HomeMy WebLinkAboutHarrison and Rousseau 2020. Artificial reefs in Nantucket soundComparison of Artificial and Natural Reef Productivity in Nantucket
Sound, MA, USA
Simonetta Harrison
1 &Mark Rousseau
2
Received: 28 November 2019 /Revised: 23 March 2020 /Accepted: 23 April 2020
#Coastal and Estuarine Research Federation 2020
Abstract
Artificial reef communities undergo long periods of succession prior to becoming stable, but funding challenges often prevent
post-deployment monitoring from evaluating long-term successional changes. The present study employed baited remote un-
derwater video surveillance (BRUVS) to compare the species richness, diversity, abundance, and age structure of fishes across a
4-year-old artificial reef, a 41-year-old artificial reef, a representative natural reef, and a bare control in Nantucket Sound, MA,
USA,to address whether the perceived success ofan artificial reefcan be determined5 years after deployment. Resultsindicated
that, while species richness and diversity were largely uniform throughout the Sound, fish appeared on camera 93.4% faster at
artificial reef sites than they did at the bare sand control. Reef-associated fish were 103.7% more abundant on the older artificial
reefthanontheyoungerartificialreef.Therefore,althoughtheyoungerartificialreefisinitsfifthyearofmonitoring,abundances
of economically important fishes on the reef may continue to increase in future years and current numbers may not accurately
reflect reef success or failure. Future management plans should consider extending monitoring programs longer than 5 years and
implementing temporal fishing closures on newly deployed reefs to facilitate earlier post-deployment community stabilization.
Keywords Artificialreef .Attraction .BRUV .Fisheriesmanagement .NantucketSound .Production
Introduction
Reef fishes are a crucial component of the biodiversity of
coastalsystemsandprovidealargesourceofbiomassforboth
recreational and commercial fisheries on a global scale
(Malcolm et al.2007; Harasti et al.2015). Excessive extrac-
tive pressures on reef fishes have driven many countries to
deploy artificial reefs within their territorial waters to promote
fisheriesprotectionandenhancement(HunterandSayer 2009;
Folpp et al.2013). Artificial reefs may be defined asapproved
structures that have intentionally been placed or constructed
for the purpose of enhancing benthic relief (Rousseau 2008).
Deploymentofsuchreefs has substantially increasedinrecent
decades, and they now form part of a broader strategy for
marine ecosystem management in many countries (Baine
2001;Beckeretal.2017).While primarilyfocusedonbolster-
ingcoastalfisheries,artificialreefsmayprovidecompounding
secondary benefits such as habitat and shoreline protection,
sediment accretion, and mitigation for habitat loss resulting
from coastal alterations (Rousseau 2008; Hunter and Sayer
2009).
Structured habitat enhancement of an otherwise featureless
substrate fosters the development of rapidly growing, highly
productive fouling communities that feed on plankton and
detritus (Baine 2001). Hard reef substrate enhances surface
area on which fouling organisms can settle and anchor to
better withstand ocean currents and the destructive force of
ocean storms. Over time, the resulting increase in biomass
enriches the surrounding water column and sediments, pro-
motes the growthofinfauna and colonizationbyfilter-feeding
invertebrates (Svane and Petersen 2001), and provides food
sources for reef-associated invertebrates such as Cancer sp.
crabs, American lobster (Homarus americanus), and finfish
such as scup (Stenotomus chrysops), black sea bass
(Centropristis striata), and tautog (Tautoga onitis) (Rooker
et al.1997; Baine 2001). Additionalfactors such as the timing
of reef installation, materials used to create structured habitat,
Communicated by Henrique Cabral
*Simonetta Harrison
Harrison.Si@husky.neu.edu
Mark Rousseau
Mark.Rousseau@mass.gov
1 Northeastern University, 430 Nahant Rd, Nahant, MA 01908, USA
2 Massachusetts Division of Marine Fisheries, 30 Emerson Ave,
Gloucester, MA 01930, USA
Estuaries and Coasts
https://doi.org/10.1007/s12237-020-00749-6
and post-deployment use (e.g., species harvesting) may also
influence community development (Carter et al.1985).
Artificial reef designs are often structurally complex and
provide vertical relief that offers more living area for the same
relative unit of seafloor. Crevices and interstitial spaces pro-
vide refuge from predation and energy-depleting currents for
demersal and pelagic fishes. Ultimately, the interspersion of
reef, natural substrate, and open-water habitats creates greater
environmental complexity that confers observable, positive
impacts on reef fishes. Increases in species richness
(Gratwicke and Speight 2005), diversity (Fabi and Fiorentini
1994), and abundance (Charbonnel et al.2002; Brickhill et al.
2005; Hunter and Sayer 2009) have been attributed to the
removal of environmental or ontogenetic bottlenecks by the
deployment artificial reefs (Hunter and Sayer 2009). Such
benefits are then returned to coastal populations in the form
of ecotourism, recreational diving and fishing, and commer-
cial fishing enhancement.
Whether the observed increases in richness, diversity, and
abundance are due to fish production or simply attraction is of
particular interest to fisheries managers. The attraction hy-
pothesis suggests that artificial reefs attract fishes from sur-
rounding habitat by providing food, shelter, and behavioral
cues that exploit the thigmotactic tendencies (inclination to
move towards structured rather than featureless habitat) of
fishes (Bohnsack 1989; Powers et al.2003; Brickhill et al.
2005; Smith et al.2015). It has been largely assumed that
attraction over production of fish by an artificial reef is a
harmful process because the aggregation of existing fish bio-
massintoa smallerareaofhabitatcanmakeiteasiertoexploit
fish stocks that have been previously cost-ineffective to pur-
sue (Grossman et al.1997; Brickhill et al.2005; Smith et al.
2015). This attractive property has been demonstrated by
higher catch rates yielded on artificial reefs compared with
natural reefs and may potentially imply that initial increases
in abundance are temporary (Gregg 1995; Smith et al.2015).
In contrast, the production hypothesis suggests that the addi-
tional habitat provided by artificial reefs may increase a re-
gion’scarryingcapacitybyallowingagreaternumberofju-
veniles to settle, survive to adulthood, and contribute new
individuals to local fish stocks by spawning (Bohnsack
1989; Powers et al.2003; Brickhill et al.2005). Such produc-
tivity of artificial reefs has been demonstrated by numerous
studies and attributed to increased habitat connectivity (Cenci
et al.2011), increased production of organic matter (Cresson
etal.2014),andincreasedbiomassandfecunditytiedtolarger
structure (Granneman and Steele 2014).
There is a general understanding that attraction to and pro-
duction of fishes by artificial reefs are not mutually exclusive
processes, but rather a continuum (Bohnsack 1989; Smith
et al.2015). Management plans implementing artificial reefs
should therefore attempt to favor increased fish production
overharvest throughappropriate sitinganddesign. Ithas been
suggested that fishes will be more attracted to lone artificial
reefs deployed in oligotrophic environments, while increased
reef complexity and connectivity will promote production
(Brickhill et al.2005). Furthermore, recent studies have in-
creasingly suggested that attraction of fishes to artificial reefs
may disperse existing fish biomass to multiple reefs rather
thanconcentratingit,thusmakingfishstockshardertoexploit
(Smith et al.2015; Becker et al.2017). Ecosystem manage-
ment should therefore favor greater habitat connectivity for
reef fishes via strategic deployment of additional artificial
reefs to promote stock dispersion over aggregation (Smith
et al.2015).
Post-deployment monitoring of artificial reefs is necessary
to distinguish between the qualities that promote attraction
versus production (Relini et al.2002; Becker et al.2017).
Such monitoring should be long-term, as communities on ar-
tificial reefs undergo long periods of succession prior to be-
coming stable (Becker et al.2017). While young artificial
reefs are quickly colonized by adult fishes, there are positive,
linear relationships between reef age and species richness,
diversity, and abundance that may extend dozens of years
after a reef is deployed (Coll et al.1998;Relinietal.2002;
Folpp et al.2013). Therefore, younger artificial reefs may
exhibit greater attractive properties, while older reefs may ex-
hibit a stronger balance between attraction and production.
However, research supporting this claim is limited as many
monitoring efforts of artificial reef productivity are restricted
to short periods of a year to a few years after reef deployment
due to challenges of funding longer monitoring programs on
artificial reefs (Relini et al.2002; Barber et al.2009;Becker
et al.2017).
A range of techniques have been employed in the post-
deployment monitoring of artificial reefs, many of which rely
on underwater visual census (UVC) by SCUBA divers or
snorkelers, or fish capture by angling and trapping (Malcolm
et al.2007; Harasti et al.2015). Such methods introduce
biases associated with SCUBA diver presence or gear selec-
tivity. Baited remote underwater video surveillance (BRUVS)
have been increasingly employed in recent years to minimize
these biases. BRUVS are valuable as non-extractive survey
tools that do not cause major benthic disturbance, can be de-
ployed in environments unsuitable for conventional UVC as-
sessments, and may reveal shy or cryptic species (Cappo et al.
2004;Harveyetal.2007; Gladstone et al.2012; Harasti et al.
2015). Permanent visual records of surveys allow for impar-
tial, repeatable measurements and enable standardized data
collection (Cappo et al.2004). Furthermore, the simultaneous
deployment of multiple BRUVS greatly increases the poten-
tial replication and spatial range of sampling (Harvey et al.
2007).Itshouldbenotedthatspecies attractedtoBRUVS bait
in large numbers may obstruct the camera view of less com-
mon or aggressive visitors; such species shading may impact
species richness survey results. Furthermore, baited sampling
Estuaries and Coasts
methods are biased toward species attracted to bait, though
this bias may be advantageous for fisheries management pur-
poses as it focuses sampling on species that are targeted by
recreational and commercial fishing.
The purpose of this study is to compare species richness,
diversity, abundance, and age structure of economically im-
portant finfish species with regard to reef age across natural
reef, artificial reef, and bare substrates in Nantucket Sound,
MA, USA. Natural bedrock outcroppings, cobble shoals, and
other hard substrate types are more common to Massachusetts
thanothercoastalAtlanticstatesintheUSA(Rousseau 2008);
however, Nantucket Sound is largely comprised of feature-
less, sandy substrate and is home to the state’s oldest and
youngest artificial reefs. For this reason, the Sound provides
a unique study system to examine variations in fish assem-
blages across different reef types. BRUV surveys were simul-
taneously conducted on the state’s oldest artificial reef
(Yarmouth, 1978), youngest artificial reef (Harwich, 2016),
a representative natural reef, and a featureless bare control
from June to September 2019. This study hypothesized that
species richness, diversity, and abundance would be largely
uniform across all reefs regardless of age and greater than the
control, while fish age structure would vary according to reef
age. Results from this study may contribute to the body of
work helping to inform the role of artificial reefs in marine
ecological management regimes.
Methods
Study System
The Massachusetts Division of Marine Fisheries (MA DMF)
has deployed two artificial reefs in Nantucket Sound:
Yarmouth reef in 1978 and Harwich reef in 2016. Yarmouth
reef is a 127-acre site comprised of 2500 reef units, each
consisting of three to five tires filled with concrete and bun-
dled together. Harwich reef is a 10-acre site comprised of
1600cubicyardsofconcreterubble.Bothreefsweredeployed
on featureless sandy substrate to provide 0.75–1.5 m of verti-
cal structured habitat for structure-oriented finfish. A shallow,
isolated rocky outcrop with a well-defined edge between
structure and sand was selected to serve as a representative
naturalreef.A featureless sandysubstrate 5kmawayfromthe
nearest reefstructure servedasa barecontrol.Meanlow water
(MLW) marks ranged from 7.1 to 10.6 m across all sites, and
sites were located no closer than 5 km from one another
(Fig.1; NOAA 2004). At this distance, no overlap of bait
plumes occurred during the deployment time, allowing for
independent deployments to be made in a single day (Taylor
et al.2013). The present study examined the effect of reef age
onreefcommunitycomposition.Thefactorreefagecontained
fourlevels: the barecontrol (controlsite),the Harwich reef(4-
year-old reef), the Yarmouth reef (41-year-old reef), and the
natural reef (reference site). A total of 20 temporally indepen-
dent replicates were sampled on each site.
Sampling Design
Five identical mono-horizontal baited remote underwater vid-
eo(monoH-BRUV)unitswereconstructedforthisstudy;one
BRUV was deployed per site and one was reserved as a back-
up. Each BRUV consisted of a weighted PVC frame, a solid
state sports camera with underwater housing attached to an
aluminumbait-pole,a baitboxlocated 80cmfromthe camera
and suspended 49.5 cm above the benthos, and a rope and
float system linking the BRUV to a surface buoy (Fig.2a;
Malcolm et al.2007; Haggitt et al.2013). All cameras were
set to 960 video resolution, 60 frames per second, and a wide
fieldofviewtomaximizebatterylife.Videofocalwidthatthe
bait box was demarcated in 7.6-cm increments using alternat-
ing black and white colored tape under the bait box and ex-
tending along the bait-pole to accommodate potential image
elongation associated with the wide camera setting; fish at the
extreme edges of the camera frame were not binned until they
approached the bait box (Fig.2b). Each camera was bolted to
the bait-pole such that fish could be viewed in a horizontal
orientation to the benthos. The field of view was standardized
to a distance of approximately 3 m in front of the camera for
analysis to minimize the effects of water clarity on estimates
of size and relative abundance.
Three to four pounds (1.4–1.8 kg) of Atlantic mackerel,
Scomber scombrus, were inserted into the bait box for each
deployment to attract piscivorous fish to a viewing area in
front of the camera. Two-thirds of the bait was chopped and
inserted into a mesh bag within the bait box to ensure fish
could not completely consume the bait before the end of a
recordingperiod. Additional whole fishwereadded tothe bait
box for each deployment.
Between June and September 2019, a total of 20 BRUV
deployments were conducted across the four sites. Sampling
was restricted to calm days with ocean swells of 0.3 m or less;
all units were deployed during daylight hours between 08:00
and 16:00 h to prevent any biases associated with diurnal
behavior (Haggitt et al.2013; Schultz et al.2018). BRUVS
wereconsecutivelydeployedfromasmallvesselandretrieved
45 min after the final deployment. This allowed for a 15-min
soakperiodandatleast 30minofoverlappingvideoacrossall
four recordings for comparison (Folpp et al.2013; Harasti
et al.2015). The desired products for analysis were four 30-
min video samples with uniform field conditions across all
sites (time of day, tide, swell, wind, cloud cover, etc.).
Video files were manually analyzed by a single reviewer
using the open-source VLC™(VideoLAN Client) media
playerto ensurevideo analysisand related biaswas consistent
across all replicates. Visibility was estimated directly from the
Estuaries and Coasts
videousingthebaitbox(80cmfromcamera)asaguide.Time
to first fish sighting was documented. Still frames for analysis
were captured from each 30-min recording in 30-s increments
for a total of 60 analyzed frames per recording. Additional
examination of up to 5 s before and/or after a given still frame
was allotted to ensure the profile of each fish was visible for
measurementortoallowanyobstructions(e.g.,floatingalgae)
to pass. The identity of each species of fish, an index of its
relative abundance (MaxN), and quantitative length estimates
of two species of economic significance, black sea bass and
scup, were documented within each frame. MaxN is the max-
imum number of a given species of fish within the field of
view at any one frame during a 30-min recording; this index
was employed to prevent double counts of individual fish
(Cappo et al.2004; Malcolm et al.2007). Due to the docu-
mented error in estimating exact fish length measurements
from mono-H-BRUV recordings (Cappo et al.2004;Folpp
et al.2013), fish of interest were binned by species into size
ranges to distinguish between juvenile, undersized adult, and
legally fishable adults. Specifically, black sea bass were
binned into 0–7.6, 7.6–38, and over 38 cm and scup were
binned into 0–7.6, 7.6–23, and over 23 cm. ImageJ 1.52a
NIH software was used to aid fish binning when necessary.
Statistical Analyses
R software V3.5.1 was used for all statistical analyses. To
determine finfish aggregation patterns, species richness, and
diversity, one-way ANOVAs were conducted on the average
time to fish arrival on site, number of species, and Shannon-
Wiener diversity index (H) across all sites. Prior to analysis,
assumptions of normality and homogenous variances were
tested for all data; species number means were square-root-
transformed and time to fish arrival means were log-trans-
formed. Tukey HSD post hoc tests were conducted to
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YARMOUTH
HARWICH
DENNIS
BARNSTABLE
CHATHAM
Harwich Reef
Bare Control
Yarmouth Reef
Natural Reef
.02.551.25 km
Fig.1 StudysiteswithinNantucketSound,MA.Lefttoright:naturalreef
(41.56829,-70.24202), Yarmouth reef (41.60832,-70.192077), bare
control (41.61255,-70.12772), and Harwich reef (41.625972,-
70.06944). Mean low water (MLW) marks for natural reef, Yarmouth
reef, bare control, and Harwich reef measured 7.10 m, 10.63 m, 9.64 m,
and 10.18 m, respectively. Sites were located at least 5 km from each
other
Estuaries and Coasts
compare the means of all significant ANOVA results, and bar
graphs were created to visualize the data.
A two-way permutational multivariate analysis of variance
(PERMANOVA) was conducted to test for differences in rel-
ative abundances of fish as a function of reef age and season-
ality using a Bray-Curtis dissimilarity measure. For each term
in the analysis, 1999 permutations of the raw data units were
computed to obtain p values. Non-metric multidimensional
scaling (nMDS) was used to examine spatial patterns and
SIMPER tests were conducted to determine the species most
responsible for driving patterns.
Generalized linear models (GLMs) with negative binomial
distributions were used to examine the relative abundances
(total MaxN) of species identified by SIMPER as the drivers
of abundance patters. Similarly, GLMs with negative binomi-
al distributions were used to examine the age structures
(MaxN of juveniles, undersized adults, and fishable adults)
of these species. Date, temperature, tide, initial depth, and
visibility were all tested as additive effects in the original
models; the Akaike information criterion (AIC) was used for
comparisontodetermine themostparsimoniousmodels.One-
way ANOVAs and subsequent pairwise comparisons were
conducted on the most parsimonious models. Estimated mar-
ginal mean abundances were plotted and included date as a
linear predictor to account for seasonal effects.
Results
A total of 14 finfish species were observed across the bare
control, Harwich reef, Yarmouth reef, and natural reef from
June to September 2019. Of these species, black sea bass,
scup, bluefish (Pomatomus saltatrix), and dogfish (Squalus
acanthias) were observed on all four sites. Finfish appeared
on camera 93.4% faster (33 s) at reef sites than they did at the
bare control (502 s) (p < 0.0001; Fig.3a). Regarding species
richness, 2.5 species were observed on the bare control, 3.4
species were observed on the Harwich reef, and 3.1 species
were observed on both the Yarmouth and natural reefs on
average (p = 0.0777; Fig.3b). Regarding species diversity,
the natural reef exhibited an average Shannon-Wiener value
26.7% higher than that of the bare control (p =0.0391; Fig.
3c).TheYarmouthreefexhibitedanaverageShannon-Wiener
value just 16.1% higher than that of the Harwich reef (p =
0.3259; Fig.3c) and both values fell between those of the
natural reef and bare control.
A two-way PERMANOVA revealed that the interac-
tion of reef age and month impacted the relative abun-
dance of species (MaxN) and resulted in distinct cluster-
ing of samples in the non-metric multidimensional scaling
(nMDS) plot (p = 0.0040; Fig.4). SIMPER identified scup
and black sea bass as the most influential species in
Fig. 2 a BRUV rig consisting of
weighted PVC frame, aluminum
bait-pole, and bait box located
0.8 m from GoPro housing
attachment point.b Bait-pole and
ruler attachment under bait box
demarcated in 7.6-cm increments
to aid fish length estimates
Estuaries and Coasts
Estuaries and Coasts
differentiating the fish assemblages across reef ages and
months (Tables 1 and 2).
Black sea bass were 103.7% more abundant on the
Yarmouth reef than on the Harwich reef (p =0.0257;
Fig.5a). This corresponds to a 36.9% difference in total black
sea bass abundance between the Yarmouth and natural reefs
(p =0.3441; Fig.5a) compared with a 99.0% difference in
total black sea bass abundance between the Harwich and nat-
ural reefs (p <0.0001;Fig.5a). Conversely, this corresponds
to a 69.0% difference in total black sea bass abundance be-
tween the Yarmouth reef and bare control (p =0.0195; Fig.
5a) compared with a 0.7% difference in total black sea bass
abundance between the Harwich reef and bare control (p =
1.000; Fig.5a). The model explained ~41% of the overall
variation. This trend varied with black sea bass age structure,
though there were too few juveniles observed on average to
determine a trend (p =0.581; Fig.6a). There was a 62.9%
difference in undersized adult black sea bass abundance be-
tween the Yarmouth and natural reefs (p =0.0077;Fig.6b)
compared with a 103.0% difference between the Harwich and
natural reefs (p <0.0001; Fig.6b). Finally, there was a
100.0% difference in fishable adult black sea bass abundance
between the Yarmouth and natural reefs (p =0.0915;Fig.6c)
compared with a 160.0% difference between the Harwich and
natural reefs (p =0.0169; Fig.6c).
Scup did not exhibit the same trends in abundance. Scup
were 23.4% more abundant on the Harwich reef than on the
Yarmouth reef (p =0.9044; Fig.5b). This corresponds to a
79.6% difference in total scup abundance between the
Yarmouth and natural reefs (p =0.0283; Fig.5b)compared
with a 61.3% difference in total scup abundance between the
Harwich and natural reefs (p =0.1534;Fig.5b). Conversely,
thiscorrespondstoa21.2%differenceintotalscupabundance
between the Yarmouth reef and bare control (p =0.9009; Fig.
5b) compared with a 0.3% difference in total scup abundance
between the Harwich reef and bare control (p =1.000; Fig.
5a). The model explained ~ 21% of the overall variation.
This trend varied with scup age structure, though there were
too few juveniles observed on average to determine a trend
(p =0.1274;Fig.7a). There was an 88.8% difference in un-
dersized adult scup abundance between the Yarmouth and
natural reefs (p =0.0400; Fig.7b) compared with a 55.7%
difference between the Harwich and natural reefs (p =
0.3724; Fig.7b). Finally, there was a 127.6% difference in
fishable adult scup abundance between the Yarmouth and
natural reefs (p <0.0001;Fig.7c) compared with a 144.3%
difference between the Harwich and natural reefs (p <0.0001;
Fig.7c).
Discussion
The results of this study support the hypothesis that seasonal
species richness and diversity are largely uniform across the
sampled natural and artificial reefs inNantucket Sound. There
were negligible differences in species richness across all reefs
and the bare control, while species diversity increased only
slightlywithreefage (Fig.3).Therefore, communitystructure
appears tobeuniform throughoutNantucketSoundregardless
of substrate type. This may imply that certain economically
important fishes known for being reef-associated, such as
black sea bass, are willing to cross sand barriers to move
between reef types in the pursuit of food; this may also reflect
the migratory nature of such fishes (Sedberry et al.1998;
Drohan et al.2007). Future research into the distances black
sea bass are willing to travel from reefs in the pursuit of food
mayhelptoinformhowcloselyartificialreefsmustbesitedto
boost habitat connectivity. Despite this uniformity of commu-
nity structure throughout the Sound, fish arrival to bait was
much faster at reef sites than it was at the bare control, imply-
ing that the species observed throughout the Sound tend to
aggregate to or are produced on natural and artificial reef
structure (Fig.3). This supports assertions that artificial reefs
increase the biomass of reef-associated prey species and pro-
vide refuge from predation and currents via structural com-
plexity, thereby bolstering the region’s fisheries stocks
(Rooker et al.1997;Baine2001).
Contrary to our hypothesis, abundance varied with reef
age. Black sea bass and scup were identified as the two
greatest determinants of variation in total abundance across
sites (Tables 1 and 2). Both species are fished commercially
and recreationally and are subject to the U.S. Atlantic States
Fig. 4 nMDS ordination plot of finfish assemblages according to species
MaxN averages across natural reef, artificial reefs, and bare control site
sampled in Nantucket Sound from June to September 2019. Stress=0.17
Fig. 3 a Average time in seconds to finfish arrival at bare versus reef
sitesafterBRUV deployment.b Average speciesrichness across all sites.
c Average Shannon-Wiener diversity index (H) across all sites. Sites are
organized by increasing reef age from left to right.N =20 and error bars
represent one standard error of the mean
R
Estuaries and Coasts
Marine Fishery Commission’s interstate fisheries manage-
ment plan and seasonal, size, and bag limits regulated by the
Massachusetts Division of Marine Fisheries. Black sea bass
are strongly associated with structurally complex habitats in-
cluding rocky reefs, cobble and rock fields, exposed stiff clay,
and mussel beds; though migratory, they exhibit enduring
habitat fidelity to their structure of choice (Sedberry et al.
1998; Drohan et al.2007). A coastwide quota increase for
black sea bass was issued in Massachusetts in 2017 and both
recreational and commercial fisheries have achieved their ex-
tractive limits in the years since, perhaps calling for the devel-
opment of additional habitat to support the habitat require-
ments of the stock in southern New England. Unlike black
sea bass, scup do not exhibit strong association to structurally
complex habitats and can be found schooling in open water or
on sandy bottoms; however, they are frequently observed
seeking food or shelter on or near structures such as rocky
reefs and mussel beds (Steimle et al.1999).
Total black sea bass abundance on the younger Harwich
reef more closely resembled that of the bare control, while
abundance on the older Yarmouth reef more closely resem-
bledthatofthenaturalreef(Fig.5).Thistrendwasreflectedin
age sub-categories, with both undersized and fishable adults
increasing in abundance as reef age increased (Fig.6). Large
variances prevent strong conclusions from being drawn re-
garding juvenile abundance (Fig.6). However, on average,
juveniles were least abundant on the Harwich reef, whereas
they were most abundant on the Yarmouth reef. This trend
Table1 SpeciescontributionsfromSIMPERanalysis(reduceddataset)
for differences in relative abundance of species (MaxN) between sites.
Average percent contributions to overall dissimilarity (δi), ratios of aver-
age to standard deviation of contribution (δi/SD (δi)), and ranks of most
influential species (Rank) are included for all pairwise comparisons.
Species regarded as most important contributors to the assemblage dis-
similarity are shown in italics
Species Harwich vs. bare Harwich vs. natural Harwich vs. Yarmouth
δi δi/SD (δi)Rankδi δi/SD (δi) Rank δi δi/SD (δi)Rank
Black sea bass 9.96 0.82 2 13.48 1.17 2 11.05 1.12 2
Scup 38.78 1.59 1 39.96 1.88 1 29.92 1.43 1
Tautog 0.52 0.43 9 0.51 0.49 9 0.99 0.56 14
Bluefish 2.54 0.56 6 0.98 0.54 6 1.69 0.51 9
Striped bass 0 0 4 0.26 0.21 10 0 0 6
Dogfish 3.46 0.7 10 2.5 0.97 12 3.67 0.75 10
Sea robin 0 0 3 0.32 0.22 4 0.43 0.31 4
Skate 0 0 12 0 0 3 0 0 3
Cunner 6.52 0.45 11 4.76 0.43 7 6.93 0.53 13
Butterfish 2.27 0.23 5 1.61 0.24 5 2.05 0.23 7
Winter flounder 0 .07 0.23 7 0.21 0.28 11 0.07 0.23 12
Summer flounder 0.24 0.32 8 1.01 0.71 13 1.15 0.23 11
Sand tiger shark 0 0 13 0.16 0.22 8 0.93 0.3 5
Blue runner 0 0 14 0 0 14 8.17 0.42 8
Bare vs. natural Bare vs. Yarmouth Natural vs. Yarmouth
δi δi/SD (δi)Rankδi δi/SD (δi) Rank δi δi/SD (δi)Rank
Black sea bass 14.77 1.27 2 11.22 1.18 2 11.01 1.18 2
Scup 36.92 1.57 1 33.35 1.46 1 31.97 1.51 1
Tautog 0.16 0.23 6 0.68 0.41 14 0.54 0.48 14
Bluefish 0.63 0.39 12 0.86 0.4 6 0.19 0.32 6
Striped bass 28 0.21 4 0 0 9 0.24 0.21 12
Dogfish 2.48 1.13 7 3.54 0.79 13 1.49 0.73 9
Sea robin 0.34 0.23 5 45 0.32 4 0.55 0.36 13
Skate 0 0 11 0 0 3 0 0 7
Cunner 0 0 3 1.67 42 7 0.84 46 3
Butterfish 0 0 13 0 0 12 0 0 5
Winter flounder 0.17 0.23 8 0 0 5 0.15 0.22 4
Summer flounder 1.05 0.72 9 0.12 0.22 8 0.93 0.7 11
Sand tiger shark 0.16 0.23 10 1.02 0.3 10 0.56 0.4 8
Blue runner 0 0 14 8.41 0.43 11 7.24 0.43 10
Estuaries and Coasts
mayinpartexplainthegreaternumberofadultspresentonthe
Yarmouth reef and support the claim that older artificial reefs
exhibit greater balance between attraction and production of
finfish than younger artificial reefs. Particularly in temperate
environments, reefs may undergo years ofcommunity succes-
sion prior to approaching the diversity and stability of natural
reefs (Becker et al.2017). Older, more stable reefs are there-
fore more likely than younger reefs to provide the structurally
complex protection and food biomass necessary to support
juvenile finfish settlement and survival to adulthood (Coll
et al.1998;Relinietal.2002;Barberetal.2009;Folpp
et al.2013).
These abundance trends were not reflected in scup popula-
tions. As with black sea bass, total scup abundance at the
Harwich reef more closely resembled that of the bare control
(Fig.5). However, scup abundance was lowest on the
Yarmouth reef, a trend that was again reflected in both the
undersized and fishable adult sub-categories (Fig.7 ).
Juveniles presented large variances across sites; yet, as with
the black sea bass, the fewest number of juveniles was ob-
served on the Harwich reef, again implying that young reefs
may not yet be able to support juvenile production (Fig.7).
The relative absence of adults on the Yarmouth reef is inter-
esting given the greater number of juveniles present. As black
sea bass are known predators of scup (Bowman et al.2000),
their success on the Yarmouth reef may in part be explained
by increases in predation on scup juveniles and young adults.
Additionally, because scup life histories are not strictly tied to
Table2 SpeciescontributionsfromSIMPERanalysis(reduceddataset)
for differences in relative abundance of species (MaxN) between months.
Average percent contributions to overall dissimilarity (δi), ratios of aver-
age to standard deviation of contribution (δi/SD (δi)), and ranks of most
influential species (Rank) are included for all pairwise comparisons.
Species regarded as being important contributors to the assemblage dis-
similarity are shown in italics
Species June vs. July June vs. August June vs. September
δi δi/SD (δi)Rankδi δi/SD (δi) Rank δi δi/SD (δi)Rank
Black sea bass 9.35 1.21 2 11.18 1.1 2 10.53 1.17 2
Scup 25.49 1.34 1 34 1.73 1 34.51 1.8 1
Tautog 0.55 0.39 9 0.33 0.34 10 0.14 0.37 14
Bluefish 0.27 0.19 10 1.32 0.45 6 0.48 0.35 10
Striped bass 0.61 0.35 6 0.6 0.33 4 0.38 0.31 6
Dogfish 3.31 1.01 7 3.23 0.93 7 2.35 81 7
Sea robin 1.38 0.57 13 125 0.52 5 0.87 0.48 4
Skate 0 0 5 0 0 11 0 0 5
Cunner 6.04 0.49 3 0.35 0.36 9 0.25 0.34 12
Butterfish 5.05 0.36 11 4.87 0.36 3 3.59 0.35 11
Winter flounder 0.43 0.4 12 0.37 0.35 12 0.27 0.34 9
Summer flounder 0.4 0.35 4 0.28 0.4 8 0.37 0.46 3
Sand tiger shark 0.72 0.3 8 0 0 13 0.08 0.26 13
Blue runner 0 0 14 0 0 14 9.92 0.47 8
July vs. August July vs. September August vs. September
δi δi/SD (δi)Rankδi δi/SD (δi) Rank δi δi/SD (δi)Rank
Black sea bass 12.02 1.08 2 10.55 1.07 2 10.93 1 2
Scup 35.9 1.62 1 35.3 1.54 1 35.48 1.39 1
Tautog 0.8 0.48 9 0.47 0.43 14 0.35 0.44 14
Bluefish 1.55 0.46 6 0.61 0.36 9 1.12 0.48 6
Striped bass 0 0 4 0 0 6 0 0 4
Dogfish 3.02 0.71 3 2.3 0.66 4 2.31 0.64 12
Sea robin 0.15 0.19 13 0.11 0.18 12 0 0 3
Skate 001200130010
Cunner 5.9 0.47 7 4.25 0.43 3 0 0 13
Butterfish 0 0 11 0.08 0.26 7 0.08 0.25 5
Winter flounder 0.05 0.21 5 0.04 0.2 10 0 0 7
Summer flounder 0.62 0.48 8 0.56 0.53 11 0.5 0.57 8
Sand tiger shark 0.77 0.28 10 0.51 0.3 5 0.08 0.25 9
Blue runner 0 0 14 9.87 0.47 8 9.63 0.47 11
Estuaries and Coasts
presence of structure (Steimle et al.1999), their abundances
may vary more freely across bare and reef sites than strictly
reef-associatedfishes.Finally,sampleerrormayhavefactored
into these results. Visibility was consistently worse (reduced
by 0.25–1 m) on the Yarmouth reef than on the other sites
throughout the sample months; while this may not have se-
verely affected the ability to discern darkly colored black sea
bass during video analysis, it may have inhibited the view of
lighter scup and impacted overall count data. Future research
should be conducted on sites with more uniform visibilities to
determine how greatly this may have impacted the present
study.
Additional error may have factored into this study.
Although BRUVS were deployed within 3 m of reef
structure during any given sampling period, the cameras
did not always capture reef structure within their frame.
As such, species strictly affiliated with structure, such as
cunner (Tautogolabrus adspersus), were only observed
when reefs fell within the camera frame and when visibil-
ity permitted. This may have skewed species richness or
diversity indices. Future research should attempt to more
directly include structures of interest within the camera
frame. Bait box elevation and camera orientation may
have further impacted species counts by limiting view of
groundfish or species unable to access bait elevated off
bottom sediments, such as flounder. Finally, the artificial
reefs monitored in this study were constructed of different
materials: Yarmouth was constructed of ballasted tires and
Harwich was constructed of repurposed concrete rubble.
Folpp et al. (2013) noted that differences in artificial
structures may yield associated differences in fish assem-
blages, implying that reef age may not have been the only
factor contributing to the observed differences in assem-
blages across reefs in the present study. Tire reefs have
historically exhibited less success than concrete reefs due
to their propensity to shift during ocean storm events
(AGSMFC 2004). However, the Yarmouth reef has with-
stood seven large hurricane and tropical cyclone events
impacting Cape Cod since its deployment, including
Hurricanes Gloria and Bob; monitoring did not reveal
any tire shifting that may have been associated with these
extreme weather events (Schwartz and Murray 2013). The
Yarmouth reef’s apparent success despite its tire compo-
sition may therefore lend more credence to the assertion
Fig. 5 Estimated marginal mean
abundances of a black sea bass
and b scup across natural reef,
artificial reefs, and bare control
site. Sites are organized by
increasing reef age from left to
right.N =20 and error bars
representonestandarderrorofthe
mean
Estuaries and Coasts
that increasing reef age subsequently increases communi-
ty stability and fish abundance. Such stability may stem
from the fact that the Yarmouth reef’s tires were ballasted
with concrete and are less likely to shift during storm
events, thereby allowing for community stabilization.
While artificial reefs provide distinct benefits to reef-
associated fishes, these benefits apparently continue to
accrue over a long timescale. Though adult fishes may
rapidly colonize young reefs, increasing reef age has been
linked to increased species richness, diversity, and
production of juveniles (Coll et al.1998;Relinietal.
2002; Folpp et al.2013). Many coastal management and
mitigation monitoring plans require a minimum of 5 years
of post-deployment monitoring to determine the effective-
ness of artificial reefs, yet it may be prudent to continue
monitoring reefs well beyond this timeframe to fully re-
cord the benefits conferred to a region’s fisheries stocks
(Barber et al.2009). This is particularly relevant when the
assessed fish stocks are migratory species with only sea-
sonal presence. It is also important to note that neither
Fig. 6 Estimated marginal mean
abundances of a juvenile,b
undersized, and c fishable black
sea bass across natural reef,
artificial reefs, and bare control
site. Sites are organized by
increasing reef age from left to
right.N =20 and error bars
representonestandarderrorofthe
mean
Estuaries and Coasts
artificial reef outperformedthenaturalreefintermsof
species richness, diversity, or abundance in this study.
This is ultimately a positive quality, as artificial reefs
should be viewed as support for rather than direct surro-
gates of naturally occurring reefs and the coordinates of
most artificial reefs are publicly available to fishing com-
munities. The Massachusetts Division of Marine Fisheries
has implemented regulatory prohibitions on commercial
fishing activity on newly deployed artificial reefs in an
effort to control early extractive pressure; perhaps these
prohibitions may be extended to allow for communities to
stabilize after fishes are initially attracted to the reefs both
within the state and more broadly in national and interna-
tional reef programs. Furthermore, such artificial reefs are
most effective when they increase habitat connectivity,
which serves to disperse rather than aggregate stocks
(Smith et al.2015; Becker et al.2017). Future manage-
ment plans may also consider increasing artificial reef
cover in Nantucket Sound and similar regions largely
characterized by sandy substrate and limited structured
Fig. 7 Estimated marginal mean
abundances of a juvenile,b
undersized, and c fishable scup
across natural reef, artificial reefs,
and bare control site. Sites are
organized by increasing reef age
from left toright.N =20anderror
bars represent one standard error
of the mean
Estuaries and Coasts
habitat. Finally, management plans should consider how
artificial reefs may fit into greater climate change mitiga-
tion strategies by restoring ecological function and help-
ing to mitigate species migrations in the wake of elevated
sea surface temperatures.
Acknowledgments Special thanks to MA DMF staff for their assistance
in data collection and analysis, including Kate Frew, Alex Boeri, Tay
Evans, Vin Malkoski, Kristen Schmicker, Steve Voss, Micah Dean, and
Jill Carr. Thanks to the Cape Cod Salties, especially Robert Dyka and C.
Randall Sherman, for their time and resources. Finally, thanks to Dr.
Jonathan Grabowski for his mentorship throughout this project, and to
Northeastern’s Three Seas faculty and cohort, especially Iris Seto.
Funding Information Fundingfor thisresearchwasmade possible bythe
MA DMF Recreation License Funds and from the Department of Fish
and Game (DFG) In-Lieu Fee (ILF) program.
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