Fig 1.
A) Geographical location of Dongsha Atoll in the northern South China Sea. B) Lagoon patch reef sites surveyed in this study.
Fig 2.
Spatial variation in benthic categories in the Dongsha lagoon.
Two-dimensional nonmetric multidimensional scaling (NMDS) of average percent cover of corals, total macroalgae (upright/crustose non-coralline seaweeds and turf), crustose coralline algae (CCA) and other substrate among 24 groups (12 sites × 2 area types). Thick arrows represent the vectors of weighted average scores of benthic categories. Green loops enclose groups with statistically similar composition by clustering analysis based on the Bayesian post-hoc analyses (posterior Cohen’s d > 0.2); a loop enclosing only one group indicates that its composition is significantly different from all other groups. Dashed lines indicate the contours of percent cover projected onto two-dimensional NMDS space.
Fig 3.
Spatial variation in G. divaricata in the Dongsha lagoon.
(A) Boxplots showing variation in the percent cover of G. divaricata between reef top and slope among 13 sites. Labels denote the ranks of percent cover according to multiple comparisons among 26 transects. Labels that with different letters indicate a statistical difference (posterior Cohen’s d > 0.2) in the G. divaricata cover. (B) The average percent cover on the reef top and slope at each site are represented by circles with different colors and sizes.
Fig 4.
Temporal variation in G. divaricata on a degraded patch reef in the southeast Dongsha lagoon.
Boxplots showing variation in the percent cover of two major benthic categories (corals and G. divaricata) among four time points over a period of 17 months (about 5 m depth at site 7).
Fig 5.
Observational photo-evidence of a prolonged Galaxaura overgrowth.
A-B) A degraded patch reef in the southeast lagoon of Dongsha Atoll has been overgrown by G. divaricata for at last 3.5 years (3–5 m depth at site 9). Photos were taken in A) February 2014, with water temperature = 22.5°C; and B) in September 2017 with water temperature = 29°C. The holdfast of G. divaricata penetrates a branching Porites coral (P. cylindrica), creating small holes (inset). D) Coral (P. solida) tissue discoloration and bleaching (arrows) following direct contact with G. divaricata, potentially caused by allelopathic chemicals.
Fig 6.
Examples showing epiphytic macroalgae that frequently grow on G. divaricata.
A) Valonia ventricosa, B) Caulerpa chemnitzia, C) Dictyota sp., D) Lobophora sp. (arrowhead), and Hypnea caespitosa (arrow).
Fig 7.
Coral overgrowth by Lobophora sp28.
A) Example showing Lobophora sp28 growing on Galaxaura divaricata (arrows), and in contact with coral (Porites solida) (arrowheads). B) Coral overgrowth (Porites cylindrica in this case) by Lobophora sp28 is widespread in the shallow lagoon of Dongsha Atoll.
Table 1.
Occurrence frequency (%) of epiphytic macroalgae on Galaxaura divaricata from the slope of site 7.