Fig 1.
Coastal land-cover (0.5 km from the coastline) with regards to the age of the islands (years emerged averaged from Geist [57]) on the western (Fernandina and Isabela), central (Santiago, Santa Cruz, Rábida, Pinzón, Floreana) and eastern (Santa Fe, Española and San Cristóbal) islands of the Galapagos Archipelago.
Table 1.
Google Earth Very High Resolution image interpretation attributes to identify mangrove patches and distinguish mangrove from other features.
Table 2.
Remotely sensed data sources used in the digitization of mangroves.
Fig 2.
Difference in the number of nodes between a simple and complex polygon.
Fig 3.
Map of the sampled sections of the coastline to test several semi-automatic classification and hybrid algorithms (red sections) and to perform the temporal 2004–2014 analysis (green sections).
Ground truth points are also shown (magenta points).
Fig 4.
Distribution of mangrove forests in the Galapagos Islands over Landsat 8 imagery composite.
Mangrove cover (ha) per bioregion (sensu Edgar et al, 2004).
Fig 5.
Comparison of mangrove area (ha) by island between this study, EcoCiencia and Rivas-Torres et al 2018.
Numbers above the bars represent mangrove area for this study per island (ha).
Fig 6.
Mangrove cover (ha) per coastline length (km) by groups of islands according to their geological age.
Fig 7.
Distribution of mangrove forests with increasing distance from coastline.
Red dot represents 90% mangrove cover.
Table 3.
Mangrove area comparison between the different studies achieved in Galapagos.
GMFD = Global Mangrove Forest Distribution.
Table 4.
Comparison of the number of mangrove patches, mean mangrove patch area, complexity measures and total number of nodes for all the studies on mangrove distribution estimation in the Galapagos.
GMFD = Global Mangrove Forest Distribution.
Table 5.
Comparison of the number of polygons and nodes per island between this study and the EcoCiencia study.
Table 6.
Result of the sampling to estimate the digitization accuracy.
Table 7.
Overall classification accuracy and Kappa coefficient based on 500 sample points, ordered by overall accuracy.
GMFD = Global Mangrove Forest Distribution.
Table 8.
Comparison of the classification accuracy between on-screen digitization and different Maximum Likelihood Classification (MLC) algorithms of Google Earth Very High Resolution imagery.
Ordered by Overall Accuracy. MLC1 = classification of the whole image; MLC2 = classification of the land and sea in different phases; HYBRID (OBIA-MLC) = hybrid classification technique consisting of an object based image analysis coupled with MLC.
Fig 8.
Mosaic showing the classification comparison between on-screen digitization and different Maximum Likelihood Classification (MLC) algorithms of Google Earth Very High Resolution imagery.
(A) Fernandina island; (B) and (C) Santa Cruz island; and (D) San Cristóbal island. MLC1 = classification of the whole image; MLC2 = classification of the land and sea in different phases; HYBRID (OBIA-MLC) = hybrid classification technique consisting of an object based image analysis coupled with MLC. [land shapefile from the Instituto Geográfico Militar, 2013, Base Nacional escala 1:50.000].
Table 9.
Mangrove cover (ha) for the three sampled areas on the islands of Fernandina, Santa Cruz and San Cristobal following on-screen Google Earth imagery digitization for images taken in 2004 and 2014.
Total cover and percentage increase are also shown.
Fig 9.
Proportion of mangrove cover change relative to the length of the coastline over the time period 2004–2014 according to a spatial–temporal analysis of moving mangrove patches for the three sampled islands.
CON = contraction, DIS = disappearance, EXP = expansion, GEN = generation, STB = stable.
Fig 10.
Total mangrove cover (ha) for the different studies in the Galapagos.
The red bar represents this study results. The year represents the date of the most common imagery used in each of the studies.
Fig 11.
Comparison of mangrove cover for sampled areas in the islands of Fernandina, Santa Cruz and San Cristobal according to previous studies (black dots and grey line) versus our study following on-screen digitization of mangroves (red dots).
Black ticked lines are linear models from previous studies, blue ticked lines are for all previous studies except Rivas et al. 2018 and red lines are for the 2004–2014 mangrove cover presented in this study. The SUM graph shows the sum of the mangrove cover of the three sampled islands. NB the vertical axis is not equivalent in all graphs. Year 2000 data is an average of the Global Mangrove Forest Distribution and TNC-CLIRSEN study, since both were done with images from 2000.
Fig 12.
Publications on mangrove mapping or mangrove cover from 1965 to 2017 in the Scopus indexed database.
Table 10.
Cost-benefit of different solutions to map Galapagos’ mangroves.
Analysis and image processing involves the working hours of technical staff and/or software. MMU = Minimum Mapping Unit, RGB = Red, Green, Blue; USD = United States Dollar.