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Identifying the consequences of ocean sprawl for sedimentary habitats

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Extensive development and construction in marine and coastal systems is driving a phenomenon known as “ocean sprawl”. Ocean sprawl removes or transforms marine habitats through the addition of artificial structures and some of the most significant impacts are occurring in sedimentary environments. Marine sediments have substantial social, ecological, and economic value, as they are rich in biodiversity, crucial to fisheries productivity, and major sites of nutrient transformation. Yet the impact of ocean sprawl on sedimentary environments has largely been ignored. Here we review current knowledge of the impacts to sedimentary ecosystems arising from artificial structures.
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Review
Identifying the consequences of ocean sprawl for sedimentary habitats
Eliza C. Heery
a,
,MelanieJ.Bishop
b
, Lincoln P. Critchley
b
, Ana B. Bugnot
c,d
, Laura Airoldi
e
,
Mariana Mayer-Pinto
c,d
,EmmaV.Sheehan
f
, Ross A. Coleman
g
, Lynette H.L. Loke
h
,EmmaL.Johnston
c,d
,
Valeriya Komyakova
i
, Rebecca L. Morris
g
, Elisabeth M.A. Strain
c
, Larissa A. Naylor
j
, Katherine A. Dafforn
c,d
a
Department of Biology, University of Washington, Box 351800, Seattle, WA 98195, USA
b
Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
c
Sydney Institute of Marine Science, Building 19 Chowder Bay Road, Mosman, New South Wales 2088, Australia
d
School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia
e
Dipartimento di Scienze Biologiche, Geologiche ed Ambientali & CentroInterdipartimentale di Ricercaper le Scienze Ambientali (CIRSA), University of Bologna, UO CoNISMa,Via San Alberto 163,
Ravenna, 48123, Italy
f
School of Biological and Marine Sciences, Marine Institute, University of Plymouth, Plymouth PL4 8AA, UK
g
Centre for Research on the Ecological Impacts of Coastal Cities, University of Sydney, Sydney, New South Wales 2006, Australia
h
Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore
i
School of BioSciences, University of Melbourne, Parkville, Victoria 3010, Australia
j
School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
abstractarticle info
Available online xxxx Extensive development and construction in marine and coastal systems is driving a phenomenon known as
ocean sprawl. Ocean sprawl removesor transforms marine habitats through the addition of articialstructures
and some of the most signicant impacts are occurring in sedimentary environments. Marine sediments have
substantial social, ecological, and economic value, as they arerich in biodiversity,crucial to sheries productivity,
and major sites of nutrient transformation. Yet the impact of ocean sprawl on sedimentary environments has
largely been ignored. Here we review current knowledge of the impacts to sedimentary ecosystems arising
from articial structures.
Articial structures alter the composition and abundance of a wide variety of sediment-dependent taxa, includ-
ing microbes,invertebrates, and benthic-feeding shes. The effects vary bystructure design andconguration, as
well as the physical, chemical, and biological characteristics of the environment in which structures are placed.
The mechanisms driving effects from articial structures include placement loss, habitat degradation, modica-
tion of sound and light conditions, hydrodynamic changes, organic enrichment and material uxes, contamina-
tion, and altered biotic interactions. Most studies have inferred mechanism based on descriptive work,
comparing biological and physical processes at various distances from structures. Further experimental studies
are needed to identify the relative importance of multiple mechanisms and to demonstrate causal relationships.
Additionally, past studies have focused on impactsat a relatively small scale, andindependently of other devel-
opment that is occurring. There is need to quantify large-scale and cumulative effects on sedimentary ecosystems
as articial structures proliferate. We highlight the importance for comprehensive monitoring using robust sur-
vey designsand outline research strategies needed to understand, value, and protect marine sedimentaryecosys-
tems in the face of a rapidly changing environment.
© 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://
creativecommons.org/licenses/by/4.0/).
Keywords:
Articial structure
Coastal defense
Ecological impact
Marine sediment
Offshore wind farm
Urbanization
Contents
1. Introduction............................................................... 0
2. Impacts of articialstructuresonsedimentaryhabitats............................................ 0
2.1. Placementloss,habitatdegradation,andrelatedeffects........................................ 0
2.2. Changestothesensoryenvironment................................................. 0
2.3. Hydrodynamiceffects ....................................................... 0
Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Corresponding author.
E-mail address: eheery@uw.edu (E.C. Heery).
JEMBE-50869; No of Pages 18
http://dx.doi.org/10.1016/j.jembe.2017.01.020
0022-0981/© 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Contents lists available at ScienceDirect
Journal of Experimental Marine Biology and Ecology
journal homepage: www.elsevier.com/locate/jembe
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
2.3.1. Large-scalehydrodynamiceffects.............................................. 0
2.3.2. Intermediate-scalehydrodynamiceffects........................................... 0
2.3.3. Small-scalehydrodynamiceffects.............................................. 0
2.4. Organic enrichment and material uxes ............................................... 0
2.5. Contaminants........................................................... 0
2.6. Bioticeffects............................................................ 0
3. Factors inuencingthedirectionandmagnitudeofimpacts.......................................... 0
4. Approachesemployedinpaststudies.................................................... 0
5. Researchgapsandfuturedirections..................................................... 0
5.1. Monitoring............................................................. 0
5.2. Futureresearchdirections...................................................... 0
6. Conclusions................................................................ 0
Acknowledgements .............................................................. 0
References................................................................... 0
1. Introduction
The intensifying development of urban foreshores, coastlines, and
offshore areas is driving a phenomenon commonly referred to as
ocean sprawl(Duarte et al., 2012). Articial structures are added to
estuarine, coastal, and marine systems to protect shorelines from ero-
sion (Dugan et al., 2011; Nordstrom, 2014), and to support marine
aquaculture (Giles, 2008; McKindsey et al., 2011; Simenstad and
Fresh, 1995), renewable energy generation (Bailey et al., 2014; Gill,
2005; Langhamer, 2010; Miller et al., 2013; Petersen and Malm, 2006),
natural resource extraction (Kingston, 1992; Peterson et al., 1996;
Wilson and Heath, 2001), and recreational and commercial activities
(Connell and Glasby, 1999; Connell, 2000). Articial structures there-
fore take a variety of forms (Fig. 1), varying in size, from small objects
such as crab-tiles(Sheehan et al., 2008) to large, articial islands
(Cavalcante et al., 2011). Collectively, these structures are causing ex-
tensive modication of marine and coastal ecosystems and the impor-
tant ecosystem services they support (Bulleri and Chapman, 2010;
Dugan et al., 2011). While these structures are added to both hard and
soft bottom habitats (Bulleri, 2005), most research has focused on the
Fig. 1. Examples of articial structures in sedimentary environments. From left to right: groyne
a
,pier
a
, revetment
a
, dumped appliance (toilet)
b
,tirereef
b
, and overwater causeway
b
.
Photo credit:
a
E. Strain,
b
E.C. Heery.
2E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
extent to which they modify and mimic natural hard substrates, with
impacts on sedimentary ecosystems, by comparison, little studied.
In marine, coastal, and estuarine environments (hereafter, collec-
tively referred to as marine), sediment is one of the most abundant eco-
systems, spanning intertidal habitats, such as sandy beaches and tidal
ats, to the deepsea oor (Masselink et a l., 2014; Paris et al., 2011). Con-
sequently, in many parts of the world, the distribution of marine sedi-
ments overlaps substantially with ocean sprawl, resulting in habitat
loss and modication of the diverse communities and ecological func-
tions that sedimentary habitats underpin (Snelgrove et al., 2014;
Bishop et al., in this issue). Microbial, meiofaunal, macrofaunal, and
macrophytic assemblages (e.g. saltmarsh, mangrove, seagrass) live on
and within the sediments (Adam, 1990; Coull, 1988; Lugo and
Snedaker, 1974; Orth et al., 1984; Paerl and Pinckney, 1996;
Snelgrove, 1998) and provide prey resources for shes, shorebirds,
and large vertebrates, such as gray whales (Eschrichtius robustus), du-
gongs (Dugong dugon), and green sea turtles (Chelonia mydas)
(Carruthers et al., 2002; Gray and Elliott, 2009; Lopez and Levinton,
1987; Weitkamp et al., 1992). These assemblages also underpin many
ecosystem services of fundamental importance to humanity, including
sheries productivity, biogeochemical cycling, remediation of contami-
nants, and shoreline stabilization (Bolam et al., 2002; Snelgrove, 1997,
1999; Snelgrove et al., 2014; Weslawski et al., 2004).
Understanding the impacts of ocean sprawl on the structure and im-
portant functions of sedimentary ecosystems is necessary for the devel-
opment of management strategies aimed at conserving biodiversity and
ecosystem services (Gray, 2002; Snelgrove, 1999). Here, we review cur-
rent knowledge of the impacts of articial structures on marine sedi-
mentary ecosystems (including the organisms living in or in close
association with benthic sediments), aswell as the limitations in current
knowledge. Our objective is not to impose value judgements on these
impacts, but rather to summarize the known literature. Sediment is a
broad term that refers to a diverse range of loose materials that are de-
rived from a parent source (i.e. bedrock, shells, plant andanimal matter)
ranging from megaliths (i.e. b1075 km diameter) through to the nest
muds (Blair and McPherson, 1999; Wentworth, 1922). In this paper
we focus on sediments that are entrained and transported under normal
wave conditions (i.e. muds, b0.06 μ, to cobbles b256 mm diameter),
thereby excluding larger cobbles and coarse boulders, which aretypical-
ly entrained only under storm or tsunami conditions (Paris et al., 2011).
We refer to all material greater than 2 mm diameter (i.e. gravels to cob-
bles) as coarse sediment and all material ner than 2 mm (i.e. sand, silt
and clay) as ne sediment. Wefocus primarily on the effects of articial
structures on un-vegetated sediments, as these habitats have been par-
ticularly underrepresented in the literature to date, but utilize examples
from vegetated sediments whererelevant and informative for sedimen-
tary ecosystems more broadly. Our review includes discussion of how
articial structures may affect sedimentary ecosystem functioning
and, hence, the provision of ecosystem services. We make the case
that the proliferation of articial structures is of vital concern for sedi-
mentary ecosystems and highlight knowledge gaps and future research
that will be needed in order to protect ecosystem services provided by
marine sedimentary habitats in the face of ocean and climate change.
2. Impacts of articial structures on sedimentary habitats
Articial structures modify soft sediment habitats directly, through
displacement of ora and fauna by their foundations, and indirectly,
by altering key physical, chemical, and biotic parameters that inuence
sediments beyond the footprint of the structure (Table 1,Fig. 2). Sedi-
mentary organisms may respond to these direct and indirect effects at
the population, community, or ecosystem level. In Sections 2.1
through 2.6, we summarize the direct and indirect effects of articial
structures on sediments, as well as the potential consequences with re-
spect to sedimentary ecosystem functions.
2.1. Placement loss, habitat degradation, and related effects
Construction of articial structures on top of surface sediments is ar-
guably the most obvious and destructive direct impact because it re-
duces the area of habitat available to resident organisms, which are
concentrated close to the seawater-sediment interface (Hines and
Comtois, 1985). The habitat that is eliminated by the footprint of arti-
cial structures is known as placement loss(Dugan et al., 2008; Griggs,
2005). In the case of structures that are deployed in clusters over large
areas, such as offshore wind farms, placement loss may be particularly
extensive (Wilson and Elliott, 2009). In the UK alone, 12008600 km
2
of sedimentary habitat is expected to be lost to offshore wind farm de-
velopment by 2020 (Byrne and Houlsby, 2003; Wilson et al., 2010).
In addition to directly impacting the organisms living in sediments
via placement loss, many structures have secondary effects on mobile
and migratory species, particularly when articial structures result in
the loss or modication of large areas of habitat. For instance, in elimi-
nating upper intertidal and supratidal beach habitat that supports inver-
tebrate communities of beach hoppers and ghost crabs, seawalls placed
in the low or mid intertidal zone negatively affect the foraging and
roosting behavior of shorebirds and seabirds (Dugan et al., 2008). Sim-
ilarly, swing mooring buoys, which uproot seagrass through chain
drag on bottom sediments, and overwater structures such as piers and
pontoons, which reduce macrophyte abundance through shading
(Section 2.2), inuence the invertebrate and nsh species that utilize
vegetated sediments for food and shelter (Collins et al., 2010; Walker
et al., 1989).
During the construction of articial structures, placement loss is
often coupled with a series of other physical and chemical changes.
For example, the construction and maintenance of marine infrastruc-
ture often requires dredging of large amounts of sediment. Increased
concentrations of suspended sediments during the dredging process
can damagethe gills and eyes of sh and prevent lter feeding by inver-
tebrates (Knott et al., 2009). Moreover, estimates of up to 2300 m
3
of
sediment loss per turbine have been linked to dredging during wind
farm construction (Lozano-Minguez et al., 2011). Dredging not only
removes sediments but also resident fauna (Jones and Candy, 1981;
Thrush and Dayton, 2002)andora (Iannuzzi et al., 1996), and recovery
of affected benthic communities can, in someinstances, take as long as 2
to 4 years (van Dalfsen et al., 2000). Dredge spoil that is dumped off-
shore or deposited intertidally to nourish eroding beaches or create ar-
ticial wetlands can have substantial and lasting impacts on the benthic
communities, arising through smothering and alteration of sediment
properties (Bishop, 2005; Bishop et al., 2006; Manning et al., 2014).
Articial structures can also act as a physical barrier or deterrent to
the movementof organisms across sedimentary seascapes. For instance,
breakwaters and seawalls can inhibit the movement of sea turtles and
terrapins from the sea to the supratidal area of sandy beaches where
they lay eggs (Bouchard et al., 1998). Seawalls can also limit the tidal
migration of sandy beach invertebrates up and down the shore to feed
and avoid desiccation stress (Dugan et al., 2011). In the subtidal, the ar-
rangement of structures, such as underwater turbines, jetties, pilings,
and bulkheads may also create barriers to the movements and migra-
tions of sediment-feeding organisms depending on their density and
spatial arrangement in the seascape (Bulleri and Chapman, 2015;
Dadswell and Rulifson, 1994; Gill, 2005). Effects of articial structures
on connectivity are reviewed by Bishop et al. (in this issue),andthere-
fore are not discussed here in detail.
2.2. Changes to the sensory environment
Articial structures alter the sensory environment for sedimentary
organisms in by modifying light and noise levels. Some structures pro-
duce light pollution (Davies et al., 2014), which may impact sedimenta-
ry organisms (Navarro-Barranco and Hughes, 2015). Conversely, many
structures cast shadows on sedimentary habitats. The light level in the
3E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
Table 1
Documented effects from articial structures, their scale, and their potential biotic effects as presented by the authors referenced.
Effect type Structure
type Abiotic change Scale Potential biotic impacts References
Placement
loss
Bulkheads &
seawalls
Elimination of upper
intertidal
Area of
structure
Reduced abundance of upper intertidal
invertebrates and their predators Dugan et al. (2008)
Physical
barrier Pilings
Act as a physical barrier
inhibiting movement of large
mobiles species
10s of
meters Reduction in nesting of sea turtles Bouchard et al. (1998)
Magnetic and
electric
currents
Cables Magnetic elds surrounding
cables
b1mto
10s of
meters
Apparently limited effect on invertebrates Andrulewicz et al. (2003),Bochert and Zettler
(2004),Petersen and Malm (2006)
Wind farms Magnetic and electric
currents from cables
10s of
meters
Possible effects on elasmobranchs and sh that
are sensitive to magnetic elds Petersen and Malm (2006)
Noise Wind farms Sound from rotors Kilometers Potential impact on cetaceans and other
organisms; may deter some sh
Wahlberg and Westerberg (2005),Petersen and
Malm (2006)
Light
Aquaculture Shading from aquaculture
structures Variable Lower abundance of macrophytes Deslous-Paoli et al. (1998),McKindsey et al.
(2011)
Marinas Increased turbidity/reduced
light levels
Area of
structure Reduced sediment microalgal production Iannuzzi et al. (1996),Rivero et al. (2013)
Piers &
docks
Shading from overwater
structures
Meters to
10s of
meters
Negative impacts on primary producers, poor
feeding conditions and suboptimal foraging by
juvenile sh, avoidance by mobile consumers,
concentration of consumer populations in
adjacent areas, altered assemblage structure
Burdick and Short (1999),Duffy-Anderson and
Able (1999, 2001),Toft et al. (2007),Munsch
et al. (2014),Ono and Simenstad (2014)
Interruption
of current
patterns
Articial
reefs
Changes in microtopography
& ripple marks b15 m May impact variation in macrofauna and
meiofauna composition Sun et al. (1993),Barros et al. (2004)
Breakwaters
& groynes
Interruption of longshore
currents & redistribution of
sediments
100s of
meters to
kilometers
Elimination of downdrift depositional habitats Duane (1976),Komar (1998),Cuadrado et al.
(2005),Bostic et al. (2015)
Bulkheads &
seawalls
Modication of water
circulation
100s of
meters
Accumulation of eggs and larvae in between
bulkheads Jackson et al. (2015)
Increases in
ow
Articial
reefs
Increased erosion & scour
(updrift side)/Coarsening of
sediment
b10 m Greater variability in infaunal community
composition
Davis et al. (1982),Ambrose and Anderson
(1990),Barros et al. (2001)
Breakwaters
& groynes
(exposed
side)
Increased erosion &
scour/Coarsening of
sediments
b10 m Shift towards larger macrofauna Bertasi et al. (2007),Munari et al. (2011)
Bulkheads &
seawalls
Increased erosion &
scour/Coarsening of
sediments
b3 m Lower density of meiofauna Weis et al. (1993),Spalding and Jackson (2001)
Narrowing of intertidal
habitat/Increased steepness Meters
Reduced nesting by sea turtles and colonization
by swash-riding mollusks; Altered population
dynamics for benthic organisms such as ghost
crabs; Reduced burrowing habitat for benthic
organisms; Reduced aquatic vegetation
Pilkey and Wright (1988),Hall and Pilkey
(1991),Peterson et al. (2000),Brown and
McLachlan (2002),Bozek and Burdick (2005),
Toft et al. (2007),Lucrezi et al. (2010),Dugan
et al. (2011),Rizkalla and Savage (2010),
Heatherington and Bishop (2012),Morley et al.
(2012)
Decreases in
ow
Aquaculture Accumulation of ne
sediment
Meters to
10s of
meters
Organic enrichment (see below) McKindsey et al. (2011)
Articial
reefs
Accumulation of ne
sediment b10 m Organic enrichment (see below)
Ambrose and Anderson (1990),Fabi et al.
(2002),Martin et al. (2005),Wilding (2006),
Zalmon et al. (2012),Machado et al. (2013),
Wilding (2014)
Breakwaters
& groynes
(protected
side)
Accumulation of ne
sediment/longer residence
time following storms
Meters
Organic enrichment (see below), Smaller
macrofauna, shift in zonation patterns with
depth; Lower abundance of benthic invertebrates
in some locations
Martin et al. (2005),Zanuttigh et al. (2005),
Bertasi et al. (2007),Munari et al. (2011)
Marinas
Accumulation of ne
sediment/longer residence
time/slight increases in
temperature and pH
Footprint Change in infaunal community structure Floerl and Inglis (2003),Balas and Inan (2010),
Rivero et al. (2013)
Organic
enrichment
Aquaculture Organic enrichment/hypoxic
& suldic sediments
10s of
meters
Decreased abundance of larger infauna and
altered vertical biomass proles in sediments;
may alter meiofaunal community composition;
Potential limitations in system-wide carrying
capacity
Weston (1990),Deslous-Paoli et al. (1998),
Wildish et al. (2001),Duarte et al. (2003),
Holmer et al. (2005),Giles (2008),Cranford
et al. (2009),Wilding (2012)
Articial
reefs
Organic
enrichment/Site-specic
reduction in sedimentary
oxygen
b2 m May alter meiofaunal community composition Fricke et al. (1986),Danovaro et al. (2002),
Wilding (2014)
Breakwaters
& groynes Increased organic content Meters Changes in infaunal community structure Bertasi et al. (2007)
Oil and gas
platforms
Organic enrichment/Lower
sedimentary oxygen b100 m Increased abundance of deposit feeding
polychaetes and nematodes
Kennicutt et al. (1996),Montagna and Harper
(1996)
Wind farms Increased ammonia, detrital 10s of Increased resource availability for infaunal Maar et al. (2009)
4E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
area directly underneath articial structures and in the nearby vicinity
can be several orders of magnitude less than that in adjacent open
water (Burdick and Short, 1999; Deslous-Paoli et al., 1998). Overwater
structures have been found to lower the growth rates and percent
cover of macrophytes (Deslous-Paoli et al., 1998), including habitat-
forming species such as seagrasses (Burdick and Short, 1999). Articial
structures are also likely to negatively affect growth of the
microphytobenthos (MPB) (Pagliosa et al., 2012; Struck et al., 2004).
MPB include microalgae and cyanobacteria that stabilize sediments
(McIntyre, 1969; Underwood and Paterson, 2003), serve as an impor-
tant food resource for several invertebrate grazers (De Jonge and Van
Beuselom, 1992; Herman et al., 2000; Simith et al., in this issue), and
x nitrogen (Piehler et al., 1998, 2010). Impacts on these organisms
due to shading effects from articial structures are therefore likely to
signicantly affect some of the functioning properties of sedimentary
systems in the photic zone. In the intertidal, shadows cast by articial
structures can lower temperatures and reduce desiccation stress,
which may alter the growth rate and success of intertidal invertebrates
and algae (Blockley and Chapman, 2006; Guichard et al., 2001). Low-
light areas under subtidal piers, jetties and wharves also reduce abun-
dances of and feeding activity by sh that rely on visual cues to forage
for prey in sedimentary environments, including juvenile salmonids
(Munsch et al., 2014; Ono and Simenstad, 2014;Toft et al., 2007) and ju-
venile winter ounder, Pseudopleuronectes americanus (Duffy-Anderson
and Able, 1999, 2001). These mobile consumers may also become con-
centrated in areas adjacent to articial structures due to avoidance be-
havior that is driven by shadows (Munsch et al., 2014), and this may
have secondary effects on sedimentary prey populations.
Construction, operation, and decommissioning of articial struc-
tures, particularly those associated with offshore energy resources,
can also signicantly change the acoustic environment (Bailey
et al., 2010; Nedwell et al., 2003, 2007). For example, the decibels
of sound produced by pile driving is almost double that of back-
ground levels 100 m away from construction sites and can be detect-
ed above background noise up to 70 km away from the source (Bailey
et al., 2010). To date, studies on the effect of structure-associated
noise have primarily focused on marine mammals (Bailey et al.,
2010; Koschinski et al., 2003; Tougaard et al., 2009) and have ex-
tended to few other taxa (Nedelec et al., 2014). We know that expo-
sure to anthropogenic noise caused by boat trafc and seismic
surveys can reduce successful development and early survival of ma-
rine invertebrates (de Soto et al., 2013; Nedelec et al., 2014). Noise
can also have physiological and behavioral effects on marine inverte-
brates (Regnault and Lagardere, 1983; Wale et al., 2013a, 2013b). For
Table 1 (continued)
Effect type Structure
type Abiotic change Scale Potential biotic impacts References
material, and fecal pellets in
down current sediments
meters deposit feeders
Material
uxes
Articial
reefs
Inux of shell fragments
from encrusting invertebrate
colonizing structure
b15 m Unknown Davis et al. (1982),Barros et al. (2001),
Machado et al. (2013)
Bulkheads &
seawalls
Decrease in beach wrack and
mangrove leaf litter Meters
Reduction in terrestrial insects, which decreases
prey resources for sh, as well as in beach
invertebrates, such as amphipods and oligochaete
worms, which may have cascading effects
Dugan et al. (2008),Sobocinski et al. (2010),
Heatherington and Bishop (2012),Heerhartz
et al. (2014, 2015, 2016)
Oil and gas
platforms Inux of shell fragments b500 m Unknown Kennicutt et al. (1996)
Contaminants
Articial
reefs
Increase in zinc,
benzothiazoles, and
polycyclic aromatic
hydrocarbons (tire reefs),
metals (coal ash reefs)
Unknown Elevated contaminants in invertebrate tissues and
potential toxicity
Collins et al. (1995, 2002),Wik and Dave
(2009)
Bulkheads &
seawalls
Increase in copper
chromated arsenate (CCA)
bulkheads constructed with
treated wood
b5 m Unknown Weis et al. (1993)
Marinas
Contamination from vessel
anti-fouling (AF) paints, CCA,
metal biocides
Area of
structure
to 10 m
Increased contaminants in tissues of macroalgae
and invertebrates, stress-induced changes in
biotic interactions
McGee et al. (1995),Schiff et al. (2004),Singh
and Turner (2009),Johnston et al. (2011),
Rivero et al. (2013),Neira et al. (2014),Sim
et al. (2015)
Oil and gas
platforms
Contamination and discharge
from drilling
100s of
meters to
kilometers
Altered macrofaunal community composition
Kingston (1992),Olsgard and Gray (1995),
Montagna and Harper (1996),Peterson et al.
(1996)
Pilings Increase in CCA b10 m May reduce richness and diversity of infauna Weis et al. (1993),Weis and Weis (1996),
Hingston et al. (2001)
Bottom-up
limitation Wind farms
Depletion of plankton
resources by sessile
invertebrates colonizing
platforms
b10 m Lower infaunal biomass and altered infaunal
community structure Maar et al. (2009)
Increased
predation
Articial
reefs
Increased predation from
reef-associated predators
Meters to
10s of
meters
Unknown Davis et al. (1982),Nelson et al. (1988),Frazer
et al. (1991),Posey et al. (1992)
Pilings Attracts consumers
(surfperch, crabs) Meters Unknown Toft et al. (2007)
Wind farms
Increase of consumers
associated with
platforms/Increased physical
disturbance from foraging
activity
b10 m Unknown Maar et al. (2009)
Change in
disturbance
from
humans
Crab tiles Increased disturbance from
trampling Variable Depletion of meiofauna Sheehan et al. (2010a)
Articial
reefs
Decreased disturbance from
reduction of bottom trawling Variable Unknown Cheung et al. (2009)
5E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
example, ship noise can negatively affect foraging and antipredator be-
havior in the shore crab, Carcinus maenas (Wale et al., 2013b). It is likely,
therefore, that organisms living in association with the sediments are
affected by the noise produced during the life-cycle of marine infra-
structures (construction, operation and decommissioning). Much of
the research on anthropogenic noise related to articial structures has
focused on pile driving when constructing offshore infrastructure. Pile
driving is regarded as one of the most extreme noises associated with
articial structures, therefore representing the worst-case scenario
when assessing impacts (Madsen et al., 2006). Research needs to be ex-
tended to other potentially important noise sources, including near-
shore renewable energy development and articial structures
associated with recreational boating, which correlate with boat trafc
(Widmer and Underwood, 2004).
Another change to the sensory environment of sediments results
from cables that connect the mainland with offshore infrastructure
and generate electromagnetic (EM) elds. Many marine species are
EM-sensitive, including cetaceans, turtles, certain groups of sh, and
some crustaceans and mollusks (Gill et al., 2014). The nudibranch
Tritonia diomedea, for instance, uses earth's magnetic eld to navigate
shallow sedimentary environments in the northeast Pacic(Lohmann
and Willows, 1987; Willows, 1999; Wyeth and Willows, 2006). The in-
tensity of EM elds emitted by submarinecables is potentially sufcient
to interfere with such behaviors (Bochert and Zettler, 2004), however,
direct evidence of EM-related impacts from cables on the navigation
and movement of sedimentary marine organisms is limited (Gill,
2005; Tricas and Gill, 2011). Andrulewicz et al. (2003) found no consis-
tent change in themacrozoobenthos of sandy substrata from before and
after the installation of a submarine cable system between Sweden and
Poland, despite a strongly altered magnetic eld. Similarly, no signi-
cant change in the behavior of the Atlantic halibut (Hippoglossus
hippoglossus), Dungeness crab (Metacarcinus magister), or the
American lobster (Homarus americanus)species closely associated
with sedimentary habitat (Woodruff et al., 2012)were observed fol-
lowing exposure to a magnetic eld in the laboratory. The mechanism
by which EM elds might impact marine organisms remains under in-
vestigation. For instance, laboratory experiments have shown that EM
elds can induce the expression of heat shock proteins (HSPs) 70 and
90 in. immunocytes of the mussel Mytilus galloprovincialis that attaches
to hard substrates (Malagoli et al., 2004). Similar effects on sediment-
dwelling invertebrates may be expected, however, further study is
needed.
2.3. Hydrodynamic effects
Articial structures change the speed and direction of water move-
ment. This results in a number of hydrodynamic effects at large, inter-
mediate, and small spatial scales.
Fig. 2. Spatial scale of effects of different typesof articial structures.
6E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
2.3.1. Large-scale hydrodynamic effects
At large spatial scales (hundreds of meters to kilometers), articial
structures can cause extensive modications to water circulation pat-
terns and sediment transport mechanisms (Bostic et al., 2015;
Cavalcante et al., 2016; Cuadrado et al., 2005; Thomalla and Vincent,
2003; Zyserman et al., 2005). For instance, groynes, breakwaters, sea-
walls, and articial reefs alter and restrict sediment dynamics by
interrupting both longshore and tidal transport (Cuadrado et al., 2005;
Pilkey and Wright, 1988). Sediment volume increases on the up drift
side of these structures and decreases in down drift areas (Duane,
1976; Komar, 1998), which can reduce the extent of adjacent wetlands
(Bostic et al., 2015) and beaches (Thomalla and Vincent, 2003).
Interrupted currents also affect gamete and larval transport (see
Bishop et al., in this issue). Eggs of horseshoe crabs (Limulus polyphe-
mus) tend to accumulate in shoreline discontinuities, such as along
jetties and in the enclaves between bulkheads (Jackson et al., 2015).
This, in turn, can increase aggregations of foraging shorebirds (Botton
et al., 1994). While the concentration of predators can have greater eco-
logical or evolutionary implications (i.e. - increasing intraspecicorin-
terspecic competition among shorebirds, altering the timing and
synchronicity of reproduction among prey), research on such effects
has been limited.
It is important to note that these large-scale hydrodynamic effects
from articial structures do not happen in isolation. They are usually
furthered by other human activities in the marine environment, such
as dredging for navigation and/or mineral extraction, the damming of
rivers, and construction of ood and shoreline defenses, which restrict
uvial and terrestrial sediment delivery to oceans (Dethier et al.,
2016; Milliman and Farnsworth, 2013). Such modications result in
less sediment being available to counteract the negative hydrodynamic
effects from articial structures on sediment supply and dynamics
(French, 2001). At the same time, modications of rivers associated
with agriculture and other development have increased supply of silts
and total suspended solids (TSS) to marine systems. Both types of mod-
ications additionally change the composition of sediment, which may
alter the quality and suitability of sedimentary habitats (Section 2.3.3).
Comparing changes in estuarine sediment communities from before to
after the undamming of rivers, which is presently occurring the US
(Gelfenbaum et al., 2015), may be a fruitful means of exploring these in-
teractions. Directly testing theinteraction effect betweenarticial struc-
tures and human modications, such as beach nourishment, can also
bring valuable insights for potential mitigating strategies (Colosio
et al., 2007).
2.3.2. Intermediate-scale hydrodynamic effects
At large to moderate spatial scales(tens of meters), the interruption
of circulation patternsby articial structures changesthe residence time
of water. Wave energy and ow decrease in areas that are enclosed by
recreational boating marinas (Balas and Inan, 2010; Floerl and Inglis,
2003; Rivero et al., 2013) and by networks of breakwaters and groynes
(Zanuttigh et al., 2005). This increases water retention and the resi-
dence time of suspended particles, particularly following storm events
(Zanuttigh et al., 2005). Longer residence times may inuence the larval
dispersal of infaunal species and affect recruitment to the benthos by
inhibiting passive transport (Sim et al., 2015). Longer residence times
also coincide with increases in turbidity, temperature, and pH
(Munari, 2013; Rivero et al., 2013). While pH and temperature are
known to impact larval and post-settlement survival of infauna
(Talmage and Gobler, 2011) and infaunal assemblage structure (Hale
et al., 2011),the extent of increases in these two factors that is attribut-
able solely to articial structures may be of little consequence biologi-
cally (Rivero et al., 2013). Increased turbidity, however, may have
signicant implications for infaunal communities, with particularly neg-
ative potential effects on suspension feeding bivalves (Bricelj et al.,
1984; Ellis et al., 2002).
Interrupted circulation patterns also lead to changes in the bathy-
metric prole of sedimentary habitats. The seaoor becomes shallower
over time in areas where articial structures have reduced ow and in-
creased sediment accumulation, such as on the landward sides of break-
waters (Scyphers et al., 2011). The shallower areas between
breakwaters and the shore are known to support distinct assemblages
of sh (Scyphers et al., 2011) and infauna (Bertasi et al., 2007; Martin
et al., 2005; Munari et al., 2011). Depth-related zonation patterns of in-
fauna also differ on the landward sides of breakwaters, with deeper-
water species inhabiting shallower depths than in sediments where
breakwaters are absent (Bertasi et al., 2007). However, these trends
may primarily be the result of other small-scale hydrodynamic-related
processes, such as changes in granularity (Section 2.3.3) or organic en-
richment (see Section 2.4). The relative importance of these multiple,
often co-occurring mechanisms, has yet to be evaluated directly in the
eld.
Seawalls and bulkheads reect waves and thus tend to increase
wave energy, scouring, and erosion of sediment (Pilkey and Wright,
1988). The extent and rate of erosion depends on local hydrodynamic
conditions as well as sediment supply, and may not be evident within
the rst few years of seawall construction (Jaramillo et al., 2002). Sedi-
ment erosion may directly affect soft-sediment communities by causing
concomitant erosion of small organisms such as meiofauna (Spalding
and Jackson, 2001). It may indirectly affect sedimentary communities
by reducing habitat availability for resident and dependent taxa
(Brown and McLachlan, 2002; Rizkalla and Savage, 2010), by altering
shoreline prole (Dugan et al., 2011), and by modifying key attributes
of the abiotic environment such as sediment grain size (Section 2.3.3).
Armored beaches tend to be steeper than unarmored beaches (Morley
et al., 2012).This can limit the growth of macrophytes andnegatively af-
fect mobile organisms, which rely on them for food and nursery habitat
(Morley et al., 2012; Peterson et al., 2000). Beach steepening is likely to
increase as sea-level rise accelerat es (Hansom, 2001), and may augment
the impact of shoreline structures depending on local conditions (Kraus
and McDougal, 1996). Additionally, intertidal habitats that are armored
with seawalls are often narrower than unarmored shorelines
(Bernatchez and Fraser, 2012; Fletcher et al., 1997; Hall and Pilkey,
1991; Heatherington and Bishop, 2012; Pilkey and Wright, 1988) and
in many instances organisms are unable to compensate for lost habitat
by increasing in density (Lucrezi et al., 2010; Schlacher et al., 2016).
Furthermore, modied currents and wave action can cause changes
in intermediate- to small-scale sediment habitat features, such as scour
holes and ripple patterns (Barros et al., 2004; Kambekar and Deo, 2003;
Uijttewaal, 2005). Such features form as waves and currents move
across surface sediments and recongure the distribution of individual
grains (Blondeaux and Vittori, 2016). An interruption in waves and cur-
rents can therefore lead to modied topographical features and changes
in structural complexity at intermediate spatial scales. In a habitat al-
ready at the low end of the complexity spectrum, this may have pro-
found effects on the diversity of species (Byers and Grabowski, 2014),
particularly communities of meiofauna (Sun et al., 1993). Ripple pat-
terns in sediments have been shown to vary depending on distance
from hard structures and coincide with distinct macrofaunal communi-
ties (Barros et al., 2004). More work is needed, however, to improve our
understanding of the effects of altered topography from articial struc-
tures on sediment community structure (Barros et al., 2004; Davis et al.,
1982).
2.3.3. Small-scale hydrodynamic effects
At small spatial scales (centimeters to meters), articial struc-
tures impact soft sediment assemblages via several ow-related
mechanisms. Altered current-ow can impact sedimentary organ-
isms directly. For instance, waves rebounding from seawalls and
bulkheads might inuence the feeding behavior of lter feeders at
small scales by altering the dimensions of feeding apparatus and re-
ducing the conditions that are suitable for feeding (see Li and Denny,
7E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
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http://dx.doi.org/10.1016/j.jembe.2017.01.020
2004; Marchinko and Palmer, 2003 for examples from other wave-
exposed settings). Reected waves may also impact the morphology
of sedimentary species, as stunting of growth forms has been ob-
served in response to other causes of wave action (La Naeetal.,
2012; Norton-Grifths, 1967).
Hydrodynamic changes also impact sedimentary organisms indi-
rectly by altering other key physical variables at relatively small spatial
scales. Modied patterns of ow cause considerable changes in granu-
larity, or grain size composition, of surrounding sediments. Finer sedi-
ments accumulate where ow is reduced, such as on the landward
sides of breakwaters (Zanuttigh et al., 2005) and articial reefs (Fricke
et al., 1986), and in areas where ow is impeded by structures for aqua-
culture (Guiral et al., 1996; McKindsey et al., 2011) and recreational
boating (Rivero et al., 2013). Conversely, sediments become coarser
where there is higher ow or wave energy increases scour, such as at
the base of seawalls (Bozek and Burdick, 2005), on the down current
sides of wind turbines (Maar et al., 2009), or surrounding anchor blocks
associated with aquaculture structures (Guichard et al., 2001). As a gen-
eral rule, the ner the sediment, the shallower the oxic layer, as ner
grains have less interstitial space for water and air passage (Byers and
Grabowski, 2014). Altered granularity may also therefore have conse-
quences for primary production and the remineralization of organic
matter in sedimentary systems as suggested by recent microbial studies
(Sun et al., 2013).
Granularity is known to inuence benthic communities (Snelgrove
and Butman, 1994) and has been highlighted in many studies as a prob-
able mechanism by which articial structures alter soft sediment com-
munity composition (Ambrose and Anderson, 1990; Barros et al.,
2001; Fricke et al., 1986). Infaunal assemblage structure tends to covary
with grain size in the sediments surrounding breakwaters, for instance
(Bertasi et al., 2007; Martin et al., 2005). In some cases, modied sedi-
ments support a higher density and abundance of deposit-feeding bur-
rowers (Munari, 2013). Bioturbation from burrowers is a key process
that inuences sediment oxygenation and nutrient cycling (e.g. Lohrer
et al., 2004; Norling et al., 2007; Olsgard et al., 2008). Changes in biotur-
bation may therefore impact nutrient and oxygen uxes (Norling et al.,
2007; Solanet al., 2004; Thrush et al., 2006). In other instances, the ad-
dition of breakwaters has been shown to increase the abundance of sus-
pension feeding bivalves on sandy beaches (Bertasi et al., 2007). In
separate experiments the removal of suspension feeders was found to
cause an increase in microphyte standing stocks as well as an increase
in NH
4
-N efux in the light (Thrush et al., 2006). The authors also
found that the removal of suspension feeders led to greater changes
than the removal of deposit feeders (Thrush et al., 2006). Structural
changes to sedimentary communities caused by articial structures
may therefore have important indirect consequences on functional
properties.
The hydrodynamic changes that result from the introduction of
articial structures tend to covary with a number of other
chemical and biotic parameters as well, each of which has
additional implications for sedimentary ecosystems (Table 1).
These and other interrelated effects are discussed below
(Sections 2.4 and 2.5).
2.4. Organic enrichment and material uxes
The accumulation of ne sediments tends to coincide with organ-
ic enrichment, which is known to impact soft sediment communities
(Pearson and Rosenberg, 1978). In low ow settings, such as those
surrounding some articial structures (Al-Bouraee, 2013), sediment
organic content is generally high (Snelgrove and Butman, 1994). Ar-
ticial structures may further enhance organic matter inputs to adja-
cent sediments by supporting ora and fauna that contribute dead
tissue and organic waste to sediment (Airoldi et al., 2010; Cranford
et al., 2009; Giles, 2008; Holmer et al., 2005; Kennicutt et al., 1996;
McKindsey et al., 2011; Montagna and Harper, 1996; Wildish et al.,
2001). For example, Maar et al. (2009) found increased ammonia,
detrital material, and fecal pellets down drift from blue mussel pop-
ulations attached to offshore wind turbines. The mussels did, howev-
er, reduce the availability of phytoplankton and certain zooplankton
species, which are food resources for infaunal suspension feeders
(Maar et al., 2009). Similarly, the production of phytodetritus by nat-
ural rocky reefs can inuence the organic content of soft sediments
(Agnew and Taylor, 1986; Riggs et al., 1998), with ow-on effects
to infaunal recruitment (Renaud et al., 1999), community composi-
tion, and trophic dynamics in some instances extending well beyond
the immediate vicinity of the source (Bishop et al., 2010).
Conversely, where articial structures enhance ow, reduce primary
and secondary productivity, and/or serve as barriers to transport of al-
lochthonous organicmatter, they may reducesediment organic content.
Wrack accumulations are often less on armored than unarmored inter-
tidal shorelines in part due to reduced wrack retention and likely also
due to reduced wrack supply (Heatherington and Bishop, 2012;
Heerhartz et al., 2014; Sobocinski et al., 2010). In some instances, sea-
walls may reduce organic matter retention by accelerating decomposi-
tion rates and/or decreasing organic matter residence times (Harris
et al., 2014). In other instances, the reduced retention of wrack may
be due to loss of the high intertidal and supratidal habitat, at which ma-
terial accumulates on unarmored shorelines (Dugan et al., 2008;
Heatherington and Bishop, 2012). The reclamation of land adjacent to
seawalls can reduce terrestrial sources of leaf litter (Higgins et al.,
2005) and the constraint by coastal armoring of intertidal habitat for
primary producers, such as mangroves, may reduce autochthonous lit-
ter supply (Heatherington and Bishop, 2012). The net effect is reduced
food and habitat for invertebrates, and consequently altered inverte-
brate communities (Dugan et al., 2008; Heerhartz and Toft, 2015;
Heerhartz et al., 2014, 2016).
The paradigm is that the abundance of suspension feeders declines
and the abundance of deposit feeders increases with sediment organic
content (Pearson and Rosenberg, 1978). Yet, while several authors
have found differences in soft sediment community structure that coin-
cide with organic content (Ambrose and Anderson, 1990; Barros et al.,
2001; Danovaro et al., 2002; Zalmon et al., 2014), they do not appear
to follow a consistent pattern. Increased organic content in sediments
surrounding articial structures can reduce oxygen concentrations,
leading in some cases to sediment hypoxia (Danovaro et al., 2002;
Wilding, 2014). Hypoxia events can potentially alter net primary and
secondary production and reduce the diversity and abundance of spe-
cies in sedimentary habitats (Diaz andRosenberg, 2008). However, hyp-
oxia probably arises only when structures are added to already oxygen-
decient sediments (Wilding, 2014). In sufciently oxygenated sedi-
ments, organic enrichment surrounding articial structures may instead
dampen seasonal variability in nutrient availability that would occur if
the structures were absent. For instance, Machado et al. (2013) found
that sediments surrounding subtidal articial reef balls did not exhibit
the same seasonal variation in reactive phosphorus, total nitrogen, or
organic carbon as a control site without reef balls (Machado et al.,
2013).
In addition to inuencing organic matter inputs to sediments, arti-
cial structures may also inuence inputs of calcareous material. Sessile
invertebrates on hard structures generate large amounts of shell mate-
rial that fall to marine sediments when the organisms die, are damaged,
or become dislodged (Ambrose and Anderson, 1990; Barros et al., 2001;
Machado et al., 2013). This inux of shell material alters sediment gran-
ularity such that it becomes coarser immediately surrounding articial
structures (Barros et al., 2001). Presumably such habitat modication
could alter sedimentary communities, by reducing the foraging efcien-
cy of some sediment-feeding predators, and by impeding burial of some
infaunal taxa (Gutiérrez et al., 2003). However, to our knowledge, no
studies have tested whether such mechanisms are responsible for dif-
ferences in infaunal community structure immediately surrounding ar-
ticial structures.
8E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
2.5. Contaminants
Articial structures can also modify sedimentary communities by di-
rectly and indirectly altering their exposure to contaminants. The effects
of contaminated sediments on aquatic communities have been exten-
sively reviewed for a range of environmental conditions (Burton and
Johnston, 2010) and here we focus solely on the role of articial struc-
tures in modifying contaminant concentrations and exposure. Articial
structures may directly inuence contaminants as a consequence of the
materials from which they are constructed. They may indirectly inu-
ence contaminants by altering properties of the sediment that affect
their afnity to bind contaminants, by inuencing water retention,
and as a consequence of the activities that they support.
The materials from which articial structures are constructed and
the biocidal coatings applied to them can have large inuences on con-
taminant loads. In recent decades, there has also been growing concern
about toxic leachate from car tires (Collins et al., 1995, 2002; Day et al.,
1993; Degaffe and Turner, 2011; Wik and Dave, 2009), which have been
used to construct articial reefs (Collins et al., 2002; Fabi et al., 2011;
Thierry, 1988), breakwaters, and other coastal defense installations
(Collins et al., 1995, 2002). Tires leach zinc and polycyclic aromatic com-
pounds (Collins et al., 1995, 2002; Degaffe and Turner, 2011). Zinc, in
particular, likely penetrates adjacent sediments (Degaffe and Turner,
2011), bioaccumulates in invertebrates (Amiard et al., 2007; Hanna
et al., 2013), and increases mortality of sedimentary organisms
(Hanna et al., 2013). Articial reefs have also been constructed from
coal and oil ash (Collins and Jensen, 1995; Collins et al., 1992, 1994;
Nelson et al., 1994; Vose and Nelson, 1998), which contain large
amounts of heavy metals that can increase invertebrate mortality
(Hamilton et al., 1993) if leachates are not contained via a stabilization
process (Breslin and Roethel, 1995; Collins and Jensen, 1995;
Pickering, 1996; Shieh and Duedall, 1994). Similarly, the treatment of
wooden pilings in marinas and jetties with copper chromated arsenate
(CCA) has been found to be a signicant source of copper contamination
(Hingston et al., 2001; Weis and Weis, 1996; Weis et al., 1993). When
metal biocides are released into waterways their ions can bind to bot-
tom sediments (Di Franco et al., 2011; Singh and Turner, 2009), and
subsequently dissociate to enter the porewater and overlying water as
free metal ions (Simpson et al., 2004). Contamination of sediments in
turn inuences sediment community structure and diversity (Neira
et al., 2014; Rivero et al., 2013; Sim et al., 2015; Wilkie et al., 2010).
Changes in ow and granularity caused by articial structures can
also inuence contamination indirectly. Increased deposition of ne
sediments, for instance, has been linked to increased contamination
due to the greater afnity and capacity of ne sediments to bind con-
taminants (Burton and Johnston, 2010; Simpson et al., 2013). Recrea-
tional marinas generally experience water retention and reduced
ushing because they are built in low energy environments or
surrounded by breakwaters. This has consequences for water quality
and contaminant retention (Johnston et al., 2011; McGee et al., 1995;
Schiff et al., 2004). Because vessel anti-fouling (AF) paints and the
cleaning of pontoons and jetties are major contaminant sources
(Srinivasan and Swain, 2007), marinas are hot spots of metal contami-
nation in coastal and estuarine systems (Dafforn et al., 2011; Rivero
et al., 2013; Schiff et al., 2007; Turner, 2010; Warnken et al., 2004).
The activities that articial structures support are also a major source
of contamination. For example, the N7000 oils and gas platforms
installed around the world (Gray et al., 1990; Wilson and Heath,
2001) pollute the marine environment through accidental spillage, dis-
charge of drill cuttings, and discharge of production water (Kingston,
1992). Studies investigating the impacts of offshore oil and gas drilling
have found impacts to benthic sediment communities extending up to
500 kilometers from the rig or platform (Gray et al., 1990; Kingston,
1992). Opportunistic species may proliferate under moderate levels of
pollution, but at high levels even opportunists are unable to persist
(Gray et al., 1990; Kingston, 1992; Olsgard and Gray, 1995)More
broadly, responses of invertebrate communities to contaminants from
oil and gas platforms can involve reduced cellular viability, considerable
changes in abundance and reductions in diversity indices such as even-
ness (Edge et al., 2016; Gray et al., 1990; Johnston and Roberts, 2009;
Kingston, 1992; Olsgard and Gray, 1995; Sandrini-Neto et al., 2016).
The severity of decreases appears to depend on the frequency with
which sedimentary communities are exposed to contaminants
(Sandrini-Neto et al., 2016). While many infaunal organisms recover
relatively quickly after contamination events, such as oil spills (Bolam
et al., 2002; Sandrini-Neto and Lana, 2014; Sandrini-Neto et al., 2016),
others are highly sensitive to oil contamination (e.g. Bulla strita,Tellina
versicolor)(Sandrini-Neto et al., 2016).
2.6. Biotic effects
An additional mechanism by which articial structures may affect
sedimentary ecosystems is by modifying biotic interactions. Articial
structures can modify predator-prey interactions by altering predator
abundance, prey abundance, or encounter rates (Caine, 1987; Davis
et al., 1982; Kneib, 1991; Firth et al., in this issue). They may also modify
positive interactions among species, such as facilitation, by altering the
abundance of habitat forming species and eco-engineers. For instance,
by aggregating green shore crabs (Carcinus maenas) for commercial har-
vest (Sheehan et al., 2008), foraging shorebirds (Sheehan et al., 2012),
and mobile epifauna (Sheehan et al., 2010a), crab tiles may enhance
predation in their vicinity. Reductions in the abundance of habitat-
forming macrophytes as a result of shading (Section 2.2) or steepening
of habitat proles (Section 2.3) can affect the composition and abun-
dance of infaunal taxa they facilitate (Eckman, 1983; Fonseca and
Fisher, 1986; Ward et al., 1984).
Subtidal articial reefs attract a variety of predatory sh (Brotto
et al., 2006; Wilhelmsson et al., 2006), which move into surrounding
areas (Henderson et al., 2014), feed on sedimentary organisms (Kurz,
1995; Lindquist et al., 1994), cause physical disturbances to sediments
(Hall et al., 1991; Thrush et al., 1991; VanBlaricom, 1982),and introduce
additional nutrients by excreting waste (Cheung et al., 2010). Off-reef
foraging distance can vary, but the greatest foraging activity tends to
occur within 10 m (Frazer et al., 1991; Nelson et al., 1988; Posey et al.,
1992). Posey and Ambrose (1994) emphasized the importance of in-
creased predation on infauna from consumers associated with natural
reefs, but noted that these dynamics may differ on articial structures
(Posey and Ambrose, 1994). Such haloeffects have been much
discussed in the literature, but few studies have employed the experi-
mental designs necessary to establish causal linkages between preda-
tion and the structure of sedimentary communities (but see Hill et al.
(2013) for a small-scale experimental study). Gradients in reef-
associated predation frequently coincide with gradients in hydrody-
namic factors that may also affect infaunal composition (Galván et al.,
2008; Jones et al., 1991; Langlois et al., 2005), raising the possibility of
confounding variables.
Conversely, feeding by predators such as gray whales (Weitkamp
et al., 1992) may be reduced in sedimentary habitats where articial
structures block their movement or foragingactivities. Similarly, shing
activities by humans, and specically bottom trawling, may be reduced
in some cases by the introduction of articial reefs, thus having positive
effects on the abundance of some taxa and on species richness (Cheung
et al., 2009; Liu et al., 2011; Munoz-Perez et al., 2000). Since bottom
trawling can affect a variety of physical, chemical, and biotic processes
(Thrush and Dayton, 2002), articial structures placed in heavily
trawled areas may indirectly affect sediment dynamics, lower sediment
nutrient levels (Ambrose and Anderson, 1990), and facilitate the
remineralization of organic matter, bioturbation, and bioirrigation of
sediments (Cheung et al., 2009). This has not been empirically tested
in the eld and is potentially applicable only in trawled, subtidal sedi-
mentary environments. Articial structures that are used to attract har-
vested species, such as crab-tilesin the Carcinus maenus shery in the
9E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
United Kingdom, tend to increase the use and trampling of soft sedi-
ment habitats by humans, which impacts infaunal communities
(Sheehan et al., 2010b).
Articial structures may also affect demographic patterns and be-
havioral traits of soft sediment predators and infauna. For instance,
Henderson et al. (2014) found that summer ounder (Paralichthys
dentatus) were larger near articial reefs than in more distant soft sed-
iments. They suggested this pattern arose at least in part due tobehav-
ior, as sh associated with articial structures tended to be more
territorial, resulting in the competitive exclusion of smaller individuals
(Henderson et al., 2014). Similarly, Long et al. (2011) found that sh
feeding on juvenile blue crabs (Callinectes sapidus) in Chesapeake Bay
were larger in size and had higher foraging rates along armored shore-
lines than near natural Spartina marshes where articial structures were
absent. Demographic responses to articial structures are also plausible
among infaunal populations. Dahlgren et al. (1999) found more larger-
bodied and fewer small-bodied macrofaunanear natural reefs. Differen-
tial demographic responses among sh and infauna would be expected
if different size classes were affected in distinct ways by the altered
physical, chemical, and biotic conditions surrounding structures. Such
responses likely vary considerably over space and time (Langlois et al.,
2006), but may be an important consideration for monitoring efforts
and future research.
Lastly, insome instances, articial structures appear to facilitate bio-
engineering species in surrounding sediments, but in areas with previ-
ously abundant bioengineers, they may have negative impacts. In
transects extending perpendicularly from subtidal articial structures
in Southern California, Ambrose and Anderson (1990) found the tube-
dwelling Onuphid polychaete Diopatra ornata was only present imme-
diately adjacent to structures. Diopatra spp. was also documented to
occur in high densities surrounding oil platforms in the same region
(Davis et al., 1982). Similarly, Heery and Sebens (unpublished data)
have observed higher densities of the tube-dwelling Chaetopterid poly-
chaete Spiochaetopterus costarum immediately adjacent to articial
structures in Puget Sound, Washington. Ambrose and Anderson
(1990) suggest that enhanced densities of polychaetes like D. ornata in
the vicinity of structures may stabilize sediment, provide refuge habitat,
or serve in some other facilitative capacity that ultimately increases in-
faunal diversity and abundance. However, they did not evaluate this hy-
pothesis directly in their study.
3. Factors inuencing the direction and magnitude of impacts
The way in which articial structures modify sedimentary commu-
nities depends on their design and spatial conguration, the character-
istics of theabiotic and biotic environment in whichthey are placed, and
the scale of the impact, including area affected and duration (Airoldi
et al., 2005; Martin et al., 2005). Unfortunately, many scientic-based
assessments often neglect these complex interactions and scaling is-
sues, which limits our current capability to predict the impacts of future
developments (Loke et al., 2015). Studies to date have found tremen-
dous variation in the patterns and trends they have observed in sedi-
mentary habitats where articial structures have been placed. This is
likely due atleast in part to inherent variation in the direction and mag-
nitude of impacts from articial structures, both over space and time,
and across multiple spatial scales. For each of the effects documented
above, there are a number of factors that likely inuence variation in ob-
served patterns in the eld and are worth considering when seeking to
identify generalizable trends.
Placement loss (Griggs, 2005;Section 2.1), by denition, increases
with the aerial extent of foundations constructed in sedimentary habi-
tat, and may be especially large in coastal areas where construction of
structures is accompanied by backll to reclaim land. In coastalenviron-
ments, losses can be amplied by passive erosion, which results from
structures inhibiting natural cycles of shoreline retreat (Griggs, 2005).
The extent of such passive erosion can depend on the tidal elevation
at which a defense structure is built, as well as whether a shoreline is
presently in an accretive or erosive state (Archetti and Romagnoli,
2011; Lin and Wu, 2014). Active erosion of sediment adjacent to struc-
tures, through wave reection, scouring, and end effects(Griggs, 2005)
can also affect the magnitude of habitat loss. The effects are greatest
where sand input is low and wave energy high (Lin and Wu, 2014;
Miles et al., 2001). They are also dependent on the extent to which
structures are designed to absorb versus reect wave energy (e.g. hol-
low seabed versus solid concrete seawall designs) (Hettiarachchi and
Mirihagalla, 1998; das Neves et al., 2015; Zanuttigh et al., 2005).
Impacts of articial structures on sediment communities also vary
spatially according to the extent to which they modify the abiotic and
biotic conditions and local processes that control soft-sediment com-
munity assembly (Airoldi et al., 2005; Martin et al., 2005). The position
(i.e. onshore vs offshore), orientation (i.e. perpendicular or parallel to
shorelines), permeability (solid versus rock wall), dimensions and spac-
ing of structures are all factors that could inuence the extent to which
structures intercept longshore drift, tidal and other currents, which in
turn shape sedimentary communities by determining sediment, larval
and resource (e.g. wrack and organic matter) transport and deposition
(Martin et al., 2005; Bishop et al., in this issue). For example, Shyue
and Yang (2002) found that the area of scour surrounding subtidal arti-
cial reefs was heavily inuenced by the structure's height, although
differences in ambient ow between locations were also important
(Shyue and Yang, 2002). The placement of seawalls with respect to
tidal height and local wave energy are important factors determining
the extent of scour and sediment coarsening in intertidal environments
(Weigel, 2002). As another example, the impacts of oil rigs on adjacent
sediment communities could be mitigated at deeper waters because of
higher environmental stability and greater potential of dilution and dis-
persion of pollutants (Burns et al., 1999; Ellis et al., 1996). Terlizzi et al.
(2008), however, reported an opposite trend, possibly because plat-
forms at deeper sites are taller, therefore leaching greater amounts of
contaminants or providing more surface area for growth of fouling in-
vertebrates which slough off to inuence sedimentary communities
(Goddard and Love, 2010; Love et al., 1999; Terlizzi et al., 2008).
The spatial arrangement and isolation of articial structures could
affect sedimentary environments both directly, by affecting patterns of
sediment deposition, and indirectly, by affecting the capability of arti-
cial reefs to attract grazing and predatory sh communities. For exam-
ple, on a Brazilian articial reef, the proximity of reef balls to one
another inuenced their effect on organic and ne sediment inputs to
adjacent habitat (Zalmon et al., 2014), with inputs greatest at a larger
spacing. Overall, the large-scale effects of multiple structures (such as
offshore structures) may differ from their local effects. For example,
parks of offshore wind farms can act as a partial blockage of the overall
current eld: the blocked water volume is forced around the park,
which leads to a decrease in the ow inside the park and an increase
in ow velocities on the sides of the park (Airoldi et al., 2016). These
blockages depend on the distance between piles (typically 600 to
1200 m), the diameter of the piles (610 m), the overall number of
wind turbines in the park and the lay-out of the farm.
The sediment grain size and hydrodynamic regime can also deter-
mine the extension and severity of some of the impacts. For example,
the effects of crab-tiles used to attract crabs for harvest depend on the
grain size of the sediments where they are placed (Sheehan et al.,
2010a). Similarly, the impacts from the sediment spills due to dredging
for foundation and cable trenches of offshore activities will primarily be
of local nature in low-current environments, while in high-current envi-
ronments far-eld impacts of lower intensity will prevail, due to advec-
tion and dilution (Airoldi et al., 2016). Further, the impacts of structures
on sediments may vary spatially according to the processes occurringat
the time of their construction, for example fouling community coloniza-
tion (Underwood and Anderson, 1994) which in turn determines re-
source subsidies to adjacent sedimentary habitats (Airoldietal.,2010;
Goddard and Love, 2010; Love et al., 1999).
10 E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
The effect of structures on sediment communities may also be ex-
pected to vary according to the diversity and identity of soft sediment
communities at disturbed sites (Martin et al., 2005). For example, the
diverse communities of dissipative beaches are more susceptible to
the effect of structures than the more depauperate assemblages of ex-
posed sandy beaches (Martin et al., 2005). Oil and gas rigs or articial
reefs that exclude shingvessels may have large positive effects on bio-
diversity by removing or alleviating dredge or trawling disturbance to
ecosystem engineers such as clams, tube worms, or seagrasses
(González-Correa et al., 2005; Pearce et al., 2014). Conversely, if arti-
cial structures have a negative effect on ecosystem engineers (e.g.
Lemasson et al., in this issue; Teagle et al., in this issue).
Not only dothe effects of structuresvary spatially according to their
abiotic and biotic context, but they may also vary temporally. Effects of
articialstructures on sedimentcommunities may strengthen or weak-
en with time since their construction. For example, because the devel-
opment of fouling communities on structures takes time (Underwood
and Anderson, 1994), indirect effects on sediment communities
resulting from sloughing of algae or shell (Airoldi et al., 2010;
Goddard and Love, 2010; Love et al., 1999) or fouling communities de-
positing feces (Maar et al., 2009), may increase with time since con-
struction. Conversely, pulse impacts associated with the construction
phase, such as those resulting from turbidity plumes or construction
noise deterring benthic predators (Slabbekoorn et al., 2010) may weak-
en over time (Jaramillo, 2012). The effect of structures on sediment
communities may also vary temporally according to natural variation
in the strength of the abiotic and biotic processes they disrupt. For ex-
ample, articial reefs in Brazil reduce current velocities predominantly
during months of high ow from the Paraiba do Sul River (Machado
et al., 2013) and, conceivably, enhancement of predator foraging pat-
terns around articial structures may vary seasonally according to the
biology of species.
4. Approaches employed in past studies
The effects of articial structures on soft sediment ecosystems can
currently be considered based on three types of information. Firstly, in-
ferential studies that examine the response of soft sediment organisms
to environmental changes associated with articial structures (e.g.
shading, modication of sediment grain size and so forth)provide prox-
imal insights, but are primarily helpful for generating hypotheses. Sec-
ondly, surveys that examine how environmental variables and
sediment communities vary spatially in the areas with and without ar-
ticial structures can lend further proximal information, but are limited
by inherent spatial variation in sedimentary ecosystems and confound-
ing variables. Lastly, Before/After and Control/Impact (BACI) designs
test for causal effects of structure construction on sedimentary systems.
BACI designs are recognized as a robust approach for documenting
environmental impacts (Hilborn and Walters, 1981; Underwood,
1994), as they test for causality (Underwood and Peterson, 1988). If ef-
fectively implemented, these designs provide the advantage of control-
ling for temporal changes that are confounded with the introduction of
an articialstructure, as well as site-specicdifferences that are unrelat-
ed to structure introduction. Reference sites used in such designs must
be selected carefully to ensure they are sufciently similar to those
where an articial structure will be introduced without being in range
of the structure's effects (Stewart-Oaten et al., 1986). In order to detect
changes, data collection in BACI-type studies must also continue over a
period of time that coincides with the temporal scale of the effects being
measured (Stewart-Oaten et al., 1986). These limitations commonly
make BACI-designs unfeasible, and the approach has been used only
rarely as a means of characterizing the effects of articial structures on
soft sediment ecosystems (Jaramillo et al., 2002).
Most studies have instead sought to characterize patterns of spatial
variation in soft sediment communities that correlate with the presence
of or the distance from an existing articial structure (Ambrose and
Anderson, 1990; Barros et al., 2001; Davis et al., 1982). Such studies
have many limitations. Sites where articial structures are constructed
are also usually non-randomly selected, so it is likely that there are
pre-existing differences between sites with and without structures
that are unrelated to the construction or presence of the structures
themselves. Even within a single site, it is difcult to discern patterns as-
sociated with articial structures in surrounding sediments due to the
inherent patchiness of soft sediment communities over time and
space (Morrisey et al., 1992a, 1992b). Observationally derived differ-
ences in community structure do not therefore demonstrate causation,
nor do they allow for conclusions regarding the mechanisms that are
behind observed differences.
Many of the observational studies we reviewed emphasized specic
physical, chemical, or biotic factors as the potential mechanism driving
community and species distribution patterns observed in the eld.
However, there remains a strong need for research that tests the impor-
tance of multiple mechanistic processes associated with articial struc-
tures on soft sediment ecosystem response. In addition, most studies
focused on relatively local impacts of articial structures on immediate-
ly surrounding soft sediments. Few studies have considered the cumu-
lative impacts of multiple structures on sediments at larger spatial
scales. There may be non-linear effects of adding more articial struc-
tures to a seascape, such as a tipping point beyond which thereis no lon-
ger sufcient sedimentary substrate to support particular groups of
organisms, or beyond which the environment is no longer tforhabita-
tion. Studies on the cumulative impacts of structures at the landscape
scale are urgently needed as marine urbanization accelerates (Dafforn
et al., 2015; Johnston et al., 2015; Bishop et al., this special issue).
5. Research gaps and future directions
As articial structures extend across an increasingly large proportion
of sedimentary seascapes (Airoldi and Beck, 2007), it is important that
we improve our understanding of impacts on sedimentary ecosystem
structure and function so that we can manage ocean sprawl in more
ecologically sustainable ways. This will require developing and
implementing rigorous monitoring programs, expanding academic re-
search to encompass a wider breadth of testable hypotheses relating
to articial structure introduction, and improving the methodology in
scientic studies so that the hypotheses in question are addressed
more effectively (Dafforn et al., 2015).
5.1. Monitoring
Articial structures can affect the ability of habitats and species to
deliver ecosystem services that have societal benets (Atkins et al.,
2011). Regulatory frameworks can help to ensure that the style and
scale of articial structures are sustainable and do not risk the provision
of ecosystem services (Mee et al., 2008). Such frameworks are only cur-
rently in place in certain areas of theworld (e.g. EU Habitats Directive).
Monitoring allows for regulatory bodies, where active, to evaluate the
changes in assemblages or communities as a result of an intervention,
such as building a seawall (Hiscock, 1998). Details about the techniques
used to obtain monitoring data are not discussed here, as there are
many other excellent sources (Kingsford and Battershill, 2000;
McIntyre and Eleftheriou, 2005). However, several important consider-
ations are worth emphasizing in relation to the design of monitoring
studies.
Beforeand aftersamples are essential in order to detect any mod-
icationsin the natural patterns in assemblages as a result of introduc-
ing an articial structure. Environmental consequences of an
intervention are actually variations in space and time of ecological pro-
cesses which control the structure of species assemblages (Green,1979;
Underwood, 1992). Impacts can therefore be detected aschanges in the
absolute or relative abundances of taxa, changes in the variance of these
abundance metrics, or changes in measured ecological processes
11E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
(Underwood, 1992). These changes need to be separated from natural
variation through time (at a variety of scales) at the sites sampled
(Underwood, 1992). In estuarine systems particularly, samples taken
at the same site a few months, or even a week apart can differ signi-
cantly (Glasby, 1997; Morrisey et al., 1992a).
It is also necessary to compare potentially impacted sites with con-
trol/reference sites not subject to the impact (Stewart-Oaten et al.,
1986). Anydifference between a single reference site and the potential-
ly impacted site may not be due to theimpact because assemblages are
naturally variable in space. To overcomeconfounding due to this natural
variation, it is desirable to have replicated reference and impacted loca-
tions (Underwood, 1989). In most cases, however, only one impacted
site exists. In such cases, patterns in the biota of the potentially impact-
ed site are compared with the average of replicated reference sites to
adequately detect the impact. This can be done using asymmetrical
ANOVA in Beyond-BACI designs (Underwood, 1992). Information
about the spatial scale of the impact is also necessary to understand
and detect impacts (Bishop et al., 2002). Spatiallynested designs can en-
able impacts to be assessed at multiple spatial scales.
Additionally, in many calls from managementagencies for scientic
information, there are requests for baseline monitoring in the belief that
such monitoring can inform the design of subsequent monitoring efforts
(Field et al., 2007). This can only be true in two sets of circumstances.
The rst is that the baseline sampling design is exactly the same as the
subsequent monitoring as this can enable the direct comparison of pre-
vious and subsequent data to allow a test of the time x treatment inter-
action (Stewart-Oaten et al., 1986; Underwood, 1992). The second is
where precision estimates and analysis outputs can be used to inform
subsequent sample designs. In an example from marine conservation,
Coleman et al. (2013) used pilot or baseline sample data to estimate
the number of samples needed to retain the null hypothesis of no im-
pact with condence (Coleman et al., 2013); this was the number of
samples used for subsequent monitoring. Only by explicitly connecting
the baseline data with the analytical frameworks necessary to test the
hypotheses of effects can we move beyond the limitations that exist in
some monitoring data of the past (Burt, 1994) to generate reliable
data on the effects of articial structures on sedimentary assemblages.
Finally, monitoring of the impacts related to articial structures are
often considered on a case by case basis and have ignored the potential
cumulative impact on sedimentary habitats (Halpern et al., 2008). Fu-
ture impact assessment of articial structures on sedimentary habitats
and assemblages would be more appropriate if multiple development
impactswere monitored as part of an integrated study, with
predetermined comparable metrics, that are able to contextualize mea-
sured effects at ecosystem-relevant scales.
5.2. Future research directions
There remain many unanswered questions as articial structures
rapidly proliferate in sedimentary environments. Sedimentary ecosys-
tems are dynamic, complex, and inuenced by processes and feedbacks
that remain poorly understood, and the introduction of articial struc-
tures may cause complex patterns that are difcult to identify in the
eld, particularly when sampling regimes are temporally and spatially
limited. Given the profusion of uncertainties surrounding sedimentary
ecosystem dynamics in general, improving our understanding of the ef-
fects of articial structures will require strategic and careful selection of
research objectives.
We suggest several areas of study that would be particularly helpful
for advancing current knowledge. Much of our understanding of the
mechanisms by which structures modify sediment communities is
inferential. There is therefore need for more studies that evaluate
mechanism directly. This is particularly important if we hope to design
structures in such a way that they have minimal impacts on sediment
communities and in some instances provide benets (i.e. ecoengineering,
Loke et al., in this issue). Additionally, most studies to date have
quantied changes in the abundance or richness of macroinvertebrates,
and future studies are needed to examine the effects on key biological pa-
rameters, such as reproduction and growth, as well as key ecological pro-
cesses, such as trophic transfer. Past studies have primarily focused on
small scale effects, and there is great need for studies that improve our
understanding of impacts across large spatial scales (Dethier and
Schoch, 2005; Thrush et al., 1994), including alterations to connectivity
(Bishop et al., in this issue) and regional-scale cumulative changes
(Duarte et al., 2003)asarticial structures proliferate across an increas-
ingly large proportion of sedimentary habitats. Along these same lines,
work that characterizes the current spatial extent of articial structures
and the scale of their effects on sedimentary ecosystems would represent
a valuable contribution.
Certain taxonomic groups within sedimentary ecosystems have also
been poorly represented in research to date. In particular, microbes in
soft sediments likely have a centralrole in the functioning of ecosystems
as they form the basal elements of food webs, affect sediment chemis-
try, and restrict nutrient availability (Gadd and Grifths, 1977). Al-
though there is no direct evidence of impacts of articial structures on
these communities at present, one study has shown that biolms in nat-
ural habitats signicantly differ from those on articial structures (sea-
walls; Tan et al., 2015). Much work is needed to evaluate whether ocean
sprawl affects the functionality of sediments via their effects on the mi-
crobiota associated with articial structures.
Lastly, there is tremendous need for work that claries the link be-
tween ecosystem structure and function in sedimentary environments.
Marine sediment ecosystems provide various important services, such
as mediating global carbon, nitrogen and sulphur cycles, inuencing
water clarity, burying, transporting and metabolizing pollutants and
stabilizing and transporting sediments (Snelgrove, 1997). These ser-
vices are dependent on the ecological functions of the species compris-
ing sedimentary communities, as well as the abiotic environment
(Bulleri and Chapman, 2015; Johnston and Mayer-Pinto, 2015; Lenihan
and Micheli, 2001; Lohrer et al., 2004). Present knowledge gaps pre-
clude any comprehensive or quantitative evaluation of the sedimentary
ecosystem functions that are most impacted by articial structures.
Throughout this paper, we have presented hypotheses linking observed
effects from structures with potential implications for ecosystem func-
tion. Such hypotheses need to be tested directly and rigorously, with di-
rect measurement of functional properties, to be useful in any further
capacity. Ultimately, it is knowledge of this link between ecosystem
structure and function, and the subsequent connection between func-
tioning and ecosystem services that will allow us to understand the ef-
fects of articial structure proliferation on human populations and
societies more broadly.
6. Conclusions
Most research to date on sediment responses to articial structures
has highlighted local patterns associated with specic structure types
(Ambrose and Anderson, 1990; Barros et al., 2001; Davis et al., 1982;
Maar et al., 2009; Martin et al., 2005). This review compiled ndings
across structures, regions, and temporal and spatial scales to create a
synthesis of the current knowledge about how ocean sprawl impacts
on soft sediment ecosystems. The primary ways that articial structures
modify soft sediments, directly and indirectly, include placement loss,
an altered sensory environment, hydrodynamic changes, organic en-
richment, toxic contamination, and changes to species interactions
and community dynamics. These changes have signicant conse-
quences for the diversity and structure of soft sediment communities,
affecting, in turn, ecosystem functioning and services provided to
humans. However, to date, empirical studies on the effect of structures
on ecosystem functioning have been lacking. Relationships between
biodiversity and ecosystem functioning in sedimentary environments
are complex (Loreau et al., 2001; Naeem et al., 2009; Schmitz et al.,
2015), and in order to accurately predict the effects of disturbances on
12 E.C. Heery et al. / Journal of Experimental Marine Biology and Ecology xxx (2017) xxxxxx
Please cite this article as: Heery, E.C., et al., Identifying the consequences of ocean sprawl for sedimentary habitats, J. Exp. Mar. Biol. Ecol. (2017),
http://dx.doi.org/10.1016/j.jembe.2017.01.020
functions and services, direct measures of functioning are necessary
(Johnston et al., 2015). Moreover, little is known about the mechanisms
driving these impacts or their scale. Consequently, at this point it is only
possible to hypothesize the large-scale functional consequences that
may arise from structural changes in the assemblages caused by arti-
cial structures and the mechanisms behind them. This knowledge can
only be achieved through rigorous monitoring programs based on ex-
plicit experimental structures alongside more studies that address the
issue of cumulative impacts from multiple structures and assess thecol-
lective impacts of ocean sprawl, rather than just considering structures
individually. Reviews such as this one and Bishop et al. (in this issue)
will be complemented and progressed by the collection of moreprimary
data from studies that incorporate neglected measures of ecosystem
functioning and large-scale impacts. This knowledge will guide the de-
sign and management of ocean sprawl. With the predicted increase of
construction in the ocean, there is a pressing need for this information
to inform solutions-based research that can mitigate the impacts on
soft sediments and protect this crucial habitat.
Acknowledgements
Heery was funded by the National Science Foundation through Uni-
versity of Washington's Integrative Graduate Education and Research
Traineeship (NSF DGE-1068839). Bishop and Critchley received support
from the NSW Ofce of Environment and Heritage through the Coastal
Processes and Responses Node of the NSW Adaptation Hub. Dafforn,
Johnston, Mayer-Pinto, and Bugnot were supported by an ARC Linkage
Grant (LP140100753) awarded to Dafforn & Johnston. This is SIMS pub-
lication number 182. Airoldi was supported from projects MERMAID
(EU FP7 Ocean 2011 - 288710) and TETRIS - Observing, modelling
and Testing synergies and TRade-offs for the adaptive management of
multiple Impacts in coastal Systems(PRIN 2011, Italian Ministry of Ed-
ucation, University and Research). Komyakova received support from
Holsworth Wildlife Research Endowment awarded by Equity Trustees.
Strain was supported by The Ian Potter Foundation and The New South
Wales Government Ofce of Science and Research. Naylor was funded
by the Engineering and Physical Sciences Research Council (EPSRC)
EP/N508792/1. We are grateful to Louise Firth, for introducing and as-
sembling the co-authors on this paper at the 2015 Aquatic Biodiversity
and Ecosystems Conference in Liverpool, UK. [SES]
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