Appunti Fundamentals of Marine Biology

Diadromous species: organisms that migrate between the sea and freshwater

Anadromous: migrations occur from the sea into freshwater to spawn (salmon, bass, sea lamprey)

Catadromous: migrations occur from freshwater into the sea to spawn (eels)

Other definitions:

Amphidromous: migration occurs from freshwater to the sea, or vice versa, but not for the purpose of breeding

Potamodromous: migrations occur within freshwater

Oceanodromous: migrations occur within the sea.

Birds play an important role in estuarine food webs. Estuaries provide feeding areas for birds undertaking migrations. Like fish, they can feed on all available trophic levels: from seagrasses to fish. The majority feeds on the rich invertebrate communities, and the distribution of invertebrates can influence the distribution of birds.

Birds should be distributed so that their proportion on a patch should approximate the proportion of resources in that patch (ideal free distribution). However, territoriality, direct and indirect

interference (ideal despotic distribution).

Estuaries are ecologically and economically valuable: they have been densely settled by human populations. Nutrient runoff and sewage: stimulation of primary production of phytoplankton decrease of water clarity. Much of the phytoplankton is not consumed by zooplankton and is decomposed by bacteria and this reduces oxygen concentration.

Two main effects: submerged aquatic vegetation (SAV) is affected by low light condition. Eutrophication may stimulate SAV through the increase of nutrients, but this stimulate the strong growth of competing seaweeds, epiphytes and phytoplankton that intercept light.

Phytoplankton that is not grazed becomes phytodetritus and sinks to the bottom. Large deposits of phytodetritus result in colonization of surface-feeding deposit feeders. Past a threshold, the deposit is decomposed and the sediment surface becomes anoxic.

Also the elimination of top predator has caused trophic cascade effects: no top-down

Control on suspension feeders. Estuaries are often largely affected by seasonal variations: interannual environmental changes in the watershed influence the salinity structure and nutrient inputs. The habitat instability, biological change, and human presence make estuaries hotspots for biological invasions of marine organisms.

The vulnerability of estuaries to ecologically significant invasions may result from three important factors:

• Frequent environmental overturns that can increase the vulnerability to invasions
• Ecological vacancies: in relatively low diversity estuaries, some habitats may be open
• Competitive superiors: some invasive species may be competitively superior to native species

Estuaries have been invaded extensively, even if introductions may fail to settle for different reasons. For example:

• No suitable habitat (temperature, salinity, substrate)
• Invasive population too small
• Inappropriate dispersal strategy (invasive organisms may survive the first

Hyposaline seas are enclosed bodies of water with low salinity levels. Some examples in Europe are the Baltic Sea (Very shallow (avg depth: 55m) with only one narrow channel with seawater and 250+ rivers. Salinity < 8 psu (gradient). A large proportion is frozen in winter and it is almost tideless. Stable salinity gradient (different from estuaries). Some taxa are absent (sharks, cephalopods) and in general organisms are distributed according to their resistance to low salinity. Living in such a low salinity implies an important energetic cost: less energies for growth (smaller individuals)); Black sea (Trio of hyposaline seas in central Asia. One narrow channel connected with the Mediterranean. Deeper than the Baltic (up to 2200m). The salinity range is 17-21 psu. Water mostly stagnant and deoxygenated. Most of the benthic production is shallow (in the NE). Highly disturbed sea: invasive species, overfishing, pollution); White

Seaweed is a type of marine algae that can be found in various forms and species. An individual seaweed is known as a thallus, which can either be undifferentiated or have highly differentiated structures for various functions such as light gathering, reproduction, support, floating, and attachment to a substratum.

The thallus can vary in form, ranging from a tar-like crust to a thin green sheet, to an erect simple filamentous branching structure, to a more elaborate and differentiated structure. It can be simply attached to a surface or attached by means of a holdfast.

Smaller seaweeds may appear as simple chains or sheets of cells, while larger ones show a considerable level of differentiation. The holdfast is a protuberance or hairlike structure that is rooted in the sand. The stipe, which is tubular and flexible, connects the holdfast with the blades. The blades are flattened leaf-like structures that are specialized for light capture. Some seaweeds also have gas bladders, which are structures specialized for flotation.

The frond refers to the entire seaweed structure excluding the holdfast. Blades are specialized structures for light capture. In some seaweeds, specialized floats called pneumatocysts keep the thallus suspended near the surface.

Gas-filled bladder (O2 and N2 in the same proportion of the airand CO2) that ensure that the blades float as high in the water as possible, maximizingexposure to light. In different species, they are found in different sizes and numbers.

Algae adjust to changing light in 2 ways:

1. As total irradiance decreases, algae increase their total pigment concentration
2. Alter the proportion of different light-harvesting pigments to adapt to the spectral composition of light.

Action spectrum:

• Green algae: use red and blue light
• Brown algae: similar to green algae
• Red algae: use the green light

Seaweeds continue to photosynthesize when exposed to air and some species even when desiccated. The productivity ofseaweeds is equal or greater to that of terrestrial plants. Seaweeds can be classified in 6 morphotypes (or functionalforms) based on the rate of photosynthetic production and consequently the morphology of the thallus:

1. Laminate thallus: Production: Very high (5.16 mgC/g/h)
2. Filamentous thallus:

1. Production: High (2.5 mgC/g/h)
   Branching and erect thallus
2. Production: Moderate (1.3 mgC/g/h)
   Thick and leathery thallus
3. Production: Low (0.8 mgC/g/h)
   Encrusting thallus
4. Production: Almost absent (0.07 mgC/g/h)
   Articulated and erect thallus

Seaweeds may be:

• Monoecious (hermaphroditic)
• Dioecious (separate sexes)

Haploid generation (Gametophyte) alternates with a diploid generation (Sporophyte). Gametes can be motile or non-motile and form the zygote which may be an attached form or a motile flagellated form. There is a great diversity in the size and form of sporophyte and gametophyte stage. In Ulva the stages are identical (Isomorphic). In the Laminariales (kelp) the sporophyte is very large, whereas the gametophyte is a small filamentous form (Heteromorphic). These differences allow greater exploitation of different ecological conditions: Different life stages can dominate in different seasons and can show different resistance to

• Chlorophyta (Green algae):
  • Photosynthetic pigments similar to those of higher plants (Chl a,b + carotenoids)
  • Same storage products of higher plants (starch in the chloroplast)
  • Chloroplast with 2 membranes and 2 or more stacked thylakoids (lamellae)
  • Most species live in freshwater (90%) and only 10% in marine habitats
  • Unicellular or pluricellular or colonial
  • Great diversity in morphology and in size
  • More than 7000 species
• Phaeophyta (Brown algae)
  • Dominate low intertidal and shallow subtidal environments in all latitudes (1500 species), especially along cold rocky shore
  • Colour due to xanthophylls and carotenes, which may mask the green of chlorophyll
  • Three stacks of thylakoids (lamellae) and motile gametes bed
  • Storage product is the Laminarin (β-1,3-glucan) in vacuoles
  • Morphologically more differentiated than green algae, having distinct holdfast, stipe, blades, and reproductive structures

Range from small

filamentous forms to the largest seaweeds in the ocean (Macrocystis),• longer than 15 m

Species with largest thallus seem to thrive in colder-water, nutrient-rich environments• Contain phycocolloids and alginate extracted for human consumption

Rhodophyta (Red algae)

The most diverse group of seaweeds in the ocean and are especially widespread in temperate and tropical waters• Found in shallow water and intertidal zone (but also deeper)• Starch in citoplasm

The photosynthetic pigment phycoerythrin gives red color masking the green chlorophyll• Non motile and non flagellated gametes• Isolated thylakoids (Phycobilisome)• Variety of forms• They grow rapidly• They contain substances of great value for food production (carrageenan, agar)

Coralline algae secrete calcium carbonate in the cell walls growing as branching forms• or encrusting. In the tropics, big and resistent structure (alg