Small tropical islands as hotspots of crustose calcifying red algal diversity and endemism

Abstract

In the tropics, crustose calcifying red algae (Corallinophycidae and Peyssonneliales; CCRA) are dominant and important reef builders that serve a suite of ecological functions affecting reef health. However, CCRA taxa have historically been overlooked in floristic and ecological studies because of their high degrees of phenotypic plasticity and morphological convergence that impede reliable identifications based on morphology. This study provides an update of the CCRA diversity of Guam (Mariana Islands) based on a recent DNA barcoding effort. This account of CCRA taxa is compared to (1) the most current species inventories for Guam based on morphological identifications and (2) similar floristic accounts of CCRA from other regions using DNA barcoding. 492 CCRA specimens were collected from Guam for which two markers, COI-5P and psbA, were used for phylogenetic analysis and species delimitation. Phylogenetic relationships were inferred using maximum likelihood. Species richness estimates were obtained through a conservative approach using the Automatic Barcode Gap Discovery method for species delimitation. A total of 154 putative CCRA species were identified, with 106 representatives of the subclass Corallinophycidae and 48 belonging to the order Peyssonneliales. When compared to previous studies based on morphological identification, molecular data suggests that all but one of the CCRA species reported for Guam were incorrectly identified and CCRA species richness is more than six times higher than previously assumed. Species accumulation curves show that CCRA species richness will continue to rise with increased sampling effort and the exploration of new (micro)habitats before reaching a plateau. Guam’s true CCRA richness might eventually exceed the currently reported species richness of all marine red algae for the island. Of the 154 putative species documented in this study, only ten closely match (≥ 98% COI-5P sequence similarity) previously described species, implying that many are probably new species to science. The here-reported CCRA diversity for Guam as a small, remote tropical island in the Western Pacific Ocean is greater than those of well-documented CCRA floras for much larger nearshore ecosystems in Brazil and New Zealand, emphasizing the value of tropical islands as hotspots of marine biodiversity.

Quantifying pigment content in crustose coralline algae using hyperspectral imaging: A case study with Tethysphytum antarcticum (Ross Sea, Antarctica)

“…Such initiatives could enhance our understanding of CCA photo‐adaptations (Burdett et al., 2014; Voerman, Ruseckas, et al., 2022) under changing irradiance regimes (Clark et al., 2013, 2017; Figueiredo et al., 2015; Irving et al., 2004; Martone et al., 2010). Moreover, the results could contribute to understanding the consequences of CCA phenotype shifts on benthic communities (De Jode et al., 2019) and the impacts of losing cryptic CCA lineages with diverse functional roles (Hind et al., 2019; Mills et al., 2022; Twist et al., 2019).…”

“…Studying CCA pigmentation patterns is challenging due to (1) the group's high cryptic and phenotypic diversity, with undescribed species possibly responding differently (Hind et al., 2019; Mills et al., 2022; Twist et al., 2019); (2) low numbers of reference studies, particularly from temperate and polar regions (reviewed in Cornwall et al., 2019; Hancock et al., 2020; McCoy & Kamenos, 2015; Page et al., 2022); and (3) constraints in pigment quantification methods that are appropriate to the micro‐spatial variability within single individual thalli (mm–cm). Standard pigment extraction techniques, such as high‐performance liquid chromatography (“the gold standard”) and spectrophotometry, are destructive, thus impeding temporal measurements, and are costly or labor‐intensive (Esteban et al., 2009).…”

Coral reefs in transition: Temporal photoquadrat analyses and validation of underwater hyperspectral imaging for resource-efficient monitoring in Guam

“…Located just outside of the Indo-Pacific center of reef biodiversity [ 76 ], Guam’s mangroves, seagrass beds, lagoons, fringing reefs, and patch reefs are among the most diverse and species-rich nearshore marine ecosystems of all US jurisdictions. Home to more than 350 scleractinian coral species, over 1,000 species of fish, well over 400 seaweed species [ 77 – 80 ], and more than 5,000 documented marine species, Guam’s reefs are among the best-studied in Micronesia [ 80 ]. Like other islands in the tropical Pacific, Guam’s reefs and marine resources are deeply rooted in the local traditions and culture and have maintained significant economic value to the present day.…”

Structural Complexity of Coral Reefs in Guam, Mariana Islands

“…Guam (13 • 28 N, 144 • 46 E) is located just outside of the Indo-Pacific center of reef biodiversity [55] and is home to more than 5000 documented marine species, making it one of the most diverse and speciose nearshore marine ecosystems of all US jurisdictions [56][57][58][59]. Despite possessing significant economic, cultural, and ecological value to the island, the health of Guam's reefs has been in decline since the 1960s [60].…”