The Colours of the Profondo Blu
A kaleidoscope of marine life
The Island of Ustica is the emerging top of a submarine volcano in the Southern Tyrrhenian: its steep rugged sea bottoms are especially celebrated for their luxuriant seascapes made up by encrusting communities and diverse fish fauna. Due to its long distance from the mainland, its small area and low population density, the island’s coastal habitat is nearly undisturbed. The island occupies a privileged position in the lower Tyrrhenian Sea along the flow of the Atlantic current that guarantees a constant contribution of planktonic and nektonic (fish and cephalopods) population dissemination. These find a particularly favourable habitat in its rocky seabed, where they are concentrated in clusters of amazing complexity and great aesthetic effect. As on, an area approximated to 0.02% of the Mediterranean it concentrates more than 20% of known species throughout the basin.
Life in the Open Waters
When you dive into the “Profondo Blu”, Deep Blue Waters of Ustica (and not for the depth itself but for the intensity of its blue) you get to know the privilege of isolation and to be surrounded by the abyss. It is the pelagic zone. Pelagic comes to us from Greek, via Latin. The Greek word pelagikos became "pelagicus" in Latin and then "pelagic" in English, first showed up in dictionaries in 1656; a definition of that time reports "of the Sea, or that liveth in the Sea”.
Pelagic organisms could be divided into two main groups: Plankton and Nekton.
Nekton includes all the pelagic animals capable of swimming against a current. This category is dominated by fish (bony fishes, sharks, rays) varying in size, trophic level and depth adaptation, but it also includes reptiles (turtles), crustaceans (crabs and shrimps), cephalopods (squids and octopuses), and mammals (whales, seals, dolphins).
Ustica Island’s iconic specie nowadays is the commonly named Barracuda - Sphyraena viridensis, a subtropical fish of the pelagic zone, definitely more frequent, gathering in dense schools especially at Scoglio del Medico, in the NW sector, in Secca della Colombara and in Secchitello. Together with the barracudas, you might want to see the Great Amberjack – Seriola dumerilii, a large predatory fish with a body colouring, which varies from brownish to bluish-grey on the dorsal surfaces contrasting with the silvery-white under parts. It is found as solitary individuals but when we get into a moderate-sized school that makes our day! They occur near reefs, deep offshore caves, drop-offs, rocky outcrops and wrecks. In Ustica, we have it all. Spawning takes place in June and July and occurs over such habitats as reefs and shipwrecks, demonstrated by the abundance of juveniles in the summer. When amberjacks are lacking, it happens to meet the Blue Runner - Caranx crysos, like a cousin of the amberjack and distinguished from similar species by several morphological features, including the extent of the upper jaw, gill raker count and lateral line scale counts. It is known to reach a maximum length of 70 cm and 5 kg in weight, but is much more common below 35 cm. The species inhabits both inshore and offshore environments, predominantly over reefs especially the juveniles. As schooling, predatory fish, the blue runner is predominantly taking fish as well as various crustaceans and other invertebrates. Spawning occurs offshore year round, although this peaks during the warmer months.
Plankton includes viruses, bacteria, plants and animals with locomotive powers, which cannot prevent passive movement by currents. Plankton can then be: Holoplankton, when the organism’s entire life cycle is spent in the plankton or Meroplankton, when only a temporary stage of life is spent in the plankton (e.g. 70% of benthic species have larval stages in the plankton). Plankton can be again divided according to size classes: macro- and megaplankton are of interest of divers. Medusae and siphonophores, ctenophoras are those gelatinous transparent animals that might be encountered during ascent in open water or in night dives.
The benthic zone is the ecological region at the lowest level of the ocean, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos and include microorganisms as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here generally live in close relationship with the substrate and many are permanently attached to the bottom.
The organisms’ part of the benthos is countless and is impossible to be listed and described in such a short article. That is why they are the main attraction of scuba divers, as it is the most frequent environment to visit: shallow waters, close to the coast, along a slope, over a sea grass. Therefore, we will try to introduce you to the main species you can expect to see in Ustica.
As already said, the groupers are the dominant specie of this area. The dusky grouper, the goldblotch and the mottled grouper are the biggest individuals of the Serranidae. Sometimes you find them alone, other times in big groups and usually quite easy to approach for a photo shot. Did you know they mature only as females and have the ability to change sex after sexual maturity?
Another common family of the benthic zone are the Sparidae, commonly called sea breams and porgies. These fish have certain distinctive features that make them easily identifiable: their bodies are relatively flat, the line from the dorsal area to the front of the fish descends very rapidly giving the face a flattened appearance, especially when viewed in profile, and colour varies widely from species to species, mainly depending on water type and environment. Of the family of sparidae we often encounter the common dentex, the two-banded seabream, the sheephead bream, saddled seabream, bogues, as well as the cow bream or goldline.
In addition, the Labridae is a huge family of the benthic zone, especially in the seagrasses, known as the brightly coloured wrasses. The family is large and diverse, with over 600 species in 81 genera, which are divided into 9 subgroups or tribes. Wrasses are identified by their protractile mouths, usually with separate jaw teeth that jut outwards, or by their thick lips, a peculiarity which gave rise the German name of "lip-fishes" (Lippfische) and the Dutch name of lipvissen. Juveniles are a mix of males and females (known as initial-phase individuals), but the largest adults become territory-holding (terminal-phase) males.
Mediterranean species of Crustaceans and cephalopods as well as nudibranches and worms are likely to be found by the divers who love to observe every crevice of the bottom.
The Best Night Life
Diving in the darkness throughout the summer season in Ustica is like visiting different places of the Mediterranean. While in the months of May, June and July you will mostly find octopuses, cuttlefishes, slipper lobsters and spider crabs, within August and September you will be surprised much more by planktonic life, such as squids and ctenophoras.
Big predators and pelagic fishes are not so common to meet as night dives are run in shallow waters along the coastline, and other benthic species are found sleeping! On the other side, what is hiding during the day comes out at night and you can encounter animals of strange shapes and sizes you never imagined they exist. These are mussels, crabs and starfishes going out to search food and taking advantage of their predators rests. However, morays look like never go to sleep, as you can find them hunting during the night and luckily assist to a catch.
One of the most fascinating aspects of night diving is the bioluminescence of plankton: few seconds without light will give you an amazing feeling to be submerged in a sky full of bright stars.
Troglobites are animal species strictly bound to underground habitats and caves. They typically have evolutionary adaptations to cave life, such as slow metabolism, reduced energy consumption, better food usage efficiency, decrease or loss of eyesight and depigmentation. The ecosystem of a cave differs from the open water environment for several factors, and it changes the more you enter in the cave. In the entrance zone, while there is sunlight and variable temperature, you still find green vegetation and plenty of sub littoral fauna. While you get into the Twilight Zone, with less light and minor temperature changes, plant life is minimal and counts schiaphilous species such as the calcareous green seaweed Halimeda tuna and the red seaweed Peyssonnellia squamaria. It is also the favourite area of many sponges: i.e. the Kidney sponge Chondrosia reniformis is very common to see, and in summer, you can note its asexual reproduction by budding. What makes this zone even more colourful are the stony coral Astroides calycularis, an orange colonial coral, consisting of a group of polyps, each of which sits in a stony cup known as a calyx, endemic of the Western Mediterranean, and the Bryozoans, also known as moss animals, living in colonies which have a skeleton of calcium carbonate. The Dark Zone is defined by no light and constant temperature, where the Serpulidae, sedentary benthic polychaete worms which secretes and live within calcareous tube, find their best life environment, as well as crustaceans. The famous shrimp of Ustica, the Plesionika narval, loves darkness and can be found in the darkest angles of any cave at any depth.
Aliens settled down
This can be an ever-changing item: alien species are so defined as they occur outside their natural range and dispersal potential and they spread by human activity, intended or unintended, to new areas.
In Ustica Island, several alien species can be encountered while scuba diving and snorkelling, such as the parrot fish Sparisoma cretensis or the very invasive Sally Lightfoot Crab Percnon gibbesi.
Divers can take part to Citizen Science projects on Invasive Alien Species, in order to help organisation to create a database and monitor their trend in growth and expanding areas.
If you are interested in marine biology and conservation and would like to use your scuba vacation for a cause, take part to MPA-ENGAGE project or Sea Sentinels to get into action with us in Ustica.
If yo are you a naturalist passionate, a sea lover or have a natural curiosity towards underwater creatures, focus your dives on fish identification and environment observation and book your Naturalist Dive Package