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AFSFT- Marine Benthos Classification and Adaptations
- 1. 1 Aswan University Faculty of Fish and Fisheries Technology
- 3. • Marine benthos comprise huge variety of species which are greatly varied in size, origin and mode of life; therefore, they can classify as following: • A- According to origin (by type): It classify into: • a- Zoobenthos: Zoobenthos are animals belonging to the benthos. • b- Phytobenthos: Phytobenthos are plants belonging to the benthos.
- 4. B- By size: 1- Macrobenthos: Macrobenthos are the larger, more visible, benthos that include all animals larger or greater than 0.5 mm in size. Some examples are polychaete worms, bivalves, echinoderms, sea anemones, corals, sponges, sea squirts, turbellarians and larger crustaceans such as crabs, lobsters and cumaceans as well as benthic fishes. • On the other hand, the macrofauna or macrobenthos are further divide according nature of occurrence into: a- Epifauna: Includes animals living on the substrates, either moving such as crabs, and other crustaceans or sedentary such as barnacles, chitons, some of bivalves, sponges, corals and other cnidrians). b- Infauna: Includes animals living within sediments either burrowing (some crabs, shrimps) or temporarily berried it selves (star fishes, heart sea urchins).
- 5. 2- Meiobenthos: Meiobenthos are tiny benthos that are less than 0.5 mm but greater than 64 μm in size (in some uncertain studies reach to 32 μm). Some examples are nematodes, foraminiferans, water bears, gastrotriches and smaller crustaceans such as copepods and ostracodes. B- By size:
- 6. 3- Microbenthos: Microbenthos are microscopic benthos that are less than 64 (32) μm in size. Some examples are bacteria, diatoms, ciliates, amoeba, and flagellates. B- By size:
- 9. 1- Rocky shores provide hard substrates for benthic macro algae. 2- The variation in topography of rocky shores provide several Substrates, shelter and refuges for benthic biota leading to increase in species richness and greatest diversity. 3- Rocky shores inhabiting species are characterized by having powerful limbs or organs for running and climbing (crab), creeping (chiton, Pattela), fixin (Brancles) or rapidly escaping under rock. 4- The rock are standing in striking against wave action, current, erosion Which makes them more table for life. 5- Most of the dominant organisms of the intertidal rocky areas are solitary or colonial animals.
- 11. As organisms are exposed to air at low tide, they lose water by evaporation. They must be able to either tolerate this water loss, or have mechanisms to reduce it until the tide comes back. - Mobile organisms can move in cracks, under seaweeds, or move with the tide. - Physiological adaptations that prevent or reduce water loss include closing an external shell (e.g. barnacles, mussels, snails), or producing mucus (e.g. some anemones, hydroids and seaweeds). - Reducing heat gain is accomplished by a large body size reducing the amount of the body touching the substrate (e.g. mucus threads produced by knobby periwinkles), and light colors. - The gill filaments of the tubicolous, polychaete and serpulids are enlarged and serve to close the mouth of the tube in the adverse conditions. - The Opercula of the gastropod molluscs and the shells of bivalves prevent evaporation of water from the interior of the animal. - The ability to remain for long periods in a condition of suspended activity is a marked feature of shore animals. Avoiding overheating and water loss (desiccation)
- 12. Avoiding wave shock Many organisms have adaptations to reduce their susceptibility to wave action in the intertidal zone. - Many are small in size, squat, with streamlined bodies which minimize drag (e.g. limpets, barnacles, chitons), or live in burrows (e.g. some urchins). - Seaweeds are flexible and bend with the waves. - Several organisms such as barnacles, many bivalves and seaweeds are permanently and strongly attached to the substrate. - Others have a non-permanent attachment but are strong nonetheless, for example several intertidal mollusks have an enlarged foot to cling strongly to rocks.
- 14. Respiration Gills of intertidal organisms are typically protected inside a body cavity, which provides protection and reduces drying during low tide. Most organisms must reduce their activity at low tide as they reduce gas exchange. Some gastropods that live high in the intertidal zone (e.g. rough periwinkles, Littorina obtusata) conduct gas exchange through their enlarged, well-vascularized mantle cavity, enabling them to conduct gas exchange at low tide (i.e. air breathers), and eliminating the need to protect fragile gills at low tide. They will drown if submerged for several hours.
- 15. Spray zone – region above the spring high tide line; covered by water only during storms Intertidal zone – region between the high and low tidal extremes
- 16. Supralittoral zone (Spray or Splash) Middlelittoral Zone Mostly shelle d orgs Many soft bodied orgs and algae Supralittoral fringe Infralittoral fringe Sublittoral Zone
- 18. Sandy shores
- 19. Sandy shores form in areas of lower wave action, where loose sediment accumulates. This loose material commonly includes quartz grains, black volcanic sand, pulverized carbonate plant and animal skeletons. The fauna is less abundant on sandy shores than it is on rocky shores. Competition does not appear to be as important as in rocky shores, as is suggested by the sparse populations, three-dimensional space and abundance of food. There also appear to be fewer predators on sandy shores. The physical factors of wave action, particle size and beach slope may be more important than biological factors in determining the distribution patterns on sandy shores.
- 20. The distribution of organisms on sandy shores is determined by particle size, wave action and slope. Wave action determines the sediment size found on a given beach. High wave action leaves coarse material and low wave action deposits finer sediment. Sediment size influences the size of interstitial spaces (space between particles), which in turn affects porosity and water retention: fine-grained sediments retain water better, and create a better habitat for aquatic organisms. Sediment size also influences the ability of organisms to burrow; fine sand is easier to burrow into.
- 21. Most macrofauna on sandy shores are infauna: they burrow into the sediment. This behavior allows animals to better resist desiccation and heat stress at low tide. With the effects of two stresses reduced, wave action is the single most important factor in determining distribution of organisms on sandy shores. In some fine-grained beaches with limited water flow between grains of sand, oxygen levels can be very low below the very top of the sand, and thereby limit organism distribution. Several animals have siphons or pumps to oxygenate their burrows and survive in hypoxic or anoxic conditions.
- 22. Since the shifting sand prevents the growth of multicellular primary producers in the sandy intertidal, primary production is limited. Benthic diatoms can provide some primary production, but in most cases, the main food source comes from detritus that comes with the tide. The activity of organisms in the sandy intertidal is strongly tied to the movement of the tides. Many organisms wait until high tide to feed and exchange gas, and quickly increase their activities when they become submerged again. High tide also brings a suite of marine predators such as whelks, sea stars and moon snails.
- 23. Meiofauna are microscopic elongate organisms between 62 μm and 0.5 mm in size that are entirely aquatic and live between sediment grains. As such, their existence is dependent on the size of the interstitial spaces, as this regulates water content. Coarser sediments, with greater interstitial volume, harbor larger organisms, yet drain more rapidly. Finer sediments harbor more burrowing forms of meiofauna. The abundance and type of organisms found as meiofauna is also dependent on temperature, salinity, wave action and oxygen availability. They exhibit a range of feeding types; carnivores, suspension feeders and deposit feeders. A unique specialized feeding type is sand licking, in which sand grains are manipulated by the mouth parts to remove minute bacterial growth and thin films of diatoms.
- 25. Zonation exists in sandy shores but it is much less defined than on rocky shores. Besides horizontal zonation such as that seen on rocky shores , sandy shores also exhibit vertical zonation: from the surface of the sediment down. The exact pattern of zonation on a sandy shore depends on many factors, including the amount of water trapped in the sediments, the time of year and the type of beach. The most important factor in determining distribution is wave action. The supralittoral fringe ranges from the high tide line to the edge of vegetation. Much of this area is uninhabitable as it is too hot and dry because of the sun. Organisms that survive in this zone are mainly arthropods, dominated by insects and isopods in temperate regions, and crabs in tropical regions. An interesting organism found in this zone in tropical regions is the ghost crab, this translucent crustacean scavenges the beach at night, repairing its burrow in the morning and sealing itself in by mid-day to avoid heat and predation.
- 27. The midlittoral zone (true intertidal) that vertical zonation is most apparent . Moisture reaches the zone of drying sand during the highest tides and gradually evaporates. The zone of retention retains moisture due to capillary action and the zone of resurgence retains water at low tide. The zone of saturation is constantly moist and supportsthe greatest diversity of organisms, including polychaetes, amphipods, isopods and bivalves. Many of these burrow and retract their feeding and gas exchange appendages during low tide to avoid desiccation and predation. Carnivorous snails, such as whelks, search for bivalves by sensing currents produced by the siphons of clams. Sea stars and sand dollars come out to search for food. Lugworms (Arenicola spp.) The infralittoral fringe is essentially a truly marine habitat, as it is exposed only during the lowest spring tides. This zone is dominated by seagrass beds, with animals such as bivalves, snails, heart urchins, sand dollars and fish.
- 29. Muddy shores
- 30. The term "mud" is loosely, applied to deposits containing a high proportion of silt or clay. The finest particles settle only from still water and shores of mud are therefore, found where conditions are normally calm and without strong currents. Thus, muddy shores occur in more protected areas from wave action. It tends to become finer grained and accumulates organic matter, and thus become muddier. Sandy and muddy shores are, therefore, the opposite ends for continuum, sand beaches having larger grain size, and muddy shores are the finest grain size.
- 31. The major feature of muddy shores is their restriction to the intertidal areas, completely protected from the wave action. Thus, muddy shores are well developed, where there is a source of fine-grained sediment particles. Therefore, these shores are located in partially enclosed bays, lagoons, harbors, and estuaries. The water in these places is calm, with minimum movement, and slope of mud tends to be flattener.
- 32. In muddy shores, the very fine particles couple with the very flat angle of sediments. This means that the interstitial water do not drain away and held within the substrate, with very poor interchange with seawater above. In addition to the previously mentioned features, the presence of high internal bacterial populations in sediments, usually results in complete depletion of the oxygen in the sediments, an anaerobic condition thus is prevails within sediments forming the deoxygenated layer under the first few centimeters of the surface, which is the most important characteristic feature of the muddy shores.
- 33. Organisms inhabit muddy shores can overcome on the prevailing conditions in several ways as following: 1- As in sandy shores, muddy shores inhibit with few organisms, and most of them show adaptation to burrowing into or through the soft substrate or inhabit permanent tubes in the substrate. In contrast with sandy beaches, organisms advertised on the surface by the presence of various holes of different sizes and shapes. Thus, primary adaptation is the ability to burrow into the substrates. 2- The second adaptation concern the anaerobic conditions, prevails in the muddy shores and organisms adapt with this feature either by using a way of bringing the overly surface water with high oxygen supply down to them, or obtain oxygen rich surface water and food that the various burrows tubes and holes appear on the surface of mudflat. 3- The third adaptation to overcome the low oxygen tension is the development of carriers (e.g. hemoglobin) that will continue to pick up oxygen at concentrations well below that of similar pigments in other organisms. Others use glycogen store for anaerobic metabolism during periods where there is little or no oxygen.
- 34. In contrast to both rocky and sandy shores, zonation does not clear on muddy shores due to the very gentle slope of theses shores, giving an extensive area of mudflats and muddy habitats. However, the supra littoral fringe is often inhabits with various species of crabs, many of which burrow in the substrate; while the very extensive midlittoral zone is the home of most common species of clams and polychaete worms. There is no sharp boundary between the supralittoral fringe and midlittoral zone, therefore, similar organisms are encountered in both areas. On the other hand, predation being the most important among both physical and biological factors prevailing on muddy shores, which effect on the structure communities of the muddy shores.