Lecture 2 Abiotic Influences on Distribution; Reproduction, Dispersal and Migration

Important Abiotic Influences on the Distribution of Marine Organisms Temperature Salinity Dissolved oxygen Light

Temperature Temperature variation is common in marine environment – Latitudinal temperature gradient, regional differences Marine species have thermal limits → geographic limits are fixed latitudinally – Seasonal temperature change Maximal in mid-latitudes and lowest at high latitudes – Short term changes (e.g., weather changes, tidal changes) – Intertidal – usually much greater daily and seasonal temperature ranges

Vertical Temperature Gradients Open Tropical OceanShallow Temperate Ocean

Temperature Tolerance Species evolve differences in temperature tolerance, e.g., Antarctic species may not be able to survive waters warmer than 10 °C Intertidal species usually tolerate a broader range of temperatures Populations living along a latitudinal gradient might evolve local physiological races, with different temperature responses – May be genetically different – May have just acclimated

Temperature Effects on Growth and Reproduction Growth and reproduction occur over a narrower range of temperature within the survival range Growth usually faster at higher temperatures – Organisms may grow more slowly but live longer in cooler waters Low-latitude range is limited by maximum summer temp High-latitude range is limited by minimum winter temp

Temperature and Reproduction Many organisms only spawn or reproduce at certain temperatures Temperature can determine whether some species will reproduce sexually or asexually Temperature can determine sex of developing embryos

Temperature can Control Seasonal Variation in Abundance FIG Seasonal variation in the abundance of colonies of the bryozoan Bugula neritinea in the northern Gulf of Mexico near the lowest latitudinal limit of its range. Because the organism is near the warm limit of its distribution, its abundance is greater in the colder part of the year. (Courtesy of M. Keough.)

Salinity Definition: g of dissolved salts per 1000g of seawater; units are o/oo or ppt or psu (practical salinity unit) Controlled by: * evaporation, sea-ice formation (↑ salinity) *precipitation, river runoff (↓ salinity) Salinity in open ocean is 32 to 37 ppt

Latitudinal Salinity Gradient Excess of evaporation over precipitation in mid-latitudes Excess of precipitation over evaporation at equator

Salinity Marine organisms generally tolerate a narrow range of salinity Salinity can change rapidly, especially in nearshore environments Marine organisms must maintain relatively constant chemical conditions within cell – Significant changes in cellular dissolved inorganics will affect function of proteins Various coping mechanisms

Oxygen in Seawater Oxygen from atmosphere dissolves in seawater at the sea surface Decreases with increasing temperature and salinity Also impacted by nutrient inputs Dissolved oxygen content is a balance between mixing with atmosphere and other oxygen-rich water bodies (+) and photosynthesis (+) and respiration (-)

Oxygen in Seawater Restriction of water circulation, decomposition of organic matter, and excess respiration can lead to anoxia (low oxygen levels) ksjtracker.mit.edu

Mississippi River Watershed

Oxygen Some habitats are low on oxygen – Low tide for many intertidal animals – Within sediment: often anoxic pore water – Oxygen minimum layers in water column: where organic matter accumulates at some depths – Seasonal oxygen changes as in estuaries: hypoxic zones, “dead zones”

Responses to Low Oxygen Levels Leave the area Decrease activity levels → reduces oxygen requirements Regulate oxygen consumption (oxygen concentration can reach a minimum where this is no longer possible) – Increase transport rates of water across gills – Increase retention efficiency Changes in blood chemistry, oxygen-binding pigments Fig 4.16

Jubilee!

Low-oxygen water on bay floor spreads into shallow waters due to a certain combination of wind direction, salinity, surface temperature, and tidal variation Organisms present in the shallow waters get trapped between the shore and the advancing mass of low-oxygen water Organisms are headed for the surface waters and waters very close to shore that usually have enough oxygen to support them for the short time frame of the jubilee

Jubilee! Almost always occur with an incoming tide and an easterly wind Usually occur in the hours just before dawn

Light Light = energy distributed in many wavelengths Light intensity declines with depth Ultraviolet and infrared wavelengths strongly attenuate with depth Surface light that is too intense can deactivate protein and DNA Too little light can limit plant growth

Light Supplies the energy used by autotrophs to convert inorganic matter into organic matter Can play a major role in behavioral adaptations – Diurnal vertical migrations, migration to and from feeding grounds, predator detection, choosing mates

Reproduction, Dispersal, and Migration

Sex and Reproduction SEX vs. REPRODUCTION Species can reproduce without sex (asexually) – Clonal growth involving fission (ex. corals, encrusting sponges, bryozoans) – Budding of individuals (ex. jellyfish, Hydra) –Fragmentation (ex. Some corals, annelids)

How Does Asexual Reproduction Occur? Budding - an offspring begins to form within or on a parent; the process is completed when the offspring breaks free and begins to grow on its own. The offspring is a miniature version of the parent. Fission - an individual simply splits into two or more descendants. Parthenogenesis - female offspring develop from unfertilized eggs. These offspring are genetically identical to the mother.

Asexual Reproduction Descendants are genetically identical - clone Colonial - individuals are genetically identical, comprise a module; each module may have arisen from a sexually formed zygote, which then underwent fission to asexually reproduce clonemodule

Asexual Reproduction Pros: – Lacks the cost of sexual reproduction – Allows spread of a successful genotype (in that habitat) – Occurs at a faster rate than sexual reproduction Cons: – No opportunity to spread to another habitat – Not much genetic diversity

Cost of Sexual Reproduction Sex involves expenditure of energy and time to find mates, combat among males So why even have sexual reproduction?

Sex and Genetic Diversity Sex increases combinations of genes Recombination produces variable gene combinations, meiosis enhances crossing over of chromosomes: new gene combinations and intragenic variants –Allows offspring to survive in a broader variety of habitats –Develop resistance to disease, parasites Asexual reproduction = clones → must wait for mutations to occur

Sexual Selection vs. Natural Selection Selection for extreme forms that breed more successfully - major claw of fiddler crabs, deer antlers, colors of male birds Can involve selection for display coloration, enhanced combat structures Female choice often involved; selection for fit males

Sexual Selection

Types of Sexuality Separate sexes = gonochoristic – Requires a mechanism for sperm transfer – Can be direct or through shedding of sperm (and possibly eggs) into water Hermaphroditism: individual can have male or female function, simultaneously or sequentially, during sexual maturity

Hermaphroditism Simultaneous – Egg and sperm cells are active within a single individual at the same time – Self-fertilization is rare Sequential – Start sexual maturity as one sex and then change into the opposite sex – Protandrous - first male, then female – Protogynous - first female, then male

Simultaneous Hermaphroditism - Acorn barnacles Barnacle penis

Sequential Hermaphroditism Protandry - size advantage model Producing eggs costs more energy than producing sperm Older/larger individuals have more available energy Being male when young/small allows for potential for producing many offspring with little energy investment Above a threshold size, females can parent more offspring because their available energy can produce more eggs Crassostrea virginica eastern oyster

Protogyny Male function must result in more offspring when male is older and larger Important when aggression is important in mating success, e.g., some fishes where males fight to maintain group of female mates Red grouper (Epinephelus morio)

Dwarf Parasitic Males Occurs in situations where it is difficult to find mates May either attach to females or reside very close to them Some males may be parasitic on the females

Factors in Reproductive Success Percent investment in reproduction - reproductive effort – The more energy that is devoted to reproduction, the less there is available for growth Age of first reproduction (generation time) Predictability of reproductive success/Environmental uncertainty Parental care Juvenile versus adult mortality rate

Life History Theory Tactics that maximize population growth Evolutionary “tactics”: variation in reproductive effort, age of reproduction, whether to reproduce more than once Presume that earlier investment in reproduction reduces resources available to invest in later growth and survival

Examples of Life History Tactics Strong variability in success of reproduction: reproduce more than once High adult mortality: earlier age of first reproduction, perhaps reproduce only once Low adult mortality: later age of first reproduction, reproduce more than once

Example: Selection in a Fishery Shrimp Pandalus jordani, protandrous Danish, Swedish catch – – stable, increased slowly – – catch tripled (2000  6300 ton/y)

Selection in a Fishery Average body size of catch decreased Threshold size of switching to females decreased – Females became rare due to fishing – New genetic variant appears that switches from male to female at a smaller size → produces more offspring – Natural selection for these variants → size of sex switch declines over time

Iteroparity vs. Semelparity Iteroparity: Having multiple reproductive cycles over the course of a lifetime Semelparity: Characterized by a single reproductive episode before death

Reproductive Tactics: r and K Selection MacArthur and Wilson (1967) r = Intrinsic (unlimited or exponential) rate of increase of a population K = the carrying capacity of the environment Individuals

Reproductive Tactics: r and K Selection r- selectedK-selected Age of 1 st ReproductionEarlyDelayed/Later Clutch SizeLargeSmall Semelparity or Iteroparity?SemelparityIteroparity Parental CareNoYes Reproductive EffortLargeSmall Generation TimeShortLonger OffspringSmall & Numerous Few, Large Assimilation EfficiencyLowHigh

Reproductive Tactics: r and K Selection r SelectionK Selection ClimateVariable or unpredictable; uncertain Fairly constant or predictable: more certain MortalityOften catastrophic, non- directed, density independent More directed, density dependent SurvivorshipOften Type IIIUsually Types I and II Population sizeTemporally variable; non- equilibrium; usually well below carrying capacity; recolonization each year Temporally constant; at or near carrying capacity; no recolonization necessary Intra- and Interspecific competition Variable, often laxUsually important Length of lifeShort, (usually < 1 year)Longer (usually > 1 year) Leads to…ProductivityEfficiency Stage in SuccessionEarlyLate, climax

Reproductive Tactics: r and K Selection Idea of r- and K-selection is a bit of an oversimplification Not all species in an environment will be r- or K- selected – Environment may result in r-selection for some species (e.g., copepods), and result in K-selection for others (e.g., whales) A species may have a combination of r- and K- selected traits (are an intermediate of the two types)

Survivorship Curves Type I - high survival in early and middle life, followed a rapid decline in survivorship in later life (Ex. humans) (K-selected) Type II -roughly constant mortality rate, regardless of age (Ex. Birds, squirrels) Type III - the greatest mortality is experienced early on in life, with relatively low rates of death past early stages (Ex. oysters, octopi)

Sex - Factors in Fertilization Planktonic sperm (and eggs in many cases): problem of timing, turbulence, polyspermy, specificity Direct sperm transfer (spermatophores, copulation): problem of finding mates (e.g., barnacles, timing of reproductive cycle)

Timing of Sperm and Egg Release Epidemic spawning - known in mussels, stimulus of one spawner causes other individuals to shed gametes Mass spawning - known in coral species, many species spawn on single nights Timing of spawning (also production of spores by seaweeds) at times of quiet water (slack high or low tide) to maximize fertilization rates. Also spawn in response to phytoplankton in water (ex. mussels)

Dispersal versus Migration Dispersal = Undirected spread of organisms, usually progeny, from one location to another Migration = A periodic directed movement of organisms between alternative habitats – Occur at predictable times – Anticipate unfavorable conditions → triggered by stimuli, biological clocks – Organisms must have sense of direction and be capable of active movement

Migration Scheme Maximizes reproductive success by feeding and spawning in sites that are optimal for that activity

Examples of Migratory Species

Migration Types DIADROMOUS = species that spend part of their lives in freshwater and part in saltwater – ANADROMOUS = live as adults in salt water, spawn in fresh water (shad, striped bass, sea lamprey), more common in higher latitudes – CATADROMOUS = live as adults in fresh water or tidal creeks, spawn in salt water (eel), more common in lower latitudes FULLY OCEANIC = feed and breed in oceanic coastal or open ocean environments (herring, cod, green turtle)

Migration Some migratory species are very site specific – return to same spawning/nesting sites Others have a lesser degree of homing – will return to a spawning ground, but maybe not the one they originated from

Herring Migration in the North Sea

Eel Migration in the Atlantic Ocean European: Anguilla anguilla, American: Anguilla rostrata

Larval Dispersal

Spatial Scales Microscale = centimeters-meters – Larvae move near final settlement site, select site, metamorphose into adult (recruitment) Mesoscale = meters-kilometers – Currents transport larvae from site of fertilization to near final settlement site Macroscale (Biogeographic Scale) = hundreds to thousands of kilometers – Currents can create isolated populations

Dispersal Types in Invertebrate Species PLANKTOTROPHIC LARVAE - feed on plankton, long dispersal time (weeks), some are very long distance - cross oceans (teleplanic). May be capable of delaying metamorphosis until suitable habitat is found LECITHOTROPHIC LARVAE – swimming larvae that depend on yolk from egg (no feeding or digestive structures), limited swimming ability. Dispersal lasts only a few hours to a day, limited distance ( m) DIRECT RELEASE - female lays eggs (oviparous) or bears live embryos (viviparous), juveniles released/hatch and crawl away. Shortest type of dispersal Species with more than one larval development mode = poecilogonic (ex. Sea slugs) – can depend on season/food availability

Lecithotrophic larva: tadpole larva of the colonial ascidian Botryllus schlosseri Planktotrophic larva of snail Cymatium parthenopetum Planktotrophic pluteus larva of an urchin

Reproductive Timing and Egg Size Must be timed to avoid gamete and larval death – Tidal cycles (daily high/low tides, spring tides) – Day/night Egg Size – Direct release > Lecithotropic > Planktotrophic Number of Eggs – Planktotrophic > Lecithotropic > Direct release

Macroscale: Separations and Biogeographic Structure Species with planktonic dispersal have greater geographic ranges than those without planktonic dispersal Biogeographic zones of shore benthic invertebrates in the western Atlantic

Macroscale: Barriers to Dispersal Distance – most planktonic larvae cannot cross broad oceans Separate current circulation systems Natural selection/suitable habitat

Mesoscale Large amounts of mortality with planktonic larvae Sources of larval mortality – predation, transport away from suitable habitat, food shortage

Movement of Benthic Larvae Swimming larvae can be carried away from appropriate habitats by water motion Planktonic larvae often settle near their origin due to cyclonic or returning currents

Coastal Species Larval Strategies Retention of larvae near suitable adult sites Use current systems to return to suitable sites Use seasonal flow reversals to move out to sea and then return to suitable coastal habitats

Larval Recruitment in Estuaries

Retention of Larvae in Estuaries Mud crab - Larvae rise on the flooding tide, sink to bottom on the ebbing tide

Movement of larvae to coastal waters, return of later stage larvae Blue crab, Callinectes sapidus

Problems of Planktonic Larvae Pre-settling problems: – Starvation – Predation in plankton – Loss to inappropriate habitats

Post-settling Problems Energetic cost of metamorphosis Predation Crowding --> mortality

So why disperse? Ensures that local habitat loss will not lead to extinction To avoid overcrowding Hedging bets - spread over habitats To take advantage of a phytoplankton food source Reduced likelihood of inbreeding