1. Examining the effects of recruitment and post-recruitment
processes on populations of the sea fan, Muricea californica
Denise Weisman1
, Stephen Schroeter1
, Dan Reed1
, and Pete Raimondi2
1
Marine Science Institute, University of California, Santa Barbara, CA 93106, USA, 2
Department of Biology and Evolutionary Ecology, University of California, Santa Cruz, CA 95064 USA
Sources of Variation in Population Size
Muricea was first observed on
SCAR in 2002 following a large
recruitment event. Recruitment
by Muricea has occurred during
each of the subsequent years.
Population size has increased
steadily since 2002 suggesting
that recruitment is an important
driver of this pattern.
The density of Muricea
recruits was strongly
related to proximity to
SMK during the first
several years of the
study (2002-2004)
implicating SMK as the
potential larval source
for SCAR. During this
period recruitment at
SMK was lower than
on SCAR. The relationship between recruitment density and
distance from SMK disappeared beginning in 2005.
Introduction
The extent to which populations of marine organisms are
structured by the supply of propagules versus post-recruitment
processes has been a topic of much discussion the last several
decades. One of the more difficult issues to resolve in this
discussion has been determining patterns and sources of
propagule dispersal, in part due to the difficulty involved in
identifying discrete source populations. Here we use a newly
constructed artificial reef off southern California to examine:
(1) the degree to which populations of the sea fan Muricea
californica are structured by recruitment vs. post-recruitment
processes, and (2) patterns and sources of larval supply.
Questions
Methods
The San Clemente Artificial
Reef (SCAR) consists of 56
40m x 40m rock and concrete
modules. The modules are
arranged in 7 blocks of 8
modules positioned at
distances ranging from 0.5 to
3.5 km from the nearest
natural reef at San Mateo
Kelp (SMK). Construction of
SCAR was completed in fall
1999 and the densities and
sizes of Muricea californica
have been sampled annually
in the summer in permanent
plots at SCAR and SMK
beginning in 2000.
00 01 02 03 04 05 06 07 08 09
0
5
10
15
20
Year
MuriceaDensity(No.m-2
)
Non-recruitRecruit Total
Recruitment
Post-recruitment
Unexplained
0.00
0.10
0.20
0.30
0.40
0.50
PartialR2
Patterns of Recruitment
Patterns of Sea Fan Colonization and
Population Growth
Conclusions
• Survivorship was high and recruitment explained nearly 40%
of the variation in Muricea population size.
• Frequent recruitment coupled with rapid colony growth led to
rapid increase in size of the reproductive population on SCAR
that allowed populations of Muricea on SCAR to become self-
sustaining within four years of initial colonization.
Reproductive Population Size
Recruitment explained
nearly three times more
of the variation in the total
population size than 10
post-recruitment factors
combined that entered
into the multiple
regression model.
• What are the primary sources of
variation in population size of
Muricea?
• How do patterns of recruitment
vary in space and time?
• How is recruitment related to the
size and location of neighboring
populations?
Prior to the initial
recruitment of Muricea
on SCAR, the only
reproductive
populations were found
on natural reefs to the
south. Newly recruited
colonies of Muricea on
SCAR grew to
reproductive size within
2 years. Continued
recruitment, coupled
with rapid colony
growth and high
survivorship (typically
~ 80% of recruits
survived to year 2) led
to a large increase in
Distance from nearest natural reef (km)
0 1 2 3 4
RecruitDensity(No.m-2
)
0
10
20
30
40
50
60
2002
2003
2005 - 2008
r2
= 0.98
r2
= 0.98
2004
r2
= 0.91
r2
< 0.35, p > 0.6
the size of the reproductive population of sea fans on SCAR.
By 2006, the density of reproductive individuals at most
locations on SCAR was higher than on the natural reef at
SMK.
• The initial colonization of
Muricea on SCAR declined
rapidly with proximity to
the nearest natural reef.
• Muricea recruitment was
dependent on the local supply
the of larvae as most dispersal
appeared to occur over scales
of 100s to 1000s of meters.
2008
Distance from nearest natural reef (km)
0.0 0.6 0.9 1.4 1.8 2.1 2.5 3.40.0 0.6 0.9 1.4 1.8 2.1 2.5 3.40.0 0.6 0.9 1.4 1.8 2.1 2.5 3.40.0 0.6 0.9 1.4 1.8 2.1 2.5 3.40.0 0.6 0.9 1.4 1.8 2.1 2.5 3.40.0 0.6 0.9 1.4 1.8 2.1 2.5 3.40.0 0.6 0.9 1.4 1.8 2.1 2.5 3.40.0 0.6 0.9 1.4 1.8 2.1 2.5 3.40.0 0.6 0.9 1.4 1.8 2.1 2.5 3.4
0
50
100
150
200
250
2007
0
50
100
150
200
250
2006
0
50
100
150
200
250
2005
ReproductivePopulationDensityIndex(No.m-2
)
0
50
100
150
200
250
2004
0
50
100
150
200
250
2003
0
50
100
150
200
250
2002
0
50
100
150
200
250
(SMK)