)

C = fragments without fronds and with rhizoids (-F +R)