Scientific Cruise at the Maldives

Every year in April, Albatros Top Boat organises what has by now become a well-known Scientific cruise in co-operation with the Int. School for Scientific Diving end eminent Italian Oceanographers:

• Prof. Paolo Colantoni (marine geologist – lecturer of the University of Urbino)
• Prof. Nike Bianchi (marine biologist – lecturer of the University of Genoa)
• Prof. Carla Morri (marine biologist – lecturer of the University of Genoa)
• Dott. Massimo Sandrini (marine geologist)

These well-known people have become veritable pillars of the world of divers. Their background and their easy presentation mean that even those with no previous knowledge in natural sciences will be able to discover and learn incredible facts on the sea and on the Maldivian atolls in a friendly environment, between dives, enjoying a drink on deck or lying on the beach of a deserted island.

The topics discussed focus on the problems surrounding tropical ecology, particularly the phenomena linked to coral mortality, its recovery and the evolution of the reef.

Particular attention will be paid to underwater caves, especially those belonging to the first Blue Hole discovered at the Maldives by Albatros Top Boat.
Other topics include the origin of the islands’ evolution, variations in the sea level and the creatures inhabiting the tropical reefs. After the dives there will be a chance to ask specific question.

MASSIVE CORAL MORTALITY AT THE MALDIVES FOLLOWING THE 1998 TEMPERATURE ANOMALY AND THE FIRST EVIDENCE OF RECOVERY (1999-2000)

Carla MORRI(1), Paolo COLANTONI(2), C.Nike BIANCHI(3) e Giuseppe BALDELLI(2)

1 Department of Land and Resources, DipTeRis, University of Genoa, Corso Europa 26, 16132 Genoa
2 Institute of Geodynamics and Sedimentology, University of Urbino, Località Crocicchia, 61029 Urbino
3 Centre for Research into the Marine Environment, ENEA Santa Teresa, CP 224, 19100 La Spezia

1998: THE FIRST SIGNS

1998 was the warmest of the last 150 years, following the most intense El Niño event ever recorded. This was assumed to have been the cause behind the widespread mortality among coral which occurred in all tropical seas and in the Indian Ocean in particular. Our project group has been studying the Maldives’ coral reef since 1989 and has been carrying out regular surveys each year in April since 1997. In 1998 we observed an abnormal rosy colouring, never recorded before (possibly a sign of distress?), bleaching and the first episodes of death, with superficial temperatures of up to 34°C.

Colony of Diploastrea heliopora which has assumed a rosy colouring, possibly a sign of distress which will then lead to bleaching and death.	Colony of Acropora with bleached but still living polyps.
First episodes of massive mortality of Acropora and Pocillopora on the coral platform

1999: CORAL MORTALITY

In April 1999 we noticed a catastrophic mortality rate on all the reefs we visited. The surveys made at different depths showed a very high mortality rate among branched coral (including the large Acropora tabulari, Pocillopora and Millepora), particularly in shallow waters. The mortality rate was lower at depths exceeding 20 m. and in general among massive species. Whereas the entire colony of branched coral died, massive coral was only partially affected. The fact that some new specimen of ‘issuing’ species (for ex. Acropora, Faviidae) and the presence of specimen of different size suggested that the first wave of re-colonisation had arrived soon after the mortality episode, possibly from colonies situated at greater depths and which had therefore survived.

Total mortality of a colony of branched coral (Acropora).	Partial mortality in a large colony of massive coral (Porites).

2000: THE RECOVERY BEGINS

In April 2000 we counted the new specimen of Acropora, Pocillopora (an incubating coral of which no new specimen had been observed in 1999) and other groups of coral (essentially Faviidae, Poritidae and other types of massive coral) at depths ranging between 5 and 20 m. There were 45 new specimen of Pocillopora, almost limitedly to a depth of 5 m. There was a slightly higher number of new specimen of Acropora, with no evidence of difference among the different depths which were being investigated. The other corals showed maximum densities of up to 15 new specimen at 2 m., and seemed to prefer a water depth of 10 m.. No new specimen of Millepora were observed. This would suggest that the physiognomy of the dominant coral on the reef tends to establish itself already in the earliest stages. The data obtained lead to a cautious optimism over the recovery of Maldivian reefs.

Abundance of young colonies ( <5cm) of Acropora, Pocillopora and other coral (essentially Faviidae, Poritidae and other massive coral) at four different depths.	Small colony of Pocillopora recently established among coralline algae which in turn encrust a dead branch of coral

METHODS

• Observations were made while diving with aqualung in various sites in the Maldives’ central atolls (North Malè, South Malè, Felidhoo, Ari, Rasdhoo).
• Mortality was estimated as a percentage between the area occupied by dead coral and the area occupied by live coral (live + dead), along 20-metre long linear transepts (three repetitions per site).
• The new specimen were assessed by counting recently established colonies (with a diameter smaller than 5cm) in squares measuring 0.25 square metres, laid out casually on the substrate (seven repetitions per site).

2nd National Conference of Marine Science - CoNISMa. 22nd – 25th November 2000 - GENOA

Work carried out as part of the research
done at the Maldives in co-operation with
ISSD (International School for Scientific Diving) and
Albatros Top Boat