We observed a total of 204 records of C. edulis in Uruguay, made by 78 users from 2008-03-16 to 2023-05-10. The species occurs within 10 km of the coastline, occupying 22 grid cells, equivalent to ca. 220 km of invaded coast. The invaded area is associated with coastal dune ecosystems (Fig. 1a) and covers a portion of the Atlantic and the outer Rio de la Plata coasts. The records spanned four departments: Montevideo (12), Canelones (46), Maldonado (98), and Rocha (48) (Fig. 1b). Nineteen records (9.3% of the total) were reported within protected areas. These were Laguna Garzón and Cabo Polonio (Fig. 1b, protected areas shown in green). We did not observe records of C. edulis in Humedales del Santa Lucía, Isla de Flores, Laguna de Rocha, or Cerro Verde, the other coastal protected areas in Uruguay.
Records of C. edulis have increased strongly in the last three years (Fig. 1c). The species has been reported across all seasons, but mainly in the summer (52.9% of the total) when more people circulate through the shores and dunes.
Spatial distribution
The coastline of Uruguay has been unevenly sampled on iNaturalist (Fig. 2a). Highly surveyed areas correspond mostly to the surroundings of urbanized or protected areas (compare blue grid cells in Fig. 2a with Fig. 1b). Conversely, areas with low sampling effort are usually located within areas of low urbanization. The spatial pattern of the national sampling effort (i.e., the total number of records) was significantly highly correlated with that of the number of C. edulis records (r = 0.665, p < 0.001). We observed that the western part of the C. edulis distribution (continuous along the coast) is located within areas of larger sampling efforts, while the gaps observed in Rocha correspond to less sampled areas (Fig 2a,b). However, this is not the case in Montevideo, an area with abundant sampling on iNaturalist but with a low number of records of C. edulis. This is consistent with finding very low levels of spatial correlation between the number of people living in the area and the number of C. edulis observations recorded (r = 0.299, p < 0.05). In this regard, we must consider that a significant portion of the dune system in the Montevideo Department has been removed or replaced (Gudynas 2000).
Density of the plants
Almost 70% of the records showed a medium (32.8%) or high (36.8 %) plant density (Table 1). Only 14.2% of the observations presented low density. The rest of the records could not be evaluated as they did not meet the minimum distance criteria.
Phenology
More than half of the C. edulis records did not show evidence of flowering or fruiting (57.4%). The rest of the records were divided into plants with flowering buds (1.5%), flowers (13.2%), or visible fruit (20.6%), and combinations of these phenological stages (5.4% of records were flowering and flower budding and 1.9% were flowering and fruiting). Carpobrotus edulis exhibited flowering primarily during the spring months, followed by fruiting in the summer. We also observed a smaller peak in flowering during the autumn, with fruits starting to appear in winter and increasing towards spring. This secondary peak in flowering during autumn suggests a potential extended reproductive period for C. edulis, which may contribute to its successful establishment and spread (Fig. 3).
Presence of human infrastructure
Infrastructure near the plants was observed in 22.5% of the records (Table 1). The majority of observations had no infrastructure (58.8%) and 18.6% could not be assessed because they did not meet the minimum distance criterion.
Table 1. Analysis of the photographic evidence of Carpobrotus edulis in Uruguay. (a) Density of plants. Low density, characterized by isolated individuals; medium density, where the species formed spaced branches; high density, with dense mats and overlapping branches; and not assessed, when the photo did not meet the distance criterion. (b) Presence of infrastructure such as streets, curbs, central flowerbeds, or parking lots on the sandy habitat. Absent for records that lacked any evidence and present for records that indicated the presence of the aforementioned infrastructure within a 5-meter distance radius.
(a)
|
Density
|
N
|
%
|
|
high
|
75
|
36.8%
|
|
medium
|
67
|
32.8%
|
|
low
|
29
|
14.2%
|
|
not assessed
|
33
|
16.2%
|
|
|
|
|
(b)
|
Infrastructure
|
N
|
%
|
|
absent
|
120
|
58.8%
|
|
present
|
46
|
22.5%
|
|
not assessed
|
38
|
18.6%
|