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Factors Affecting Species Richness and Abundance of
Fish in Seagrass Meadows in the Saipan Lagoon
Northern Arizona University ™
Field experience in
Conservation
Biology
Northern Mariana Islands
Erica Alling
Department of Biological Sciences, Northern Arizona University,
Field Experience in Conservation Biology
!Methods!
Abstract!
!!
!!
! Seagrass ecosystems are among the most productive in
the world. The role of seagrass as fish nurseries have been
described
throughout their range, but a notable omission is in
!
fisheries-dependent Saipan. In Saipan, two species of seagrass
(Halodule
uninervis and Enhalus acoroides) could contribute to
!
fish nursery productivity but are susceptible to fragmentation from
algae
and sand. To address this, I quantified the number of fish
!
species and individuals and the level of fragmentation along
transects
at sites where each species of seagrass was abundant. I
!
found that species richness and abundance of fish is higher in H.
uninervis
meadows, but is negatively affected by habitat
!
fragmentation. Habitat fragmentation in the E. acoroides meadows
has no effect on the species richness and abundance of fish. This
suggests that management for increasing size and abundance of
H. uninervis seagrass meadows and reducing sand and algae
fragmentation would benefit fisheries in the Saipan lagoon. !
-  The abundance of fish in Halodule seagrass
decreased with fragmentation!
- I chose 4 independent sites for both seagrass species (total of
8 sites) using a benthic habitat map of the Saipan Lagoon
(Houk and van Woesik 2008) and Google Earth satellite images!
Juvenile Fish!
- I swam 4 belt transects that were 50 meters long and 50
meters apart at each site!
- I photographed all fish within 5 meters of my transect line and
recorded species and number !
- I measured the length of any interruption in the seagrass
along my transect line by sand, coral, algae, etc (i.e.
fragmentation)!
- I ran all transects at a consistent tide level and time of day
(Unsworth et al. 2007)!
(N = 16; R2 = 0.62; F ratio = 22.67; P = 0.0003)
All Fish!
!Introduction!
! Seagrass ecosystems make significant contributions to
global fisheries. Research demonstrates the connectivity between
seagrass and coral reef habitats through the movement of reef
fish as they grow from juveniles to adults (Unsworth et al. 2008).
In Saipan, the barrier reef shelters an inner lagoon and allows for
seagrass growth along the shore. The proximity of the seagrass
meadows
!! !! !! to the barrier reef suggests potential for a seagrass
nursery for reef fish and habitat for other lagoon dwelling fish.
Recent studies in the Saipan lagoon show that the seagrass
meadows have decreased in area and have become more
fragmented over the last 60 years (Houk and van Woesik 2008).
The reef fishery, which is the most valued fishery in Saipan
commercially and culturally (DFW Fishery Statistics Report 2010),
could be affected by this habitat loss due to this nursery role of the
seagrass ecosystems. !
Seagrass
Meadow!
* What are the factors affecting the species richness
and abundance of juvenile reef fish and all fish in
the seagrass meadows of Saipan? !
Site 5 (Enhalus)!
(N = 16; R2 = 0.44; F ratio = 11.22; P = 0.004)
!Results
- There was a higher species richness and abundance of juvenile
reef fish in Halodule seagrass!
Richness!
- There was no significant relationship between the
abundance and richness of fish in Enhalus
seagrass and fragmentation !
Abundance!
!
H1: Seagrass Species affects…!
!
-  Juvenile reef fish richness !
!
-  Juvenile reef fish abundance!
!
-  All fish richness!
!
!
-  All fish abundance!
(N = 32; Wilcoxon
X2
= 9.40; P = 0.0022)
(N = 32, Wilcoxon
X2
= 14.26; P = 0.0002)
- There was a higher species richness and abundance of all fish
in the Halodule seagrass!
H2: Habitat fragmentation affects the species richness
and abundance of fish!
!
Richness!
-  All fish abundance!
! Although, the effects of habitat fragmentation on fish
populations in seagrass meadows vary greatly among studies, the
majority of these studies conclude that habitat fragmentation does
not affect species richness and abundance of fish (Arponon and
Boström 2012). My study is the first to show that the abundance of
fish in H. uninervis seagrass is negatively affected by habitat
fragmentation.!
! In the Saipan lagoon seagrass are in decline (Houk and
van Woesik 2008). Further, H. uninervis seagrass is declining at a
faster rate and is more susceptible to fragmentation due to macroalgae than the E. acoroides seagrass (Houk and van Woesik
2008). My results suggest that the decline of H. uninervis in the
Saipan lagoon should be a major concern to fishermen and
fisheries managers. !
!!
fish in seagrass meadows investigated in my study were
seagrass species and habitat fragmentation. Due to the results
of my study I would recommend a re-seeding or transplant
program focused on increasing the area and filling in gaps of H.
uninervis meadows. !
For fishermen and other stakeholders?
!!
!!
!!
A Healthy seagrass ecosystem = Healthy reef = Happy people!
!References
Aponon, H., Bostrom, C. (2012). Responses of mobile epifauna to small-scale
seagrass patchiness. Hydrobiologia, 680, 1-10. !
CNMI Division of Fish and Wildlife 2010 Fishery Statistics Report, NOAA WpacFIN
program!
Houk, P., van Woesik, R. (2008). Dynamics of shallow-water assemblages in the
Saipan Lagoon. Mar Ecol Prog Ser, 356, 39-50.!
Unsworth, R.K.F., Bell, J.J., Smith, D.J. (2007). Tidal fish connectivity of reef and sea
grass habitats in the Indo-Pacific. J. Mar. Biol. Ass. U.K., 87, 1287-1296.!
Unsworth, R.K.F., De León, P.S., Garrard, S.L., Jompa, J., Smith, D.J., Bell, J.J.
(2008). High connectivity of Indo-Pacific seagrass fish assemblages with
mangrove and coral reef habitats. Mar Ecol Prog Ser, 353, 213-224. !
Vonk, J. A., Christianen, M. J. A., Stapel, J. (2008). Redefining the trophic importance
of seagrasses for fauna in the tropical Indo-Pacific meadows. Estuarine, Coastal,
and Shelf Science, 79, 653-660. !
!Acknowledgments
!
!
!
!
-  Juvenile reef fish richness!
-  All fish richness!
!
!
Research!
H2: Fragmentation affects…!
-  Juvenile reef fish abundance!
!
Enhalus acoroides!
consisting of both H. uninervis and E. acoroides has been done in
previous study (Vonk et al. 2008). However, the numbers for fish
density were not separated by seagrass species and therefore no
comparison between the fish populations in either seagrass
species was made. My study is the first to show a significant effect
of seagrass species on species richness and abundance of fish. !
! The factors affecting species richness and abundance of
H1: Seagrass species affects the species richness and
abundance of fish!
Halodule uninervis!
! Quantification of fish densities in a seagrass meadow
What does this mean for management?
!Conclusions
Barrier Reef!
Discussion
(N = 32; t = 5.59; P = 0.0001)
(N = 32; Welch F= 77.75; P = 0.0001)
Drs. Russell Benford, Nashelly Meneses and Steve Shuster; Monique Brown,
Karah Roof, Sarah Raber, Natalie Senini; FECB colleagues; Department of
Land and Natural Resources: Arnold Palacios; Division of Fish and Wildlife:
Manny Pangelinan, Todd Miller; Local Fishermen on Saipan; John Furey,
APASEEM, Northern Marianas College; Northern Arizona University; my family
and friends!