A total of 317 documents were retrieved using the search strings, and the publication and citation trends from 1981 to 2024, are presented in Fig. 1. The trend fluctuates annually but shows an overall general upward pattern in both publications and citations. The trends are tentatively divided into three phases. The first phase, from 1981 to 2000 represents the formative years of research output, during which only a small number of papers were published annually, commonly fewer than five per year. This period reflects the early exploration of the field, with publications appearing sporadically and a relatively low cumulative citation count. The second phase between 2001 and 2012 marked as a period of steady growth. During this time, the annual publication rate gradually increased, consistently exceeding five papers per year, with several peaks reaching 10 to 15 publications. In the recent phase (i.e., 2013 to 2024), the period is characterized by higher productivity, with annual publications frequently ranging between 15 to 25 documents. The cumulative citation curve continued to climb steeply, surpassing 9,000 citations by 2024, reflecting both the maturity of the field and its wider impact. Despite some fluctuations in annual outputs, the overall trend shows sustained and intensive research interest during this phase.

Following the search criteria, 24 publications of benthic foraminifera from coral reefs were selected comprising seven locations from Atlantic Ocean (i.e., Norway, Puerto Rico, Ireland, Alboran Sea, Brazil, Panama, and Columbia), seven from Pacific Ocean (i.e., Malaysia, New Caledonia, Australia, Philippines, Ecuador, Polynesia, and Bora bora) and five from Indian Ocean (i.e., Iran, Indonesia, Tanzania, Maldives and Mozambique) (Fig. 2; Table S1). Overall, the data collection recorded 1,054 species (γ diversity) of benthic foraminifera that are represented by 371 genera, 123 families, and 13 orders (Table 1; Table S2). The most diverse order belonged to Rotaliida, with a total of 65 families, followed by Lituolida (15 families) and Miliolida (13 families). Moderate diversification was observed in orders like Astrorhizida (nine families), Textulariida (six families), and Nodosariida (four families). The Order Loftusiida and Spirillinida was less common, with only two families, while the orders Robertinida, Allogromiida, Carterinida, and Vaginulinida were represented by a single family.

Bold families indicate symbiont-bearing type.

Figure 2: (A) Worldwide corals distribution modified from Allen Coral Atlas (2022). Red shaded colour showed cold-water corals while green shaded colour indicates the warm-water corals. (B) Map showing location of studied benthic foraminifera from coral reefs worldwide: Malaysia: 1-Tioman Island, 2- Bidong Island, 3- Redang Island; Philippines: 4- Palawan, 5- Nogas Island; Indonesia: 6- Tambelan Island, 7- Kepulauan Seribu, 8- Bali; Australia: 9- Great Barrier Reef, 10- Moreton Bay; 11- New Caledonia; Polynesia: 12- Niue; French Polynesia: 13- Bora bora; 14- Galapagos Island; Panama: 15- Punta Galeta; Colombia: 16- Isla Barú; Puerto Rico: 17- Jobos Bay; Brazil: 18- Pirangi and Maracajaú; Ireland: 19- Rockall Bank; Norway: 20- Norway Margin; 21- Alboran Sea; 22- Qeshm Island; Maldives: 23- Ari Atoll, 24- Rasdhoo Atoll; Tanzania: 25- Zanzibar; Ecuador: 26- Galapagos Archipelagos.

The family Hauerinidae represented the most taxonomically diverse group, comprising 47 genera, the highest recorded among benthic foraminifera family. Notably, it encompassed a wide range of genera, including Quinqueloculina (109 species), Triloculina (35 species), Pyrgo (17 species), and Miliolinella (14 species). Other diverse genera were Elphidium with 31 species and Textularia with 27 species as well as Rosalina (16 species), Bolivina (17 species), and Cibicides (12 species). Despite the occurrence of symbiont-bearing foraminifera in coral reefs, these families only represented a minor part of the species. Among them were reported Alveolinidae (i.e., Alveolinella, Borelis), Peneroplidae (i.e., Coscinospira, Dendritina, Euthymonacha, Laevipeneroplis, Monalysidium, Peneroplis, Parasorites), Amphisteginidae (i.e., Amphistegina), Nummulitidae (i.e., Heterostegina, Nummulites, Planostegina, Operculina, Operculinella, Neoassillina, Planoperculina), Calcarinidae (i.e., Baculogypsina, Baculogypsinoides, Calcarina, Neorotalia, Pararotalia, Schlumbergerella), and Soritidae (i.e., Archaias, Amphisorus, Cycloputeolina, Cyclorbiculina, Marginopora, Sorites).

The global distribution of benthic foraminiferal assemblages in coral reefs reveals distinct regional patterns in terms of species richness, dominant taxa, and ecological strategies (i.e., heterotrophic, symbiont-bearing, and opportunistic). The highest overall species richness is recorded in Europe (γ = 391) and Oceania (γ = 319), followed by America (γ = 356), Asia (γ = 264), and Africa (γ = 191). However, these figures are strongly influenced by environmental settings, sampling effort and ecological diversity within study sites.

European cold-water coral reefs (e.g., Rockall Bank, Porcupine Seabight) are dominated by small heterotrophic taxa, as symbiont-bearing forms are absent at bathyal depths. This pattern reflects the oligotrophic, deep-water environments where cold-water corals prevail, limiting light availability necessary for photosymbionts (Chen & Lin, 2017; Avnaim-Katav et al., 2020; Vicente et al., 2021). In contrast, tropical reefs in America, Africa, Asia, and Oceania exhibit mixed assemblages with varying proportions of symbiont-bearing and opportunistic taxa, consistent with warmer, shallower reef habitats.

In American reefs, although the number of shared species among sites was low, the dominance of miliolid genera such as Quinqueloculina, Triloculina, and Spiroloculina reflects a robust heterotrophic community. Several larger symbiont-bearing taxa, including A. angulatus and H. depressa, suggest healthy carbonate platforms and reef systems. African reefs, particularly from the Zanzibar and Bazaruto Archipelagos, show comparable proportions of heterotrophic, symbiont-bearing, and opportunistic taxa. The occurrences of both Amphistegina and Elphidium species points to transitional reef conditions, potentially affected by both coral reef development and environmental disturbances (Murray, 2006; Girard et al., 2021; O’Brien et al., 2021). Asian assemblages, being the most geographically diverse in the study, harbor a relatively high diversity of both symbiont-bearing and opportunistic foraminifera. The consistent presence of taxa such as A. lessonii, N. calcar, and P. planatus across multiple sites underlines their resilience and ecological success in Indo-Pacific reefs. In Oceania, particularly in the Great Barrier Reef and Bora Bora, a high diversity of both small heterotrophic and symbiont-bearing taxa is observed. The identification of new species (e.g., T. boraboraensis) underscores the region’s importance as a hotspot for foraminiferal diversity. The overlap of species such as S. orbiculus and P. acervalis across multiple sites indicates broad ecological tolerances and potential for wide biogeographic dispersal (Alve & Goldstein, 2003; Murray, 2013; Prazeres et al., 2020).

Beta diversity analyses reveal clear biogeographic segregation among regions. The higher similarity of benthic foraminiferal assemblages in certain areas can be attributed to the lack of recent and past geographic or environmental separation. Such limited separation reduces habitat heterogeneity and environmental gradients, leading to lower beta diversity and greater faunal overlap among sites (Renema, 2006; Uthicke et al., 2009; Diaz et al., 2024).

Europe exhibits the highest species turnover, when compared to other continents, that can be ascribed to the peculiar environmental setting hosting cold-water reef ecosystems. In contrast, Asia, Africa, and Oceania exhibit a lower turnover (β ≈ 0.54–0.60), suggesting regional continuity and biogeographic connectivity in the Indo-Pacific (Förderer et al., 2018). Oceanic comparisons further reinforce this pattern. The Atlantic Ocean stands out as the most distinct, exhibiting the least similarity with both the Indian and Pacific Oceans (D_J ≈ 0.90–0.91), likely due to historical isolation and contrasting environmental conditions. Conversely, Pacific and Indian Ocean reefs share a high degree of similarity (D_J = 0.72), reflecting the contiguous reef systems across Southeast Asia and Melanesia. The pronounced dissimilarity between Atlantic and Pacific benthic foraminiferal assemblages likely reflects the closure of the Isthmus of Panama (~ 3 Ma), which terminated faunal exchange between the two oceanic realms, reorganized ocean circulation, and created distinct environmental regimes that promoted biogeographic divergence (Collins et al., 1996; McDougall, 1996; Bornmalm, 1997; Groeneveld et al., 2014).

Despite regional differences, several cosmopolitan species are recorded across all oceanic regions, indicating their ecological behaviors. Notably, three opportunistic taxa (A. beccarii, A. tepida, and E. advena) and five symbiont-bearing species (A. hemprichii, B. pulchra, B. schlumbergeri, H. depressa, P. pertusus) are found globally. These taxa are commonly associated with both healthy reef conditions (in the case of larger symbiont-bearers) and environments under anthropogenic stress (in the case of opportunists).

The compiled dataset (n = 1,054 species) indicates that the coral reefs is the hotspot for biodiversity, as this number is higher than previous compilation from other location such as Gulf of Mexico (n = 987 species) (Gupta & Smith, 2010), Sahul Shelf and Timor Sea (n = 946 species) (Loeblich & Tappan, 1994), (n = 304 species) Korean Peninsula ( Kim et al., 2016) and Aegen Sea, Mediterranean (n = 267 species). However, it is important to note that these studies were not exclusively based on carbonate platform environments, where foraminifera typically reach their highest diversity. A slightly higher species diversity has been reported by Dorst et al. (2013) from continental shelf of North-East Atlantic with 1,486 species. This highlights the ecological adaptability of benthic foraminifera, which can thrive across a wider range of substrates than previously emphasized. By contrast, studies restricted to larger benthic foraminifera (n = 105 species) have identified peak richness in the Western Coral Triangle and Sahul Shelf provinces of the Central Indo-Pacific, reflecting the well-established role of these provinces as global biodiversity hotspots (Förderer et al., 2022). Interestingly, even in the oligotrophic Arabian Gulf, more than 492 benthic foraminiferal species have been recorded, and these assemblages extend beyond reef environments into adjacent habitats (Amao et al., 2025). Comparable findings have also been reported in the Mediterranean Sea, where benthic foraminiferal assemblages associated with cold-water coral ecosystems, vermetid reef platforms, and algal-dominated hard substrates display unexpectedly high diversity beyond classic reefal systems (Stalder et al., 2021; Rossbach et al., 2022; Manda et al., 2024). This highlights that high species richness is not confined to classic reefal systems but can also emerge in marginal and environmentally extreme settings. Nonetheless, it is important to acknowledge that these sensitive coral environments remain poorly studied, and many taxa have not yet been identified to the species level, which likely underestimates true diversity. Moreover, none of the existing studies accounted for allogromids (i.e., naked forams). This suggests that the actual number of taxa is expected to be much higher than currently reported.

Foraminiferal assemblages in coral reef environments are predominantly composed of a mixture of calcareous hyaline and porcelaneous forms, particularly among the small heterotrophic species, consistent with the observations of Murray (2006). Although symbiont-bearing foraminifera are ecologically dominant in these habitats, the most numerically abundant group consists of small heterotrophic species, with a minor proportion of opportunistic taxa. The extensive list of small heterotrophic species with global distributions (n = 38) further highlights the ecological flexibility and dispersal capability of these taxa. Some of these, such as L. lobatula, Q. philippinensis, and S. communis, are well-known for their euryhaline and eurytopic nature.

By 2023, the projection that nearly 90% of global reefs will face degradation was alarming (Narayan et al., 2021). The ocean warming, ocean acidification, and habitat loss threaten coral reefs where increasing coral bleaching event frequency occurred worldwide since 1998 (Eakin et al., 2019; Thangadurai et al., 2024). Symbiont-bearing taxa such as Amphistegina, Sorites and Peneroplis are highly sensitive to thermal stress and bleaching (Hallock, 2000; Schmidt et al., 2016; Narayan et al., 2021), while acidification reduces calcification and test integrity (Prazeres et al., 2015; Guamán-Guevara et al., 2019). As coral cover declines, the loss of reef habitat further reduces assemblage diversity (Doo et al., 2020), with potential consequences for carbonate production and reef resilience. Consequently, climate-driven reef degradation poses a critical risk to benthic foraminiferal diversity, particularly for symbiont-bearing species that serve as key bioindicators of reef health.

Despite the inclusion of a high number of publications, one of the key limitations of this study is the presence of incomplete or inconsistent species names in the original sources, which may have constrained the comprehensiveness and accuracy of the species database. Although we carefully selected and validated species lists from each continent and ocean basin, the reliance on published records introduces potential biases due to taxonomic discrepancies, synonymy, or unidentified taxa. Furthermore, while the analysis captures broad-scale biogeographic patterns, the generalizations derived from this dataset may overlook finer ecological or regional variations. Additionally, several other limitations should be noted: (a) naked foraminifera were not accounted for in the reviewed studies; (b) sampling efforts in some regions remain comparatively lower than in others; (c) many species are still left in open nomenclature, which further obscures true diversity; and (d) differences in sampling strategies across studies may introduce inconsistencies in diversity estimates.

As such, caution is advised in interpreting the findings as fully representative of global foraminiferal diversity. Future efforts should aim to integrate molecular data, high-resolution taxonomic revisions, and standardized sampling protocols to enhance the reliability of beta diversity assessments.