Table 1.
Sampling details: Location, tidal level occupied and the number of specimens collected for each analysis are shown for each species.
Fig 1.
Prokaryotic colonization imaging of crab gills.
Two representative SEM images of the microbial communities associated with gills are shown for each of the 12 crab species studied (A–L). The colours indicate the intertidal level inhabited: Blue subtidal, green = intertidal, yellow = supratidal. Letters in intertidal species show define each taxon-related intertidal group: Gr = Grapsidae, Ge = Gelasminidae, M = Macrophtalmidae, S = Sesarmidae. Scale bar corresponds to 10 μm (photo credit and copyright: Marco Fusi A-F, H-K, and Elisa Garuglieri G, L. Marco Fusi and Elisa Garuglieri publish these pictures under a CC BY licence).
Fig 2.
Gill structure morphology in the crab species Cranuca inversa.
Image of a single gill observed with cryo-SEM at low magnification (A). Higher magnification showing gill lamellae connected by a membrane-like structure, black arrows indicate the preservation of the spine and bulb-like structures (B). Overview of the gill structure and lamellae organisation and the arrow shows the thicker part of the lamellae that prevent the collapse of the structure during emersion (C). Image of a single gill observed with conventional SEM at low magnification (D). Magnification of panel D showing separate gill lamellae covered by dark rough patches corresponding to bacterial coverage (E). Images of the bacterial community attached to the surface of the gill lamellae: Conventional SEM (E) and TEM—black arrows indicate the prokaryotic cells (F).
Fig 3.
SEM images of bacteria associated with gills of Cranuca inversa (A–C) and TEM images of prokaryotes associated with gills of Parisesarma guttatum (D–F). Different morphologies are visible within the groups of prokaryotes on the gill surface: Rough (white arrow) and smooth horizontal rod-shaped, and cocci (black arrow) (A). Smooth and rough (white arrow) spindle-like prokaryotes with visible distal peduncles (black arrows) lying horizontally on the gill chitinous cuticle (B). Dividing prokaryotic cells (*). Prokaryotes perpendicularly attached to the gill cuticle (C). Filaments showing cell-gill attachment are visible (black arrow). Groups of prokaryotes near the gill (g) (D). Arrows = pili, arrowhead = large electron-dense filaments that extend from the terminal part of the prokaryotes towards the branchial cuticle. This image appears to indicate the mechanism of adhesion of the bacteria to the gills, while the pili are oriented on the opposite side of the gills. Groups of prokaryotes in contact with the gill (g) (E). The prokaryotes appear to be enveloped in a layer of amorphous material (*). Electron-dense filaments are evident, extending from the terminal part of the prokaryote towards the branchial cuticle (arrows). Detail of the large electron-dense filaments (*) which extend from the terminal part of the prokaryote towards the g, branchial cuticle (g) (F).
Table 2.
Prokaryotic cell abundance on the gills’ surface of crab species.
Fig 4.
Prokaryotes morphology on the outer surface of the gill lamellae in Tubuca urvillei.
Gill lamellae surface is indicated by ‘g’. Dense multilayers of bacteria are observed on the gill lamellae surface (A, B). The presence of pili and electron-dense filaments from the prokaryote cells to the gill lamellae surface is indicated by the arrow (B, C).
Fig 5.
Prokaryote abundance computed through SEM imaging.
Bacterial abundance on gills of crabs with different lifestyles along the tidal gradient. Letters are related to pairwise comparisons (A). Abundance of smooth horizontal rod-shaped prokaryotes across different intertidal levels. Letters show statistical significance from multiple comparisons (B). Abundance of smooth perpendicular rod-shaped prokaryotes across different intertidal levels (C). Letters indicate statistical significance among the groups resulting from multiple pairwise comparisons. The colours indicate the intertidal level: Blue = subtidal, green = intertidal, yellow = supratidal.
Fig 6.
Bacterial quantification using qPCR analysis.
Bacterial abundance on gills of five different mangrove crab species with different lifestyles along the tidal gradient. Letters indicate statistical significance (p < 0.05) among the groups resulting from multiple pairwise comparisons. The colours indicate the intertidal levels: Blue = subtidal, green = intertidal, yellow = supratidal.