Population fluctuations of the fungiid coral Cycloseris curvata, Galápagos Islands, Ecuador.

Fungiid corals (Cnidaria: Anthozoa: Scleractinia) occur at isolated locations scattered throughout the eastern tropical Pacific. They can be reef-associated but are often found on sand and rubble substrata distant from reef coral habitat. Cycloseris curvata is known in this region from the southern Gulf of California, through Mexico, Costa Rica, and Panamá, and with the southern-most populations occurring in the Galápagos Islands, Ecuador. During Archipelago-wide surveys (1988-2019), living individuals of Cycloseris curvata were observed at only two locations, Devil's Crown (near Floreana Island) and Xarifa Island (near Española Island). The Devil's Crown population was observed from 1988 to 2017, whereas living individuals in the Xarifa population were observed from 2005 to 2009. In 2012 a death assemblage (dead skeletons) was discovered at Darwin Island, at the northern-most extent of the Archipelago. At Devil's Crown, visual surveys were performed annually or biennially from 1990 to 2012, with two more surveys in 2017 and 2019. The living Cycloseris curvata population consisted of 15 individuals in 1990 that gradually increased to 78 individuals by 1995. Over 200 individuals were observed in 1996, and high numbers persisted through 1998 with 335 individuals. Live tissue surface area per polyp ranged from 0.5 to 95.0cm2. The population decreased to 112 individuals in 1999 (following warming associated with the 1997-98 El Niño), with further declines to 20 in 2009 (following cooling associated with the 2007 La Niña) and a rebound to 91 in 2012. After a 5y break in data collection, only one individual (28.3cm2) was observed in 2017, and in 2019 none were observed. Although undetected living Cycloseris curvata populations may exist, and renewed recruitment provides some hope for population reestablishment, it is possible that this fungiid coral species is now extirpated from the Galápagos Archipelago.

Some environmental and biological determinants of coral richness, resilience and reef building in Galápagos (Ecuador).

Throughout the Galápagos, differences in coral reef development and coral population dynamics were evaluated by monitoring populations from 2000-2019, and environmental parameters (sea temperatures, pH, NO3-, PO43-) from 2015-19. The chief goal was to explain apparent coral community differences between the northern (Darwin and Wolf) and southern (Sta. Cruz, Fernandina, San Cristóbal, Española, Isabela) islands. Site coral species richness was highest at Darwin and Wolf. In the three most common coral taxa, a declining North (N)-South (S) trend in colony sizes existed for Porites lobata and Pocillopora spp., but not for Pavona  spp. Frequent coral recruitment was observed in all areas. Algal competition was highest at Darwin, but competition by bioeroding sea urchins and burrowing fauna (polychaete worms, bivalve mollusks) increased from N to S with declining coral skeletal density. A biophysical model suggested strong connectivity among southern islands with weaker connectivity to Wolf and even less to Darwin. Also, strong connectivity was observed between Darwin and Wolf, but from there only intermittently to the south. From prevailing ocean current trajectories, coral larvae from Darwin and Wolf drift primarily towards Malpelo and Cocos Islands, some reaching Costa Rica and Colombia. Mean temperature, pH, and PO43- declined from N to S. Strong thermocline shoaling, especially in the warm season, was observed at most sites. A single environmental factor could not explain the variability in observed coral community characteristics, with minimum temperature, pH and nutrient levels the strongest determinants. Thus, complex environmental determinants combined with larval connectivity patterns may explain why the northern Galápagos Islands (Darwin, Wolf) have higher coral richness and cover and also recover more rapidly than central/southern islands after region-wide disturbances. These northern islands are therefore potentially of critical conservation importance as important reservoirs of regional coral biodiversity and source of larvae.

State of corals and coral reefs of the Galápagos Islands (Ecuador): Past, present and future.

Coral populations and structural coral reefs have undergone severe reductions and losses respectively over large parts of the Galápagos Islands during and following the 1982-83 El Niño event. Coral tissue loss amounted to 95% across the Archipelago. Also at that time, all coral reefs in the central and southern islands disappeared following severe degradation and eventual collapse due primarily to intense bioerosion and low recruitment. Six sites in the southern islands have demonstrated low to moderate coral community (scattered colonies, but no carbonate framework) recovery. The iconic pocilloporid reef at Devil's Crown (Floreana Island) experienced recovery to 2007, then severe mortality during a La Niña cooling event, and is again (as of 2017) undergoing rapid recovery. Notable recovery has occurred at the central (Marchena) and northern islands (Darwin and Wolf). Of the 17 structural reefs first observed in the mid-1970s, the single surviving reef (Wellington Reef) at Darwin Island remains in a positive growth mode. The remainder either degraded to a coral community or was lost. Retrospective analyses of the age structure of corals killed in 1983, and isotopic signatures of the skeletal growth record of massive corals suggest the occurrence of robust coral populations during at least a 500-year period before 1983. The greatest potential threats to the recovery and persistence of coral reefs include: ocean warming and acidification, bioerosion, coral diseases, human population growth (increasing numbers of residents and tourists), overfishing, invasive species, pollution, and habitat destruction. Such a diverse spectrum of disturbances, acting alone or in combination, are expected to continue to cause local and archipelago-wide mortality and degradation of the coral reef ecosystem.