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Abstract

Understanding the resilience and recovery processes of coastal marine ecosystems is of increasing importance in the face of increasing disturbances and stressors. Large-scale, catastrophic events can re-set the structure and functioning of ecosystems, and potentially lead to different stable states. Such an event occurred in south-eastern New Zealand when a Mw 7.8 earthquake lifted the coastline by up to 6 m. This caused widespread mortality of intertidal algal and invertebrate communities over 130 km of coast. This study involved structured and detailed sampling of three intertidal zones at 16 sites nested into four degree of uplift (none, 0.4–1, 1.5–2.5, and 4.5–6 m). Recovery of large brown algal assemblages, the canopy species of which were almost entirely fucoids, were devastated by the uplift, and recovery after 4 years was generally poor except at sites with < 1 m of uplift. The physical infrastructural changes to reefs were severe, with intertidal emersion temperatures frequently above 35°C and up to 50°C, which was lethal to remnant populations and recruiting algae. Erosion of the reefs composed of soft sedimentary rocks was severe. Shifting sand and gravel covered some lower reef areas during storms, and the nearshore light environment was frequently below compensation points for algal production, especially for the largest fucoid Durvillaea antarctica/poha. Low uplift sites recovered much of their pre-earthquake assemblages, but only in the low tidal zone. The mid and high tidal zones of all uplifted sites remained depauperate. Fucoids recruited well in the low zone of low uplift sites but then were affected by a severe heat wave a year after the earthquake that reduced their cover. This was followed by a great increase in fleshy red algae, which then precluded recruitment of large brown algae. The interactions of species’ life histories and the altered physical and ecological infrastructure on which they rely are instructive for attempts to lessen manageable stressors in coastal environments and help future-proof against the effects of compounded impacts.
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ORIGINAL RESEARCH
published: 19 November 2021
doi: 10.3389/fevo.2021.767548
Edited by:
Yun-wei Dong,
Xiamen University, China
Reviewed by:
Maura Geraldine Chapman,
The University of Sydney, Australia
Nelson Valdivia,
Universidad Austral de Chile, Chile
Megan Tyrrell,
Waquoit Bay National Estuarine
Research Reserve, United States
*Correspondence:
David R. Schiel
david.schiel@canterbury.ac.nz
Specialty section:
This article was submitted to
Biogeography and Macroecology,
a section of the journal
Frontiers in Ecology and Evolution
Received: 31 August 2021
Accepted: 28 October 2021
Published: 19 November 2021
Citation:
Schiel DR, Gerrity S, Orchard S,
Alestra T, Dunmore RA, Falconer T,
Thomsen MS and Tait LW (2021)
Cataclysmic Disturbances to an
Intertidal Ecosystem: Loss
of Ecological Infrastructure Slows
Recovery of Biogenic Habitats
and Diversity.
Front. Ecol. Evol. 9:767548.
doi: 10.3389/fevo.2021.767548
Cataclysmic Disturbances to an
Intertidal Ecosystem: Loss of
Ecological Infrastructure Slows
Recovery of Biogenic Habitats and
Diversity
David R. Schiel1*, Shawn Gerrity1, Shane Orchard1, Tommaso Alestra1,
Robyn A. Dunmore2, Thomas Falconer1, Mads S. Thomsen1and Leigh W. Tait3
1Marine Ecology Research Group, School of Biological Science, University of Canterbury, Christchurch, New Zealand,
2Cawthron Institute, Nelson, New Zealand, 3National Institute of Water and Atmospheric Research, Christchurch,
New Zealand
Understanding the resilience and recovery processes of coastal marine ecosystems is
of increasing importance in the face of increasing disturbances and stressors. Large-
scale, catastrophic events can re-set the structure and functioning of ecosystems,
and potentially lead to different stable states. Such an event occurred in south-eastern
New Zealand when a Mw 7.8 earthquake lifted the coastline by up to 6 m. This caused
widespread mortality of intertidal algal and invertebrate communities over 130 km of
coast. This study involved structured and detailed sampling of three intertidal zones
at 16 sites nested into four degree of uplift (none, 0.4–1, 1.5–2.5, and 4.5–6 m).
Recovery of large brown algal assemblages, the canopy species of which were almost
entirely fucoids, were devastated by the uplift, and recovery after 4 years was generally
poor except at sites with <1 m of uplift. The physical infrastructural changes to
reefs were severe, with intertidal emersion temperatures frequently above 35C and
up to 50C, which was lethal to remnant populations and recruiting algae. Erosion of
the reefs composed of soft sedimentary rocks was severe. Shifting sand and gravel
covered some lower reef areas during storms, and the nearshore light environment
was frequently below compensation points for algal production, especially for the
largest fucoid Durvillaea antarctica/poha. Low uplift sites recovered much of their pre-
earthquake assemblages, but only in the low tidal zone. The mid and high tidal zones
of all uplifted sites remained depauperate. Fucoids recruited well in the low zone of low
uplift sites but then were affected by a severe heat wave a year after the earthquake that
reduced their cover. This was followed by a great increase in fleshy red algae, which then
precluded recruitment of large brown algae. The interactions of species’ life histories and
the altered physical and ecological infrastructure on which they rely are instructive for
attempts to lessen manageable stressors in coastal environments and help future-proof
against the effects of compounded impacts.
Keywords: earthquake, intertidal, communities, resilience, recovery, fucoid, algae, invertebrate
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Schiel et al. Intertidal Community Response to Cataclysmic Earthquake
INTRODUCTION
There has been renewed interest in large and usually infrequent
disturbances. As the pace of change in climatic extremes
has increased, there is an increasingly urgent need to better
understand processes underlying the persistence, resistance,
resilience, adaptive capacity and recovery from events such as
catastrophic fires, heat waves, hurricanes, and floods across
all of earth’s ecosystems (Lubchenco and Karl, 2012). Such
understanding is a fundamental requirement for the design
of effective management (Dale et al., 1998;Chambers et al.,
2019). The basic concept involves attention to the vulnerabilities
and resilience of ecosystems and communities. Hollings (1973)
initial definition of resilience was a measure of the ability of
systems to absorb changes of state and driving variables, and
yet still persist, and stability as the ability of a system to return
to an equilibrium state after a temporary disturbance. Many
definitions and the implications of component processes and
thresholds have been a focus of subsequent discussions (e.g.,
Walker et al., 2004;Brand and Jax, 2007). The severity or
intensity, frequency or return time, and scale of disturbances
have been repeatedly highlighted as features that underpin
the robustness of ecosystems and their ability to resist and
recover from disturbance (e.g., Levin and Lubchenco, 2008).
Large disturbances can re-set the “successional clock,” leaving a
residual assemblage that provides a legacy on which subsequent
patterns build (Paine et al., 1998). Falk et al. (2019) state that
resilience responses are emergent properties from the component
processes of persistence, recovery and re-organization. Recovery
is influenced by the spatial and temporal scale of initial impacts,
as well as the interactions and requirements of key species in the
post-disturbance environment. Depending on all of these factors,
an ecosystem may or may not return to its former state.
Many recovery outcomes depend on the extent to which the
fundamental ecological “infrastructure” has been altered by a
disturbance. The concept of “ecosystems as infrastructure” has
been discussed since the 1980s and has many definitions and
uses involving the elements of inter-related systems providing
goods and services to humans (Fulmer, 2009;da Silva and
Wheeler, 2017). The concept can be extended, however, to
include inter-relationships between species, and the provision
of conditions conducive to the survival and persistence of the
ecosystems themselves. These “goods and services” of their own
making underpin the health and resilience of many characteristic
ecosystems, particularly those that have become adapted to
survive and thrive in harsh environments.
In the case of intertidal marine systems, much of the
biophysical infrastructure on which species and communities
build is affected by a wide range of stressors operating over
many spatial and temporal scales. The litany of stressors is long
and includes eutrophication, marine heat waves, overfishing,
invasive species, storms and wave events, coastal development,
and sediment from intensive land use, among others (e.g., Schiel,
2009), and additional step-change events (e.g., Orchard et al.,
2021). Each of these is known to affect coastal ecosystems through
impacts on vulnerable species, ecological structure, and diversity,
thereby altering ecological functions and services. Although
highly context-dependent because of varying species’ life history
traits, life spans and ecological niches, natural recovery is
compromised by the degree of change in the physical conditions
on which they rely and to which they have adapted (e.g., Bekkby
et al., 2020). On nearshore rocky reefs, such changes may involve
increased air or sea temperatures (Schiel et al., 2004;Cavanaugh
et al., 2019;Smale et al., 2019;Thomsen et al., 2019), smothering
by sediments (Airoldi, 2003;Schiel, 2006), a compromised light
environment in the water column (Tait et al., 2021), human access
and direct impacts on reef communities (Povey and Keough,
1991;Schiel and Taylor, 1999;Van De Werfhorst and Pearse,
2007), and altered wave forces (Denny, 1985;Gaylord and Denny,
1997;Schiel et al., 2016), all of which can affect the fundamental
requirements of benthic species to attach, survive and thrive.
These issues came to the fore when a large earthquake struck
the northeast coast of the South Island of New Zealand (NZ)
in November 2016. The Mw 7.8 Kaikôura earthquake event was
one of the most complex ever recorded (Hamling et al., 2017;
Holden et al., 2017;Shi et al., 2017;Xu et al., 2018). Although
originating inland, the stress release activated a large number of
faults in a northeasterly direction affecting extensive areas of land
and sea (Clark et al., 2017;Hamling et al., 2017;Gusman et al.,
2018). Vertical displacement affected over 130 km of coastline
in a highly variable manner but predominantly in the direction
of uplift (Clark et al., 2017;Orchard et al., 2021). Impacts on
anthropogenic infrastructure included severe damage to road
and rail networks that run close to the sea in this area (Kaiser
et al., 2017). Major changes to relative sea-levels, associated with
displacement, caused long-lasting effects in comparison to the
tidal range of c.2 m. Broad-scale land and seascape changes
included the generation of over 170 ha of new terrestrial land
and extensive remodeling of intertidal ecosystems (Orchard et al.,
2021). Environmental impacts included widespread mortality of
algae, invertebrates and fish along virtually the entire coastline,
which effectively reset the nearshore ecosystem (Schiel et al.,
2019). Some remnant populations remained in areas of lesser
uplift but the natural stage was mostly a blank slate for the
ecological communities to re-assemble (Orchard et al., 2021).
Ecological resilience was greatly tested, with “recovery” to the
former state being far from certain because of the loss of
connectivity between remaining patches of key habitat-formers
such as large algal species. Previous small-scale experiments in
which dominant algal canopies had been removed showed that
it took up to 8 years for canopies to re-develop and associated
communities to re-assemble, even though clearances of <10 m2
were surrounded by reproductively active adults (Lilley and
Schiel, 2006;Schiel and Lilley, 2011).
Initial post-earthquake surveys showed that some species of
large brown algae, almost all of them fucoids, were functionally
extinct along many areas of the uplifted coast, so there were few
local sources of propagules to re-colonize affected areas (Schiel
et al., 2019;Thomsen et al., 2019). It was anticipated, therefore,
that re-establishment of algal assemblages would take many years,
and that there would likely be a successional sequence as canopies
re-formed and understory species that relied on facilitative
effects of canopy cover eventually became established (Schiel
and Lilley, 2007). There was also ongoing disturbance from
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post-earthquake shifting of gravels and sand that buried some
reefs, while erosion effects were prominent at others (Orchard
et al., 2021). Invertebrate populations suffered high mortality
with most limpets, and turbinid and trochid gastropods dying
relatively soon after the earthquake. Of particular importance
economically was the great mortality of NZ black-foot abalone,
Haliotis iris (Gerrity et al., 2020). Tens of thousands of individuals
were propelled upwards beyond the tidal influence where they
suffered severe heat stress and died (picture in Schiel et al.,
2019). Their recruitment habitats among small rocks in the lowest
intertidal and upper subtidal zone were also uplifted along much
of the coast, causing concerns about future recruitment rates.
The earthquake, therefore, provided a novel opportunity
to test recovery dynamics of a severe and rare large-scale
disturbance on a coastal marine system. Other similar studies,
primarily from earthquake-prone Chile (e.g., Castilla, 1988;
Castilla et al., 2010;Jaramillo et al., 2012;Ortega et al., 2014) and
Japan (Sato and Chiba, 2016;Muraoka et al., 2017) have shown
multi-year effects on the recovery of both soft shore and rocky
reef communities.
The initial hypothesis of our study was that the intertidal
zone would eventually shift downward to re-establish on newly
available boulders and reefs pushed up from the subtidal zone.
We set out to test this with intensive, field-based quantitative
surveys done annually for 4 years after the earthquake. To
relate recovery dynamics and trajectories to physical changes, we
monitored temperatures at many sites, gauged erosion and break-
up of the soft sedimentary rocks and substrate accretion effects,
and monitored the nearshore light environment. We evaluated
changes across tidal zones relative to the initial community
structure, which was known from surveys and prior data. We also
tested to what extent recovery was related to the degree of uplift,
as a gauge of the degree of initial disturbance and relative sea-
level change. The results facilitate an evaluation of the recovery
dynamics and resilience of this complex reef system.
MATERIALS AND METHODS
Sites and Design
The Mw 7.8 earthquake struck just after midnight, at low tide on
14 November 2016, near the start of austral summer. The coastal
zone was lifted by up to c. 6 m around Waipapa Bay, over 2 m
near Cape Campbell in the north, <1 m on Kaikôura Peninsula,
and around 1.7 m at Omihi further south with a considerable
degree of variation between sites in localized areas (Orchard et al.,
2021;Figure 1). Coastal cliffs fell over the main coastal highway
in many places, blocking access from the north and south, and
roads remained closed for over a year. The coast is sparsely
populated except around the town of Kaikôura, which is a major
tourism destination, and access to coastal sites was difficult. There
were few detailed data for intertidal and subtidal communities
along this coast except for sites to the north and south, which
have been surveyed annually for >20 y (Schiel, 2011, 2019).
Nevertheless, we were able to access sites via air within a week
of the earthquake to begin structured surveys of the former
intertidal zone over the following few weeks when most species
were readily identifiable, even down to small understory species.
From these data we established the pre-earthquake condition
of most of our sites, which serves as a reference for recovery
over the past four years. The extensive rocky shore habitats
of this coast support a rich diversity of intertidal and shallow
subtidal marine species including habitat-dominating seaweeds,
understory species, rock lobsters, New Zealand abalone (pâua)
and other invertebrates (Lilley and Schiel, 2006;Schiel, 2006;
Gerrity et al., 2020). Physical habitats include a wide variety
of substrate types and topographies including near-horizontal
platforms and extensive boulder fields, interspersed with dynamic
mixed sand-gravel and sandy beaches.
Intertidal Community Surveys
Intertidal surveys were done at eight locations. Replicate sites
(usually two) within each location were separated by at least 500
m. Sites and locations were selected to encompass the length of
the earthquake-affected coastline and represent different levels
of uplift. These were: control (no uplift); low uplift (0.5–1.4
m); medium uplift (1.5–2.5 m); high uplift (4–5.5 m, Figure 1).
Many were areas of particular ecological, cultural, or commercial
importance. Note that there were no unaffected sites to the north
that could serve as “controls” due to the predominance of sandy
beaches in this area. Rocky reefs and boulders occupy around a
third of the earthquake-affected coastline (Gerrity et al., 2020;
Orchard et al., 2021). Around 2 km of coastline experienced
uplift beyond 4 m.
Surveys were done along 30 m permanent transects, one
each within three intertidal zones (low, mid, and high) that are
associated with characteristic flora and fauna and have been
the subject of many years of surveys and experimental studies
on South Island shores (Schiel, 2011). We tried to sample on
the lowest tides, generally 0–0.2 above Lowest Astronomical
Tide (LAT), with the tidal range being 2 m (Land Information
New Zealand, 2018). Tidal heights for the three zones varied
by wave exposure but were generally around 0–0.5 m, 0.6–1.2
m, and >1.2 m above LAT. Initial sampling was completed
immediately after the earthquake in the former high, mid and
low zones. Most of the uplifted organisms died and disappeared
within several weeks. Subsequent “post-earthquake” surveys were
done in the newly formed equivalent zones, and these comprise
the time series on which recovery trajectories are based. Algae
and invertebrates were identified to species level when feasible
or to the finest possible taxonomic resolution. Their abundances
were recorded in ten 1 m2quadrats located randomly along the
30 m transect in each tidal zone. Abundances were expressed
as% cover for sessile organisms and as counts for mobile animals
(mostly gastropods).
Intertidal community structure was analyzed statistically
using a distance-based permutational analysis (PERMANOVA),
testing for differences on the final sampling date among uplift
groups and sites within them (Uplift- fixed, 4 levels: Control,
low, medium, high, and Site- random, nested within Uplift,
16 levels). Data were square-root transformed to de-emphasize
the influence of abundant taxa, and analyses were based on
Bray-Curtis similarities. For the Bray-Curtis similarity matrices,
a dummy variable of 0.01 was used so that double zero data
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FIGURE 1 | The sites used for repeated monitoring were within 8 “locations,” across c.130 km of coastline. The numbers in brackets indicate the number of sites
per location. Uplift categories are indicated. Inset shows the km of coastline within different substratum categories (from Orchard et al., 2021). Sampling was done
only in “rocky reef” and “boulder” habitats.
were treated as 100% similar. SIMPER was used to identify taxa
contributing to dissimilarity between communities (PRIMER,
Clarke and Gorley, 2015). The results included here mainly
relate to broad taxonomic groups (i.e., groups of species
sharing common morphological and life-history traits: canopy-
forming large brown algae, lower lying fleshy red algae, and
limpets) and not to individual species. PERMANOVA was also
used to test uplift and site effects on the full community in
the last survey. Principal Coordinate Analysis was used for
multidimensional scaling graphs.
The relationship between the degree of uplift and the% cover
of large brown algae was tested using an exponential decay model
with log-data. The relationship in abundance trends of large
brown and fleshy red algae was further explored using a mixed-
effects linear regression model including the cover of large brown
algae as the response variable and that of fleshy red algae as a
fixed effect. Sites were treated as random effects to account for
the geographical heterogeneity of the surveys and to partition
among- and within-site variability. A random intercept model
was used and conditional and marginal pseudo-coefficients of
determination were calculated to account for the proportion of
variance explained by the fixed factor alone and the proportion
of variance explained by both the fixed and random factors (so
it accounts for site-by-site differences in addition to the effect of
the fixed factor). To address the large variability in the data, a
quantile regression model was also developed to test whether the
relationship between these algal classes remained stable across
the entire range of the data set. One site (Waipapa Bay 1)
was excluded from analyses because large brown and fleshy red
algae were absent.
Temperature and Light
HOBO temperature data loggers were placed in the low, medium
and high tidal zones of each site, and maintained over the study.
These were used to assess thermal conditions over the study,
and were placed in areas adjacent to our survey transects. Some
loggers failed (as is typical) so data sets are not always complete.
Each logger was attached to a cage on the reef, so they were not
in touch with the reef itself. This provided an accurate assessment
of near-reef temperatures of air and water as the tide came in, but
not of the surface temperatures of the rocks themselves on which
organisms settled.
To gauge the light environment, PAR (photosynthetically
active radiation) loggers (OdysseyR
, Dataflow Systems Ltd) were
deployed in the shallow subtidal zone, and above maximum high
water at four locations 16 months post-earthquake (February
2018). These loggers were set to record integrated irradiance
every 10 min and were downloaded and cleaned every 2 months
for 1 year. Antifouling paint was applied to the top of the
sensors (avoiding the sensor) and very little fouling of the
sensors was observed over the course of the deployments.
Using PAR data collected in the subtidal and at the surface,
the daily PFD (photo flux density) was calculated. With daily
PFD from the surface and at depth (average depth of the
subtidal sensor accounting for tidal flux) the diffuse attenuation
coefficient [Kd (PAR), hereafter referred to as Kd] was calculated
daily. The daily Kd, the surface PFD and the compensating
irradiance of Durvillaea antarctica/poha (Tait et al., 2015) were
used to calculate the maximum habitable depth threshold for
this important foundation species (see Tait, 2019). We then
examined the proportion of days for which maximum habitat
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Schiel et al. Intertidal Community Response to Cataclysmic Earthquake
depth thresholds were shallower than 10 m (as an indication of
light levels which may affect productivity of this species) and
shallower than 5 m (as an indication of light levels which threaten
growth, reproduction and survival).
RESULTS
The most obvious change to the habitats after the earthquake
involved widespread algal mortality on the uplifted reefs. For
example, Wairepo Reef (Kaikôura) is one of the most studied
reefs in NZ and was noted for its lush beds of the desiccation-
resistant fucoid alga Hormosira banksii (Table 1) across large
stretches of the reef platform. Numerous experimental studies
showed the high diversity of its understory, comprised of over
100 species, many of which relied on the moist canopy cover
of Hormosira (e.g., Lilley and Schiel, 2006). This reef was lifted
by c 0.9 m (Orchard et al., 2021). Temperatures spiked quickly
after the earthquake, reaching well over 30C on many daytime
low tides for the next month (Figure 2A). Water still covered
this reef at high tide, but emersion times increased to 4–4.5 h in
the semi-diurnal tidal cycle. Virtually all algae disappeared from
this extensive series of platforms over several weeks (Schiel et al.,
2019). This pattern of high temperatures in the new mid and
low tidal zones persisted in subsequent summers. From winter
2018 to mid-summer 2019, for example, the temperatures in these
tidal zones frequently exceeded 35C for protracted periods from
December onward (Figure 2B). Any large algae that had recruited
over the cooler months could be seen to be desiccating and then
dying. This was especially evident in the summer of 2017–18
(Figure 3A) when a severe marine heat wave affected the coast
of southern NZ, and in conjunction with very low tides and hot
air temperatures caused mass mortality of intertidal seaweeds
along the east coast of the South Island (Thomsen et al., 2019).
Experimental data showed that when a canopy of Hormosira was
artificially placed onto a reef, temperatures below the canopy
never reached a lethal level over the hottest part of summer
(2018–19), indicating the potential facilitative effects of a canopy,
should one become established, on species below (Figure 3B).
One of the formerly dominant species in the low tidal
zone along the exposed coast was Durvillaea antarctica/poha
(these two species occupy the same habitats and are generally
indistinguishable in the field; Fraser et al., 2009, 2012). Durvillaea
species have a massive holdfast, thick stipe, and long leathery
blades that both dampen the swell (Hay and South, 1979) and
affect the understory species’ composition (Santelices et al., 1980;
Westermeier et al., 1994). Durvillaea had high mortality on
virtually all reefs due to uplift and desiccation, and population
recovery has been slow. The analysis of the maximum habitable
depth threshold for Durvillaea showed that some of the most
uplifted sites were frequently light-limited (Figure 4A). For
example, Waipapa Bay sites experienced >5 m of uplift that
was followed by numerous high-sediment events during rainfall
because of the erosion of earthquake-damaged hills in nearby
catchments, and the light environment was frequently below its
compensation point (Figure 4A). An initial cover of bull kelp
of around 55% at these sites has remained at zero after 4 years.
There was some recovery of Durvillaea at Omihi (from around
30% cover pre-earthquake to around 15% cover after 4 years), a
site of around 1.7 m of uplift. This site frequently experienced
TABLE 1 | Key habitat-forming large brown algae in the study area.
Species Zone Repro season Life span (year) Notes related to earthquake effects
Durvillaea
antarctica/poha
Very low
intertidal
Winter >10 Abundant at most sites pre-EQ; virtually disappeared post-EQ and poor
recovery; grows to 10 m long as adults, with great biomass (>20 kg)
Durvillaea willana Shallow
subtidal
Winter >10 Greatly affected by EQ; occasionally found in lowest tidal zone; fronds grow
to several m; great biomass (>20 kg per individual)
Carpophyllum
maschalocarpum
Low intertidal
band
Spring-summer Prob v long-lived Very tough, dense intertwined holdfasts; fronds up to 40 cm; high initial
mortality in some sites, but recovered well in sites it previously occupied
Cystophora
torulosa
Lower-mid
intertidal
Spring-summer c. 7 Common and abundant pre-EQ; high initial mortality; recovery observed in
some places
Cystophora
retroflexa
Lower-mid
intertidal
Spring-summer c. 7 Not as abundant as C. torulosa, tends to occur slightly lower on shore; high
initial mortality, some recovery observed
Cystophora
scalaris
Low intertidal Spring-summer c. 7 Least abundant of the Cystophora spp.; mostly found in tide pools and
found only in a few sites in any abundance post-EQ
Hormosira banksii Mid intertidal Year round c. 7 This species was ubiquitous in the mid-intertidal zone of rocky reefs;
provides extensive cover on reef platforms, biomass up to 6 kg/m2wet wt.
Extensive post-EQ mortality and little recovery despite being the most
desiccation-resistant fucoid.
Marginarialla
boryana
Subtidal Spring-summer ??? Mainly a subtidal species that occurs occasionally in the lowest tidal zone
on exposed shores; high initial mortality post-EQ, but recovered slightly in
some places
Lessonia
variegata
Subtidal Winter ???, but probably
long-lived
A laminarian species; mainly subtidal that occurs occasionally in the lowest
tidal zone on exposed shores; high initial mortality post-EQ, but recovered
slightly in some places
Only species with >1% cover at any time are shown. Estimates of reproductive periodicity and life span are derived mostly from long-term experimental studies of the
authors. ??? = unknown.
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FIGURE 2 | (A) Temperatures within the mid-tide Hormosira zone of Wairepo
Reef, Kaikoura, before, during and after the earthquake on 14 November
2016; vertical line indicates timing of the earthquake. (B) Maximum daily
temperatures for the upper mid (red) and lower mid tidal zones at Wairepo
Reef, Kaikoura from 2018 to 2019. Inset line indicates approximate lethal
temperature for fucoid algae exposed for c 4 h at low tide.
a compromised light environment below the depth threshold.
Furthermore, a moderate rainfall event in April 2018 caused an
immediate and dramatic reduction in light availability for all
sites monitored, the effects of which lasted for several weeks,
especially at Waipapa (Figure 4B). Across the full time series,
the Waipapa sites experienced very shallow maximum habitable
depth thresholds 30% of the time, while the two least uplifted sites
had sufficient light >70% of the time (Figure 4C).
Four years post-earthquake, algal cover varied significantly
between tidal zones, across uplift levels, and at sites within uplift
levels. There was very limited recovery of algae in the high and
mid tidal zones of uplifted reefs, with <10% cover of encrusting
coralline and ephemeral green algae, so the focus here is on
the abundance of key taxa in the low tidal zones of sites across
uplift levels. In the low zone, there were significant differences
between uplift levels [Pseudo-F(3,12)= 2.56, p<0.01] and
sites within uplift levels [Pseudo-F(12,144)= 9.31, p<0.01].
The abundance of large brown algae generally decreased with
increasing uplift across the control and uplift groups (Figure 5).
One prominent feature was the decline in brown algal cover at
12–16 months at all sites and uplift levels, which coincided with a
marine heat wave and high air temperatures combined with calm
FIGURE 3 | (A) Color-fade graph of low shore temperatures across all sites
from January 2017 to 2019. Note the numerous periods for most sites when
temperatures exceed 40C during the summer of 2018. (B) Effects of canopy
facilitation of understory temperatures, above and below experimental canopy
of Hormosira banksii on a lower mid tidal zone site.
sea conditions over several days. Large brown algal cover at the
Oaro control sites recovered over the next 2 years (Figure 5A).
Similarly, the large brown algae cover of low uplift sites mostly
recovered to pre-earthquake levels by 4 years, although there
was considerable variation among sites (Figure 5B). Medium
uplift sites remained below their pre-earthquake cover, except
for one site at Omihi (Figure 5C). The high uplift sites around
Waipapa, which formerly had around 70% cover of large brown
algae (mostly Durvillaea spp.) had <20% cover after 4 years,
with one site having no brown algal cover at all (Figure 5D). The
large brown algae species found on uplifted recovering reefs were
primarily Carpophyllum maschalocarpum and Cystophora spp.,
with some Marginariella boryana and a small cover of the kelp
Lessonia variegata at a couple of sites (cf. Table 1). Overall, the
low-uplift and control sites had the highest average large brown
algal cover (c. 60%), followed by the medium-uplift (38%), and
the high-uplift sites (8%).
Fleshy red algae were the other dominant group of habitat-
defining seaweeds along the coast, and they were generally not
as affected by the heat wave in the summer of 2017–18 as were
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Schiel et al. Intertidal Community Response to Cataclysmic Earthquake
FIGURE 4 | (A) Maximum depth threshold for Durvillaea antarctica/poha (as estimated by compensating irradiance) based on measured PAR at multiple sites, (B)
associated timing of wave events and rainfall, and (C) the proportion of days where the light availability depth threshold for Durvillaea antarctica/poha is below 10
and 5 m. Depth threshold (A) is log transformed.
large brown algae (Figure 6). After 4 years, there were significant
differences between uplift levels [Pseudo-F(3,12)= 1.82, p<0.05]
and sites within uplift levels [Pseudo-F(12,144)= 11.10, p<0.01].
At the control sites, red algae fluctuated over the years and had a
slightly lower cover (–10%, Table 2) after 4 years than at the start
of the study (Figure 6A). Red algae in low uplift sites generally
had the same cover throughout the study and seemed to be little
affected by the earthquake (Figure 6B and Table 2). However,
medium uplift sites showed increases of 25% in cover (across
all sites, Table 2) over the 4 years (Figure 6C), and high uplift
sites showed overall increases of 22% in red algal cover over the
years in comparison to pre-earthquake conditions (Figure 6D).
The high-uplift areas had the greatest variation among sites. The
taxa of fleshy red algae primarily responsible for these patterns
were Gelidium microphyllum,Pterocladia lucida,Ceramium spp.,
Gigartina chapmanii,Chondria macrocarpa,Polysiphonia spp.,
Echinothamnion spp., and Champia sp.
Two prominent features of the recovery process were the
relationships between uplift and percentage cover of large brown
algae, and between the percentage cover of brown and fleshy
red algae. There was an exponential fall-off in brown algal
cover with degree of uplift (Y= 75.5 e0.499 X;r2= 0.89,
Figure 7A) after 4 years. Regression analyses highlighted a
negative relationship between the cover of large brown algae
and fleshy red algae. This relationship accounted for 10%
of the variability in the abundance of large brown algae in
the mixed-effects linear regression, whereas the whole model
(accounting also for site-by-site differences) accounted for 36%
of the variability. Quantile regression analyses confirmed the
presence of a strong negative relationship between the two groups
across five different quantiles (q10 slope –0.25, p<0.001; q25
slope –0.35, P<0.001; Q50 slope –0.41, p<0.001; q75 slope –
0.44, p<0.001; q90 slope –0.4, p<0.01, Figure 7B). These
relationships contribute to the observed percentage gains and
losses of red and brown algae across tidal zones in the different
uplift levels (Table 2).
Limpets are the dominant grazers at all study sites and were
typically abundant from the mid tidal zone upwards. At 6 months
post-quake, control and low uplift sites had the greatest densities
of limpets (c. 30 m2) but after 4 years had the fewest (<20 m2;
Figure 8A). The medium and high uplift sites showed increases
in limpets over the 4 years. In particular, the medium uplift sites
TABLE 2 | Overall changes in percentage cover of major taxonomic groups
between abundances pre-earthquake (November 2016) and 4 years later
(Nov–Dec 2020).
Tidal zone
Low Mid High
Uplift level Control Brown algae –10% +1% 0%
Red algae –17% –4% +2%
Low Brown algae +4% –28% –13%
Red algae +5% 0% +2%
Medium Brown algae –20% –48% –10%
Red algae +24% –14% –9%
High Brown algae –58% –19% –1%
Red algae +22% –9% –1%
Data are compiled across all sites within each uplift category.
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Schiel et al. Intertidal Community Response to Cataclysmic Earthquake
FIGURE 5 | The percentage cover (±SE) of large brown algae at each site within control (A), low (B), medium (C) and high (D) uplift areas. Note the decline at
12 months, due to a severe heat wave. For the sites sampled in November 2016, the average abundance of large brown algae in the pre-earthquake low zone is
displayed in the gray panels.
had an average of 60 limpets m2, but this was driven mainly
by one of the sites (Okiwi Bay) within this uplift level that had
216 limpets m2. There was therefore a significant difference
in sites within uplift levels [Pseudo F(12,144)= 2.99, p<0.01],
but not among uplift levels [Pseudo F(3,12)= 2.66, p= 0.10].
The limpets were mostly Cellana species, but also included
Notoacmea and pulmonate limpets (Siphonaria). The decline in
limpet numbers in the control and low-uplift sites did not reflect a
widespread decline in the abundance of all limpet species, but was
due to the absence of large clusters of Siphonaria spp. Another
gastropod, the commercially valuable pâua (abalone, Haliotis
iris) recruited well in all post-earthquake years, with numbers
accumulating through to year 4 (Figure 8B). This was related to
recovering juvenile habitat of small boulder-fields in the lowest
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Schiel et al. Intertidal Community Response to Cataclysmic Earthquake
FIGURE 6 | The percentage cover (±SE) of fleshy red algae at each site within control (A), low (B), medium (C) and high (D) uplift areas. Note the decline at
12 months, due to a severe heat wave. For the sites sampled in November 2016, the average abundance of large brown algae in the pre-earthquake low zone is
displayed in the gray panels.
tidal zone, and accumulating numbers of reproductive adults in
most shallow rocky habitats (Gerrity et al., 2020).
Taken together, there remained large differences in
community structure between sites and uplift levels within
tidal zones at 4 years post-quake (Figure 9). Multivariate analysis
showed uplift had a significant effect on intertidal community
composition in the post-earthquake high tidal zone [Uplift:
Pseudo-F(3,12)= 2.42, p<0.05] as did sites within uplift levels
[Pseudo-F(12,144)= 4.96, p<0.01; Figure 4A]. In particular,
the control and the low-uplift groups differed from the medium-
uplift group because of higher covers of ephemeral green (Ulva
spp.) and red algae (Pyropia spp.). However, this was a reflection
of occasional blooms in the abundance of ephemeral algae
rather than a real earthquake legacy. Long-lasting earthquake
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Schiel et al. Intertidal Community Response to Cataclysmic Earthquake
FIGURE 7 | (A) The relationship between percentage cover (±SE) of large
brown algae across degrees of uplift. (B) Relationship between the
abundance of large brown and fleshy red algae 3 years after the earthquake
estimated through a quantile regression model. Regression lines are displayed
for significant relationships. Symbol colors indicate different levels of uplift
(white = no uplift, green = low uplift, yellow = medium uplift, red = high uplift).
Data from the high-uplift site of Waipapa Bay 1, where both large brown and
fleshy red algae were not present, were not included in this analysis.
effects were especially evident in mid zone, where abundant
algal communities occurred only at control sites (Figure 9B).
This led to a significant effect of uplift [Pseudo-F(2,8)= 2.62,
p<0.01], but there was also a significant site effect [Pseudo-F(8,
99)= 9.37, p<0.01]. In the low zone, the composition of benthic
communities was different in the low-uplift group (where large
brown algae, particularly Carpophyllum maschalocarpum, had
recovered) compared to the medium- and high-uplift groups
[which were characterized by high percentage cover of red algae;
Uplift: Pseudo-F(3,12)= 2.43, P<0.01, Figure 9C]. No other
uplift group differed from the others but there was significant
variability in the structure of benthic communities among sites
within each uplift group [Pseudo-F(12,144)= 7.66, P<0.01,
Figure 9C].
FIGURE 8 | | (A) Time series of the mean number (±SE) of limpets per m2
across uplift levels. The dotted blue line indicates the average abundance of
limpets across sites sampled in November 2016. (B) The abundance of
juvenile (<80 mm shell length) and adult (>80 mm) pâua (Haliotis iris) in the
low intertidal zone of study sites in different degrees of uplift over 3 years
post-earthquake.
DISCUSSION
This study has been instructive in understanding the dynamics
of recovery from a major disturbance event involving species,
communities and the infrastructure on which they build and
depend. It was unusual, if not completely novel, to witness such
extensive damage to a coastal ecosystem. Rocky reef communities
that had been dynamic but intact in structure and function
over many decades in the face of periodic storm and wave
impacts (Schiel, 2011, 2019) were obliterated by a major event
that occurred over a matter of minutes (Clark et al., 2017). The
horizontal distance between the former and post-earthquake high
tide marks reached c. 200 m in areas of major uplift. It was
somewhat disconcerting to see entire shallow coastal assemblages
high and dry out of tidal influence. This, however, provided the
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Schiel et al. Intertidal Community Response to Cataclysmic Earthquake
FIGURE 9 | Principal coordinates analysis (PCO) plots showing differences in the composition of benthic communities in the post-earthquake high (A), mid (B) and
low zone (C) across sites with different degrees of uplift 48 months after the earthquake. The symbols represent the centroid of each site and the colors the different
levels of uplift (white = no uplift, green = low uplift, yellow = medium uplift, red = high uplift). Sites are ordered north to south within each uplift group. Only the high
and the low zone were sampled at high-uplift sites.
opportunity to assess pre-earthquake communities quantitatively
that were previously difficult to access and therefore rarely
studied in detail.
At most sites, uplifted reef platforms were not compensated
by new rocky substrates uplifted from the subtidal zone; this
led to a new configuration of low and mid tidal zones that
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Schiel et al. Intertidal Community Response to Cataclysmic Earthquake
are now near-vertical in places. This morphological change
was important in recovery because there was a much smaller
tidally influenced zone in which communities could re-assemble.
A surprise that unfolded within a month post-earthquake was
the loss of speciose algal communities, which had been the
focus of decades of studies, in the mid and upper tidal zones of
extensive reef platforms, even though they still had tidal coverage.
Furthermore, recovery of the low tidal zone was substantially
set back by the severe heat wave a year after the earthquake,
the timing of which coincided with the replacement of large
brown algae by a suite of tough, fleshy red algae. The density and
longevity of the latter have precluded settlement of large brown
algae in the period since the heat wave. Intertidal platforms
and boulders, composed of Paleocene limestone overlain by
Oligocene gray mudstones (Kirk, 1977), have also eroded at
annual rates >35 mm at several sites post-quake (Schiel et al.,
2019) compared to a long-term average of 1.13 mm yr1(Kirk,
1977;Stephenson and Kirk, 1998).
Studies from Chile have shown that recovery from coastal
uplift can take several years. For example, Castilla (1988)
found that uplift of 0.4–0.6 m caused extensive mortality of
the laminarian alga Lessonia nigrescens, which had formed a
conspicuous band on the low shore. As understory species also
died, the areas they occupied became covered in barnacles,
and Lessonia populations were still recovering 3 years after the
earthquake. In 2010, a mega-earthquake of Mw 8.8 caused coastal
lifting up to 3.1 m (Castilla et al., 2010). Similar to our study,
there was widespread mortality of intertidal organisms after being
exposed to solar radiation and elevated temperatures, especially
Durvillaea antarctica and red algae which became bleached and
desiccated. Jaramillo et al. (2012) also documented broad-scale
impacts of this earthquake and found, as in our study, that the
ecological impacts varied strongly with magnitude and direction
of land-level change across different shore types and with the
mobility of characteristic biota. Because of structural changes
to the intertidal zones, the likelihood of recovery to a former
state was unclear.
One of the novel features of recovery of the shores in southern
NZ is the role of mostly long-lived fucoid algae that are the
dominant habitat-formers. These generally have short dispersal
distances of propagules, often a matter of meters, and rely on
drifting, reproductively active adults for long distance dispersal
(Schiel, 2011). Because of the patchy nature of post-earthquake
fucoid populations, connectivity to previously occupied areas
was compromised and mostly relied on drifting adults for
recolonization. This is illustrated by one of the hardest hit taxa,
Durvillaea. Chilean studies have shown that drift Durvillaea
antarctica can be abundant onshore (Tala et al., 2019) and it
is known that this species can drift extensively in southern
seas (Waters, 2008). However, the deposition of drifting fucoids
at distant inshore sites is probabilistically low over short time
periods (Hawes et al., 2017). Additionally, Durvillaea is dioecious,
so male and female fronds must arrive inshore together, and this
needs to coincide with their relatively short reproductive season
(c. 8 weeks) in winter. Few drift Durvillaea have been seen at our
study sites since the earthquake. As well, its sporelings are known
to be highly vulnerable to heat stress (Hay, 1979), and in at least
some sites of former abundance the water clarity is so poor that
effective growth would be compromised.
Similar impediments to establishment are faced by other
fucoids. For example, Hormosira banksii is the most desiccation-
resistant fucoid because of its mucilage-filled fronds (Brown,
1987). However, the reduced period of tidal immersion, erosion
of reefs and increases in fine sediments can all compromise
effective recruitment (Alestra and Schiel, 2015). This is coupled
with low-tide temperatures frequently exceeding 35C during
summer, killing off the sparse annual recruitment in the lower
mid-tide zone and effectively turning this perennial and formerly
dominating species into an ephemeral one. This species has
declining productivity beyond 25C (Tait and Schiel, 2013),
and its canopy interacts synergistically with other fucoids, such
as Cystophora torulosa and Carpophyllum maschalocarpum, to
increase per-area primary productivity (Tait and Schiel, 2011,
2013), which is similar to fucoids elsewhere (Colvard et al.,
2014). By comparison to the low-shore fucoids, fleshy red
algae seem to be more resistant to heat stress and can remain
productive and recover from desiccation at temperatures above
30C (Smith and Berry, 1986).
In contrast to algae, broadcast-spawning invertebrates
recovered quickly, as would be expected. In the first 6 months
post-earthquake, the mid and lower intertidal zone was bright
green along much of the coast from a massive bloom of mostly
Ulva spp. As grazers recruited, such blooms became more patchy
and ephemeral. One surprise, however, was the recovery of pâua
(abalone, Haliotis iris) populations in the low intertidal—subtidal
margins. Despite the initial loss of recruitment habitat in the
lower zone, there was good recruitment in each year following
the earthquake (Gerrity et al., 2020). Adult pâua were lifted into
this zone from uplifted subtidal reefs and also migrated there
from deeper areas, and there was a ban imposed on recreational
and commercial fishing along the coast. The combined result
was an abundance of shallow pâua populations at levels not
seen in decades.
Resilience and recovery clearly need to be considered within
the context of species’ life histories, life spans, their interactions
with each other, and prevailing conditions, which can involve
long time trajectories. In this study, recovery has been influenced
by a combination of altered topography, increased temperatures
at the reef surface, erosion of rocky substrata, sedimentation
from earthquake-damaged catchments, a compromised light
environment in nearshore waters, and human-induced stressors
from increased coastal access around headlands. These processes
are acting on a pattern of widespread initial mortality that
occurred even at lesser uplifted sites, and are consistent with
major re-assembly processes being driven by relatively small
increments of relative sea-level change (Orchard et al., 2021).
The variable patterns of recovery we have observed reflect
the influence of complex site-specific combinations of stressors
that are mostly hindering the re-establishment of supportive
ecological infrastructure. Exceptions, however, include the
recovery of large brown algae at several of the low uplift (<1 m)
sites which likely reflects the influence of surviving population
remnants, and the expansion of fleshy red algal cover at others in
absence of the recovery of brown algae. In relation to the degree
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of uplift, there are confounding factors among sites from the rate
of weathering characteristic of softer substrata that predominate
at them. The associated erosion effects are a likely cause of
slow recovery on these reefs and exhibit further interactions
with turbidity and alterations to the light environment that we
recorded in these areas.
It may turn out that there are multiple stable states depending
on the level of uplift and its interactions with other factors.
These complex interactions affect how communities re-align
themselves over longer time periods but notably exert their most
pervasive effects through the key habitat-forming species that
generate the ecological infrastructure and supportive conditions
upon which others depend. Scheffer et al. (2001) point out that
state shifts in ecosystems can be reflected more by biological
than physical factors because biotic feedbacks can stabilize
communities in different ways, and that such shifts may be
triggered by catastrophic physical events. So far, our time
scales for recovery have not coincided with those needed
for stabilization of the most earthquake-affected ecological
infrastructure, notably that provided by the large brown fucoid
species characteristic of this coast.
Much of the resilience and ecological infrastructure literature
addresses nature’s goods and services, and potential management
interventions to maintain them (da Silva and Wheeler, 2017;
Chambers et al., 2019). It would initially seem that there
would be few management strategies for ecosystem recovery
that could be effective in the face of cataclysmic earthquake
impacts followed by a major heatwave. And yet manageable
stressors and potentially effective pathways to facilitate recovery
trajectories can be identified. For example, there is a current
legislative initiative to restrict vehicular traffic on the recovering
beaches and tidal platforms around Cape Campbell in the north
of the study area. The coast-wide closure of the pâua fishery
also resulted in an unanticipated and quick rebound of pâua
stocks, which led to current proposals favoring the reduction
of commercial and recreational fisheries, and an adoption of
a more adaptive and resilience-based management strategy.
Additionally, there were lightly affected areas representing
ecological “safe havens” along the coast at locations such as Oaro,
where traditional management practices of restricted fishing have
been overseen by customary Mâori tikanga (practices). These
highlight the value of multiple protected areas along coastlines
which, perhaps by chance and good fortune, can act as insurance
policies to provide sources of reproductive propagules to aid the
recovery of key habitat-forming species. These examples illustrate
that a focus on the protection of ecological infrastructure is
a tractable objective for the facilitation of disaster recovery.
It can be promoted by the strategy of addressing manageable
stressors such as sediment loss and overharvesting, and is indeed
essential for the return of desirable states in the aftermath of
natural disasters.
DATA AVAILABILITY STATEMENT
The raw data supporting the conclusions of this article will be
made available by the authors, without undue reservation.
AUTHOR CONTRIBUTIONS
DS wrote the manuscript and led the research program. SG and
TA led the field team and collected much of the data. TA and
TF did data analyses. RD led subtidal research and helped set up
the program and did initial surveys. SO led community liaison
and did the analyses of physical changes to the coastline. MT
analyzed heat wave effects. LT did photophysiology and light
studies. All authors contributed to the article and approved the
submitted version.
FUNDING
This research was funded by the MBIE contract UOCX1704 and
the Ministry of Primary Industries grant KAI2016-05. Aligned
funding was by the Sustainable Seas National Science Challenge
(CO1X1901).
ACKNOWLEDGMENTS
We thank Dr. John Pirker for iwi liaison, Jason Ruawai and
Te Runanga o Kaikoura for input and support throughout
the study, Dr. Sharyn Goldstien for helping with logistics and
involvement in the hectic days following the earthquake, NCTIR
for granting us access to field sites during the extensive period
or cliff stabilization and road closure, Dr. Rich Ford of MPI for
support throughout the program, Dr. Mike Hickford for help
with logistics, Dan Crossett who helped with field work in parts
of the program not reported here, and many others who helped
at times with field work and other support.
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