Marine Ecol

Marine Ecology exam notes


1 (a) Describe the nursery role concept and discuss how you would test which habitats were nursery habitats

  • Beck et al. (2001): "a habitat is a nursery for juveniles of a particular species if its contribution per unit area to the production of individuals that recruit to adult populations is greater, on average, than production from other habitats in which juveniles occur."
  • Dahlgren et al. (2006) - Effective Juvenile Habitat as a habitat for a particular species that contributes a greater proportion of individuals to the adult population than the mean level contributed by all habitats used by juveniles, regardless of area coverage. This definition compares overall contribution rather than per-unit-area.
  • Beck et al. (2001) also argue that "the ecological processes operating in nursery habitats, when compared to other habitats, must support greater contributions to adult recruitment from any combination of 4 factors: (1) density, (2) growth, (3) survival of juveniles and (4) movement to adult habitats."
  • Areas of high potential for transport of biomass (to other areas)
  • Past instances of seagrass loss have been linked to reductions in commercial species thought to be linked to the nursery habitats, however the associations were not always clear. The habitats could have been replaced with other communities (such as a macroalgae nursery) that provide a similar role, or unaffected nearby nurseries could take over.
  • Use otolith microchemistry to identify juvenile habitats of adults
  • Tagging of individuals, where possible
  • Juvenile habitats are assumed to have better food availability and lower predation risk - you could try to measure that.
  • analysis of size classes in different places
  • internal and external tags
  • stable isotopes (reflecting differences in food in different habitats)
  • trace elements
  • parasites as tags
  • freeze branding

1 (b) Describe the nursery role concept and discuss the evidence supporting mangrove habitats as nursery habitats.

  • Dahlgren et al - mangroves are effective juvenile habitats, but not nursery habitats due to their limited area.
  • Elemental fingerprinting of juveniles - Fry /et al./ (1999) used 15N isotope analysis to compare diet with fish and found limited support for mangroves as nurseries - seagrass meadows were a better fit.
  • Sheridan and Hays concluded that lower densities may be typical of mangroves when compared to seagrass, coral reef, marsh, and non-vegetated habitats. Little direct consumption of mangrove detritus by nekton. C, N, and S isotope studies reveal little retention of mangrove production by higher consumers. Experimental evidence indicates that mangrove roots and debris provide refuge for small nekton from predators. No evidence that more individuals move to adult habitats from mangroves than from alternate inshore habitats.
  • Few comparative studies of density and survival, none of growth and few for movement. Need more research.

2 (a) A new fishery is being developed. Describe what information you would require to determine whether the fishery is likely to be sustainable and discuss how marine protected areas may enhance the fishery.

  • Assess the growth of fish through mark-recapture experiments and examination of otoliths appearance, captive rearing.
  • Assess fecundity - frequency of spawning, number of eggs
  • MPA may allow fish numbers to build up such that they spill over to fished areas and sustain numbers, depending on species. Have been found to increase abundance near boundaries. Maintain population size/age structure. Preserve genetic diversity.

2 (b) Describe suitable monitoring studies for determining the effects of a marine protected area in the presence and absence of data prior to the marine protected area being setup.

  • Examine trophic web interactions - if MPA is intended to increase large carnivorous fish, examine how urchin abundance and size is influenced by the presence of MPA. This can be done before and after establishment, or by comparing similar habitats inside and outside the MPA and excluding fish inside.
  • Examine abundance, size and fecundity of fish before and after, inside and out
  • Examine density of substrate (kelp:barrens etc.)
  • BACIP - sampling paired in time

3 (a) What is landscape ecology? What are some of the ways ecological processes can vary as a function of the landscape context?

  • The study of processes occurring on spatially heterogeneous mosaics, and especially biotic responses to these spatial patterns
  • Physical scale varies with the organism being studied. Compare albatross to bacterium. Scale can be the extent of an environment encountered during an organism's life.
  • Size and fragmentation of patches can affect abundance, predation and survival
  • Shape and orientation of patches can affect abundance, species diversity and recruitment
  • The surrounding matrix can affect the faunal composition.

3 (b) Why are long-term ecological studies important? Give some examples of some of the processes that can only be studied using long-term studies and how these studies have influenced our understanding of ecology.

  • Not often studied
  • Ecological processes vary on many temporal scales, from minutes to millions of years.
  • For example, El Nino and La Nina operate 5-10 years and alter weather patterns, influencing drought, flood and fire in terrestrial systems, coral bleaching cyclones and upwelling in marine.
  • Climate change.
  • Interactions between short-term processes
  • Intrinsic processes - succession, learned behaviours
  • Study of rare events such as cyclones, fires and oil spills
  • Studies can be scaled to organism life-spams (as well as to the scale of movement of the organism)
  • Variability in ecological data can keep increasing over long periods of time. It takes decades (or longer) to see the full range of responses in a system.
  • Case study: Jamaica.
    • Reef had been overfished and affected by hurricanes and algae.
    • A combination of natural and anthropogenic influences caused a phase shift from corals to algae.
    • Almost no large fish remain. These were responsible for controlling algae, sea grass and sea urchins
    • Thick algal mats prevent recruitment of coral.
    • Lesson: the importance of ecological processes (such as competition) can vary greatly over time, depending on other conditions.
    • Lesson: many systems have a high degree of ecological resilience, but eventually some event will result in the ecosystem collapsing (the straw that breaks the camel's back)
    • Can't understand the notes at all! Read references.

4 a) Describe and discuss the potential benefits of improved knowledge about the biodiversity, life-cycles, ecology, biology and pathogenicity of marine parasites to South Australian aquaculture.

  • Concentration of any species in a confined area is likely to promote disease
  • Crowding increases stress
  • Parasites can exert destabilising influence.. kill or reduce quality of fish
  • Influence weight, reproduction, growth and population characteristics of the host
  • Understanding ecology and lifecycle allows intermediate hosts to be controlled (if they exist) or host and environmental conditions to be manipulated to reduce them.
  • Understanding if humans are possible intermediate hosts is important (eg for raw fish consumption)

4 (b) 'Being bisexual doubles your chances of finding a date'! In terms of marine parasites of fish, discuss this statement with reference to ideas about habitat selection, the distribution of hermaphrodite and dioecious parasites and niche restriction.

  • Parasites may be hermaphroditic, but self-fertilisation may not be as successful and lead to less fit offspring.
  • Niche restriction - parasites may be very specific about their location. Other species with similar reproductive organs may be spatially separated to prevent interspecific hybridisation.
  • Even if parasites are concentrated in one area, mathematical modeling suggests that the chance of encountering another individual during life span when moving randomly may be low. Bisexuality means that any encounter can potentially lead to reproduction.


3 (a) Discuss the importance of considering large spatial and/or temporal scales in ecology. Your answer should include specific examples of some of the unique insights studies at these scales give.

See above for temporal scale notes.

  • Different physical and biological processes act at different scales
  • Small-scale studies provide limited insight into regional or global phenomena
  • Organisms experience different evolutionary forces at different scales.
  • Sea grass example
    • Small scales - negative association due to competition
    • Medium scales - positive association because of habitat selection (both rely on shallow soft sediments)
    • Global scale - distribution might be climatically determined (eg restricted to temperate areas)
  • Local distribution can be determined by chance (who recruits there first). At wider scales, it might be more predictable due to habitat selection.

3 (b) Discuss the important differences between hard and soft substrate marine environments, and what the consequences of these differences are for the organisms living in these environments.

  • Soft sediment - sandy beaches, mudflats, seagrass meadows, mangrove forests, estuaries, subtidal sand/mud flats
    • Highly abundant. Poorly studied. Mobile. Few attachment points. Intertidal retains water. 3 dimensional. Infauna (= things live in substrates, esp soft)
    • Poorly studied because there are no fixed reference points, sampling is destructive, working at depth is harder, and it doesn't look as interesting.
    • Structuring processes - sediment supply, sediment sorting (water movement), oxygen supply. Biological - binding, bioturbation, competiton/predation
    • Sediment supply affected by coastal development, removal of macrofauna
    • Sediment characteristics influence biological assemblage - eg larger pore size gives space for interstitial fauna, oxygen content.
  • Hard - rock. Coral?
    • Relatively rare. Well studied. Stable. Abundant attachment points. Intertidal doesn't water. 2 dimensional. Epifauna (= things live on substrates)

4 (a) Explain niches as they may apply to marine parasites and discuss their biological function(s). Use information from experiments on parasites of fish to support your answer.

  • Niche - that combination of environmental variables, abiotic and biotic, which are capable of supporting life.
  • The place of an organism in the ecosystem, including its habitat and its effect on other organisms and the environment.
  • To describe a niche completely is impossible because there are likely to be an infinite number of parameters. A few niche dimensions are usually sufficient to describe an organism's niche with reasonable accuracy.
  • Intricately bound up with features of host biology. Host specificity, microhabitat, geographic range, sex and age of host, season.
  • Much harder to characterise niches for endoparasites because it's harder to quantify niche dimensions internally.
  • Niches are clearly restricted because there are no universal parasites.
  • How do numerous closely-related species, presumably making similar demands on available resources, survive?
    • Are all available niches filled by parasites?
    • Try to estimate the number of available niches and compare with number of existing parasite species
    • Parasite distribution could also be restricted due to interspecific competition (not much evidence), predation, hyperparasitism, reinforcement of reproductive barriers.
    • Modeling suggests that restriction to certain area dramatically increases chance of finding a mate within lifetime.

4 (b) Host-specificity and site-specificity are among the most noticeable, important and informative spatial distributions of marine parasites among potential hosts in the sea. Define and explain host- and site-specificity and discuss the factors that may influence them.

also, from notes - How may parasites be distributed among their marine hosts? In your answer, consider parasite distributions from a zoogeographic to a local, finer scale. What factors may contribute to observed distributions of marine parasites?

  • No parasite infects all animals - host specificity appears to be universal
  • Host specificity
    • Topographic relationship between parasite and host (attachment organs? Their size and morphology?)
    • Basic ecology - do parasite and host coexist?
    • Diet - what does a host organism eat? Does the definitive host consume an infected intermediate host or infective stage?
    • Physiological and environmental - pH, temperature, osmolarity, food, oxygen, metabolic rate.
    • Characteristics of host size, eg patterns of blood flow, food retention time, volumes of organs/tissues, diameters of ducts, length and morphology of gut
    • Immunological factors
  • Not all hosts of one species are infected
    • Density dependent processes.
    • Immunological factors
    • Parasite-induced host mortality when death rate of host is positively correlated with parasite burdens
    • Heterogeneity in host behaviour and immunity
    • Spatial heterogeneity in the distribution of parasite's infective stages (back to ecology)
    • Overdispersion is common - many hosts are 'empty' or almost empty. A few hosts are more heavily infected than would be expected randomly.
  • Site specificity
    • Parasites are not distributed randomly throughout body of the host. Microhabitats.
    • Appears to be the result of active behavioural discrimination by the parasite. Migrations from site of infection to final site.
    • Considerable energy spent doing this - nutrition sources? Protection from predation? Better opportunities to find a mate?
    • Specialization to sites - eg parasites that are adapted for particular sites and fit perfectly over them. Unable to live anywhere else.
    • Sites also have different variables - eg water flow, nutrition, proximity to other tissues.
    • Shaped by inter and intraspecific factors.
    • Overlap with morphologically similarly (eg male copulatory organ) may be avoided by partitioning available space in order to reduce chance of interspecific hybridisation and wasting gametes


3 (a) From your knowledge of marine parasitology, describe a plan outlining how you would increase our understanding of marine parasites in Australia. Why is this necessary? In your plan, cover the following aspects: aquaculture; life-cycle studies; parasite distributions; biodiversity surveys; assessment of the impacts of parasites; disease; imports, exports and quarantine (biosecurity).

3(b) What is a niche? Are all available niches on a marine host fish occupied by parasites? Explain Rohde's 'mating hypothesis' concerning niche restriction in some marine parasites from the gills of teleosts.

4 (a) Why is encrusting coralline algae or geniculate coralline algae one of the most important and widespread marine habitats of the globe?

Dunno. I think it was all about sea grass and algae this year.

4 (b) Describe the biology and life-history of one species of invertebrate that has invaded Australian waters. Explain why this species has successfully expanded its range and what efforts have been undertaken to stop more unwanted invaders.

5 (a) Explain why the isolation of habitats has negative effects on biodiversity when the amount of remnant habitat is sparse.

5 (b) Discuss the theory of patch dynamics and its application to marine ecology.

From example question list

Ectoparasites inhabiting the gills of marine fishes are thought to be good models to study various theories about the distribution of parasites in the sea. Discuss.

Discuss why an understanding of the ecology of marine parasites is important? Explain some of the difficulties inherent in studying parasites in the sea.

  • Ecology gives us an understanding of biogeography, pathology and disease, distributions, host species affected, their impact
  • Difficult to examine endoparasites in situ.. most studies kill the host.
  • Gill parasites more readily studied
  • Sole (/Entobdella soleae/) can be immobilised/killed and parasites attached.


1. (a) Describe the patterns of zonation of the dominant plants (i.e., zonal dominants - Spartina alterniflora, Spartina patens, Juncus gerardi) in salt marshes of the northeast USA. Explain the primary ecological processes determining these patterns of zonation (describing the experiments used to determine these processes would be helpful)

  • Physiological - can test for presence of heat shock proteins
  • Exclude grazing
  • Transplant experiments can test for physiological tolerance, but need to consider other factors such as food availability

(b) How do the processes determining the zonation of these salt marsh plants differ from those setting the upper and lower limits of distribution of species according to "Connell's Rule"

(c) If eutrophication (i.e., excess nutrient availability) of salt marshes in the northeast USA were to reverse the competitive hierarchy among zonal dominants, describe and explain how you might expect these new conditions to shift the patterns of plant abundance and change the ecological processes determining these patterns. What changes in the mechanism of plant competition could explain the shift in species distribution? (2 points)

2. Describe, explain, and compare the history of ideas concerning the ecological processes determining the patterns of zonation of species on rocky intertidal shores. (10 points)

3. Describe and explain how predation and disturbance can influence patterns of species diversity in marine communities. Give examples. (10 points)

MC notes

Lecture 1

  • Zonation
    • Repeatable patterns in the distribution of a species along a vertical gradient
    • Defined by species present, not tidal heights
  • What process structure upper boundary?
    • Physiological tolerances.
    • Sometimes grazing and recruitment (ie actually dispersing to the upper boundary)
  • What process structure lower boundary?
    • Competition
    • Sometimes predation and grazing
  • What alters patterns of zonation?
    • Wave action, topography of shore, type of shore, geography, types of organisms present
    • Not always a general phenomena
    • Variable in time and space and among species

Lecture 2

  • Recruitment is the time that an individual is observed to enter a defined population
  • Pre- and post-settlement processes can influence patterns of recruitment
    • Pre - availability of propagules, predation, water temperature, distribution and abundance of adult plants, dispersion of propagules - currents, wave action, condition, swimming ability, substratum type, dislodgement, chemical cues, presence of conspecifics
    • Post - grazing from fish, urchins, gastropods, micro-invertebrates etc. Remove, damage. Waves, scour (canopy species), smothering with sediment, competition from same species (density dependent survival), competition from other species.
  • The timing of clearances and their size and shape can determine what recruits
    • ie when bare space is created
  • The microhabitat and complexity of habitat into which an organism settles influences recruitment

Lecture 3

  • Synchronous gamete release - lunar, tidal, spawning aggregations
  • Release during 'calm' periods - low water motion, low or neap tides
    • Can sense height of tide with levels of blue and green light
    • Calmness can be detected by dissolved organic carbon (bicarbonate) levels in boundary layer around reproductive structures
  • Buoyancy - coral gametes float, seaweed sink.
  • Phototactic - seaweed sperm swim away from light
  • Pheromones
  • Sessile eggs, egg packets and mucous
  • Mechanisms to enhance fertilisation success might also restrict dispersal. Trade-off.

Lecture 4

  • Past dispersal can be inferred from microsatellite (fast mutation) or mtDNA (slow). mtDNA can be used to show where past barriers to dispersal were.
  • Should use a combination of direct and indirect genetic and ecological studies to test hypotheses regarding dispersal
  • Brooding vs spawning - may not be any difference in dispersal.