Predicted disappearance of coral‐reef ramparts: a direct result of major ecological disturbances

Abstract

Summary Two coral cays near La Parguera, Puerto Rico, have large, exposed coral ramparts composed almost entirely of loose pieces of elkhorn coral Acropora palmata (88% of horizontal transects, 98% of vertical transects). The total volume of elkhorn coral in the ramparts of the two cays was estimated at 3600 and 12 800 m3. The present volume of living elkhorn coral on these two reefs was estimated at 7 and 14 m3 and previous volumes at 11 000 and 34 900 m3. White‐band disease was found on 8.5% of living elkhorn colonies. Lang’s boring sponge Cliona langae covered 10.8% of the total transect area, overgrowing both dead and living corals. White‐band disease and coral‐reef bleaching have drastically reduced the populations of elkhorn coral, thus, skeletal coral materials to replenish the plate ramparts are severely reduced, disrupting the process of forming and maintaining these coral reef ramparts. We predict that the next series of major storms striking these prominent cay ramparts will remove them. These disappearances will represent a quick, obvious and permanent consequence of global disturbances. Loss of cay ramparts will modify the environments on and around Atlantic coral reefs. Ramparts may be similarly lost from Indo‐Pacific reefs. The lack of any other indisputable definitive indicators of long‐term, major disturbances on coral reefs makes the distinct loss of coral‐reef ramparts an important physical sign.

Alternative states on coral reefs: beyond coral–macroalgal phase shifts

“…Subsequently, Cliona langae monopolized much of the shallow reef substrate that was formerly occupied by live Acropora sp., rapidly overgrowing remaining coral colonies and fragments, and preventing coral recovery. Live hard coral cover is now 0.3%, whereas cover of C. langae is 11% (Williams et al 1999). A similar scenario seems to be unfolding in the Florida reef tract (USA).…”

“…Hughes 1994). However, Ward-Paige et al (2005) documented increasing abundances of Cliona delitrix and C. lampa throughout the Florida reef tract between 1996 and 2001, and clionid sponges dominate large parts of the reef seascape in the central Caribbean region (Antonius & Ballesteros 1998, Williams et al 1999, Rützler 2002, Lopez-Victoria & Zea 2004. One determinant of the spatial scale of phase shifts lies in the scale and nature of the disturbance causing the shift (deYoung et al 2008).…”

Effects of pCO2 on the interaction between an excavating sponge, Cliona varians, and a hermatypic coral, Porites furcata

“…Calcium carbonate removal rates for tropical excavating sponges can range from 0.84 to 23 kg CaCO 3 m −2 year −1 (Hill 1996;Zundelevich et al 2007;nava and Carballo 2008), with some of the highest rates reported for Cliona varians (Hill 1996) and Cliona lampa (neumann 1966) at 22.8 kg calcite m −2 year −1 and 22-23 kg CaCO 3 m −2 year −1 , respectively. excavating sponges are important to healthy reef ecosystems and perform vital functions such as recycling minerals, restructuring coral colonies (goreau and Hartman 1963), creating new space for settlement and easing spatial competition among benthic taxa (Williams et al 1999). In recent years, however, there has been a global increase in the prevalence of excavating sponges on threatened and impacted reefs, likely facilitated by wide-spread declines in coral health (rose and risk 1985;Holmes 2000;rüt-zler 2002;lopez-Victoria and Zea 2004;Ward-Paige et al 2005;Schönberg and Ortiz 2008;Carballo et al 2013).…”

Coral colonization by the encrusting excavating Caribbean sponge Cliona delitrix

“…Excavating sponges from the genus Cliona are the most abundant bioeroder organisms and among the strongest competitors for substratum space in Caribbean reefs (Hein & Risk 1975). They are notoriously able to modify coral reef morphology and ecology (Goreau & Hartman 1963; Williams et al. 1999).…”