Adaptations and Responses to Physiochemical Conditions:

• Hutchinson, 1957: Fundamental niche - hypervolume (>3 axes) within which a species can survive or reproduce: 2 bivalve species (see graph)

• Realized niche - actually occupied by the species

• If niche is a lot smaller than the fundamental niche - genetic adaptations might be lost

• Thus, we would expect a loss of physiological adaptation to varying temperatures when a species has lived in a constant environment over time.

Time Scales:

• Ecological time vs. evolutionary time

• Ecological time - individuals in a population must respond to environmental change while restrained by genetic makeup

• Evolutionary time - time scale in which changes in genetic structure of species through time permit adaptations to change

• Acclimatization - changes in tolerance with seasonal environmental change

• If collect mussels from field and place in lab conditions that are different (i.e., temperature) the bivalves may survive - in doing so there may be a shift (i.e., oxygen consumption rate)

• Such a compensatory process is known as acclimation (see graphs)

Adaptive Response:

EA = EG + ER + EM

• A = energy assimilation/time

• G = growth

• R = reproduction

• M = respiration

S = EG + ER - EM : when surplus energy is available there is a positive (S) - E can be partitioned between somatic growth and gametes (see Fig. 2-3)

• Lethality is more commonly measured than scope for growth

• Experimental population kept at standard lab conditions permitting acclimation

• Lethal temperature can be determined by (a) slow decline or rise in temperature, or (b) rapid transfer of the lab-acclimated individual to a constant extreme temperature

• LD50 - lethal dose required to kill 50% of the experimental population after a specific shock time (24 hr common period) is determined

• LD50 - common to vary parameters (i.e.,Temp.) in steps, then interpolate LD50 (see Fig. 2-6)

Temperature:

• Probably the most pervasively important and best-studied environmental factor affecting marine organisms

• Large latitudinal gradient because many of our continents have N-S trending coasts

• Major shifts in marine biota at these latitudinal shifts (i.e., Cape Cod, MA, Cape Hatteras, NC, Point Conception, CA)

• Tropical intertidal invertebrates have lower body temperatures than would be predicted from an inanimate object

• Color of shells - temperature affects the rate of metabolic processes – example later

• Oxygen consumption - with an increase of 10°C, the corresponding change in metabolic rate as measured by O2 consumption is called the Q10 - for most poikilotherms, Q10 is 2-3. Q10 will decrease as the upper lethal limit is approached. Homeotherms regulate body temp. (marine mammals).

• Emerita talpoida - burrowing sand crabs common in surf zone on beaches - in the winter at 3°C, consume oxygen at a rate of 4x greater than animals collected in summer that are tested at the same temp. – results from acclimation.

Latitudinal gradients - oysters

• Crassostrea virginica and sea-squirt Ciona intestinalis, from different regions, have different breeding temperatures - termed physiological races

• Eurythermal- wide in temp. tolerance

•Stenothermal – narrow range in temp. tolerance

•Heat Death - protein denaturation - thermal deactivation of enzymes; lower solubility of oxygen at higher temperatures might limit the individual capacity for efficient respiration

• In algae, rate of photosynthesis typically decreases

Cold Temperatures:

• In tropical fishes, cold can depress the respiratory system and lead to anoxia and death

• Freezing in marine environments presents problems - fish larvae and forams - found encased in pack ice in Antarctic

• Body fluids freeze - intertidal fleshy algae can survive extended periods of -40°C and some -70°C shock for 24 hours

• Salts depress freezing point - similarly, freezing point depressed in organismal fluids

• In Labrador temperatures reach freezing points of seawater and cellular fluids of many invertebrates and fishes

• Shallow-water fish Trematomus counteracts freezing by synthesizing glycoproteins - which depress freezing point

• Temperature also affects growth and reproduction; in bivalves, members of the same species have been found to grow more slowly, but survive to older age and reach larger size in higher latitudes

• Pisaster ochraceus - gamete synthesis is correlated with temperature

• Temperature can also affect morphology - ribs on mussel shells - Mytilus edulis occurs in 2 color morphs, blue and light brown stripes. It has a genetic basis - blue mussels absorb more heat and have higher body temperatures than light brown mussels (blue morph inc. from VA to ME)

Salinity:

• Diffusion / Osmosis - see table 2-1

• Organisms actively regulate ionic concentration

• Scyphozoans and Ctenophores actively eliminate sulfate, replace it with a lighter ion - lowering overall specific gravity

• Some organisms are osmoconformers (or poikilosmotic) – others are osmoregulators

• Porphyra tenera in dilute seawater take up water and elongate over time

• Bivalve mollusks - do not osmoregulate extracellular fluids but do regulate the osmotic character of intracellular fluids

• They achieve constant volume by regulating the concentration of dissolved free amino acids; concentration of amino acids change with salinity gradient (Bayne et al., 1976)

• Lysozomes have been implicated at site of protein degradation and amino acid release

• Anguilla rostrata reproduce in Sargasso Sea and juveniles return to salt marshes; they mature and live in freshwater - Catadromous

• Fundulis leteroclitus can live in fresh and seawater

• Salmonids born in freshwater, migrate to sea, return to spawn

• Teleosts are hypoosmotic, subject to water loss in seawater, and salts must actually be eliminated to maintain lower salt content

• As Teleosts drink to maintain water balance - salts are also taken in - gills maintain salt balance by excreting salts (see Fig.)

• Elasmobranchs (sharks and rays) can also actively eliminate ions such as Na; high concentration of urea to maintain osmotic balance - similar to amino acids for bivalve mollusks

Oxygen:

• Controlled by diffusion and biological processes; oxygen increases with decrease in temperature

• Cold deep water - high or low oxygen?

• Photosynthetic plankton in shallow waters can supersaturate the water with oxygen

• Oxygen consumption - ml/g-1/hr-1

• ml oxygen cons. = kWb

• b = fitted exponent

• W = body weight

• k = constant

• Many poikilotherms have b less than 1.0, indicating that metabolic rate fails to increase linearly with increased body weight

• Several reasons:

1) surf./vol. ratio

2) increase in non-respiring mass (skeleton, fat) in organisms with respiratory apparatus

• Active species consume more oxygen (see Fig. 2-9)

• At low tide animals (infaunal) are subjected to oxygen depletion

• The end products of anaerobic metabolism (alanine and succinic acid) build up in tissues. In mollusks, a portion of the succinic acid is neutralized by dissolution of CaCO3. In winter the inner layer of the shell of Guekenzia demissa is pitted due to a dissolution process. Low temp. causes decrease in transport rates of oxygen to cell.

• Blood pigments (Hb) - Hemocyanin - copper pigment - Cephalopods (Limulus)

• More pigments in animals that live in environment with little or no oxygen - M. californianus consumes oxygen in air at comparable raters to its respiration in water (Bayne et al., 1976)

Waves and Currents - Table 2-3

Light:

• Ascophyllum nodosum & Fucus vesiculosus - photosynthetic rate relatively constant over a wide range of light regimes

• Acclimatization - changes in plant pigments

• chlorophyll-b, phycobiliproteins - dim light

• carotenoids - high light adaptation

Marine Biotic Diversity

• The # of species in a region is the end product of a long evolutionary process of speciation events balanced by extinction events

• There are less than 10 species of benthic forams in the northeastern U.S. shallow subtidal regions, but more than 80 living on the abyssal plain of the N. Atlantic. WHY? What evolutionary and ecological processes caused this?

Good Fossil Record Needed:

• 2 types of among-species change seem to accompany the evolution of diverse communities

1) Variety can be increased through the multiplication of trophic levels. This is a limited process because energy is lost through trophic levels (Slobodkin ca. 10% efficiency)

Inshore low-diversity plankton communities usually have about 3 trophic levels or more. Blue-water high diversity plankton communities rarely exceed 5 trophic levels

2) Increase in ecological specialization with increased diversity. Given that resources are limiting, the evolution and migration of species into communities should be accompanied by greater levels of specialization.

• Is there a limit to how diverse a community can get?

• Theoretically, the number of species cannot exceed the number of resources

• Eveness- Rare species are especially important in disturbed communities in the process of recovery. This will come out in this measure - unlike H’ which largely ignores common or rare species

•*Newly disturbed environments have low species richness. High dominance and hence low H’ and J’. With further succession, species richness increases, but dominance may be high due to competitive superiority of a few species. H’ generally increases in later successional stages.

• In any comparative study of diversity, a homogeneous habitat with few resources or microhabitats will support fewer species than one with more

• A comparison of diversities between 2 habitats of different structural complexity would be a between-habitat comparison

• A within-habitat approach is preferable in comparing diversity between different regions (i.e. muddy bottoms of the deep sea and muddy bottoms of shallow-water lagoons)

• Still problems - other variables change within

Patterns and Gradients of Species Diversity:

• Latitudinal - most well-known gradient is an increase of S from high to low latitudes in continental-shelf and planktonic organisms - see Fig. 5-2

• This pattern has been recorded in detail for bivalve mollusks, gastropods, plankton, forams, and many terrestrial groups

• Spight 1977 compared species richness to habitat diversity at differing latitudes

Prosobranch Gastropod Diversity

• Washington vs. Costa Rica beaches

• Spight found that the tropical site contained more habitat specialists. Substrate diversity was greater in tropics - not due to competing species

Between Ocean Basins:

• The Pacific Ocean has more species than the Atlantic. This fact has been documented for hermatypic corals, bivalves, fishes and probably most other groups

• Table 5-1 - Polychaetes are the exception; climate more variable on the east coast

Continental Shelf - Deep-Sea Gradient:

• Sanders 1968 - samples from mud bottoms ranging from shelf to deep-sea depths

• Diversity of polychaetes and bivalves increased dramatically with water depth

• Rex 1973 - similar pattern for benthic forams and gastropods

• Diversity decreased again from continental rise to the abyssal plain - decrease in food supply (will discuss Sanders later)

Inshore - Offshore Plankton Community:

• Temperate zone planktonic communities near shores (bays) support fewer species than offshore assemblages. Fewer trophic levels inshore

• Similar pattern can be seen from species-poor upwelling areas (i.e. Humbolt current off Peru) relative to high diversity blue-water plankton communities at the same latitudes

•Estuary versus open marine habitats: In estuaries, decrease in diversity often accompanied by expansion of the species that penetrate brackish water -relaxation of competiton - salinity gradient as well

Area:

• Habitat area - (MacArthur & Wilson 1967) -

• Islands - at a given distance from the mainland - larger islands support more species than smaller islands

• Also holds for species on continents (Flessa 1975)

• Area complicates matters when comparing the larger Pacific coral reef province with that of the smaller Caribbean province

Models Explaining Diversity Gradients:

• Stability-Time Hypothesis - Community in physically stable and geologically ancient environment accumulates more species than variable environments

• The age of an environment is thought to determine the extent to which more specialized species have been added

• This hypothesis finds support in the high species richness of large, stable, and ancient lakes (i.e.,Rift valley lakes of east Africa; Lake Baikal, Siberia)

• Unpredictable environments are thought to be more important in depressing diversity than predictable variable environments

• Sanders 1968 - fluctuating-environment, low diversity communities physically controlled and the constant-environment, high diversity communities biologically accommodated

•(not really true)

• The time aspect of the “hypothesis” is different to consider since it is based on ancient lakes (east Africa and Lake Baikal) and large young lakes such as the Great Lakes and Great Slave Lake of Canada. These lakes are only 11,000 years old or less - making them too young to expect major evolutionary events

• Furthermore, there is no evidence that the deep-sea is older than shelf or intertidal zones.

•Shallow water platforms have been present in varying abundance through geologic time (Valentine, 1973)

Abyssal faunas, if anything, are younger than shelf faunas – so the stability aspect seems to be more important.

Resource Stability:

• This explanation emphasizes the fluctuation of primary production and its role in selecting for generalized and specialized species (Valentine 1973, 1999)

Predation:

• Cropping of prey species prevents competitive displacement and allows the coexistence of more species

• Dayton & Hessler, 1972 - cropping increases diversity in deep-sea

• As diversity increases - the # of trophic levels increases - resulting in a greater incidence of predatory depression of competition in the lower trophic levels

• Competition Hypothesis difficult to test

• No current evidence that predation is more important quantitatively in tropics than in temperate zone

• However, it is true that trophic gastropods seem morphologically superior in resisting predation (Vermeij, 1977, 1998)

• Jackson 1977 presents compelling evidence that the co-occurring array of nearly 300 species of invertebrates living under colonies (cryptic species) of the foliaceous coral Agaricia do not experience much predation at all and occupy nearly 100% of the available space

Environmental Stress:

• An extreme environment can be successfully colonized by fewer species than a less extreme environment

• Although some species may inhabit hot springs (bacteria) most phyla have not evolved representatives capable of such an invasion

• Other Stress Zones: Highly polluted environments, estuaries, intertidal areas scoured by ice, hypersaline lagoons