Abstract
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.
Highlights
Recent changes in climate and local environments have turned many coral reefs into highly endangered ecosystems[1]
Diaseris distorta is currently known from several extensive assemblages at Floreana near Corona del Diablo Island[49], dead skeletons were observed near Gardner Bay, Española
While many species occur throughout the archipelago and beyond in the Eastern Tropical Pacific (ETP), not all species are found at all sites and a marked gradient of species-richness is observed from the western to the southern and to the northern islands
Summary
Recent changes in climate and local environments have turned many coral reefs into highly endangered ecosystems[1]. Climate change affects atmospheric dynamics and may amplify the impacts of phenomena of global-scale importance such as the El Niño Southern Oscillation[5,6,7] (ENSO) This event results from coupled ocean-atmosphere perturbations[8,9] and has been implicated, in its warm phase, with regional to world-wide coral www.nature.com/scientificreports/. The southern archipelago has more typical cool-water carbonates with a strong heterozoan upwelling overprint[26], which is less clearly developed in the north[27] It is well-known that the northern islands harbor denser scleractinian coral populations and the only remaining framework reef in the entire Galápagos Archipelago[17,25]. Of particular interest was the apparent difference in coral size, density, reef-building and recovery dynamics between the northern islands and the rest of the archipelago[18], and we sought to determine whether these differences are based primarily on physical factors (such as mean seawater temperature, short-term temperature excursions, aragonite saturation state) or if biological dynamics and connectivity alone would suffice to create this gradient
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
