Parent document

Intro + Plankton
Phytal + Nekton

The Phytal describes the dense epibentic plant coverage (seaweeds) on hard substrate of algal forests (e.g. Kelp, Cualerpa sp.) or of sea-grass beds of the family Potamogetonacea such as Cymodocea sp., Zostera sp. on soft substrate. Both provide the structural habitat required for subsequently settling flora and fauna such as epizoa at the lower end, and epiphyta near the canopy of the plant. Thus, are nurseries providing food and shelter for many animals including juvenile fish.

  • Algae (Seaweed) possess a holdfast (require hard substrate for attachment), stipe, and blades. Nutrients and gasses are absorbed from the water. Algae can be divided into groups based on their pigments. Chlorophyta (green algae with chlorophyll as their main pigment) are moderate in size and may form fine branched structures or thin, flat sheets. Phaeophyta (brown algae with a substantial amount of yellowish carotenoids) range from microscopic chains of cells to kelps like laminariales (Fucus sp. Sargassum sp.). Rhodophyta (red algae) are the most abundant and widespread marine algae. Their body forms vary from flat, ruffled, lacy, or intricately branched. They also contain phycobilin pigments that give them the reddish hue and masks the green chlorophyll.
    Although the algae are commonly classified by color, the visible color can be misleading. Some red algae appear brown, green, or violet, and some brown algae appear black or greenish. Green algae grow in shallow water (eu- to sublittoral zone) because their chlorophyll absorbs light from the visible spectrum available at the sea surface. Brown algae are found at moderate depths (sublitoral zone); their browning pigment is more efficient in trapping the shorter wavelengths of light available at these depths. At maximum growing depths (infralittoral zone), rhodophyta dominate in that the red pigment can best absorb the remaining blue-green light. Some exception to this rule of thumb are some less light tolerant organisms such as Udotea petiolata (chlorophyta) that frequents shadier sites and Peyssonnelia squamaria (rhodophyta) which can also be found near the water surface as well as in caves.

Chlorophyta (55kB)

Phaeophyta (45kB)

Snails of the phytal (45kB)

gastropods and neirids (50kB)

  • Sea-grass Beds: In locations protected from waves and currents, certain monocotyledons of the family potamogetonaceae (spermatophyta) help stabilizing the small-particle sediments and provide shelter, substrate, and food, creating a special habitat for other plants and animals. Sea-grass as the name might suggest, is not a simple plant; instead, at the embryonic stage it has one cotyledon only; flower parts usually in multiples of three (decussate); it does not show true secondary growth, but a fibrous root system, seeds, leaves, and stems with a widely distributed vascular cambium.
    The Mediterranean houses about four distinct species of sea-grasses, each requiring a distinct substrate satisfying the species' basic requirements:

    1. Cymodocea nodosa, characteristically with up to 30cm long slender blades that prefers flat and protected shallow waters. It prefers flat calm sandy bays and in conjunction with Zostera can form large meadows.
    2. Posidonia oceanica, the largest of all Mediterranean grasses; its blades can reach 1m in length, and grow at depths as far down as 40m; therefore, the widespread grasslands below 10m are predomenantely Possedonia. It is a slow growing plant that prefers clear, unpolluted waters with a low sedimentation rate.
    3. Zostera marina prefers sandy to silty bottoms of flat shallow bays, not deeper than 10m. Blades of Z.marina have 3-7 parallel veins.
    4. Zostera noltii, a small-growing plant with slender leafs and a dominating central vein, is usually found in silty to sandy bottoms; like Z.marina, it does not grow below 10m depth.

Feeding patterns of herbivores on Possidonia sp. (40kB)

Zystosira (80kB)

organisms of the seagrass (35kB)

Any species of sea grass sheds off its leaves regularly to avoid suffocation due to the intense epiphytic coverage. Decussation is brought about by a perforation line at the base of each leaf. These leaves, once stranded onto the shore, form huge embarkments that slowly degrade, offering certain isopods and gammerids a perfect habitat.
It is important to note that sea grass beds contribute significantly to the oxygenation of the marine environment.

Shed blades of sea grass on the beach (XXkB)

The Nekton characterizes those species that actively swim through the pelagic and neritic regions of the Mediterranean Sea. The only invertebrate animals among these are the squid and a few species of shrimp. Squids are elusive, abundant, and until recently, scarcely known inhabitants of oceans at all depths. They swim rapidly, and their wide range of bioluminescence and coloration allows them to camouflage and disappear swiftly.

The other members of the nekton are vertebrates, such as fish, reptiles, and mammals. The fish dominate the nekton, thus are found at all depths, but their distribution is determined directly or indirectly by their dependence on primary producers upon which they feed on. Fish are concentrated in upwelling areas, shallow coastal areas, and estuaries. The surface waters support much greater populations per unit of water volume than the deeper zones, where food resources are sparser.

Juvenile squid (XXkB)
  • The pelagial is that compartment of the marine environment that is located away from the bottom and not in close proximity to continental land masses; it is sometimes also referred to as the oceanic division, outlining the water body above the deep sea floor. It is lower in species number and diversity than the benthos.
  • Epipelagic Zone: Portion of the oceanic province extending from the surface (pleuston, neuston) to depths of about 200m.

Zonation of the Mediterranean (100kB)
Telostei (end bone fish) belong to the phylum osteichtyes (bony fish) which represents the prevailing majority of fish in the Adriatic Sea and includes perches, salmons, soles, sturgeons, breams, mullets, pickerels, wrasses, scorpion fish, and the small benthic fish like blenniidae, gobbiidae, and triperygiidae.
Most commercially valuable fish are found between the oceans surface and up to a depth of 200m (epipelagial). Most of these fish are streamlined, predators, and capable of high-speed, long distance travel. Among the most important species fished commercially are the enormously abundant sardines, mackerels. As planktonic filter feeders, they are found in large schools in areas of high primary production. Schooling probably developed as a means of protection, since each fish in the school has a less chance of being eaten than it does alone. The school may also keep reproductive members of the population together, thus, limiting the loss of offsprings by predation.
Epilagic fish have either a swim bladder or lungs. A swim bladder is homologous to lungs and represents the primary hydrostatic organ that allows the fish to adjust its density to that of the surrounding water and maintain neutral buoyancy at different depths. Another feature of epipelagic fish is the presence of scales which increase swimming efficiency considerably.
Fish that live on or near the bottom do not swim as rapidly as those that swim freely in the water. The flounder, halibut, turbot, and sole are commercially valuable bottom fish. Perch and snapper tend to congregate along the sea floor in the shallower, nearshore areas. They are often called rock fish because they hide among the rocks and live in cracks. Benthic fishes tend to reduce or even lose bith their swim bladder and scales. They hug the bottom as they feed and hide. Angler fish are flattened dorsoventrally, have a concealing color pattern, and lie on the bottom with their large mouths directed upward. Flounders, soles, and halibut are flattened from side to side and lie on or swim slowly over the bottom on one side as they feed on invertebrates. The downward side, according to the species, has lost its pigment, but the upward side has a concealing color pattern that can adjust according to the surrounding substrate. The larvae of these fish are perfectly symmetrical, but during the course of embryonic development, much of the head is remodeled and the eye that would be on the downward side migrates to the upward side.

To distinguish a fish's dietery preferences, the intestinal length is a good indicator to determine the dietary habits. In general a long intestine indicates a herbivorous preference, whereas a short intestinal length strongly suggest a carnivorous feeding habit.

All pelagic fish require a profound navigational knowledge. For this purpose, bony fish possess a vital sensing organ. A calcareous particle that lies on hair cells in the organs of equilibrium are the otholites. Each fish species evolved a distinctive form and by counting the ring-like perforations of an otholite, one obtains precise information about the age of that particular individual.

Fish of the neritic zone (110kB)


Sparidae + Scombridae (XXkB)

Benthic fish (65kB)

Trachinus draco (160kB)


Otolithes of Labridae + Sparidae (55kB)

References: Underwater pictures were taken with a Sea&Sea camera (MX-10) using the external strobe (YS-40), macro- and the 20mm wide-angle conversion lens kit.
The painters and the actors (40kB)
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Intro + Plankton
Phytal + Nekton