Marine ecology

Marine ecology

The study of interactions between organisms and their environment determines their distribution and abundance, as well as how organisms adapt to their environment and, in turn, alter it.

Ecological and evolutionary principles of marine biology

Ecological interactions

Ecological interactions between individuals, community, and population can be divided into two:

• Biological interactions: predator interactions, biological dependencies, parasite host
• Abiotic interactions: effects of abiotic factors on the functioning of organisms. This can be geological, physical, or chemical.

Resources are any material whose abundance in the natural environment can limit survival, growth, and reproduction, such as light. These can be renewable or nonrenewable.

All ecological processes can be analyzed at many levels of a hierarchy: biological analysis at small scales (cellular) or ecological analysis at a community or group of populations. From cell to biosphere.

• Individual level: organism physiologically independent
• Population level: group of individuals of the same species that are responding to the same environmental factors and freely mix. Species: a single population that is genetically isolated from others
• Community level: group of populations belonging to different species and all living in the same place
• Ecosystem level: an entire habitat including all the abiotic features and all the living species within it that interact
• Biosphere level: all the living organisms on Earth and the environment with which they interact

Interactions among the levels

It's difficult to define an ecosystem, e.g., the coral ecosystem has fish, corals, and other little organisms living in association. Not always is it possible to study all the organisms separately. We focus on a single individual.

Ecological niche: is the range of environments over which a species is found (the habitat of the species), a multidimensional concept that defines a species' place in a community in relation to other species. Two species cannot coexist in a community if their niches are identical. An example can be Balanus and Chthamalus, which occupy two different strata of the rocks. Balanus is a stronger competitor for the lower stratum but cannot colonize the upper stratum. Chthamalus, otherwise, can colonize the upper stratum and the lower too, but in the presence of Balanus can colonize only the upper stratum. This explains the difference between fundamental (niche potentially occupied by the species under ideal conditions) and realized niche (portion of the fundamental niche occupied by the species).

The +0- system can be used to explain the win or lose to organisms or no effects:

• Territoriality + - : maintenance of a home range and its defense against intruders (competition for space). In most cases, it is intraspecific; they get feeding areas, breeding sites, or specific nest sites.
• Competition + - or - -
• Predation + - : may be stationary (cnidarian) or mobile (fishes, starfish, gastropods), divided into territorial or they can cover large distances. Predators may adjust their hunting behavior to optimize the rate of ingestion → optimal foraging theory: maximize the amount of energy gained, minimizing the time spent feeding.

4 points that characterize the theory:

• When food density is high, it is better to specialize on food with high nutritional value
• The time spent in a patch of prey should increase with an increase in travel time between patches
• Choice of the best-sized prey
• Consider the presence of predators because he can become a prey too

To avoid predators

• Crypsis or blending with the background by maintaining a fixed color similar to the background. E.g., the association between scorpion fish and Lutjanus sebae.
• Camouflage coverings. E.g., a crab covered completely by hydrozoans.
• Deceptive coloration and behavior, coloration create strange effects on the predators. E.g., the false eye of butterfly fish.
• Escape response used by vagile organisms. E.g., scallop expels water and then escapes.
• Retreating to inaccessible habitats such as the triggerfish with a trigger to block the fish. Some (razorfish) bury themselves in the sand. Shrimps with a coat, e.g., amphipod hiding in the mantle of Coriocella hibyae to prevent being attacked by predators.
• Mimicry, evolved morphology that allows an organism to resemble another species with the function of reducing attacks by predators such as blackfish in seagrasses. It is possible to have Batesian mimics that occur when an animal species harmless against predators resembles a dangerous species that live in the same territory, imitating coloration and behavior, e.g., the octopus resembles poisonous animals like lionfish or sea snakes.
• Mechanical and chemical defenses such as surgeonfish have spines or conus which is a poisoned species, coral produce mucus. A category is an inducible defense, providing an advantage to the prey only when the predator is present, but at the expense of other processes, they can die.
• Toxic compounds, synthesized by the organism acquired through another toxic organism.
• Conspicuous color (aposematic), some colors are very bright, e.g., nudibranchs have very poisonous toxins.
• Alteration of microhabitats

Commensalism + 0 : only one species has benefit but without damaging the other. It could be facultative or obligatory. Some can be considered parasitism, e.g., barnacles and turtles, manta and remora fish.

Mutualism + + : mutualistic relationships benefit all the species involved. Began as facultative but led to complete dependence. Many mutualistic relationships involved protection from predators for almost one of the species and/or food acquisition. E.g., corals and zooxanthellae is the most important mutualism in the coral reef habitat. Anemone and clownfish (live within an organism that is very dangerous for other organisms, so he is protective) clownfish protect his home and let it take clean. Some goby (obtain the home) and shrimps (blind), the goby advises if there are any animals. When the goby produces special movements, he advises the presence of other animals. Pagurus and anemone is a species-specific relationship, the anemone got to the back of the crab and the crab get protection. Mutualistic relationships created to gain food, e.g., cleaning fish acquired food and the fish that are cleaned get removed all parasites. There is the false cleaner fish which uses mimics to eat in addition to parasites also the tissue of the fish.

Parasitism + - : parasites live at the expense of other species and may get nutrients or shelter by damaging the host, but without consuming the hosts totally and without killing them. There are different cycles of virulence: too ineffective (competition with other parasites), too effective (kill the host, extinction of both species).

2 categories:

• Ectoparasites, live attached or embedded within the eternal body surface
• Endoparasites, live within the body, organ, or tissues. Have highly modified morphologies to adapt to life within cavities and to food uptake and absorption of fluids. Have lost locomotory appendages. Invade specific tissues, such as reproductive tissue of the host. Such as Sacculina and the crabs, Sacculina invade the reproductive organs of the crabs and if it is male could also change in female and reproduce again. Definitive host: is where the parasite reproduces himself.

The population level

A population is a group of individuals of the same species that are responding to the same environmental factors and freely mix. Marine populations are more dynamic than terrestrial ones. There are 3 different growths in time:

• Exponential growth with unlimited resources
• Resource-limited growth, leading to the carrying capacity then decreases slowly intraspecific competition for resources
• Random growth with many factors that affect the growth of the population

There are other factors that affect the growth of the population such as the rate of mortality, reproduction, emigration, and immigration. We can predict the size of the population in the future by using this formula:

dN/dT = f (N, M, R, I, E)

• N = population size
• M = mortality (dead, D)
• R = reproduction (number of birth B)
• I = immigration
• E = emigration

Important is also spatial distribution patterns:

• Random, an individual has the same chances to be in one or another position
• Uniform, there is maximization of the distance between organisms
• Aggregate, mating to get protection against predators.

Metapopulations: a group of populations that are living in separate habitats but are connected by dispersal. A group of interconnected subpopulations living in different spaces but still in connection. 2 types of subpopulations:

• Sink, they only receive immigrants
• Source, contribute more individuals to the metapopulations. High reproduction rate and dispersal rate. Metapopulation model is very appropriate for marine systems where dispersal of larvae between relatively isolated subpopulations is common.

2 ways to structure a metapopulation into subpopulations:

• Equally sized subpopulations
• Island mainland scheme, one large subpopulation can donate or receive from the small one.

The community level

Ecological communities consist of a series of coexisting species that interact by means of biological processes. Factors that determine the community structure:

• Structural habitat
• Foundation species
• Interacting species
• Environmental parameters
• Processes between species:

Dispersal of larvae, most of the species of fish and invertebrates have planktonic larvae, which can disperse great distances. In most marine habitats, there are "good" and "bad" recruitment years (wide variation in adult population size). Some of this variation may result from the effects of local currents. Feeding larvae may be short of food in some years, with a consequent reduction in successful settlement.

Interspecific competition occurs when individuals of different species exploit a limiting resource (space/food). A Guild is a group of species that exploit the same resource.

• Hard substrata mechanisms of competition for space: overgrowth of neighbors, shading of competitors, secretion of poison, presence of special aggressive structures.
• Outcomes 2 types: competitive exclusion, one species outcompetes another for a resource; coexistence, some process allows two species to exploit the same resources without displacement.

Predation and disturbance both phenomena may prevent the domination by superior competitors over inferior spaces. Which is the effect of the rate of predation and disturbance on the number of species? Species tend to be predation and disturbance. Such as optimal theory maximized at intermediate levels of predation/disturbance.

• Predation and herbivory, biological processes that act on singular individuals, so it is a one-at-a-time removal process;
• Disturbance, generally is any physical process and usually operates on larger spatial scales, removing patches of the community, often initiates a sequence of dominance by different species over time known as succession.

Succession is a predictable ordering of appearance and dominance of species, usually following an initial disturbance. A predictable final state is called a climax community. Succession could be a trend toward a more stable assemblage of species or the simple sum of colonization and persistence of the species.

Effect of the rate of predation and disturbance on the number of species: species diversity tends to be maximized at intermediate levels of predation/disturbance.

• Low levels of disturbance or predation: only one competitive dominant species. No species diversity Intermediate levels: more resource space opened, more competing species allowed to coexist
• High levels: all the individuals of all species removed, reducing the total number of species

Parasites and disease are major causes of massive and widespread mortality. Caused by microorganisms, the knowledge about marine pathogens is very limited. Environmental factors may increase the spread and virulence of diseases and the host susceptibility.

Facilitation is when some species depend on the presence of other species. Facilitation is the necessity of a form of cooperation among species. The species that benefits may eventually displace the facilitating species. Foundation species often alter the structural environment, which facilitates the presence of many other species. E.g., seagrasses and hydrozoans.

Direct effects: Predator consumes prey, and prey population decreases. Sea otter consumes urchins that decrease.

Indirect effects: Effects are propagated to other species of the communities. Sea otter consumes urchins; as a consequence, prey of urchins (seaweeds) increases in population size.

• Density-mediated indirect effect (DMII): Density at one feeding level increases, reducing the density of another species (second) and resulting in an increase of the prey of the second species.
• Trait-mediated indirect effect (TMII): Presence of a predator causes prey (second species) to be active less and feed less on their prey. So prey of the second species increase in abundance, even though the second species did not decline (their feeding activity declined).

The ecosystem level

A group of communities that interact with the physical-chemical environment within a specific geographic area. An ecosystem is not necessarily independent of other ecosystems. All ecosystems exchange nutrients and organisms with other ecosystems.

All ecosystems have special food chains: primary producers, e.g., phytoplankton, then herbivorous, and keep going.

• Productivity: the amount of living material produced per unit area per unit time.
• Primary productivity > Secondary productivity > Tertiary productivity.
• Food chain: a set of connected feeding levels of primary, secondary, and tertiary sources of productivity. Each organism occupies a trophic level.
• Food web: in more complicated systems, a simple chain cannot be constructed. A food web has many links and complex branching between and among the various trophic levels.

Keystone species: a predator at the top of a food web that exerts strong effects on competitive interactions and on the entire ecosystem. Their removal could cause a trophic cascade.

Food webs may be controlled by:

• Top-down processes where top predators have strong effects
• Bottom-up processes where changes in primary production drive changes in the food web

Strong top-down linkages or bottom-up linkages generate a trophic cascade through the food web.

The chemical and physical environment

Abiotic factors

Different parameter abiotic factors affect the marine environment, in the shallow area can change very fast:

• Measure of physiological performance
• Temperature
• Salinity
• Oxygen
• Light
• Cycles

Measure of physiological performance

Animals must have receptors to sense the change, such as eyes for the difference of light, which is translated into an adaptive response:

• Behavioral to escape an environmental change, most of the animals can move and escape;
• Biochemical changes, they can change the concentrations of hormones or enzymes;
• Physiological cellular changes at a large level
• Gene regulation, activation of genes

They use acclimatization: a change of function and tolerance that results in a change of response to new physiochemical conditions. If stress changes too high, the organism is able to do acclimatization and also die.

2 organisms:

• Regulators: organisms that can maintain constancy in their parameters despite environmental change.
• Conformers: organisms whose parameters and internal state change in conformance to environmental change.

Cost of metabolism is the greater energetic cost of overall cellular reactions.

Scope for growth: difference between the amount of energy assimilated and the cost of the metabolism. Differences in temperature tolerance by exposing groups of animals to different temperatures and measuring mortality after 24 hours. The LD50 is the temperature at which 50% cumulative mortality occurs. In this example, the shrimp, N. americana, appeared to be less tolerant of high temperature than the crab R. harrisii.

Temperature

The range in the ocean (-2 to +40) is lower than terrestrial (-88 to +58) because of the higher evaporation rate, ocean mixing, higher heat capacity of water, and ocean radiation. The temperature determines the distribution and abundance of the organisms, but also in the ocean, it can change very highly.

Latitudinal gradient: Atlantic Ocean is one with lower temperature. Polar water is about 0°C, and tropical water is constantly above 25°C. The marginal seas have restricted circulation and shallow depth have great annual ranges. In the deeper part, the temperature drops, but depending on the latitude, the temperature profile can acquire different:

• Low latitude: no season, same profile in summer and winter;
• Mid-latitude: strong thermocline warm in summer and cold in winter, no thermocline in winter only in summer;
• High latitude: the temperature is very low, no season always below 5° even in the shallower part.

Homeotherm organisms are the temperature regulators keeping the body at a constant level above that of the ambient environment.

• + constancy of cellular and biochemical reaction at high rate
• - higher temperature than seawater lead to heat loss

Poikilotherms organisms whose body temperature conforms to that of the ambient environment.

• + no cost of keeping high and constant temperature
• - low metabolic efficiency

There is an intermediate category such as strong-swimming fishes that have an intermediate status, some parts of the body have higher temperatures than seawater. Some intertidal animals are not true poikilotherms since they have temperatures lower than seawater. In fact, they developed this in order to avoid being heated. They can have a circulation of body fluids so can be dissipated, and evaporation allows heat loss to avoid overheating. Behavior mobile forms can move to burrows. The most important problems to the homeotherms are to reduce the loss of heat. 2 different systems:

• Insulated body surface, used by many vertebrates
• Countercurrent heat exchange, circulating venous and arterial blood in opposite directions