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1284
Modeling Larval Connectivity of Coral Reef Organisms in the Kenyan-Tanzanian region
C. Gaby Mayorga Adame*, Hal P. Batchelder , P. Ted Strub, Yvette H. Spitz
College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis OR 97331
*[email protected]
Abstract
Conclusions
Model Set Up
Marine Protected Areas (MPAs) have been widely implemented as a
conservation effort on coral reef systems. The extent to which they achieve
the dual goals of protecting biodiversity and enhancing productivity of reef
associated species beyond their boundaries depends on the larval
connectivity among protected and unprotected reefs
Connections among MPAs and with unprotected reefs enhance regional
resilience and individual reef recovery from disturbance. Potential
connectivity patterns of larvae, along with other criteria (reef size, quality,
productivity), should be considered when designing spatial management
policies to protect coral reef systems
An individual-based particle tracking model (IBM) was coupled to an ocean
circulation model to examine connections among coral reefs in the KenyanTanzanian reef region of East Africa and to evaluate connectivity among
existing MPAs. We explored the effects of:
Spawning date, by simulating 3 alternating months during the spawning
season
Ocean Circulation Model
Regional Ocean Modeling System (ROMS)1 application for the
coastal region of Kenya and Tanzania (0-10°S, 38.7-46.98°E)
4 km horizontal grid resolution, 31 terrain-following s-vertical levels
Forced by daily atmospheric variables from NCEP/NCAR2 and
monthly open boundary forcing from OFES3 global Ocean General
Circulation Model
Individual Based Model
POPCYCLE4 was used to track particles in the 3D simulated flow
~20 000 particles were released daily from 290 protected reefs
during Oct, Dec and Feb of two years 2000-1 and 2003-4
The number of particles released per reef was proportional to the
reef area with a density of 25 particles/km2
All particles were released at 3m depth
Particles were characterized as two species groups with different
behaviors:
Inter-annual environmental variability by simulating 2 non-consecutive
years
Connectivity matrices, derived from IBM particle tracking of reef
species, describe potential recruitment pathways among individual
reefs in the region, and could contribute to the design and
implementation of a more efficient network of MPAs
The different life history and behavior of the two species groups
generate different connectivity patterns and a very different potential
of successful settlement (2.5% Acroporids vs 50% Acanthurids)
There is substantial inter-annual and intra-seasonal variability in
the percentage of successful settlers per release date, and some,
less striking, inter-annual variability in the connectivity pattern of both
species groups. This is related to the variability in the 3D velocity
fields, perhaps due to the interaction of the seasonal circulation
pattern with a highly variable eddy field
Protected reefs in latitudinal section 7 are the common source for
most successful settlers of both species groups. Conservation efforts
may wish to focus in this key region that seems to seed many of the
other reefs
“Successful settlers” - % per release date
Larval behaviors by simulating 2 species groups: Acanthurids and
Acroporids
Full model domain with
bathymetry contours
The black arrows show the
northward flowing East
African Coastal Current
(EACC) that is present all
year long and its branch that
affects the archipelago. The
southward arrow shows the
Somali Current present only
during the NE monsoon (Dec
to Mar). To analyze
connectivity the study region
was subdivided in to 9
latitudinal sections denoted
by a number and a color. The
coral reefs in each section
are shown in their
corresponding color. North to
south the 3 big islands are
Pemba, Zanzibar and Mafia
Study Region
4000
2000
100
500
1000
Success of settlers for all the regions expressed as the percentage
of the total number of larvae released on a given day. This
illustrates which spawning events are likely to generate high
recruitment
20
40
Source & Sink maps
Connectivity Matrices
Oct
Dec
Feb
Potential of success is very different for the two species groups
with less than 2.5% for Acroporids and up to 50% for
Acanthurids. Sensitivity analyses show that sensory and
swimming capabilities are in part driving this difference. Duration of
the competency period is likely to be another important factor, as a
longer competency period provides a greater probability of the
larvae encountering suitable reef habitat. This remains to be tested
Both species groups show high inter-annual and intra-seasonal
variability, which is related to the strength of the EACC. The interannual variability of the circulation has different effects on the
potential settlement success of the two species groups. For
example, the higher Acanthurids' settlement success in February
2004 compared to 2001 is due to a stronger coastal jet in 2004,
which resulted in dispersal among all reef regions. Acroporids in
the other hand show little difference between the two years
“Sink Section”
Oct00
Dec00
Feb01
1m.s-1
Source maps show where the successful settlers come from.
Sink maps show the most popular destinations for successful
settlers. The color scale indicates the fraction of the total
successful settlers that came/ended up in a given location for
the two species groups: Acanthurids (blue) and Acroporids
(purple)
“Source Section”
Illustration of the connectivity among reefs in the 9 latitudinal sections for the two
species groups (Acanthurids (Upper panels in blue) and Acroporids (Lower panels
in purple)), and for two years 2000-1 (O) and 2003-4 (
). The size of the symbols
is proportional to the number of connections
In general, sections with few protected areas (e.g. 5 and 9) and therefore less
seeding have little connectivity. Region 8, while having few protected areas, shows
high connectivity with the surrounding areas due to favorable circulation. Particles
from region 1 quickly leave the northern boundary of the domain
The self seeding pattern shown by Acroporids suggests that high retention at the
release location is an important mechanisms controlling their settlement success.
The pattern shown by Acanthurids suggests that this species group is capable of
long distance dispersal and that the southern sections supply larvae to the northern
sections. These different patterns are a consequence of their pelagic larval duration
.
Oct03
Dec03
Feb04
Both species groups have their source 'hot spot' in section 7,
but they differ in their sink pattern. Section 8 is a major
destination, however Acanthurids show also high settlement
potential in the northeast coast of Zanzibar Island. This
suggests that their long pelagic larval duration allows them to
take advantage of both recirculation patterns caused by reefs
and islands and long distance transport caused by the EACC
Acknowledgements
This work is supported through a CONACYT Scholarship
Travel support comes from NOAA
CIOSS
For unconditional support to my family (Italo, Ian, Mom and Sis) and
officemates (Martin Hoecker-Martinez, Atul Dhage, Byungho Lim, et al)
Vectors of monthly mean surface velocity and sea surface height in
meters are a “proxy” for the ocean conditions that larvae experience
when they are released
References
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System. Journal of Computational Physics, 227, 3595–3624. http://www.myroms.org
2. National Centers of Environmental Prediction. http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html
3. Masumoto, Y., et al. (2004), A fifty-year eddy-resolving simulation of the World Ocean: Preliminary outcomes of OFES (OGCM for the Earth
Simulator), J. Earth Simulator, 1, 35– 56. http://www.jamstec.go.jp/esc/ofes/eng/index.html
4. H. P. Batchelder (2006),Forward-in-time-/backward-in-time-trajectory (FITT/BITT)
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