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18 June 2015

RESEARCH ACTIVITIES CONDUCTED DURING THE SCIENTIFIC CRUISE IN MALDIVES 2016 (SCM2016 PAOLO COLANTONI)

Montefalcone M., Oprandi A., Morri C., Bianchi C.N. The NOAA (the US agency for the study of the oceans and atmosphere) have foreseen, on the base of the maps of surface temperature of the oceans recorded with satellites, a huge bleaching phenomenon of the corals at a planetary wide spatial-scale due to thermal anomalies following a new episode of El Niño expected between the end of 2015 and the 2016 (Fig. 1). In the winter of 2015-2016, El Niño was in fact particularly intense, and the temperatures were among the hottest ever recorded in recent centuries: as a result, large parts of reefs in the world, especially on the Australian Great Barrier Reef, have been hit by coral bleaching, which in many cases resulted in high mortality. Starting from April 2016, also the Maldives have been reached by warm water masses (2-3° C above the seasonal average), which were maintained for several weeks and which have therefore caused phenomena of mass coral bleaching. The 19th Scientific Cruise in Maldives (SCM) “Paolo Colantoni”, organized by the International School for Scientific Diving (ISSD) and Albatros Top Boat, has been conducted from the 8th to the 16th of May 2016 between the atolls of North Malé, South Malé and Ari, while the effects of El Niño were in the their phase of maximum intensity. The data collected during this cruise are therefore essential for assessing the impact of this new phenomenon of thermal anomaly and coral bleaching. The cruise was attended by researchers from the University of Genoa, with the help of a graduated student in Biological Sciences at the University of Urbino (Nicholas Noli), with a technician from the University La Sapienza of Rome (Giovanni Gaglianone), of graduating and PhD students from the University of Genoa (Stefano Aicardi, Marianna Ambrosio, Ombretta Dell'Acqua, Federica Mariano, Angelica Miglioli, Erika Oteri, Irene Pancrazi, Giulia Passerini, Luca Rondena, Camilla Roveta) and of external collaborators (Francesca Brignone, Renato Drusiani, Anna Ferrero, Chiara Momo, Clara Negro, Marcello Panero), all associated ISSD. This year, for the first time, attended the cruise also two members of the association “Save The Beach Maldives” (Hassan Ahmed and Mohamed Shuhaan). During the cruise a number of parameters characterizing the reef were monitored at various depths, such as the cover of biotic (corals, algae, sponges, etc.) and abiotic (rock, sand, debris, dead coral) descriptors, the number and size of recruits, the structure and geomorphology of the reef, the abundance of fish and macro-invertebrates, and the presence of colonies of bleached corals also showing signs of disease. Already in the 1998 the Maldivian reefs have suffered a massive coral bleaching event due to thermal anomalies, and the annual collection of data in the following years during the SCMs on the state of the Maldivian reefs, coupled with the analysis of available data in the literature, allowed the assessment of their condition before, during and after this impacts that caused mass mortality of corals and, finally, to evaluate resilience of corals reefs over time. The recovery of corals began immediately after 1998, thanks to their high rate of recruitment and to the rapid growth of colonies. In the following years we observed a slow but continuous recovery of Maldivian reefs and, in 2014, 16 years later the bleaching event, most of the monitored reefs had reached again cover values of hard corals comparable to the original values registered before the bleaching (cover between 60- 80%). In some sites, however, the reef was still dominated by abiotic descriptors, such as sand and debris, due to local impacts. During the SCM2016 of this year we observed, in most of the sites monitored, massive phenomena of bleaching and many episodes of coral mortality (Fig. 2 and 3). The surveys made at different depths have shown a very high rate of bleaching in the branching corals (including large tabular Acropora, most of which were already dead in May), especially at the shallowest depths (between 3-10 m) (Fig. 4). Under 20 m depth, and especially in the massive corals, bleaching and mortality were lower. The branching corals showed signs of total bleaching (that is, the entire colony), while the massive corals showed mostly partial mortality (Fig. 5). Many corals also showed obvious signs of diseases such as “pink spotted” (Fig. 6), “black spotted” (Fig. 7) and stains and blue-purple bands (Fig. 8), the latter being a possible symptom of coral disease not yet reported in the literature for the Maldives. Bleaching phenomena have also been observed in other zooxanthellate animals such as anemones and clams (Fig. 9). In many of the sites monitored, finally, there were a conspicuous presence of the crown of thorns (Acanthaster planci) and of the mollusk gastropod Drupella spp., both predators of corals (Fig. 9). As in the past, it will be important to keep on monitoring the effects of this new bleaching event in order to assess the actual mortality rate of corals and the recovery that will follow in time. The collaboration between DiSTAV, ISSD, Albatros Top Boat and Save the Beach, the last being active participants of the SCM2016, will also allow us to increase our knowledge about the state of the Maldivian reefs and to promote a greater local and international awareness about the importance to preserve the unique heritage that the Maldivian coral reefs represent. 
 

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