Disturbance in Marine Systems Flashcards
When does disturbance occur?
A disturbance has occurred when a force:
• Kills one or more resident organisms
• Stress that merely affects growth, but does not remove biomass is not a ‘disturbance’
Stress that that merely affects growth negatively but does not remove biomass is not technically defined as disturbance.
Define disturbance
“…. Any relatively discrete event in time, that disrupts ecosystem, community or population structure, and changes resources, substrate availability or the physical environment.”
White and Pickett, 1985
List some abiotic disturbance agents
Abiotic • ice scour • storm-related water motion • boulders, logs, sand scour • aerial exposure temperature extremes
List some biotic disturbance agents
Biotic • bulldozing • whiplashing • bioturbation • foraging by stingrays, dugongs
(predation and herbivory is not included)
WIDER READING: Abiotic disturbance agents
Brown et al 2004 - Ice Scour frequency effecting diversity
‘Links between the structure of an Antarctic shallow-water community and ice scour frequency’
• North cove hit twice as often as south cove
• North cove bryozoan communities had half the number of species and two thirds the space occupation
• Predict that ice scour disturbance at high latitudes is more significant than same magnitude of disturbance at lower latitudes due as high latitude communities have slower recovery rates.
WIDER READING: Biotic disturbance agents
Oliver and Slattery 1985 - Disturbance caused by feeding
‘Destruction and opportunity on the sea floor: effects of Gray Whale feeding’
· Gray Whales disrupt sea floor whilst feeding
· The numbers of some colonists remained elevated in disturbed areas for >2 mo.
· Early colonists were characterized by much greater abundances inside excavations relative to the adjacent tube mat
· Species were more abundant in excavations containing debris versus excavations without debris
(Eschrichtius robustus are highly disruptive bottom feeders that remove infaunal invertebrate prey and sediments by suction. The response of the benthos to gray whale feeding was examined in the primary feeding grounds of the Bering Sea and in an ecological analog of these prey communities along the W coast of Vancouver Island. Large feeding excavations (often 2-20m2) were rapidly colonized by scavenging lysianassid amphipods, especially Anonyx spp. that attacked injured and dislodged infauna. Many of the attacked animals were small crustaceans (<1cm long) and polychaete worms. Anonyx spp. was 20-30 times more abundant inside fresh excavations than in the surrounding tube mat, where they dispersed within hours after the initial feeding disturbance. A smaller species of lysianassid, Orchomene minuta, invaded less rapidly and remained much longer in excavations than the larger, Anonyx spp. Within days and weeks, gray whale feeding excavations trapped organic debris. Most invading species were much more abundant in debris patches compared to debris-free areas of the same excavations. The numbers of some colonists remained elevated in disturbed areas for >2mo.-from Authors)
Define bioturbation
The ongoing burrowing of animals through sediment, which can disrupt, bury and dislodge organisms, alongside positive effect such as aeration, deoxygenate and change the water chemistry of the interstitial area.
How do Features Of A Disturbance Regime Influence What Happens To The Community.
• Magnitude of disturbance
○ Intensity of force - what size boulders does a storm turn over?
○ Severity of disturbance - Split boulders to expose sterile rock surfaces, giving way to different succession
• Size of area affected. Scale depend on the dominant organisms you are considering zooplankon / mammals
• Shape of patch created. Different patch shape will affect the succession and recovery
• Location and Type (I or II)
• Temporal aspects
○ Frequency. This includes the extent to which an individual has grown and its inherent vulnerability, at the level of the population has it had the opportunity to reproduce? At the level of the community how succession has proceeded – community structure.
Connell et al., 1997 discusses a gradient of frequencies from very small percentages of an organisms lifespan to continuously occurring. Acute to chronic.
○ Timing. For example, storm events being more frequent in winter or more predation in the summer. (Kelp forests, southern California, disturbed by storms that vary among years depending on ENSO conditions (Dayton et al., 1992))
Duration
WIDER READING: Patch size and seasonality effecting succession after disturbance
Paine and levin 1981- Patch size and seasonality effecting succession after disturbance
‘Intertidal landscapes and disturbance: The dynamics of pattern’
• Winter disturbance regime is 5-10 greater than summer, and patches created are larger
• Small patches are removed quickly due to leaning response of neighbouring mussels
• ‘Lateral encroachment’ more important in recolonization of small patches than dispersal of propagules.
What are some forms of Resistance to natural disturbance?
Resistance to natural disturbance
• Individual attributes. Many macro-algae are highly resistant, and many seaweeds have two different morphological forms, upright foliose and low-lying crust forms. • Structural features and morphology • Size of individual (greater relative drag with greater size (area) greater acceleration forces with greater volume) • Age of individual • Reproductive status, after breeding and spawning nutritional reserves will be quite low, less able to sustain a disturbance impact. Genetic composition
Give two types of succession
○ Embedded - patch opens up in the middle of a habitat, for example a empty space in a mussel bed. Can be recolonised by the arrival of propagules and spores from the plankton or by lateral encroachment in from algae reproducing asexually or mussels moving in.
○ Isolated - when succession can only start through settlement in from planktonic propagules and larvae.
Intermediate Disturbance Hypothesis
- Put forward by Connell and Euston
- Low diversity with frequent disturbance as nearly all species have been removed.
- Low diversity when the competitive dominance outcompetes all other species with low disturbance
- At moderate levels of disturbance the competitive dominance is kept in check and removed and the highest diversity is reached.
WIDER READING: intermediate disturbance hypothesis
Souza 1979- paper reinforcing Intermediate disturbance hypothesis
‘Experimental Investigations of Disturbance and Ecological Succession in a Rocky Intertidal Algal Community’
· Overturning boulders through wave action= disturbance
· Intermediate-disturbance hypothesis experiment in a marine intertidal situation
· Small boulders were easily disturbed and only had a mean 1.7 sessile plant and animal species
· Large boulders were rarely moved by waves, and had a mean of 2.5 species
· Intermediate-sized boulders had the most species, with a mean of 3.7 species
The effects of disturbance on local species diversity were investigated in an algaldominated intertidal boulder field in southern California.
Large boulders also usually have fewer species, except in the spring, when defoliation of the algal canopy during the previous winter has opened space for colonization. Species richness on these boulders declines during summer months, and is less than that on boulders of intermediate size in the fall. Small boulders, with a shorter disturbance interval, support only sparse early successional communities of the green alga, Ulva, and barnacles. Large, infrequently disturbed boulders are dominated by the late successional red alga, Gigartina canaliculata. Intermediate—sized boulders support the most diverse communities composed of Ulva, barnacles, several middle successional species of red algae, and Gigartina canaliculata.
Key disturbance terms
• Resistance to disturbance
• Resilience is the capacity of a population or community to recover.
○ Elasticity: speed of return to original state
○ Amplitude: maximal disturbance from which a community can recover. Threshold over which species may not be able to bounce back.
Human disturbance:
• Human disturbances occur over longer times
○ chronic, persistent impacts, over large spatial scales
○ marine communities not adapted and response less predictable
• HD alters regime of natural disturbance or influences resistance and resilience to it
○ Habitat clearing and fragmentation; addition of pollutants; spread of alien species ; overharvesting of resources ; global climate change
• HD is a selective agent
○ e.g selective taking out of larger cod, shifting genetic profile
• HD disturbs incidentally as well as directly
○ e.g trampling seedlings while harvesting mangrove
