Hosts of the Plio-Pleistocene Past Reflect Modern-Day Coral Vulnerability
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Proc. R. Soc. B (2012) 279, 2448–2456 doi:10.1098/rspb.2011.2621 Published online 15 February 2012 Hosts of the Plio-Pleistocene past reflect modern-day coral vulnerability Robert van Woesik1,*, Erik C. Franklin2, Jennifer O’Leary3, Tim R. McClanahan4, James S. Klaus5 and Ann F. Budd6 1Department of Biological Sciences, Florida Institute of Technology, Melbourne 32901 FL, USA 2Hawaii Institute of Marine Biology, School of Ocean and Earth Science and Technology, University of Hawaii, Kaneohe 96744, HI, USA 3National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara 93101 CA, USA 4Coral Reef Conservation Project, Wildlife Conservation Society, Mombasa, Kenya 5Department of Geological Sciences, University of Miami, Coral Gables 33146 FL, USA 6Department of Geoscience, University of Iowa, Iowa City 52242 IA, USA The risk of global extinction of reef-building coral species is increasing. Weevaluated extinction risk using a bio- logical trait-based resiliency index that was compared with Caribbean extinction during the Plio-Pleistocene, andwithextinctionriskdeterminedbytheInternationalUnionforConservationofNature(IUCN).Through the Plio-Pleistocene, the Caribbean supported more diverse coral assemblages than today and shared consi- derable overlap with contemporary Indo-Pacific reefs. A clear association was found between extant Plio- Pleistocene coral genera and our positive resilience scores. Regional extinction in the past and vulnerability in the present suggests that Pocillopora, Stylophora and foliose Pavona areamongthemostsusceptibletaxato local and regional isolation. These same taxa were among the most abundant corals in the Caribbean Pliocene. Therefore, a widespread distribution did not equate with immunity to regional extinction. The strong relation- ship between past and present vulnerability suggests that regional extinction events are trait-based and not merely random episodes. We found several inconsistencies between our data and the IUCN scores, which suggest a need to critically re-examine what constitutes coral vulnerability. Keywords: biological trait; coral; extinction risk; Plio-Pleistocene; resilience; vulnerability 1. INTRODUCTION with persisting congenerics in the present-day Indo-Pacific Climate change is increasing the severity and the intensity of (Alveopora, Caulastraea, Galaxea, Gardinoseris, Goniopora, thermal stress events on modern coral reefs [1–4]. One of Isopora, Pavona, Pocillopora, Psammocora, Stylophora the primary concerns of conservation biologists and ecosys- and Trachyphyllia), whereas others went globally extinct tem managers is assessing the vulnerability of ecologically (Antillia, Antillophyllia, Hadrophyllia, Pironastrea, Placo- important taxa and mitigating their risk. The risk of global cyathus and Thysanus)[9]. The rates of change towards extinction of coral species is currently assigned by the Inter- regional and global extinction in the Caribbean varied national Union for Conservation of Nature (IUCN) using considerably; some genera gradually declined, whereas population reduction thresholds. For the vast majority of others declined rapidly [10]. coral species, IUCN conservation status is evaluated from In the early Pliocene, large colonies of Pocillopora domi- a weighted average calculated by multiplying the area of nated the shallow reefs along with Stylophora [11,12]. reef, within a species’ distribution range, by the per cent of Stylophora was highly vulnerable to the climate shifts of the total coral cover loss in 17 different geographical regions. Plio-Pleistocene, and went regionally extinct approximately Using this method, the IUCN has documented an increase 1.8 Ma from the Caribbean. By contrast, Pocillopora gradu- in the elevated extinction risk status for coral species from 2 ally diminished over millions of years, shifting from a per cent of 704 species during pre-1998 to 33 per cent by ubiquitous distribution of predominantly large colonies, to 2008 [5]. This approach is currently the only comprehen- a patchy distribution of small colonies, and eventually to sive assessment of coral extinction risk, but it is calculated regional extinction during the last interglacial. The foliose with limited data on species-specific trends, and lacks a Pavona that went extinct in the Caribbean through the historical validation process [6,7]. Plio-Pleistocene was never dominant but diminished over The regional extinctions in the Plio-Pleistocene may shed several million years through repeated isolation [10]. The light on which coral genera may be vulnerable or resistant two Caribbean Acropora species (Acropora palmata and to stress during contemporary ocean warming. During Acropora cervicornis), increased in relative abundance the Plio-Pleistocene turnover, 25 coral genera persisted, through the Pliocene and Pleistocene. The Montastraea while 18 were lost from the Caribbean region (figure 1). annularis complex, Siderastrea and branched Porites changed During this period, some corals went regionally extinct little over this 5 Myr period [10]. If indeed biological traits lead to differences in fitness, then the march to regional extinction during the Plio- * Author for correspondence (rvw@fit.edu). Pleistocene in the Caribbean should be reflected in the Received 15 December 2011 Accepted 27 January 2012 2448 This journal is q 2012 The Royal Society Past reflects modern vulnerability R. van Woesik et al. 2449 extant Caribbean global sea level Caribbean genera (R) extinctions (+) extinctions (‡) –100 0 –50 (m) 50 R R R R R R R R R R R R R R R R R R R R R R R R R R R R R +++++ 0 ++ ‡ ‡ middle ‡ ‡ + ‡ 100 k.y. cycles 100 k.y. Pleistocene + 2 lower onset of NHG 41 k.y. cycles 41 k.y. + ‡ late + + age (Ma) 4 Pliocene closure of early CAS 6 late [8] Miocene Favia Mussa Porites Pavona Antillia Isopora Galaxea Undaria Diploria Agaricia Eusmilia Scolymia Acropora Thysanus Madracis Manicina Isophyllia Helioseris Alveopora Leptoseris Cladocora Goniopora Stylophora Meandrina Siderastrea Pocillopora Solenastrea Pironastrea Dendrogyra Mussismilia Caulastraea Dichocoenia Montastraea Colpophyllia Psammocora Hadrophyllia Placocyathus Antillophyllia Trachyphyllia Isophyllastrea Mycetophyllia Gardineroseris Stephanocoenia Figure 1. Stratigraphic ranges of recorded reef coral genera (total ¼ 43) within the Caribbean region from 6.8 Ma to Recent. Of the 18 genera that went regionally extinct in the Caribbean, 12 persist in the Indo-Pacific today. Key palaeo-environmental events, including closure of the Central American Seaway (CAS) and the onset of Northern Hemisphere glaciation (NHG), are highlighted next to the global sea-level curve of Miller et al.[8]. genealogy of contemporary species in the warming decision-making [16] constituted that the traits and scoring Indo-Pacific. By contrast, if individuals on coral reefs are were purposefully decided a priori (table 1), and that all responding to changing conditions equally and indepen- traits were maintained throughout the analysis to avoid tau- dently of species traits [13], species may march through tology. A consensus was reached among 10 coral-reef time showing random episodes of extinction. Here, we scientists on the general principle underlying each trait and test an alternative to the concept of random episodes of the methodology of the scoring protocol (table 1)[16]. For regional extinctions, and propose that biological traits analysis, we selected 14 dominant (modern) coral genera could play a larger role than suggested by neutral theory for the Indo-Pacific Ocean and 15 for the Caribbean Sea. [13]. We test these ideas by comparing modern corals Two genera were subdivided based on morphology with with coral populations that lived on ancient Plio- Pavona classified as either foliose or encrusting/submassive Pleistocene reefs of the Caribbean that experienced a and Porites as branching or massive. Montastraea in the protracted period of complex environmental change and Caribbean were evaluated as either Montastraea annularis extinction [9,14,15]. Our objective was to evaluate whe- complex or Montastraea cavernosa. Although both genera ther regional extinction events of the Plio-Pleistocene and subgenera groups were examined, we refer to all corals Caribbean region lend insight into future events in the at the genus level. Each coral genus was then evaluated on Indo-Pacific. Our central hypothesis was that trends through their tolerance to a hypothetical two-month þ 38C thermal the Plio-Pleistocene will reflect contemporary trends on stress anomaly, during the solar insolation maximum. Simi- Indo-Pacific reefs. A mismatch between past and present larly, four key process variables were scored for a suite of trends would lend support to neutral theory, which suggests coral taxa, to address whether each process would affect that species extinctions are a random process. By contrast, recovery from the temperature anomaly (table 1). The a match between past and present trends would suggest a scores for the traits and processes were summed for each non-random, biological trait-based process. coral genus and classified as a resilience score. Although con- temporary species within each genus differs in terms of their geographical distribution—some are widespread and 2. MATERIAL AND METHODS others are restricted—classic taxonomic texts [17] and (a) Modern genera resilience scores recent molecular techniques show evidence that many We examined whether biological traits play a large role in the genera (e.g. Acropora, Porites, Stylophora,