Dynamic Interplay of ENSO Events and Local Hydrodynamic Parameters Drives Demography and Health Status of Gorgonian Sea Fan Populations on a Remote Tropical Eastern Pacific Island

Abstract

Gorgonian corals occurring in shallow waters are vulnerable to changing environmental conditions and human-related pressures such as pollution, overfishing, and diseases. However, anthropogenic effects on coral systems are difficult to quantify due to the lack of base-line data of unaffected populations. In order to assess the impact of global and local environmental parameters on gorgonian populations removed from direct anthropogenic impact, we evaluated demographic parameters and the health status of Pacifigorgia cairnsi (Gorgoniidae: Octocorallia) populations in Malpelo Island, a remote and pristine marine area in the Tropical Eastern Pacific of Colombia. Specifically, we studied P. cairnsi densities and population size structures under different habitat and local environmental conditions. We also studied whether ENSO events and local hydrodynamic features including locality, water depth, and upwelling conditions drive P. cairnsi growth rates. Finally, we evaluated the prevalence of the necrotic patch disease and rates of disease recovery. Major findings were that local hydrodynamic parameters shaped P. cairnsi size structures, that growth rates were affected by thermal anomalies associated to ENSO events and partly by water depth, that overall disease prevalence was low (6%) and that it did not correlate with the environmental parameters studied, and that most diseased colonies (57%) recovered via tissue breakage. The fact that P. cairnsi, a keystone species within the regional benthic food web, is affected by thermal anomalies remains of concern because these global events are predicted to increase in frequencies and severity in the future. Nonetheless, the low level of disease prevalence found indicates that the island's pristine conditions might facilitate disease resistance. Moreover, the findings suggest an interesting trade-off between growth rates and colony recovery in shallow waters related to tissue breakage. This study provides crucial base-line data for future investigations aiming at understanding coral responses to anthropogenic pressures and the impact of global climate change on coral communities.

The Influence of Climate Variability on Holoplanktonic Polychaetes Populations of Ocean Sector of the Colombian Pacific Basin

“…The Central sector has factors that generate higher productivity and more changes during the year. In this sector is Malpelo Island [56], which generates local conditions such as upwelling areas [57], benefiting phytoplankton. Furthermore, due to the movement of nutation of the earth, the ITCZ in the Central sector generates contrasting seasons during the year.…”

Microbial shifts associated to ENSO-derived thermal anomalies reveal coral acclimation at holobiont level

“…Increasing seawater temperatures associated with global warming represent a severe threat to corals (either Scleractinia or Octocorallia) worldwide since there are upper thermal limits that once exceeded, corals experience significant declines 2 , 3 . Among the most common consequences of thermal stress are coral bleaching together with growth, calcification and abundance decline which have lead to massive coral die-offs worldwide 4 – 6 .…”

“…Gorgonian corals (Anthozoa, Octocorallia) present in shallow waters are among the most vulnerable organisms of coral ecosystems 6 , 29 , 30 . Being long-lived, sessile and slow-growing species, gorgonians are particularly sensitive to environmental changes and anthropogenic disturbances 31 , 32 .…”

“…Being long-lived, sessile and slow-growing species, gorgonians are particularly sensitive to environmental changes and anthropogenic disturbances 31 , 32 . One example is Pacifigorgia cairnsi , an azooxanthellate sea fan inhabiting the remote and pristine island Malpelo located in the Colombian Tropical Eastern Pacific (TEP) 6 , 33 , 34 . This species dominates the seascape of the island forming dense aggregations on rocky reefs and walls up to 30 m depth 35 , 36 .…”

“…Malpelo Fauna and Flora Sanctuary is a marine protected area and a World Heritage Site, considered a hot spot of biodiversity under pristine conditions 34 , 37 . Gorgonian populations in Malpelo cope with cold waters and high levels of suspended matter during seasonal upwelling (from December to March), as well as anomalous increases in seawater temperature during sporadic ENSO events 6 , 38 , 39 . Recently, the vulnerability of P. cairnsi growth rates facing anomalous increases in seawater temperature during sporadic El Niño–Southern Oscillation (ENSO) events in Malpelo has been registered 6 .…”