damage due to the effects of liquefaction, lateral spreading, and bank collapse that occur when seismic ground
accelerations meet the shallow water tables, coastal and
fluvial deposits, and unsupported margins of estuarine
environments. As a result of infrastructure damage,
untreated sewage, nutrients, and industrial waste may be
released into estuaries in large volumes, posing significant
health risks to humans, shellfish, and other biota. Following the Canterbury, New Zealand, earthquake sequence of
2010–2011, initiated by the 7.1M w event in September
2010, estuarine sediment eutrophication and high levels
of pathogenic microbes continued for many months
(Christchurch City Council data), forcing recreational
beach closures of up to 12 months per event (Hart,
2011). The pulses of allochthonous fine sediments disturb
the estuary and can contain high levels of contaminants
such as trace metals, having negative impacts on estuarine
communities (Ilayaraja et al., 2012). Because of increased
anthropogenic modification of catchment and coastal
areas, sediments, and resources, the effects of earthquakes
may become more important in shaping biological communities in the future. Here we review the limited but
revealing records of the effects of twentieth- and early
twenty-first-century earthquakes and associated disturbances on estuarine communities and environment.
Habitat changes
The ecological effects of large-scale seismic events can be
negative or positive and persist for years, decades, and
centuries. For estuaries, which are by their nature transitional environments at the interface of fluvial and marine
systems, changes can be particularly persistent where significant subsidence or uplift occurs, resulting in changes
to their physical (e.g., salinity, exposure) and biological
zonation. In Chile, following the 1960 M w 9.5 Valdivia
earthquake and tsunami, land subsidence of more than
1 m in the Rio Cruces resulted in the creation of a large
wetland, which is now recognized as a Ramsar site with
high biodiversity. After the Chile 2010 M w 8.8 earthquake, habitat loss and sediment transport have led to the
formation of new coastlines with similar geomorphic and
habitat properties to those lost. Similarly, following the
M w 9.3 earthquake in the Indian Ocean, recovery of habitats was rapid following the large tsunami of Dec 2004
(Liew et al., 2010). Reports from various parts of the
world describe the scouring effects of debris-laden tsunami waters on coastal ecosystems, with sediment
removal resulting in the displacement and subsequent
removal to higher levels of animals and shells living above
mid-tide (Alaska and elsewhere, but not in Canterbury).
Where subsidence occurs against heavily modified hinterlands with artificially hardened or recontoured banks,
intertidal communities can be lost due to “coastal
squeeze.” Some of the best pre-quake salt marsh resources
of Christchurch City, for example, were lost after the
2010–2012 Canterbury earthquakes when the northern
end of the city’s estuary subsided in areas where housing
and stopbanks had been developed adjacent to the shoreline so that no landward space was available over which
the salt marsh could retreat.
Effects on estuarine species
Good Friday Great Alaska M w 9.2 earthquake of 1964,
and subsequent landslides and submarine slumping,
which triggered local tsunamis, produced the best
documented account of the effects of a seismic event on
coastal ecosystems. This account relates to the southern
coast of Alaska in Prince William Sound, a 9,000 km
semi-enclosed fjord-type estuary that is home to a highly
productive, relatively pristine ecosystem supporting
extensive populations of seabirds, marine mammals, and
fisheries. Vertical displacements of up to 10 m affected
the estuary’s intertidal mudflats, coastal vegetation, bird
nesting sites, and salmon streams (Hanna, 1971; Haven,
1971; Hubbard, 1971; Harwell et al., 2010). On land,
“ghost forests” were produced when saltwater inundation
and intrusion of the water table killed off and then preserved swathes of coastal pine. On a smaller scale, trees
and other terrestrial plants died off, and adjacent salt
marsh ecosystems were drowned, along the subsided margins of the Avon-Heathcote Estuary/Ihutai after the Christchurch earthquakes of 2010–2012.
The ecological effects of sudden catastrophic changes
in natural habitats have been widely debated with the suggestion that these result in long-term changes, involving
several generations of organisms and effects extending
over several years (Castilla and Oliva, 1990). The ecological effects of earthquakes on rocky outcrops are thought
to be less severe than for soft sediment ecosystems. Mussels, barnacles, and algae are attached organisms normally
found on mid- or lower intertidal rocky outcrops. These
organisms function as key indicator species and rarely survive coseismic uplift exceeding 2 m due to exposure to air,
temperature extremes, and desiccation. Mytilids suffered
100 % mortality following large earthquakes in Alaska
in 1964 and Chile in 2010 (Hanna, 1971; Castilla et al.,
2010). The 11–60 cm uplift recorded in Chile resulted in
initial mortality, shrinking the kelp band, and then the
downward vertical extension of kelp beds. The resultant
successional changes vacated space, which was invaded
by barnacles, enhancing the mosaic areas, increasing
diversity, and modifying the shoreline zonation (Castilla
and Oliva, 1990). Observations 2 years post-quake
recorded a reduction in biomass and no settlement of the
dominant mussel.
Following the 1964 earthquake disturbances in Prince
William Sound, Alaska, some communities appeared to
have recolonized areas within 15 months, with the initial
recolonizers differing from pre-quake species in terms of
fewer species and individuals. Successional trends were
obvious; the pre-earthquake Verrucaria zone was colonized
first by small filamentous algae and diatoms; and Fucus,
which had previously dominated the mid-intertidal areas,
was replaced by Porphyra in the upper littoral and
208
EARTHQUAKE DISTURBANCES
accelerations meet the shallow water tables, coastal and
fluvial deposits, and unsupported margins of estuarine
environments. As a result of infrastructure damage,
untreated sewage, nutrients, and industrial waste may be
released into estuaries in large volumes, posing significant
health risks to humans, shellfish, and other biota. Following the Canterbury, New Zealand, earthquake sequence of
2010–2011, initiated by the 7.1M w event in September
2010, estuarine sediment eutrophication and high levels
of pathogenic microbes continued for many months
(Christchurch City Council data), forcing recreational
beach closures of up to 12 months per event (Hart,
2011). The pulses of allochthonous fine sediments disturb
the estuary and can contain high levels of contaminants
such as trace metals, having negative impacts on estuarine
communities (Ilayaraja et al., 2012). Because of increased
anthropogenic modification of catchment and coastal
areas, sediments, and resources, the effects of earthquakes
may become more important in shaping biological communities in the future. Here we review the limited but
revealing records of the effects of twentieth- and early
twenty-first-century earthquakes and associated disturbances on estuarine communities and environment.
Habitat changes
The ecological effects of large-scale seismic events can be
negative or positive and persist for years, decades, and
centuries. For estuaries, which are by their nature transitional environments at the interface of fluvial and marine
systems, changes can be particularly persistent where significant subsidence or uplift occurs, resulting in changes
to their physical (e.g., salinity, exposure) and biological
zonation. In Chile, following the 1960 M w 9.5 Valdivia
earthquake and tsunami, land subsidence of more than
1 m in the Rio Cruces resulted in the creation of a large
wetland, which is now recognized as a Ramsar site with
high biodiversity. After the Chile 2010 M w 8.8 earthquake, habitat loss and sediment transport have led to the
formation of new coastlines with similar geomorphic and
habitat properties to those lost. Similarly, following the
M w 9.3 earthquake in the Indian Ocean, recovery of habitats was rapid following the large tsunami of Dec 2004
(Liew et al., 2010). Reports from various parts of the
world describe the scouring effects of debris-laden tsunami waters on coastal ecosystems, with sediment
removal resulting in the displacement and subsequent
removal to higher levels of animals and shells living above
mid-tide (Alaska and elsewhere, but not in Canterbury).
Where subsidence occurs against heavily modified hinterlands with artificially hardened or recontoured banks,
intertidal communities can be lost due to “coastal
squeeze.” Some of the best pre-quake salt marsh resources
of Christchurch City, for example, were lost after the
2010–2012 Canterbury earthquakes when the northern
end of the city’s estuary subsided in areas where housing
and stopbanks had been developed adjacent to the shoreline so that no landward space was available over which
the salt marsh could retreat.
Effects on estuarine species
Good Friday Great Alaska M w 9.2 earthquake of 1964,
and subsequent landslides and submarine slumping,
which triggered local tsunamis, produced the best
documented account of the effects of a seismic event on
coastal ecosystems. This account relates to the southern
coast of Alaska in Prince William Sound, a 9,000 km
semi-enclosed fjord-type estuary that is home to a highly
productive, relatively pristine ecosystem supporting
extensive populations of seabirds, marine mammals, and
fisheries. Vertical displacements of up to 10 m affected
the estuary’s intertidal mudflats, coastal vegetation, bird
nesting sites, and salmon streams (Hanna, 1971; Haven,
1971; Hubbard, 1971; Harwell et al., 2010). On land,
“ghost forests” were produced when saltwater inundation
and intrusion of the water table killed off and then preserved swathes of coastal pine. On a smaller scale, trees
and other terrestrial plants died off, and adjacent salt
marsh ecosystems were drowned, along the subsided margins of the Avon-Heathcote Estuary/Ihutai after the Christchurch earthquakes of 2010–2012.
The ecological effects of sudden catastrophic changes
in natural habitats have been widely debated with the suggestion that these result in long-term changes, involving
several generations of organisms and effects extending
over several years (Castilla and Oliva, 1990). The ecological effects of earthquakes on rocky outcrops are thought
to be less severe than for soft sediment ecosystems. Mussels, barnacles, and algae are attached organisms normally
found on mid- or lower intertidal rocky outcrops. These
organisms function as key indicator species and rarely survive coseismic uplift exceeding 2 m due to exposure to air,
temperature extremes, and desiccation. Mytilids suffered
100 % mortality following large earthquakes in Alaska
in 1964 and Chile in 2010 (Hanna, 1971; Castilla et al.,
2010). The 11–60 cm uplift recorded in Chile resulted in
initial mortality, shrinking the kelp band, and then the
downward vertical extension of kelp beds. The resultant
successional changes vacated space, which was invaded
by barnacles, enhancing the mosaic areas, increasing
diversity, and modifying the shoreline zonation (Castilla
and Oliva, 1990). Observations 2 years post-quake
recorded a reduction in biomass and no settlement of the
dominant mussel.
Following the 1964 earthquake disturbances in Prince
William Sound, Alaska, some communities appeared to
have recolonized areas within 15 months, with the initial
recolonizers differing from pre-quake species in terms of
fewer species and individuals. Successional trends were
obvious; the pre-earthquake Verrucaria zone was colonized
first by small filamentous algae and diatoms; and Fucus,
which had previously dominated the mid-intertidal areas,
was replaced by Porphyra in the upper littoral and
208
EARTHQUAKE DISTURBANCES