High coral reef connectivity across the Indian Ocean is revealed 6\u20137\xa0Ma ago by a turbid-water scleractinian assemblage from Tanzania (Eastern Africa)

Markus Reuter,Stjepan Ćorić,Mathias Harzhauser,Werner E Piller,Ann F Budd,Francesca R Bosellini

doi:10.1007/s00338-019-01830-8

Abstract

The present centre of coral diversity in the Western Indian Ocean is defined by the northern Mozambique Channel with an extension northward to Mafia Island in Tanzania (Eastern Africa). The geological and evolutionary history of this hotspot of marine biodiversity remains so far completely obscure, because Cenozoic fossil reef communities of this area are not well known. This study presents a new fossil scleractinian fauna from the Mikindani Formation in southern Tanzania. It comprises 16 symbiotic coral taxa of which nine could be identified to the species and five to the genus level. Coral habitat consisted of low-relief biostromes that developed in shallow water at the front of the Rovuma Delta under conditions of variable sediment input. The biostromes are dated to be Messinian based on associated calcareous nannoplankton and planktic foraminifers. The studied coral assemblage shows close affinities with the Recent Western Indian Ocean biogeographic province and Central Indo-West Pacific biogeographic region as well as with the Miocene of Indonesia. Faunistic relations with the Oligocene-early Miocene of Somalia and Iran do not exist. The patterns of species distribution document a major palaeobiogeographic change in the Indian Ocean that correlates with the onset of the Miocene Indian Ocean Equatorial Jet during the middle Miocene. The clear Indonesian affinity of the Messinian coral fauna from southern Tanzania implies that this westerly oceanic surface current provided high biogeographic connectivity across the Indian Ocean during the late Miocene. Today, the coastal waters of Indonesia are located in the Coral Triangle. Diversification of this global epicentre of marine biodiversity started in the early Miocene and it was established already during the middle Miocene. Our results indicate that the East African hotspot of coral biodiversity originated as an offshoot of the Coral Triangle in the middle to late Miocene.

Highlights

The Indo-West Pacific is the largest biogeographic realm of the world’s oceans, comprising the tropical waters of the Indian Ocean (Western Indo-West Pacific biogeographic region), the western (Central Indo-West Pacific biogeographic region) and central Pacific Ocean (Eastern Indo-Coral Reefs (2019) 38:1023–1037Pacific biogeographic region), and the seas connecting the two in the general area of the Malay Archipelago (Central Indo-West Pacific biogeographic region; Spalding et al 2007)
Coral habitat consisted of low-relief biostromes that developed in shallow water at the front of the Rovuma Delta under conditions of
Our results indicate that the East African hotspot of coral biodiversity originated as an offshoot of the Coral Triangle in the middle to late Miocene

Summary

Introduction

Pacific biogeographic region), and the seas connecting the two in the general area of the Malay Archipelago (Central Indo-West Pacific biogeographic region; Spalding et al 2007). The latter region includes the most important centre of marine biodiversity (across diverse taxa) on Earth (Tittensor et al 2010). This biodiversity hotspot is a vast network of coral reef in the waters surrounding the Philipines, Indonesia, Malaysia, Papua New Guinea, the Solomon Islands and Timor-Leste and has been named the Coral Triangle (Hoeksema 2007). In contrast to the Coral Triangle, the Western Indian Ocean centre of coral reef biodiversity has no fossil record and, the geological and evolutionary origins of this species richness are totally unknown

Methods

Results

Conclusion