ArticlePDF Available

Colonization and substratum preference of an introduced burrowing crustacean in a temperate estuary

Article

Colonization and substratum preference of an introduced burrowing crustacean in a temperate estuary

Abstract and Figures

Habitat use in marine invertebrates is often influenced by multiple abiotic and biotic factors. Substratum composition is one factor known to have a dramatic effect on habitat selection. The Australasian burrowing isopod (Sphaeroma quoianum, H. Milne Edwards 1840) is a common introduced species in many estuaries on the Pacific coast of North America. S. quoianum burrows into a variety of firm substrata including marsh banks (composed of peat, clay, and/or mud), wood, friable rock, and Styrofoam floats. In some areas, isopods achieve high densities and may accelerate the rate of shoreline erosion and damage marine structures; thus, understanding the substratum preference of this species may be important for conservation and management efforts. Field experiments were conducted in Coos Bay, Oregon to examine substratum preference, burrowing rates, and the life stage of colonizers. In three experimental trials (Fall 2005, Spring 2006, Fall 2006), replicates of four intertidal substrata (marsh banks, decayed wood, sandstone, Styrofoam) were deployed near intertidal populations of S. quoianum. The numbers of burrows created in each substratum were enumerated weekly or daily (depending on trial). After the trials were completed, the total numbers of isopods inhabiting each substratum were counted. In weeks, S. quoianum extensively burrowed the substrata but exhibited a distinct preference for decayed wood. Significantly more isopods were present in wood than the other substrata at the end of the experiments and rates of burrowing were greatest in wood, although significance varied across time in one trial. Nearly 90% of colonizing isopods were under 5 mm in length suggesting that juvenile isopods primarily colonize intertidal substrata. Differences between burrow densities measured in the field and the results from these preference trials may indicate other factors, such as relative availability of substrata, recruitment and dispersal limitations, and possible gregarious behavior also influence local isopod densities. (C) 2007 Elsevier B.V. All rights reserved.
Content may be subject to copyright.
This article was published in an Elsevier journal. The attached copy
is furnished to the author for non-commercial research and
education use, including for instruction at the author’s institution,
sharing with colleagues and providing to institution administration.
Other uses, including reproduction and distribution, or selling or
licensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of the
article (e.g. in Word or Tex form) to their personal website or
institutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies are
encouraged to visit:
http://www.elsevier.com/copyright
Author's personal copy
Colonization and substratum preference of an introduced burrowing
crustacean in a temperate estuary
Timothy M. Davidson
a,
, Steven S. Rumrill
b,1
, Alan L. Shanks
a,2
a
Oregon Institute of Marine Biology, University of Oregon, P.O. Box 5389, Charleston, Oregon, 97420, USA
b
South Slough National Estuarine Research Reserve, P.O. Box 5417, Charleston, Oregon, 97420, USA
Received 25 July 2007; received in revised form 28 October 2007; accepted 31 October 2007
Abstract
Habitat use in marine invertebrates is often influenced by multiple abiotic and biotic factors. Substratum composition is one
factor known to have a dramatic effect on habitat selection. The Australasian burrowing isopod (Sphaeroma quoianum, H. Milne
Edwards 1840) is a common introduced species in many estuaries on the Pacific coast of North America. S. quoianum burrows into
a variety of firm substrata including marsh banks (composed of peat, clay, and/or mud), wood, friable rock, and Styrofoam floats.
In some areas, isopods achieve high densities and may accelerate the rate of shoreline erosion and damage marine structures; thus,
understanding the substratum preference of this species may be important for conservation and management efforts. Field
experiments were conducted in Coos Bay, Oregon to examine substratum preference, burrowing rates, and the life stage of
colonizers. In three experimental trials (Fall 2005, Spring 2006, Fall 2006), replicates of four intertidal substrata (marsh banks,
decayed wood, sandstone, Styrofoam) were deployed near intertidal populations of S. quoianum. The numbers of burrows created
in each substratum were enumerated weekly or daily (depending on trial). After the trials were completed, the total numbers of
isopods inhabiting each substratum were counted. In weeks, S. quoianum extensively burrowed the substrata but exhibited a
distinct preference for decayed wood. Significantly more isopods were present in wood than the other substrata at the end of the
experiments and rates of burrowing were greatest in wood, although significance varied across time in one trial. Nearly 90% of
colonizing isopods were under 5 mm in length suggesting that juvenile isopods primarily colonize intertidal substrata. Differences
between burrow densities measured in the field and the results from these preference trials may indicate other factors, such as
relative availability of substrata, recruitment and dispersal limitations, and possible gregarious behavior also influence local isopod
densities.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Biological invasions; Burrowing isopod; Colonization; Habitat preference; Sphaeroma quoianum; Substratum preference
Journal of Experimental Marine Biology and Ecology 354 (2008) 144 149
www.elsevier.com/locate/jembe
Corresponding author. Present address: Aquatic Bioinvasions Research and Policy Institute, Environmental Sciences and Resources Department,
Portland State University, P.O. Box 751, Portland, Oregon 97207-0751, USA. Tel.: +1 503 725 9076; fax: +1 503 725 3834.
E-mail addresses: tid@pdx.edu (T.M. Davidson), steve.rumrill@state.or.us (S.S. Rumrill), ashanks@uoregon.edu (A.L. Shanks).
1
Tel.: +1 541 888 2581x302; fax: +1 541 888 3250.
2
Tel.: +1 541 888 2581x277; fax: +1 541 888 3250.
0022-0981/$ - see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jembe.2007.10.015
Author's personal copy
1. Introduction
The distribution and density of many marine inver-
tebrates are mediated by habitat preferences exhibited by
different life stages. For example, preferences for specif-
ic habitats can occur during site-selection and settlement
of larvae (Keough and Downes, 1981; Highsmith, 1982),
during exploratory behavior of post-larvae and juveniles
(Wahle and Steneck, 1991; Hedvall et al., 1998; Pardo
et al., 2007), and during the period of adult life (Richard,
1992; Aikins and Kikuchi, 2001; Stanhope and Levings,
1985). Occupation of habitats by motile invertebrates is
complex and can be obligatory with survival occurring
only on specific substrata (Choat and Black, 1979;
Carlton et al., 1991; Williams and McDermott, 2004).
Alternatively, habitat use by motile species can also be
facultative and dynamic, with higher quality habitat
preferred but not essential to survival (Stanhope and
Levings, 1985; Fernandez et al., 1993; Aikins and
Kikuchi, 2001). Moreover, the degree of habitat fidelity
is also frequently influenced by several external factors
that operate on all life stages including predation, com-
petition, facilitation, and physiological tolerances to a
suite of ambient environmental factors.
The introduced isopod Sphaeroma quoianum (H.
Milne Edwards 1840; = S. quoyanum) is a prodigious
burrower in a variety of shallow subtidal and intertidal
substrata including mud, clay, and peat banks (hereafter:
marsh banks), wood, sandstone, and styrene plastic
floats (Styrofoam). By creating extensive anastomizing
networks of burrows, S. quoianum may accelerate the
rate of shoreline erosion and damage maritime structures
(Higgins, 1956; Carlton, 1979; Talley et al., 2001; per.
obs.). S. quoianum has successfully invaded at least 15
estuaries along the Pacific coast of North America
ranging from Baja California to Yaquina Bay, Oregon
(reviewed by Davidson, 2008). These isopods were
initially introduced to San Francisco Bay during the late
19th century, presumably from its native region of
Australia, Tasmania, and New Zealand (Carlton, 1979).
Intraregional travel likely facilitated the spread of this
invader to other estuaries on the Pacific coast.
In Coos Bay, Oregon (USA), S. quoianum inhabits and
burrows into marsh banks, decayed wood, sandstone, and
Styrofoam floats in varying densities (Davidson et al., in
prep; unpublished data), suggesting isopods exhibit a
preference for inhabiting certain substrata. Based upon
these observations, we hypothesize that: 1) significantly
more isopods would colonize wood, sandstone, and
Styrofoam substrata than marsh bank substrata and 2) the
mean burrowing rate would be higher in wood, sandstone,
and Styrofoam substrata than marsh bank substrata. Also,
since it appears many juvenile isopods leave (or are pos-
sibly expelled from) the parental burrow (per. obs), we
predicted more juveniles of S. quoianum would colonize
substrata than adults. Results from this study will elucidate
some aspects of the biology of a detrimental and under-
studied introduced species, provide information important
to the management of this species, and provide information
pertinent to other burrowing direct developers.
2. Methods
2.1. Study site and trials
Experiments were conducted in Haynes Inlet, located
in the northeast corner of Coos Bay, Oregon, USA
(43.35°N, 124.34°W). Haynes Inlet is a predominantly
polyhaline region of the bay with salinities in the
summer ranging from 2532 and water temperatures in
the summer from 1621 °C. The shoreline of Haynes
Inlet is primarily composed of sandstone terraces
harboring large intertidal populations of S. quoianum.
Three experimental trials to test for substratum pre-
ference and to examine burrowing rate were conducted.
Trial one was conducted for nine weeks beginning on
August 25, 2005. The second trial began on April 19,
2006 and lasted two weeks. The third trial commenced
on September 12, 2006 and lasted 12 days. All trials
utilized the methodology described below.
2.2. Experimental design
Replicates consisting of four substrata (marsh bank,
decayed wood, sandstone, and Styrofoam) were placed
in the high intertidal near existing populations of
S. quoianum. Six replicates were used during trial one
and five replicates were used in trials two and three.
Most replicates were separated by over 100 m, although
two replicates were separated by 20 m due to logistical
constraints. Each substratum used in these experiments
was obtained from identical intertidal locations. To
ensure the substrata used in the experiment were suitable
for burrowing, burrow-free pieces of substrata were
removed from larger sections already harboring inter-
tidal populations of S. quoianum. All substrata were
defaunated by freezing prior to experimentation and cut
and shaped to a standard volume (800 cm
3
). Substrata
were then secured within a cinder block, exposing only
one side of the substratum (surface area = 100 cm
2
).
Each replicate of the four substratum types were ran-
domly placed in a row within 6 cm of each other. The
exposed sides of substratum blocks were placed facing
burrows of S. quoianum at a distance of 10 cm.
145T.M. Davidson et al. / Journal of Experimental Marine Biology and Ecology 354 (2008) 144149
Author's personal copy
During low tide, each substratum block was photo-
graphed and the numbers of burrows present were
counted. Burrows were enumerated weekly for trial one
and daily for trials two and three. Digital photographs of
heavily burrowed substrata were later analyzed using
ImageTool 3.0 to verify field burrow counts. Preference
was determined by measuring 1) the first substrata
colonized in each replicate, 2) the percentage of isopods
present in each substratum at the end of the experiment
and 3) the rate of burrowing in each substratum during
the experiments. We converted isopod numbers to a
percentage (isopods in the substratum block/total iso-
pods in each respective replicate) to account for the
variable number of colonizers between replicates.
2.3. Statistical analysis
The duration of trials differed, thus we separately
tested whether the mean percentage of S. quoianum
differed in each substratum (for each trial) using one-
way ANOVA. Since isopods may be gregarious in their
settlement, we used two-way repeated measures
ANOVA with substratum as a fixed factor and time
(either Week or Day) as the repeated factor to determine
if the mean burrowing rate differed between substrata
for both trials. We did not analyze trial two because few
isopods burrowed during the experiment (only five
burrows created over two weeks).
Assumptions of normality and homogenous variance
were visually evaluated using residual and box plots. Data
were then arcsin( ffiffi
x
p) transformed (for percentage data) or
ffiffi
x
ptransformed to improve normality and reduce
heteroscadacity. The transformations failed to normalize
and homogenize the variances, thus we reduced the sig-
nificance level to α
crit
0.025 (Underwood, 1981). We
also used HuynhFeldt corrected P-values to account for
the violation of sphaerocity. Tukey HSD tests were used
for all aposterioricomparisons. When a significant
interaction was detected, we examined the effect of
substratum at each repeated measurement with one-way
ANOVA using significance values at α/p(where pequals
the number of levels of the time effect; reviewed by
Looney and Stanley, 1989). Due to logistical constraints,
our initial measurements for trial one occurred after two
weeks. Thus, our measurements of burrowing rate for
week two was calculated from the mean of those two
weeks. Some replicates in trial one were also retrieved
earlier than others due to the erosion of marsh bank
blocks, (two replicates of trial one were removed at week
six and eight, respectively). The blocks were analyzed as
if they were deployed for the same number of days.
3. Results
The first burrows created by S. quoianum appeared
after one day in trial three (Fall 2006) and ten days in
Table 1
Day the first burrow was observed in each substratum block within
each replicate (AE) of trial three
Day of first burrow observation
Trial 3Fall 2006 Replicate
ABCDE
Marsh Bank 1 2 2 1 3
Wood 1 1 1 1 1
Sandstone 5 3 6 1 3
Styrofoam 7 6 6 1 5
Since substrata were examined weekly in trial one, the initial substrata
burrowed by S. quoianum were not recorded; although after two
weeks, nearly all substrata in all six replicates were burrowed by at
least one isopod.
In trial two, burrows were only observed in two marsh bank blocks and
one wood block after 10, 12, and 14 days, respectively.
Fig. 1. Mean number of isopods (±SE) present in substratum blocks after
A. Trial one Fall 2005 and B. Trial three Fall 2006; the duration of
trial one was nine weeks, trial three was twelve days. Different letters
denote a significant difference using Tukey HSD (P0.025).
146 T.M. Davidson et al. / Journal of Experimental Marine Biology and Ecology 354 (2008) 144149
Author's personal copy
trial two (Spring 2006). As substrata were examined
weekly in trial one, the initial substrata burrowed by S.
quoianum were not recorded; although after two weeks,
nearly all substrata in all six replicates were burrowed by
at least one isopod. Wood and marsh banks were the first
substrata to be burrowed in nearly all replicates from
trial three (Table 1). In trial two, burrows were only
observed in two marsh bank blocks and one wood block
after 10, 12, and 14 days, respectively.
The numbers of S. quoianum present at the end of the
experiment were significantly different between sub-
strata in both trials (trial one: F
3,20
= 21.67, Pb0.0001;
trial three: F
3,16
= 40.21, Pb0.0001). Mean numbers of
S. quoianum within wood substratum were significantly
greater than all other substrata in both trials (Fig. 1;
Pb0.001 for all contrasts, Tukey HSD). In trial
three, there were also significantly more individuals of
S. quoianum in sandstone than marsh bank substrata
(P= 0.001, Tukey HSD).
The burrowing rate varied according to substratum and
time for both trials (Tabl e 2,Fig. 2). Over the nine weeks
of exposure during trial one, the weekly mean burrowing
rates were consistently higher in wood than sandstone
and Styrofoam substrata (Tabl e 2,Fig. 2; all contrasts
P0.01, Tukey HSD). The maximum burrowing rate
observed was 157 burrows (per 100 cm
2
) in one week,
with 421 burrows created overthe nine weeks. We did not
detect a significant difference in the rates of burrowing
between marsh bank and all other substrata (PN0.025,
Tukey HSD). In trial three, the mean burrowing rate was
highest in wood nearly every day during the twelve-day
experiment, but the statistical significance of those
differences varied according to day (Ta ble 2;Fig. 2).
We detected a significant difference in the mean bur-
rowing rates on days 16(Pα/p,=0.004).Onthose
days, the burrowing rate in wood substratum was sig-
nificantly higher than all other substrata (all contrasts
P0.001, Tukey HSD). We did not detect a significant
Table 2
Results of two-way repeated measures ANOVA tests examining the
difference in the mean burrowing rate of Sphaeroma quoianum in
different substrata and across time during trials one and three
A. Trial 1 Fall 2005
Between subjects
Source of variation df MS FP
Substratum 3 87.61 6.28 0.008
Error 12 13.96 ––
Within subjects
Source of Variation df MS FP
Week 7 25.31 7.88 b0.001
WS 21 4.79 1.49 0.114
Error 84 3.21 ––
HuynhFeldt Epsilon: 0.895
B. Trial 3 Fall 2006
Between subjects
Source of variation df MS FP
Substratum 3 66.23 62.10 b0.001
Error 16 1.07 ––
Within subjects
Source of variation df MS FP
Day 11 2.25 2.62 0.005
DS 33 1.75 2.04 0.002
Error 176 0.86 ––
HuynhFeldt Epsilon: 0.952
The HuynhFeldt correction was applied to P-values.
Fig. 2. Mean burrowing rate (burrows created per week/day± SE) during trial one (Fall 2005 August 25October 27) and trial three (Fall 2006
September 1224) in marsh bank, wood, sandstone, and Styrofoam (n= 6 for Fall 2005, n=5 for Fall 2006) substrata.
147T.M. Davidson et al. / Journal of Experimental Marine Biology and Ecology 354 (2008) 144149
Author's personal copy
difference in burrowing rates on days 712, due to the
high variation in the number of burrows created in all
substrata during those days. The number of burrows
within marsh bank blocks in trial one were 530 times
greater than in trial three during the same duration of
exposure (2 weeks). The reasons for these anomalous
results are unclear; they cannot be attributed to location or
methodology differences since both trials were conducted
in the same location with the same methods and using the
same source of marsh bank substrata.
Approximately 90% of the colonizers in trials
one and three were juveniles of S. quoianum (5 mm;
Table 3). The mean percentages of colonizers that were
juveniles were lower in marsh bank substrata than other
substrata in both trials, but we did not detect a signifi-
cant difference (PN0.025). Adult isopods were also
observed inhabiting the coalesced patches of burrows
previously occupied by several juveniles, which may be
evidence of intraspecific competition.
4. Discussion
While S. quoianum is a habitat generalist capable of
rapidly colonizing a variety of substrata, results from
this study indicate intertidal populations of S. quoianum
exhibit a strong preference for decayed wood. This
preference for wood by S. quoianum could be related to
the physical characteristics of this substratum. Intertidal
wood is often soft and spongy and can hold considerable
amounts of water while maintaining its integrity; other
common intertidal substrata do not share these char-
acteristics. Often, other intertidal substrata are either
harder (sandstone), more dynamic and prone to erosion
(marsh banks), or hold relatively little moisture during
low tide (Styrofoam) in comparison to decayed wood
(per. obs.). However, as many Styrofoam floats are
constantly submerged, the Styrofoam blocks placed in
the intertidal may not have simulated the habitat utilized
by subtidal populations of S. quoianum. Future studies
will examine how burrowing rate is affected by sub-
stratum type while under subtidal conditions. The
habitat preference of S. quoianum may also be genetic
in nature as with some amphipods (Stanhope et al.,
1992) and a variety of other arthropods and mollusks
(reviewed by Jaenike and Holt, 1991). Despite any
physical or genetic predilections towards decayed wood,
the presence of large populations of S. quoianum in a
diversity of intertidal and subtidal substrata illustrate an
ability to adapt to changing quality, quantity, and type of
intertidal habitat.
While intertidal populations of S. quoianum exhibit a
preference for wood, other factors such as relative avail-
ability of substrata, recruitment and dispersal limitations,
and possible gregarious behavior may be important
determinants of local densities of S. quoianum. In pre-
vious surveys, we found the densities of isopods and
burrows in intertidal wood and sandstone substrata were
significantly higher than the densities in marsh bank
substrata (Davidson et al., in prep). Further surveys have
shown that the density of burrows in Styrofoam substrata
(intertidal and subtidal) appears higher than the other
substrata (Davidson, unpublished data). The inconsis-
tency between field measurements and results from this
study are a reminder that the habitat association of a
species does not necessarily indicate preference for that
habitat.
Nearly 90% of the colonizers were juvenile isopods,
which suggest juveniles disperse more often than adults.
Although more juvenile isopods were present than adult
isopods during August (58% of the total isopods;
Davidson et al., in prep), this difference cannot solely
explain the high percentage (68.499%) of juveniles
colonizing substrata. Thus, this pattern could be due to
an innate dispersive behavior or their active eviction
from a burrow by a larger isopod. Evictions are common
in the congeneric burrowing isopod S. terebrans, which
ejects juveniles from the burrow, likely when they reach
a size that interferes with feeding (Thiel, 1999). Our
results also indicate that adults will occasionally leave
existing burrows and colonize substrata, perhaps due to
competition with other isopods or to find a mate.
Colonization by S. quoianum was rapid and in some
substrata, resulted in heavily burrowed substrata blocks.
The greatest impact was within wood: in only nine
weeks, individuals of S. quoianum completely riddled
the wood blocks with burrows (up to 421 burrows per
100 cm
2
). Since burrowing rates were substantially
greater during trials one and three than trial two, recruit-
ment may be lower in mid-April than between August
October. The large variation in burrowing rate across
Table 3
The mean percentages (± SE) of the colonizers that are juveniles within
each substratum for trials 1 and 3
% Juvenile colonizers (5 mm)
Trial 1 Trial 3 Both trials pooled
Marsh Bank 82.8 (±13.2) 44.4 (±29.4) 68.4 (±14.7)
Wood 91.0 (±2.7) 96.1 (±1.7) 93.3 (±1.7)
Sandstone 95.0 (± 5.0) 90.4 (± 8.3) 92.5 (± 4.9)
Styrofoam 98.1 (±1.9) 100.0 (± 0.0) 99.0 (± 1.0)
All 91.5 (±3.8) 87.0 (±6.6) 89.4 (±3.7)
We did not detect a statistical difference between the mean percent of
colonizers that were juveniles between substrata in either trial one or
three (PN0.025).
148 T.M. Davidson et al. / Journal of Experimental Marine Biology and Ecology 354 (2008) 144149
Author's personal copy
time may be an expression of variable reproductive
timing and release of juveniles.
5. Conclusion
S. quoianum is a common invasive species in many
estuaries along the Pacific coast of North America and its
prodigious burrowing may erode shorelines and damage
maritime structures (Higgins, 1956; Carlton, 1979;
Talley et al., 2001). Results from this study indicate
S. quoianum can rapidly colonize intertidal substrata and
in a matter of weeks completely riddle wood and other
substrata. Burrowing rates can exceed 157 burrows per
week within wood (of a surface area of 100 cm
2
) in areas
with substantial populations of S. quoianum. The effects
of burrowing are not limited to wood as S. quoianum can
also riddle marsh banks, sandstone terraces, and Styro-
foam floating docks. The ability to rapidly colonize and
exploit a variety of habitats may explain why this isopod
has successfully invaded some Pacific coast estuaries.
Understanding the substratum preference of S. quoia-
num and aspects of colonization may also help determine
methods to manage and control this species and other
direct developers. For example, by outplanting a preferred
substratum such as wood, and allowing S. quoianum to
colonize, managers may be able to remove the newest
cohort from an area. If this process were continued for
several seasons, populations of S. quoianum may be
lowered enough to reduce their impacts. Future research
will examine the efficacy of different management stra-
tegies in reducing populations of S. quoianum.
Acknowledgements
We thank Sylvia Behrens-Yamada, Catherine de
Rivera, Scott Groth, Ben Grupe, Jan Hodder, Mike
Holmes, Jose Marin Jarrin, Tracey Smart, and Maya
Wolf, for their helpful advice and field assistance. We
also thank two anonymous reviewers whose comments
greatly improved a previous version of this manuscript.
Timothy M. Davidson was supported by a National
Science Foundation GK-12 Graduate Fellowship (DGE-
0338153 to A. Shanks and J. Hodder). The research was
also supported by Sigma Xi: the Scientific Research
Society Grant-in-aid of Research and the American
Museum of Natural History Lerner Gray grant for
marine research. [ST]
References
Aikins, S., Kikuchi, E., 2001. Studies on habitat selection by
amphipods using artificial substrates within an estuarine environ-
ment. Hydrobiologia 457, 7786.
Carlton, J.T., 1979. History, Biogeography, and Ecology of the
Introduced Marine and Estuarine Invertebrates of the Pacific Coast
of North America. Dissertation. University of California, Davis.
Carlton, J.T., Vermeij, G.J., Lindberg, D.R., Carlton, D.A., Dudley, E.C.,
1991. The first historical extinction of a marine invertebrate in an
ocean basin: the demise of the eelgrass limpet Lottia alveus.Biol.
Bull. (Woods Hole) 180, 7280.
Choat, J.H., Black, R., 1979. Life histories of limpets and the limpet
laminarian relationship. J. Exp. Mar. Biol. Ecol. 41, 2550.
Davidson, T.M., 2008. Prevalence and distribution of the introduced
burrowing isopod, Sphaeroma quoianum in the intertidal zone of
a temperate northeast Pacific estuary (Isopoda, Flabellifera).
Crustaceana 81, 155167.
Fernandez, M., Iribarne, O., Armstrong, D., 1993. Habitat selection by
young-of-the-year Dungeness crab Cancer magister and predation
risk in intertidal habitats. Mar. Ecol. Prog. Ser. 92, 171177.
Hedvall, O., Moksnes, P.O., Pihl, L., 1998. Active habitat selection by
megalopae and juvenile shore crabs Carcinus maenas: a laboratory
study in an annular flume. Hydrobiologia 375376, 89100.
Higgins, C.G., 1956. Rock-boring isopod. Bull. Geol. Soc. Am. 67,
1770.
Highsmith, R.C., 1982. Induced settlement and metamorphosis of sand
dollar (Dendraster ecentricus) larvae in predator-free sites: adult
sand dollar beds. Ecology 63, 329337.
Jaenike, J., Holt, R.D., 1991. Genetic variation for habitat preference:
evidence and explanations. Am. Nat. 137, S67S90.
Keough, M.J., Downes, B.J., 1981. Recruitment of marine inverte-
brates: the role of active choices and early mortality. Oecologia 54,
348352.
Looney, S.W., Stanley, W.B., 1989. Exploratory repeated measures
analysis for two or more groups: review and update. Am. Stat. 43,
220225.
Pardo, L.M., Palma, A.T., Prieto, C., Sepulveda, P., Valdivia, I., Ojeda,
F.P., 2007. Processes regulating early post-settlement habitat use in
a subtidal assemblage of brachyuran decapods. J. Exp. Mar. Biol.
Ecol. 344, 1022.
Richard, R.A., 1992. Habitat selection and predator avoidance:
ontogenetic shifts in habitat use by the Jonah crab Cancer borealis
(Stimpson). J. Exp. Mar. Biol. Ecol. 156, 187197.
Stanhope, M.J., Connelly, M.M., Hartwick, B., 1992. Evolution of a
crustacean chemical communication channel: behavioral and
ecological genetic evidence for a habitat-modified, race-specific
pheromone. J. Chem. Ecol. 18, 18711887.
Stanhope, M.J., Levings, C.D., 1985. Growth and production of Eo-
gammarus confervicolus (Amphipoda: Anisogammaridae) at a log
storage site and in areas of undisturbed habitat within the Squamish
Estuary, British Columbia. Can. J. Fish. Aquat. Sci. 42, 17331740.
Talley, T.S., Crooks, J.A., Levin, L.A., 2001. Habitat utilization and
alteration by the invasive burrowing isopod, Sphaeroma quoya-
num, in California salt marshes. Mar. Biol. 138, 561573.
Thiel, M., 1999. Reproductive biology of a wood-boring isopod,
Sphaeroma terebrans, with extended parental care. Mar. Biol. 135,
321333.
Underwood, A.J., 1981. Techniques of analysis of variance in
experimental marine biology and ecology. Oceanogr. Mar. Biol.
Ann. Rev. 19, 513605.
Williams, J.D., McDermott, J.J., 2004. Hermit crab biocoenoses: a
worldwide review of the diversity and natural history of hermit
crab associates. J. Exp. Mar. Biol. Ecol. 305, 1128.
Wahle, R.A., Steneck, R.S., 1991. Recruitment habitats and nursery
grounds of the American lobster Homarus americanus:a
demographic bottleneck? Mar. Ecol. Prog. Ser. 69, 231243.
149T.M. Davidson et al. / Journal of Experimental Marine Biology and Ecology 354 (2008) 144149
... The purpose of boring activity by S. triste has not been investigated in this study. In general, boring and burrowing by isopods may be for defense from predators, protection from environmental stresses at low tide, for feeding, for mating and reproduction, or a combination of these (Cragg, Pitman, and Henderson, 1999;Davidson, Rumrill, and Shanks, 2008;Talley, Crooks, and Levin, 2001). In the case of North Sarawak populations, the position of the borings suggests that they provide protection from desiccation, from sunlight exposure, and possibly also from wave agitation. ...
Article
Full-text available
Dodge-Wan, D. and Nagarajan, R., 2020. Boring of intertidal sandstones by isopod Sphaeroma triste in NW Borneo (Sarawak, Malaysia). Journal of Coastal Research, 36(2), 238–248. Coconut Creek (Florida), ISSN 0749-0208. Sphaeromatid isopods are known for their ability to bore into wood and friable rock and to cause damage to mangrove plant roots, wooden structures, and polystyrene dock floats in the intertidal zone. The ability of isopods to bore extensively into rock and accelerate coastal erosion is less well known and has not been previously reported in Malaysia. This study investigated the presence, the identity, and the erosive effect of rock-boring isopods in sandstones of the NW Borneo coastal region (Sarawak, East Malaysia). A multidisciplinary approach was used, including field and laboratory observations (geological and biological) of rocks and wood. This study revealed that abundant cylindrical borings in soft intertidal rock are created by the boring isopod Sphaeroma triste (S. triste). Bioerosion by this species can result in the direct removal of up to 50% of the exposed surface of the rock and penetrate the rock up to a few centimeters depth. This has a significant but localised impact on coastal erosion, contributing to the development of concavities in the rock, enlargement of joints, deepening of wave cut notches, widening of rock pools, and erosion of fallen blocks and sea-cave walls. There is evidence of modification of the isopods' mandible incisor processes by abrasion during rock boring. Although several Sphaeromatid species are known to bore into soft rocks, this is the first report and comprehensive description of boring into sandstone substrates by S. triste. The S. triste borings are compared with those made by other species reported elsewhere. In terms of neoichnology, the borings belong to deep-tier Trypanites ichnofacies, and fossil equivalents may be useful in palaeogeographic reconstructions of ancient shorelines, although they may have poor preservation potential.
... In some cases, physical removal can be easily achieved, especially where the target species has specific habitat preferences, for example, the aquatic isopod Sphaeroma quoianum that is invasive in the USA; where control in this instance has been achieved by placing artificial rotting wood habitats into water systems, allowing colonisation, then removing to lower the population (Davidson et al. 2008). ...
Thesis
Full-text available
This is a full text by request for my thesis. Please see published papers for citable information. Invasive species are one of the foremost damaging environmental problems for biodiversity and conservation, and can affect human health and man-made structures. They pose a great challenge for pest management, with little known about their control and few available success stories. Many crustacean species are invasive and can affect both biodiversity and aquaculture. Controlling invasive Crustacea is a complex and arduous process, but success could lead to increased environmental protection and conservation. Invasive Crustacea also comprise a significant pathway for the introduction of invasive pathogens. If these invaders carry pathogens, parasites or commensals to a new site they may threaten native species. Alternatively, pathogens can control their invasive host and could be utilised in a targeted biological control effort as a biocontrol agent. Looking specifically at one species of invasive brachyuran crab (Carcinus maenas) collected from the UK, Faroes Islands and Atlantic Canada, and several species of invasive amphipod from the UK and Poland, I explore which groups of microorganisms are carried alongside invasions, and if any could be used as biocontrol agents or whether they pose a threat to native wildlife. This thesis involves wide-scale screening of Carcinus maenas and several amphipod species, identifying a range of metazoans, fungi, protozoa, bacteria and viruses; many new to science. Taxonomic descriptions are provided for previously unknown taxa: Parahepatospora carcini; Cucumispora ornata; Cucumispora roeselii; and Aquarickettsiella crustaci. The application of metagenomics to pathogen invasion ecology is also explored, determining that it can be used as an early screening system to detect rare and/or asymptomatic microbial associations. Finally, I used experimental systems to assess the impact of pathogens carried by Dikerogammarus haemobaphes upon both itself and alternate host species (Dikerogammarus villosus and Gammarus pulex), identifying that C. ornata can infect native species and decrease their chance of survival. Overall this thesis describes a research process following through three main steps: i) invasive pathogen detection, ii) taxonomic identification, and iii) host range and pathological risk assessment and impact. Screening invasive and non-native hosts for pathogens is recommended for invasive species entering the UK, to provide a fast and informed risk assessment process for hazardous hitchhiking microbes. Please refer to the White Rose eThesis submission for further information or published papers.
... Sphaeroma quoianum is a species native to Australasia that was transported to the US west coast on boat hulls. It burrows into mud, soft rock, wood, and Styrofoam, largely to create living space and not for direct access to food resources Talley and Crooks 2007;Davidson, 2008;Davidson et al., 2008). As an invader this isopod is commonly found at densities of over 10 000 m −2 in burrows on vertical mud banks of tidal creeks and exposed bay fronts of salt marshes. ...
Chapter
Rapid change is a major feature of modern estuaries and coasts. In numerous systems, invasive species are a primary force altering the structure and function of communities. Nonindigenous species take on nearly all possible ecological roles, serving as agents of disease, parasites, primary and secondary producers, predators, competitors, facilitators, and disturbers. Here, major functional impacts are assessed by considering invasive species as nutrient and biogeochemical modifiers, trophic transformers, and structural engineers. Both plant and animal invasions have the ability to dramatically alter habitat properties and energy flows, shifting ecosystems from one type or state to another, with different functional attributes. Invaders can also impact longer-term, evolutionary dynamics through alteration of selection regimes and hybridization. The ecosystem-level consequences involve changes to emergent structural and functional properties and to ecosystem services. Biodiversity, spatial heterogeneity, connectivity, succession, stability, and resilience all may be modified by invasion. Ecological impacts are often heavily intertwined with ecosystem services, in terms of both positive and negative consequences for humans. Invaders play key roles in fisheries, aquaculture, shoreline stabilization, remediation and restoration, and carbon sequestration. Several decades of invasion research allow us to identify the settings most likely to experience highly modified functions when invaded, and to synthesize the nature and magnitude of invasion effects on ecosystem function.
... In 9 weeks, they completely riddled wood blocks with burrows. However, they can colonize and exploit a variety of habitats, including marsh banks, styrofoam floating docks, and other types of substrata (Davidson et al. 2008). In their home range in Australia, they are not reported to cause bank erosion problems and are found predominantly under stones, in crevices, empty barnacle tests, and wood substrates (Hass and Knott 1998). ...
Article
Full-text available
Many crustaceans have been moved to new locations where they have caused ecological or economic problems, that is, have become invasive. This article focuses on the role of animal behavior in contributing to their success. Certain behaviors are particularly relevant, including (1) feeding: outcompeting native species for food or eating native species of concern; (2) predator avoidance: the invader may be more successful at avoiding predators than native species; (3) habitat: invasive species may displace natives from their habitat or may alter the environment; (4) aggressive behavior: may contribute to (1) or (3) above; (5) movements: if the invader undergoes extensive migrations, it can spread more rapidly; (6) plasticity: (learning) if the invader is “smarter” than native species, it may be more likely to outcompete them for habitat and/or food; and (7) reproduction (though not strictly reproductive behavior per se). These behaviors are discussed with respect to invasive crustaceans, including freshwater and marine examples.
... The Australasian isopod Sphaeroma quoyanum H. Milne Edwards, invasive in North America, has a clear preference for decayed wood. A potential control method could thus involve out-planting the preferred substrate and removing it once it has been colonised (Davidson et al. 2008). Harvesting edible crustaceans for consumption and sale can be a productive alternative strategy under the philosophy of ''making the best of a bad situation'' (Gherardi et al. 2011). ...
Article
Full-text available
The subphylum Crustacea includes the most successful species among aquatic alien invaders. The impacts of invasive alien crustaceans (IAC) are often substantial, due to the complex trophic role of most of these species leading to cascading effects throughout the invaded ecosystems. IAC also have the potential to cause a shift in the ‘keystone’ ecosystem functions, changing energy flux and nutrient cycles which together affect critical ecosystem services such as biodiversity, fisheries yield and water quality. Although no individual trait appears to be a good predictor of invasion success, a combination of some characteristics such as eurytolerance, omnivory and certain r-selected life-history traits results in a high probability of alien crustacean species becoming invasive. Both environmental factors, such as habitat heterogeneity in the invaded ecosystems, and evolutionary factors, such as adaptations to new environmental conditions, also play important roles during establishment. Therefore, individual environmental niche models, including genetic algorithm, have the highest likelihood of providing useful predictive information about invasion success and spread of alien Crustacea. Attempts to control IAC through biocides or mechanical removal have had mixed success in the past but a strategic combination of different methods may lead to some success in the future. KeywordsAquatic habitats–Genetic diversity–Prevention–Control–Ballast water–Invasions–Crustacea
... quoyanum; Milne Edwards 1840). This isopod creates dense burrow networks in a variety of habitats including marsh banks, decayed wood, friable rock cobble and ledges, and Styrofoam floats used in floating docks (Carlton 1979; Davidson et al. 2008b). In some bays, high densities of burrows of S. quoianum increase the rate of erosion of marsh banks (Talley et al. 2001) and friable rock (Higgins 1956) and damage some marine structures (Carlton 1979; Davidson 2008). ...
Article
Full-text available
The non-native isopod, Sphaeroma quoianum, has invaded many estuaries of the Pacific coast of North America. It creates extensive burrow microhabitats in intertidal and subtidal substrata that provide habitat for estuarine organisms. We sampled burrows to determine the effects of substratum type on the community of inquilines (burrow inhabitants). The density of inquilines was higher in wood and sandstone than marsh banks. Inquilines, representing 58 species from seven phyla, were present in 86% of samples. Inquilines equaled or outnumbered S. quoianum in 49% of the samples. Non-native fauna comprised 29% of the species and 35% of the abundance of inquilines, which is higher than other estuarine habitats in Coos Bay. Sessile non-native species were found living within burrows at tidal heights higher than their typical range. Thus, the novel habitat provided by burrows of S. quoianum may alter the densities and intertidal distribution of both native and non-native estuarine fauna. KeywordsBioeroder-Ecosystem engineer-Facilitation-Habitat alteration-Inquilines- Sphaeroma quoianum
Article
Full-text available
Background Dispersal is an important process affecting population dynamics and connectivity. For marine direct developers, both adults and juveniles may disperse. Although the distribution of juveniles can be initially constrained by their mothers’ choice, they may be able to leave the parental habitat and colonize other habitats. We investigated the effect of habitat quality, patch size and presence of conspecific adults on the colonization of novel habitats by juveniles of the tube-dwelling amphipod Cymadusa filosa associated with the macroalgal host Sargassum filipendula . Methods We tested the factors listed above on the colonization of juveniles by manipulating natural and artificial plants in both the field and laboratory. Results In the laboratory, juveniles selected high-quality habitats (i.e., natural alga), where both food and shelter are provided, when low-quality resources (i.e., artificial alga) were also available. In contrast, habitat quality and algal patch size did not affect the colonization by juveniles in the field. Finally, the presence of conspecific adults did not affect the colonization of juveniles under laboratory condition but had a weak effect in the field experiment. Our results suggest that C. filosa juveniles can select and colonize novel habitats, and that such process can be partially affected by habitat quality, but not by patch size. Also, the presence of conspecifics may affect the colonization by juveniles. Successful colonization by this specific developmental stage under different scenarios indicates that juveniles may act as a dispersal agent in this species.
Article
Marine wood-borers and burrowers can substantially alter habitats and human-created structures in the marine environment. While many marine borers and burrowers occur only in a few substrata, burrowing sphaeromatid isopods can damage a variety of substrata. On the Pacific coast of North America, burrowing by the non-native isopod, Sphaeroma quoianum, accelerates shoreline erosion and damages marine structures. We conducted a lab experiment to quantify the per capita burrowing effect of 5. quoianum on four common estuarine substrata. After two months, isopods created longer and more voluminous burrows and removed the most material (per capita) in marsh banks and Styrofoam followed by sandstone and non-decayed wood. We also examined the burrow morphology (length, diameter, volume) of burrows of S. quoianum from those four substrata collected in the field. We observed longer and more voluminous burrows in marsh bank and Styrofoam substrata, although we only detected a significant difference in length between substrata. Based on our lab results, we estimate a population of 100000 adult isopods burrowing for two months could remove approximately 176 liters of marsh bank, 103 1 of Styrofoam, 72 1 of sandstone, or 29 1 of non-decayed wood. While the per capita bioerosion effects are lower than some bioeroders, e.g., the shipworm Bankia setacea, the pholad Penitella peniþa, high densities and wide distributions of S. quoianum suggest it is a substantial bioeroder within the intertidal and shallow subtidal in temperate Coos Bay, Oregon, and perhaps the other estuaries it has invaded.
Article
Full-text available
The association of invertebrate communities with macroalgae rafts has received much attention over recent decades, yet significant gaps in our knowledge remain with respect to the colonization process. Using laboratory-based experiments and in situ field trials in Strangford Lough, Northern Ireland, this study investigated whether members of the known rafting genus Idotea (sub-phylum Crustacea; order Isopoda) could effectively colonize rafts after shore seaweed detachment, or if their presence merely reflected a passive marooning process. Test tank arenas were used to identify traits that may influence the rafting potential of the dominant shore species Idotea granulosa and the well known rafter Idotea baltica. When released mid-water, I. granulosa initially ascended and associated with floating seaweed whereas I. baltica tended to descend with no clear habitat association. These findings conflict with the differential distribution of these Idotea species among rafts and shore algae, thus highlighting the complex nature of the potential of organisms to raft. In the field we considered the relative ability of different Idotea species to colonize tethered rafts composed of Ascophyllum nodosum and Fucus vesiculosus, cleaned of all vagile organisms and deployed at locations adjacent to established intertidal Idotea species populations. At the end of the experiment (after 44 days) rafts were inhabited by known rafting and shoreline species, confirming that colonization can occur after algal detachment. Previously considered shoreline species on occasion outnumbered well known rafters suggesting that a wide range of Idotea species can readily avail of macroalgal rafts as a potential dispersal mechanism or alternative habitat.
Article
Full-text available
Habitat selection by megalopae, and habitat preference and relative mortality of young-of-the-year (YOY) Dungeness crab Cancer magister Dana were evaluated in 4 habitat types: bivalve shell middens (Crassostrea gigas), eelgrass Zostera marina, mud with scattered shell and bare mud. Under laboratory conditions shell was the most preferred habitat by megalopae and YOY; eelgrass ranked second. Field tethering experiments showed that shell habitat provided the best protection from predation, and that the proportion of crab eaten was highest on bare mud. Field tethering experiments using small hooks attached to tether lines and glued to the crab showed that the sculpin Leptocottus armatus was the most important fish preying on YOY crab in this area. Cannibalism by larger instars of YOY, 1+ and 2+ Dungeness crab also may account for part of the YOY mortality. Most evidence suggests that intertidal shell habitat enhances Dungeness crab survival during the first several months of benthic life. It has led to the use of artificial shell habitat as a technique to increase juvenile crab abundance and compensate crab losses due to dredging.
Article
Full-text available
We have identified benthic recruitment habitats and nursery grounds of the American lobster Homarus americanus Milne Edwards in the coastal Gulf of Maine, USA, by systematically censusing subtidal sediment, cobble, and ledge substrata. We distinguish lobsters between settlement size (5 mm carapace length (CL) to ca 40 mm CL as the 'early benthic phase' (EBP) because they are ecologically and behaviorally distinct from larger lobsters. EBP lobsters are cryptic and apparently restricted to shelter-providing habitats (primarily cobble substratum) in coastal Gulf of Maine. In these habitats we found average population densities of EBP lobsters as high as 6.9 m-2. EBP lobsters were virtually absent from ledge and sedimentary substrata devoid of vegetation although larger lobsters are commonly found there. It is possible that the requirement for shelter-providing substrata by this life phase creates a natural demographic 'bottleneck' to benthic recruitment for the species. Prime cobble recruitment habitat is relatively rare and comprises ca 11 % of the 60.2 km of shoreline at our study area in midcoast Maine. If this low availability of cobble exists throughout the Gulf of Maine, as other studies indicate, it could limit lobster production potential. We verified the geographic extent of recruitment to cobble habitats censused in 3 of 4 regions spanning ca 300 km of the coastal Gulf of Maine (from Nahant, Massachusetts to Swans Island, Maine). Early benthic phase lobsters were absent from cobble censused in the northeastern extreme of our survey (Swans Island). This pattern is consistent with earlier speculation that relatively cool water temperatures may limit larval settlement in this region.
Article
Full-text available
In this article, the exploratory analysis of data from a repeated measures design with one repeated factor and one treatment factor is considered. Recent developments in repeated measures analysis are reviewed and incorporated into an overall strategy for the analysis of such data. An example is given to illustrate the techniques.
Article
Full-text available
Because adaptive shifts may often be initiated by evolutionary changes in behavior, it is of interest to determine the extent to which natural populations harbor genetic variation for ecologically important behaviors. Habitat preference is an especially significant behavior, because it determines the regime of natural selection acting on loci that affect adaptation to the environment. A survey of the literature reveals that genetic variation for habitat selection is common, especially in arthropods and mollusks, the groups that have been studied most frequently. Possible adaptive mechanisms by which this variation could be maintained within populations include a genetic correlation between density-independent fitness in a habitat and a preference for it; and soft selection, whereby density-dependent population regulation occurs independently in separate habitats. Several studies have documented a phenotypic correlation between preference and performance, but as yet, no such genetic correlations have been unequivocally demonstrated. We show theoretically that under hard selection, optimal habitat selection may often lower the probability of maintaining a polymorphism at a locus that affects adaptation to different habitats. Soft selection appears much more likely to promote variation for habitat preference. Mechanisms including resource competition and natural enemies whose numbers build up in a habitat-specific manner in response to host or prey density have the capacity to bring about selection favoring alleles whose carriers prefer relatively underused habitats. We believe that more progress in understanding the evolution of habitat preference will come from studies of these ecological mechanism than from further demonstrations of the mere existence of genetic variation for such preferences.
Article
Dendraster excentricus larvae capable of metamorphosis presented with various substrates show a significant preference for adult-associated sand. Adult D. excentricus produce a chemical cue, possibly a small peptide that is sequestered by some component in the sand and that is stable for at least 7 wk. Thus, larval settlement occurs within or adjacent to existing sand dollar beds which often contain several hundred adults per square metre. Survival of newly metamorphosed D. excentricus is significantly reduced by an extremely abundant, tube-building predator, Leptochelia dubia (Crustacea: Tanaidacea). Tanaidacean and possibly other micropredators, however, are excluded from sand dollar beds by the reworking activities of adult sand dollars. Thus, preferential settlement of D. excentricus larvae near adults of the species should result in increased larval and juvenile survival. -from Author
Article
An earlier study of population genetics of an estuarine amphipod provided evidence from genomic DNA analysis for a habitat-specific race of amphipods within the speciesEogammarus confervicolus. In some estuaries of the northeast Pacific, this race of amphipods exists sympatrically with other members of the species. Here we present evidence for a race-specific pheromone that appears to be the consequence of differential metabolism of the algae (Fucus distichus andPelvetia fastigiata) characteristic of the habitat occupied by this race. The race-specific pheromone identified in this study is a subtle modification of an already existing communication system: females of the habitat-specific race produce the pheromone characteristic of the species as a whole but have an ability not shared by other females of the species to modify this pheromone when raised on the algal substrate characteristic of their habitat. Only males of this race make a distinction between the more specific pheromone and the species pheromone. The formation of hybrids (conceived and raised on the algal substrate) between members of the habitat-specific race and the other members of the species disrupted the ability to produce and distinguish the race-specific pheromone; hybrids still produced a pheromone, but it was indistinguishable from that produced by the species as a whole. Behavioral assays and the results of reciprocal, interpopulation crosses indicated pheromone response in males had evolved with production; males however, did not have to be raised on the algal substrate to respond to the alternate pheromone. No evidence for maternal effects or sex linkage were detected in the results of the crosses; more specific indications of the genetics underlying pheromone production were not evident.
Article
We studied megalopae (postlarvae) and young juveniles of the shore crab (Carcinus maenas L.) in laboratory experiments to examine four potentially important processes for juvenile distribution and recruitment: (1) hydrodynamic processes and passive deposition of megalopae, (2) active habitat selection of megalopae, (3) habitat specific predation rates, and (4) active habitat selection by juveniles. In an annular flume, simulating natural current velocities in nursery areas on the Swedish west coast, we assessed the distribution of dead megalopae, live megalopae, live megalopae with predators (juvenile conspecifics and brown shrimp, Crangon crangon), and first instar crabs, in four simultaneously presented habitats: blue mussels (Mytilus edulis), eelgrass (Zostera marina), filamentous green algae (Cladophora sp. and Chaetomorpha linum) and bare sand. In a second experiment we studied the distribution of live megalopae between four different ephemeral macroalgae with different structural complexity (Ulva lactuca, Enteromorpha sp., Cladophora sp. and Ectocarpus siliculosus). Dead megalopae were evenly distributed between the four habitats, whereas all other treatments showed significantly lower proportions of megalopae and juvenile crabs in the sand habitat (0–2%) compared to the structurally complex habitats (24–40%). The distribution between mussels, eelgrass and filamentous algae of live megalopae in absence of predators did not differ significantly from the hydrodynamical null hypothesis, i.e. distribution of dead megalopae. However, predation increased the proportion of megalopae significantly in the filamentous algae, providing the best refuge from predation of these habitats. First instar crabs showed a significantly different distribution compared to megalopae, with higher proportion in the algal habitat, whereas juvenile predatory crabs were found in significantly higher proportion among mussels. Megalopae selected all four different macroalgae species over open sand, but a significantly lower proportion were found in the algae with the highest structural complexity (Ectocarpus siliculosus; 14%) compared to the other algal species (26–30%). These results indicate that passive deposition have little influence on the small scale (< 10 s of meters) distribution of shore crab megalopae during normal current velocities, but that active habitat selection by megalopae is the major process responsible for the non-random distribution of megalopae and juvenile shore crabs. The results further suggest that the initial distribution of megalopae between nursery habitats is quickly modified by habitat specific predation rates and size-specific movements and habitat choices by juveniles. The correlation between the habitat choice of megalopae and juvenile crabs, and the refuge value of the examined habitats suggests that habitat specific predation rates is a major selective force behind the behavior of active habitat selection in this species.
Article
In California, two species of acmaeid limpets display contrasting life history patterns. Acmaea insessa (Hinds) has an obligate association with the brown alga, Egregia laevigata (Setchell), which has an annual life cycle in the intertidal zone. Acmaea insessa must be able to grow to maturity and produce gametes before the inevitable but unpredictable loss of its attachment and feeding substratum. On the other hand, A. digitalis (Rathke), like most limpets, lives on permanent hard surfaces not subject to catastrophic loss. Predictably, A. insessa has a shorter expectation of further life, higher growth rate, greater reproductive effort, and shorter time to sexual maturity compared with A. digitalis.Habitat selection of A. insessa ensures that it will not interact with any of the other co-occurring species of acmaeid limpets during its adult life history; it avoids interspecific competition and in relation to other conventional limpets has a specialized mode of life. It may be argued that previous episodes of interspecific competition influenced this pattern of habitat selection and that these Californian limpets provide an example of a positive relationship between specialized modes of life and the number of co-occurring ecologically similar species.Data on limpet species abundance and habitat selection from other parts of the world are confusing. Both southern Africa and northern Europe support well established limpet-algal associations but the former has many and the latter few related limpet species. Northern New Zealand has a more diverse fauna of limpets and herbivorous gastropods than northern Europe but has no algal associated limpets despite the presence of suitable hosts. The relative abundance of limpet species does not provide a good basis for predicting the occurrence of obligate limpet-algal associations.
Article
In highly mobile animals post-settlement dispersion of juveniles can strongly influence the observed patterns of abundance and distribution. To explore the relative importance of factors regulating the use of habitat by crabs we performed a multi-species manipulative experiment in a subtidal environment of the central Chilean coast. First, demographic patterns were established by performing a year-round crab survey in three discrete and well-known subtidal crab habitats: (1) algal turf, (2) cobbles and (3) shell hash. Second, habitat preferences were experimentally evaluated using concrete trays that were filled with different substrate types that simulate natural habitats. Settlement and recruitment rates were estimated from experimental trays that were left in the field and surveyed after 2 weeks (complete experiment was repeated 7 times throughout 1 year). Third, mortality, due to predation, was assessed by covering 50% of the trays with a 4-mm mesh-size screen that excluded large predators (i.e., fishes, shrimps). Fourth, habitat colonization rates were evaluated by quantifying the arrival, into open trays, of large juveniles (secondary dispersal). The most abundant species in this system (Paraxhantus barbiger, Cancer setosus, Taliepus dentatus and Pilumnoides perlatus) displayed clear habitat preferences at the time of settlement, evidenced by differences in density of recruits among habitats. Recruitment regulation by predation seemed to explain the observed patterns in only one case. For most species, however, evidence of ontogenetic change in the use of habitat, through active habitat redistribution by large juveniles, was detected. Thus, secondary dispersal among habitats seems to outweigh the influence of megalopae's habitat selection and post-settlement mortality as responsible for the observed demographic patterns.