Marine biology Marine organisms that live on or inside the bottom, different types of beaches, and biodiversity in these different types of beaches #Environment

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.