Appunti di Marine Ecology

Marine ecology oral test

Introduction

Ecology and marine ecology: study of interactions between organism and their environment

• Study of how these interactions determine their distribution and abundance
• Study of how organisms adapt to their environment and alter it
• It's a huge matter, so it includes many other disciplines. Different approaches can be used to study it

Ecological interactions

Interactions can be biological or abiotic. With resources, interactions are the base of the study of ecology. Biological interactions are created by organism (Ex. Predator/prey, parasite-host, biological dependencies). Abiotic interactions are the effect of abiotic factors on the function of organism, like geological, physical and chemical. They are both connected (Ex. Cold temperature can reduce the capability of a cold-blooded animal to escape from a predator). Resources are every material whose abundance can limit survival, growth, reproduction (ex. Food, light). They can be both renewable and non-renewable.

An ecological process can be investigated at different levels of a hierarchy. It is important to define which are the different components of the hierarchy. When we focus on each of these levels, we focus on different questions. These various levels can't be studied separately.

Interaction on the scale of individuals

Both biotic and abiotic factors are important. They define the ecological niche = Range of environment created by biotic and abiotic factors where the species is found. It is a multidimensional concept which defines a species' place in a community in relation to other species. Two species cannot coexist in a community if their niches are identical. (This phenomenon was described by Connell’s experiment with Barnacle: Chthamalus inhabits the upper part of the rocky bottom even if it can live in both parts of the rocky bottom. It couldn’t live in the bottom part because there it lives Balanus, which is a strong competitor of Chthamalus. If we remove Balanus then Chthamalus can occupy the whole rocky bottom)

Niches can be divided into two different concepts:

• Fundamental niche: the one which is potentially occupied by the species (Upper rocky bottom)
• Realized niche: Portion of the fundamental niche actually occupied by the species (upper part of the rocky bottom for Chthamalus)

Interactions between individuals can be:

• Territoriality: Maintenance of a home range and its defense against intruders. Protection of feeding area or breeding area (ex. Clownfish, very aggressive when it releases the eggs, the same is triggerfish, which can be also aggressive against humans, he can bite, he protects all the water column above the eggs) or specific nest site. In most cases, it is intraspecific.
• Competition
• Predation: A successful predator has to locate the prey, trap it, and assimilate it. Predators can be stationary (ex. cnidarian) or mobile (territorial, they don’t cover large areas or large distances). Even below the sediments, there are predators. Predators must adjust their hunting behavior to optimize the rate of ingestion of prey — optimal foraging theory: maximize the amount of energy gained, minimizing the time spent feeding. Predators don’t hunt randomly. Some examples: When food density is high, it is better to specialize in food with high nutritional value; the time spent in a patch of prey should increase with an increase of travel time between patches; choices of the best-sized prey (crabs prey mussels of intermediate size, which are nutrient enough and not too difficult to prey); consider the presence of predators by modulating the frequency of feeding (bivalve feeds use a siphon but this made it visible to predators). Prey can avoid predators by using crypsis or blending with the background, using chromatophores (like cuttlefish, octopus) or by maintaining fixed color similar to the background (seahorses, shrimps). An example of this is the color of red emperor snapper, a small fish, which is always associated with lionfish, which is venomous and has the same color as the snapper. They spend all their juvenile stadium with the lionfish (and not with the sea urchin, that are not present in the area). Another method is to use camouflage coverings, many crustaceans cover them with algae, little piece of stone, polyps of soft corals in which they live. They can also use deceptive coloration and behavior (production of ink by sea hare, black band like zebras that seems to break in many parts the animal and it confuses the predator, false eye of butterflyfish while the real eye is covered by a black band) and escape responses (for example a scallop which is able to escape by opening and closing his shell very fast). Another mechanism is to retreat themselves to inaccessible habitats (REFUGE), used by blue triggerfish for examples, which use a spine to get themselves stuck inside a cave and make it impossible to get him out by pulling his tail. This mechanism is used also by a type of shrimp that lives in the mantle of a nudibranch, below the skin, in order to protect himself from the predator (we still don’t know much about this interaction, we don’t know if it is parasitism or commensalism). It can also be used mimicry, using morphology similar to the one of other species. Batesian mimics occur when an animal species harmless against the predator resembles a dangerous species, that live in the same territory, imitating coloration and behavior (Ex. , the mimic Thaumoctopus mimicus octopus). Then there are mechanical and chemical defenses like blades, spines, darts of conus, mucus (chemical defense, it is full of bacteria). Some cases the defenses are inducible, they are active only when the predator is present but at the expense of other process (porcupinefish after three or 4 times he did his defense mechanism dies because his internal organs are distressed). Organism can produce toxic compounds, synthesized by, conspicuous color (aposematic) and alternation of microhabitats.
• Parasitism: Parasite live at the expense of other species and may get the nutrients or shelter by damaging the host, but without consuming the host totally and without killing it. Parasitic species evolve through cycles of varying virulence: if they are too ineffective they incur in competition with other parasites, otherwise if they are too effective they may kill their host. They can be ecto or endoparasites (lose completely their locomotory appendages, invading specific tissues like reproduction system ex. Sacculina, a parasitic barnacle that invade the reproductive system of crabs. They use a dart called. the sacculina is able to control the crab, it changes his behaviour. Crab stopped eating, reproduce but he just.. he then produce a sacculina sac where eggs of sacculina can get fertilised and led to the birth of new sacculina individuals.) Parasite have complex lifecycle and they can also change hosts during life: the intermediate host in where the parasite reproduce asexually, the definite host is where it reproduce sexually. More examples on the slides. There are also mollusc that can be parasite, using fish for reproduction.

Mutualism: Benefit all the species involved, began as facultative but genetic variation allowed complete dependence. They can be protection from predators or food acquisition. (Ex coral polyps and zooxanthellae, Anemone and clownfish, anemone is cleaned by clownfish and it gets protection because clownfish are very aggressive). Another important example is the one between Goby and a shrimp: the shrimp is blind but he is building a home so the gobi lives with him to use his house, but it also says to the shrimp when there is danger around by moving his body (they are always near each other, constant contact). Hermit crab and anemones: anemones protect crab because they are stingy, hermit crab takes around the anemones. When the hermit crab changes his shell he also move the anemones from the old shell to the new one in a way he only knows. A mutualistic relationship created to gain food is the one of the cleaning stations, located in specific part of the coral reef. Shark lays in a vertical position in order to get their mouth clean.

Commensalism: It benefit one species but without damaging the other it can be facultative or obligatory. Some examples are borderline between commensalism and parasitism: Barnacles is an example of this. Are we sure that barnacles aren’t harming turtles or whales? The same is true for remora: is the manta free of harm?

+ means that an organism benefit from this interaction, - means that he suffer from this interaction, 0 means it is neutral.

Population level

A population is a group of individuals of the same species that are responding to the same environmental factors and freely mix. It is necessary to know:

• Population size (number of organism)
• Population density (index of crowding, number per unit of area or volume)
• Biomass (mass of individuals per unit of area or volume)

Marine populations are very dynamic, more than the terrestrial, because there are fewer barriers.

Temporal pattern: 3 different modes of growth:

• Exponential — increase with the same proportion as the time pass, resources are unlimited so growth is unlimited. (Very rare, resources are limited)
• Resources-limited growth — limit is carrying capacity is the number of individuals that the resources can sustain. Involved intraspecific competitions for resources.
• Random growth — is the most widespread, population change appears to be random. Factors regulating are too complex to show any simple pattern.

Not only the resources can affect the pattern of growth, other factors are: survival of adults (if the survival time is high then there will be many sons in the future), reproduction and successful survival of young (many eggs show a little capability to survive as adults), immigrations, emigrations. We can use survivorship curve (probability of survival of different stages of life) or population model.

Spatial distribution is the measure of the type of spacing among individual in a given area:

• Random, an individual has the same chance of being located in a spot or in another, is rare
• Uniform, organism maximize distances between them
• Aggregate, present in many period such as mating, protection against predators. More individual in a specific subarea

We have to introduce the concept of metapopulation: it is a group of populations, or subpopulations that are living in separate habitats but are connected by dispersal. It is a group of interconnected subpopulations. Ex coral reef, in particular patchy reef.

There are two types of subpopulations:

• Sink, only receive immigrants or larvae from other subpopulations;
• Source, receive and donate individuals, high reproduction and dispersal rate.

2 ways of structuring a metapopulation into subpopulations:

• Equally sized subpopulations;
• Island-mainland scheme (one large subpopulation close to small island subpopulation, ex big coral reef surrounded by small patch reef)

In marine system we mainly talk about metapopulation, not single populations.

Community level

A community is a group of species which coexist and interact together by means of biological process. Factors that determine the structure:

• Structural habitat
• Foundation species (species that contribute to the structure of the local habitat, determining the chemical and physical characteristics of the habitat. They are called ecosystem engineers, ex. Mangroves)
• Interacting species
• Environmental parameters
• Process between species like dispersal of larvae, competition, predation, disease, facilitation

1. Larval dispersal: larvae can disperse great distances. In the marine environment there are good and bad recruitment years (wide variations in population sizes), depending sometimes by the currents.

2. Interspecific competition occurs when individuals of different species exploit the same limiting resource (food, substrate). A guild is group of species that exploit the same resources. Competition can proceed in different ways:

• Direct displacement
• Preemption (The first who arrives gets the advantage)
• Exploitation competition (who better exploits the resources wins) Hard substrata has this mechanism of competition: an overgrowth of neighbors, shading of competitors (used in photosynthetic organisms), secretion of poison, presence of special aggressive structures (ex aggressive polyps who fight with competitors). The possible outcomes of a competition are competitive exclusion: one species outcompetes another for a resource; and coexistence: exploitation of a resource without displacement. This can be possible thanks to the complexity of the habitat, a complex network of competition, adult extinctions and recolonization and complex pattern of disturbances.

3. Predation and disturbance may prevent the domination of a superior competitor over inferior species. Predation acts on singular individuals, disturbance is a physical process operated on a large scale of space (storms, wave action). Disturbance can initiate a sequence of dominance by different species over time known as succession. Climax is the last stage of ecological succession, it is a predictable final state. Ex of this in slides. (The first colonizing species are called pioneer species, they reproduce very fast, not specialized. They facilitate the appearance of the other species.)

The effect of the rate of predation and disturbance is shown in the graph below. If there is no predation we expect just 1 dominant specie. If we have high level of predation or disturbance all the species are removed, so we may have a 0 number of species. It is necessary to have a medium level of predation or disturbance: in this way we may have biodiversity, many species coexisting.

4. Parasite and disease: diseases are the major cause of massive widespread mortality. They are caused by microorganism. Parasites are ubiquitous and reduce the capability of reproduction of the host.

5. Facilitation — many species can’t invade a specific environment unless another species invades it first. It is a necessity of a form of cooperation among species. The species that benefits may eventually displace the facilitating species, becoming parasites. Facilitating species may be called foundation species, they facilitate the presence of other organisms (they are habitat engineering). Ex. Forest kelp ecosystem are the foundation species. Two other species are important for the structure: sea otter that eats sea urchin. If the sea otter consumes urchins, they decrease (direct effect), but there is also an indirect effect: algae, prey of urchins, increase in size. Indirect effect can be a density mediated indirect effect, DMII = density at one feeding level increase reducing the density of another species and resulting in an increase of the prey of the second species; or a trait mediated indirect effect TMII = presence of a predator causes prey to be active less and feed less on their own prey. So prey of second species increase in abundance, even though the second species did not decline, their feeding activity decline.

Ecosystem level

It is a group of communities that interact with the physical - chemical environment within a specific geographic area. An ecosystem is not necessarily independent from other ecosystems (ex. Coral reef and open ocean, because larvae of corals stay in open ocean). Productivity is the amount of living material produced per unit area per unit time (g/m²/y). There is an energy loss along the pyramid. Also part of the organic matter is lost, it goes on the sea floor or in the water column and it is decomposed (this leads to a different trophic pyramid).

In the ecosystem we have a food chain in which each organism occupies a trophic level. Most of the time we have a food web, way more complicated than a chain. Predators are always at the top of the web, and some of this predator may have a strong effect on the entire ecosystem. They are called keystone species. Removal of this predator is very dangerous for the ecosystem, creating a trophic cascade: it can be generated by a top-down process (top predator has a strong effect, ex sharks it can lead to an increase of phytoplankton which is no good) or by a bottom-up process (changes in primary production drives changes in food web).

Chemical and physical environment

When an environmental change occurs individuals need to have sensor to get the change. Then this information needs to be translated into an adaptive response: there are 4 different types of adaptive response:

• Behavior adaptive response
• Biochemical adaptive response (change of enzyme activity, hormones, ions)
• Physiological (cellular changes at large systemic levels)
• Gene regulation, activation of genes, pathways

After the adaptive response individuals reach a new equilibrium thanks to acclimation, involved the modulation of the 4 up. We can see it in the graph: after an environmental change we have an immediate response, followed by an adjustment period that ends with acclimation.

There are two types of organism basing on the ability of acclimate:

• Regulators organism — can maintain constant their parameters despite environmental change (ex. Osmoregulator, homeotherms)
• Conformers organism — internal state and parameters change according to the environmental change
• Some species can show an intermediate behavior, like regulators for some parameters or conformer for other, or they can be regulator until a certain parameter.

The effect of extreme variations can be measured using scope for growth: consuming and digesting food represent the most energetic cost and it is called cost of metabolism. The scope for growth is the difference between the amount of energy assimilated by food and the cost of metabolism. If the result is:

• 0 maintenance metabolism
• + energy available for growth and reproduction
• - cost of m