Benthic foraminifera in the Arabian Gulf: Biodiversity and geographical trends
Introduction
Past and ongoing climate changes have shaped and deeply modified global biodiversity (Antão et al., 2019; Rastelli et al., 2020). The ongoing loss of biodiversity involves most biotic realms and taxonomic groups (Pilotto et al., 2020) and threatens the functioning of ecosystems and their supply of goods and services (Hooper et al., 2005; Cardinale et al., 2012; Lindegren et al., 2018). Marine biodiversity is also locally affected by pollution, physical disturbance, habitat destruction, dumping, exploitation, and introduction of alien species (Worm et al., 2006; Zeppilli et al., 2015). In this context, the evaluation of marine biodiversity through checklists represents an essential tool for understanding the distribution of life on the planet, as well as for effectively implementing conservation and management plans (Al-Enezi et al., 2020). Baseline information and checklists become even more essential in areas that are characterized by unique conditions or known to be heavily influenced by human activities and where the effects of the ongoing climatic changes are expected to be extreme (e.g. Arabian Gulf).
Foraminifera, as single-celled organisms, play a significant role in biogeochemical cycles and in food chains (Moodley et al., 2002). Benthic foraminifera are relatively small, diverse, cosmopolitan, inexpensive to sample and abundant compared to other meiobenthic organisms (Hallock et al., 2003). Despite the extensive and different applications of benthic foraminifera (e.g., biomonitoring), relatively few studies have applied a regional-synoptic approach to evaluate diversity and its trends (e.g., Hayward, 1999; Hayward et al., 2011; Hayward, 2010; Dorst and Schönfeld, 2013). Although many benthic foraminiferal studies have been carried out in the Arabian Gulf since the 1960's, overall diversity has not been comprehensively evaluated.
The primary objectives of this paper are to a) provide a checklist of recent benthic foraminiferal species, b) infer their total biodiversity, c) determine geographical trends of diversity, and d) compare trends in diversities of test-wall structure with trends in salinity within the Gulf. These objectives are achieved by integrating all available data on benthic foraminifera in the last sixty years within the region. This effort will also help to unify and resolve issues relating to the use of synonyms and taxonomic-name revisions. By addressing these issues, one goal is to produce more precise species counts. These challenges have become particularly acute as researchers work with larger number of samples, high diversities of species and cover wide areas, which may limit the resources or substantive taxonomic expertise for all clades (Norman et al., 2020).
Section snippets
Geography and oceanography of the Arabian Gulf
The Arabian/Persian Gulf is a late Pliocene to Pleistocene shallow tectonic depression, a result of the Zagros Orogeny, created by collision and compression between the Arabian and Asian plates (Fig. 1). This marginal sea is an extension of the Indian Ocean and covers an area of approximately 22,600 km2 (Kassler, 1973; Seibold et al., 1973). The Gulf is elongated along its NW-SE axis, measures 1000 km in length, is 300 km at its widest point and 60 km at the Strait of Hormuz, where it opens
Previous benthic foraminiferal studies in the Gulf
Studies on benthic foraminifera in the Gulf date back to the early 1960s (Table 1), just before the oil boom in the region. In a series of papers considering ecology, distribution and systematics of the benthic foraminifera from several locations (Abu Dhabi, Khor al Bazam, Halat al Bahrani) in the southern Arabian Gulf, Murray, 1965a, Murray, 1965b, Murray, 1966a, Murray, 1966b, Murray, 1966c, Murray, 1970a recognized 58 species of benthic foraminifera. Most of the recognized taxa, particularly
Materials and methods
A total of 60 published and unpublished research works on benthic foraminifera in the Gulf were collated; topics included taxonomy, distribution, ecology, pollution, and classification (Table 1 and Fig. 3b). Sampling techniques differed among these studies. Some researchers scooped samples directly from the top layer of marine sediments, particularly studies from Arabian side of the Gulf due to the shallow nature of the area. Other studies were based on sample collected using techniques such as
Results
A total of 753 benthic foraminiferal species belonging to 236 genera, 99 families, 43 superfamilies and 11 orders were identified (Supplementary Table 1). They were further grouped by wall types, that are, porcelaneous (44.6%), hyaline (42.9%), and agglutinated (12.4%) taxa, while the spirillinid group, which is referred to as having an optically single crystal or a mosaic of a few crystals, had about 0.1% representation. The most diverse families are Hauerinidae (43 genera), Bolivinitidae (11
Discussion
The conservative estimate of 753 benthic foraminiferal species (γ diversity) reported in this study is quite high for a basin of comparable size and much higher than any previous estimate for the region (Murray, 2007). The Gulf is known to have several endemic species (Amao and Kaminski, 2016; Garrison, 2019; Kaminski and Fiorini, 2021) and species that have evolved mechanisms to cope with the harsh conditions (Hottinger et al., 1993). For example, fan-shaped peneroplids occur frequently in the
Conclusions
A review of 60 published and unpublished research documents revealed that 753 benthic foraminiferal species and subspecies have been reported from the Arabian Gulf pointing to a γ diversity comparable to those reported for the Aegean Sea and the Korean Peninsula. The γ diversity is lower than that reported for regions such as the Sahul Shelf and Timor Sea, the Gulf of Mexico, and the European continental margin, which likely reflects the lack of bathyal and abyssal benthic habitats in the
Declarations
‘Not applicable’.
Funding
The current research was supported by project DF191042 (Prof. Kaminski), Start-Up Grant SF21010, held by Dr. Amao (College of Petroleum Engineering and Geosciences, King Fahd University of Petroleum & Minerals) and by the Kuwait Foundation for the Advancement of Sciences and the Kuwait Institute for Scientific Research, grant number EM084C (Dr. Al-Enezi).
Availability of data and material (data transparency)
All dataset, raw and interpreted are provided as supplementary materials.
Code availability (software application or custom code)
Not applicable.
Authors' contributions
Abduljamiu O. Amao (AOA), Michael A. Kaminski (MAK), Carla Bucci (CB), Pamela Hallock (PH), Eqbal Al-Enezi (EA), Amr S. Zaky (ASZ), Fabrizio Frontalini (FF).
Ethics approval (include appropriate approvals or waivers)
‘Not applicable’.
Consent to participate (include appropriate statements)
‘Not applicable’.
Consent for publication (include appropriate statements)
‘Not applicable’.
Declaration of Competing Interest
None.
Acknowledgements
The authors are very grateful to two anonymous reviewers and the associate editor Prof. Valeria Luciani for their thoughtful and valuable comments that have greatly improved the present paper. We would also like to extend our deepest gratitude to Kuwait Foundation for the Advancement of Sciences (KFAS) for the financial support of the project (EM084C) and to the Kuwait Institutes for Scientific Research (KISR) for the great support.
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