Parent document

Intro + Plankton
Benthos
Littoral
Phytal + Nekton


The Rocky Shore (Felslittoral) is the zone of infrequent or periodically wettened area of the rocky shoreline. Being influenced by the tides, this section can extend from a few decimeters in calm bays to over 10m at wind- and wave- exposed sites. The rocky coast is a region of rich and complex algal and animal communities living in an area of environmental extremes. Such distributions is governed by their ability to cope with the stresses that accompany exposure, turbulence, extreme conditions of salinity as well as temperature, and dehydration. This typical pattern arises as seaweeds and animals sort themselves out over the intertidal zone.

  • The Supralittoral zone (splash zone, sometimes also referred to as the white zone) outlines the stretch above the high water level, i.e.seawater penetratesthese elevated areas only during storms with highest tides. Organisms here must cope with long periods of exposure to air as well as heat, cold, rain (fresh water), and predation by land animals and seabirds. At the top of this area, patches of dark crusty lichens Verrucaria amphibia and some cyanobacterial species (Placoma vesiculosa, Schizothrix calcicola) appear as crusts on rocks. A dominant appearance of the lower supralitoral is a prosobranchia Melaraphe (=Littorina) neritoides and the detritus feeding isopoda (Ligia italica).
    The width of this zone changes with the slope of the shore, variations in light and shade, exposure to waves and spray, tidal range, and the frequency of cool days and damp fog.
    Rocky shorelines show a wide variety of depressions and tubs (tidepools), that are filled with seawater at lower altitudes and rainwater at higher elavations. Even though salinity and temperature levels change drastically, they give rise to a mosaik of many small biotopes.
    A tide pool, left by the receding tide in a rock depression or basin, provides a habitat for animals common to the upper eulittoral zone. Some small, isolated tide pools provide a very specialized habitat of increased salinity and temperature due to solar heating and evaporation. Supralittoral tide pools act as catch basins for rainwater, lowering the salinity and temperature in fall and winter. These isolated pools often support blooms of microscopic algae that give the water the appearance of a pea soup. Each pool is a specialized environment populated with organisms that are able to survive under the conditions established in that particular pond.
The increasing presence of the cirripedia (barnacles like Chthamalus depressus and C. stellatus) at wind and water-exposed rocks mark the interface form the lower supra- to the upper eulitoral. Cirripedia are sessile, filter-feeding crustacea enclosed within a bivalved carapace covered with protective calcareous plates. The trunk bears six pairs of long, coiled, biramous cirri that perform a rhythmic scooping motion to remove planktonic organisms. Barnacles molt like other crustaceans but they do not shed the outer surface, instead they increase the carapace size by secretion of additional CaCO3 at their margins.

 

 


Supra-, Eu-, Sublittoral (165kB)

 

 

 

 

 


Chitons and barnacles (150kB)
  • The Eulittoral (mid- or medio-littoral) is the intertidal band, in-between the low and the high water line. The wave action and turbulance of the returning tides shape and reform cliffs, gaps, and caves, offering a vast choice of different habitats for potential sedentary organisms.
    Protected rocky shorelines usually show a narrow almost homogenous eulitoral strip, whereas exposed sites show a wider extension clearly dividing itself into two sections.
    Conspicious members of the upper eulittoral (also named the gray band) include several other species of cyanobacteria Hyella caespitosa , cirripedia (Chthalamus depressus in the upper extremes, and C. stellatus at the lower extremes), gastropoda (i.e. limpets such as Patella caerula, P.rustica, P.ulissiponensis, and P.ferruginea), chitonida (Chiton olivaceus), molluscs (Littorina neritoides).
    Chitons and limpets are molluscs that use their radula to graze on the algeal substrate surrounding their hard surface environment. A muscular foot anchors them to the rocks, and in the case of limpets their edge of the shell has acquired the same contours as the substrate which brings them back to a distinct resting site after each grazing circle.
    Shore crustaceans of varied colors and patterns belong to the phylum arthropods (order decapods) and are found in the moist shelter of the rocks. They typically have a saddlelike carapace, covering the head and front of the body, and a large, jointed abdomen. The abdomen usually has swimming or egg-carrying appendages. In crabs the body layout is essentially the same, but the carapace is expanded and flattened. The abdomen is folded forward and hidden beneath the carapace which is much reduced in size. The terminology of crustacean appendages is based on the assumption that each appendage is a simple biramous structure. The outer exopodite and the inner endopodite that are attached to the basal protopodite.

Placophora & Conchifera (40kB)

 

 

 

 


Crabs of the eulittoral (55kB)

The lower eulitoral (black band) which is subject to more frequent flooding than the upper eulitoral, is outlined by the growth of certain light-loving crusty rhodophyta Lithophyllum lichenoides (=L. tortuosum can form extensive sidewalk-like banks just below the MWL), whereas, the sea anemones Actinia equina indicates the mid water line (MWL). The sea anomenes feed by spreading their tentacles and paralyzing grasped prey that accidentally blunder into them.
Again crustaceans seem to have successfully conquered this particular habitat. The hermit crab's first pair is probably homologous to the antenna of insects, centipeds, and millipeds, but the second pair is unique to crustaceans. The feeding appendages, located just behind the mouth consists of a pair of heavy biting mandibles and two pairs of small maxillae. The trunk of hermits Clibinarius erythropus differs greatly from other crabs. Its shape easily enebles them to penetrate and at the same time protecting this soft body any cone shaped shell.

Anemone (80kB)

Hermit crab (90kB)

Littoral crabs (65kB)
  • The Sublitoral, the stretch below the low water line, outlines the upper limit of the underwater world. The hard substrate of the sublitoral is crowded, and the competition for space is extreme. Light-loving phaeophyta Cystoseira spicata, and certain rhodphyta (Laurencia obtusa and Ceramium rubrum) form dense carpets (which are yet another subject of discussion further down this report). This substrate is also a perfect settling ground for Mytilus galloprovincialis, of the class bivalvia which extend widely among seaweeds.
    Although bivalvia belong to the phylum molluscs, they lack a radula and a head. The shell is composed of two lateral valves hinged together dorsally. The muscular inner fold of the mantle fold edge of one side is pressed against that of the other side when the valves close (adductor muscle). The calcareous portion of the shell consists of several layers and is secreted by the mantle surface. The periostracum functions to protect the underlying calcareous layers from dissolution, which is of essential importance in hard-substrate burrowing species such as Lithophaga lithophaga. The hinge ligament that connects the two valves dorsally is composed of elastic protein covered with periostracum.
    Bivalves can be further grouped in protobranchs which posses a single pair of posterior-lateral bipectinate gills like those of primitive gastropods and are exclusively deposit feeders; whereas, the other group involve the lamellibranchs in which the gills and ventilating current preadapted them for filter feeding in sandy to muddy substrates.
    Other mollusc members involve the gastropod Monodonta turbinata. These are quite common and settle in the few empty spaces untouched by bivalves.
    Hard substrate is not only attractive to epifauna but also the perfect settling site for many seaweeds, which is dealt with further down this report.

Apects of the sublittoral (85kB)

Drawing of mussles (135kB)


Lithophaga lithophaga (85kB)

  • The upper Adriatic Sea with is rather flat and shallow thus hardly exceeds 40m in depth. Since diving tours were not planed at all (apart from seafloor dredging and mud/sand sampling) the infralittoral has not been surveyed to such an extent.

The Underwater Cave. The island of Banjole, a mere 20min boat ride from Rovigno, houses an attraction not to be missed out. A cave at the southern end proceeds deeply into the rocky island, with the last couple of meters falling below the MWL, only to reemerge at its center that allows light from top to penetrate. The cave displays a perfect gradient of marine organisms that have to cope with the diminishing light resources as one penetrates deeper into it.

  • At the entrance of the cave, a wide selection of sublittoral organisms characteristic for hard substrates are found. The firmly attach flowerlike anthozoa (sea anemones) stretch out their tentacles into the currents and use their nestling batteries of nematocytes to trap potential floating and swimming animals.
    Larger sedentary actinaria use their dominant fleshy tentacles to feed on larger organisms that are located higher in the trophic pyramid. These organisms belong to the phylum cnidaria which are radially symmetrical and have at the oral end of the axis a circle of tentacles. The mouth opens blind into the gastrovascular cavity which is lined by the gastrodermis; whereas, the epidermis covers the outer surface of the body. The mesoglea located between these layers, varies from a thin noncellular membrane as in hydras, to a thick jellylike layer without cells as in jellyfish.
  • Hydrozoan colonies, yet another member of the phylum cnidaria, are found at the upper infralittoral, thus do not support stronger water movements, and are located in shadier and calmer section of the supralittoral. Every branch of the colony houses many tiny polyps interconnected via the stolon which represents the gastrovascular cavity. Similarly like anthozoa, the polyps capture minute planktonic organisms with their tentacles situated around the oral end. Circulation of food within the stolon is enough so that even if the polyps on only one end of the colony are fed, those on the unfed end will live just as long.
    As mentioned previously, cnidarians capture their prey with the aid of cnidocytes, located largely in the epidermal layer and are especially prevalent on the tentacles. A cnidocyte contains the triggering surface cnidocil and the actual stinging element, the nematocyst. An ejected nematocyst facilitates the penetration of the toxin-injecting thread. Cnidocytes are replaced quickly by the differentiation of interstitial cells.
  • Colorful nudibranchs (class opistobranchs) are active predators, feeding on sponges, anemones, and the spawn of other organisms. Although soft-bodied andoften vividly colored, sea-slugs have few, if any predators, because they produce poisonous acid secretions obtained from the organisms they feed on.
    The shellbearing prosobranchs of the family holiotidae are sometimes found at shady places and among protecting rocks. Although well camouflaged, they become easily evident due to the tentacular processes that protrude from the ear-shaped shell.

Cave on Banjole
(166kB)

Anthozoa ?? (100kB)
Cadylactis aurantiaca (XXkB)

Eudendrium recemosum (XXkB)

 


Nudibranchs (100kB)

Haliotis lamellosa (XXkB)
  • The filter-feeding porifera (sponges) encrust the rocks which constitute for the most dominant group of sedentary animals; The interior cavity, called the atrium opens to the outside through the large osculum. The body of the sponge surrounding the atrium is perforated by pores. The outer surface of the spongy body is covered by the pinacoderm (flattened cells). Pores derive from porocytes, cells that ere perforated like a ring. The atrium is lined with flagellated choanocytes. Between the pinacoderm and the choanocytes lies a layer of mesenchyme containing amoebocytes. The skeleton of most sponges consist of spicules of CaCO3 or SiO2 secreted by amoebocytes, while other sponges posses an organic skeleton of coarse spongin fibers, and some even both. Each spicule may be a single needle-like array or several rays joined at certain angles to each other. They are generally microscopic and unconnected, but in some sponges the spicules are fused together to form long strands. The size and shape of the spicule and the number of rays present vary greatly and each species of sponge possesses a characteristic combination of several different spicule types; thus, are an important feature in the classification of sponges.

    Sponge structure can be simplified into three basic structural entities. The asconoid sponges represent a simple vaselike structure that are not more than a few centimeters tall. Syconoid sponges exhibit a folding pattern of the flagellated layer giving the entire organisms an outwardly directed finger-like appearance. The great majority of sponges display the leuconid structure in which the surface area of the flagellated layer form many small chambers in which choanocytes are located.


Selected sponges (34kB)

Sclerospongia (130kB)

Clathrina sp. (60kB)

Agelas sp. (60kB)
  • Another filter feeder present in the cave are large aggregations of bryozoa. These are sessile polymorphic colonial organisms encased in a chitinous exoskeleton. Individual zooids are cylindrically shaped. The principal organ projecting into the coelom is the U-shaped gut. At the anterior end, the skeletal housing is perforated by a circular orifice through which the two ends of the gut project. The feeding organ of bryozoa is the ciliated lophophore to which a retractor muscle is attached for withdrawal.
    Bryozoan colonies display a large variety of shapes - they range from upright branching forms attached only at the base, to thin encrusting sheets, to lacy, delicate folds, or even to massive calcified coral-like forms.

Selected bryozoa (46kB)
  • The subphylum urochordata includes the filter-feeding, sessile ascidiacea (sea squirts) that can be colonial (synascidia) or solitary (monascidia). The body is covered by a tunica which is composed of quite robust fibers of tunicin. Tunicata posses two openings. One stream of water, created by cilia in the pharynx, carries water and plankton through the buccal siphon into the pharyngeal basket. The plankton is trapped in a sheet of mucus secreted by the endostyle and carried by ciliary movement to the stomach. Filtered water escapes through numerous minute pharyngeal slits into the atrium from where it is discharged through the atrial siphon. In Monascidia there is only one atrial siphon, whereas in synascidia, several organisms share one common atrial siphon. Halocynthia papillosa is present on hard substrate; whereas, as the dredging sample revealed, Microcosmos sulcatus was predominantly found on soft substrate.

Monascidiacea, Halocynthia papilosa (100kB)

Synacidiacea Microcosmos sulcatus (100kB)
  • Echinodermata of many colors (star fish, sea urchins) graze the substrate and make it their home. One interesting feature should be mentioned here. The pedicellarias of sea urchins are more complex than those of sea stars. They are on tall moveable stalks, and most have three jaws (rather than two jaws common in sea stars). In some urchins like large pedicellarias, acting mainly for defense, contain poison sacs, and the tips of the jaws are grooved or hollow like a hypodermic needle. Other types seize and crush swimming larvae and other plankters, which are not only prevented from settling and growing on the urchin but also provide an extra source of nutrition. Small flexible pedicellarias probe among the spines, keeping the surface clean and free of foreign growth.

Sphaerechinus sp. (63kB)

Pedicillaria of sea urchins (87kB)
  • Octopuses of the class cephalopods are seen occasionally while snorkeling around the island of Banjole. These very intelligent animals, feed on crabs and shellfish, live in caves or dens, and are known for their ability to flash color changes and move gracefully and swiftly over the bottom and through the water.

Octopus vulgaris (70kB)


Intro + Plankton
Benthos
Littoral
Phytal + Nekton