patrickbdevaney/mia9 · Datasets at Hugging Face

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ADJ SC 0.95 N/A 1.03 1.01 0.98 0.96 0.96 0.95 0.97
DIS CK 1.03 1.03 0.93 0.95 1.03 1.00 0.96 0.93 0.98
DIS BL 1.02 1.00 0.91 1.02 0.92 1.16 0.98 1.15 1.02
ADJ BP 1.00 0.93 0.97 1.19 0.94 .96 1.14 0.97 1.01
ADJ CP 1.02 1.05 1.05 1.04 0.96 0.96 1.06 0.98 1.01
DIS TP 0.92 1.03 N/A 0.96 0.97 1.06 0.96 0.92 0.97
Average 0.99 1.00 0.98 1.03 0.97 1.02 1.01 0.97
Std. Dev. 0.044 0.047 0.061 0.086 0.04 0.077 0.076 0.092
ADJ: Adjacent to canals, DIS: Distant from canals.
https://doi.org/10.1371/journal.pone.0229147.t002
Resilience of seagrass communities exposed to pulsed freshwater discharges
PLOS ONE \| https://doi.org/10.1371/journal.pone.0229147 February 21, 2020 9 / 15
was 1.07 (SD± = 0.08), recorded during the 1985–1991 time step. The lowest λ recorded for
adjacent sites was 0.95, displayed in 2003–2009. The lowest λ for distant sites was 0.92 recorded
from 1950–1963. No significant differences in average λ were found between distant (mean λ
= 0.99 (±0.07)) and adjacent sites (mean λ = 1.0 (±0.07)) (t-test, p>0.05).
The stable population proportions determined by the eigenvectors showed that size-3
patches composed the highest, on average, proportion of the population at 0.38 when all sites
are combined (Table 3). Size 1 had the next highest proportion at 0.23, with size 2 composing
0.21 of the population. Sizes 4 and 5 had the lowest proportions with values of 0.12 and 0.05
respectively.
Population projections and fragmentation scenarios
All scenarios were run over 17, 5-year intervals. Low fragmentation and high fragmentation
scenarios used a fragmentation rate of 0.8 and 10.2 patches created per existing patch, respectively. Low recruitment scenarios used a recruitment rate of 0.007 patches created per existing
patch, average recruitment was 0.15 patches created per existing patch, and high recruitment
was 0.6 patches created per existing patch. The stable size distribution for the high fragmentation/low recruitment scenario was 0.39, 0.43, 0.11, 0.01, and 0.06 for the respective size classes.
The stable size distribution for the low fragmentation/low recruitment scenario was 0.06, 0.32,
0.41, 0.11, and 0.10 for the respective size classes. The stable size distribution for the high fragmentation/average recruitment scenario was 0.55, 0.37, 0.01, 0.02, and 0.05 for the respective
size classes. The stable size distribution for the low fragmentation/average recruitment site was
0.21, 0.08, 0.33, 0.20, and 0.17 for the respective size classes. The stable size distribution for the
high fragmentation/high recruitment scenario was 0.66, 0.29, 0.01, 0.01, and 0.03 for the
respective size classes. The stable size distribution for the low fragmentation/high recruitment
scenario was 0.27, 0.04, 0.32, 0.18, and 0.19 for the respective size classes.
Scenarios were run with an initial population vector composed of 200 patches divided into
48 (size 1), 56 (size 2), 72 (size 3), 17 (size 4), and 7 (size 5) patches based on the average conditions recorded in this study. SAV population abundance declined to near zero in the high fragmentation scenarios regardless of recruitment rates (Fig 4). In contrast, seagrass populations
persisted under low fragmentation scenarios and abundances for the larger size classes (4 and
5) increased as recruitment increases (Fig 4).
Discussion
Seagrasses around the world have experienced multiple disturbances that have resulted in
accelerating rates of loss of these important coastal ecosystems [10, 34]. Within this worldwide
Table 3. Proportion of the population (i.e., eigenvectors) composed by each seagrass patch size class over time averaged across the six sites.
Time Step Size 1 Size 2 Size 3 Size 4 Size 5
1938–1944 0.11 0.20 0.45 0.17 0.06
1944–1953 0.27 0.20 0.37 0.12 0.05
1953–1963 0.23 0.20 0.42 0.10 0.07
1963–1973 0.22 0.19 0.42 0.10 0.07
1973–1985 0.16 0.24 0.36 0.17 0.07
1985–1991 0.31 0.23 0.33 0.09 0.04
1991–2003 0.31 0.21 0.38 0.07 0.03
2003–2008 0.25 0.23 0.32 0.17 0.04
Average (±STD) 0.23 (0.07) 0.21 (0.02) 0.38 (0.05) 0.12 (0.04) 0.05 (0.02)
https://doi.org/10.1371/journal.pone.0229147.t003
Resilience of seagrass communities exposed to pulsed freshwater discharges
PLOS ONE \| https://doi.org/10.1371/journal.pone.0229147 February 21, 2020 10 / 15
context of degradation, nearshore habitats of Biscayne Bay have shown remarkable resilience,
having experienced, on average, only < 4% declines in SAV cover over 70 years [23]. This limited decline is also noteworthy considering that the nearshore habitats of Biscayne Bay have
been significantly modified over the past 5–6 decades by the construction of a canal system
Fig 4. SAV patch abundance patterns over time simulated under high fragmentation (left panels) and low fragmentation (right panels) for (A, D)
low recruitment, (B, E) average recruitment, and (C, F) high recruitment scenarios.
https://doi.org/10.1371/journal.pone.0229147.g004
Resilience of seagrass communities exposed to pulsed freshwater discharges
PLOS ONE \| https://doi.org/10.1371/journal.pone.0229147 February 21, 2020 11 / 15
that has not only reduced the overall amount of fresh water reaching Biscayne Bay but also created large gradients in salinity [16, 35]. Our historical seascape and patch dynamic analyses
shows that seagrass stability has not been greatly affected by these changes and that seagrass
meadows appear to be both resistant and resilient to the modified salinity patterns. The fluctuation in lambda values documented, showing alternating periods of population decline with
periods of population growth due to variable disturbance regimes, are further evidence of SAV
resilience patterns in Biscayne Bay.
While the limited historical loss of seagrasses cover documented here and previously by
Santos et al. [23] is a positive result compared to the multiple reports of declines elsewhere, our
patch-based seagrass population model developed based on the historical imagery showed that
fluctuating salinity found near canals does have a negative impact through the fragmentation
of seagrass meadows. Thus, even if seagrass habitats in Biscayne Bay have retained areal coverage, they are showing signs of salinity-driven fragmentation. Reports from other systems have
shown that fragmented habitats are more susceptible to further disturbance and that they can
decline rapidly [36–38]. Our simulation scenarios suggest that, under persistent high rates of
fragmentation, seagrass populations may fall below a resistance threshold and decline rapidly
thereafter. While recruitment of new seagrass patches through sexual or asexual reproduction
may, to some extent, mitigate the impacts of high fragmentation, here we found that populations under simulated continuous high fragmentation scenarios can disappear within 50 years.
This study is the first to quantify the patch dynamics of seagrass communities in South Florida and our seascape approach has revealed key aspects of how seagrass populations respond
to differing environmental conditions. The mortality rate of seagrass patches was significantly
affected by patch size, with the mortality rate of the smallest patches (57%) being an order of
magnitude higher than that of the largest patches (< 5%). Similar size-based patterns of mortality were documented for corals and sponges, clonal/colonial taxa that also showed higher
mortality of the smaller size classes [28, 39]. Smaller seagrass patches have been shown in other
studies to have higher susceptibility to physical disturbances [25, 38]. The high mortality rate
of smaller patches could be due to their lower biomass-to-perimeter ratio that may limit their
anchoring capabilities as well as expose them to higher erosion rates along the patch perimeter
[23]. Larger patches may have a more extensive root system with higher storage of belowground biomass that can help increase their resilience and lead to lower mortality rates.
Considering the large difference in mortality rates among patch sizes, any shift in population structure that reduces mean patch size (e.g., fragmentation) would reduce the resilience of
seagrass populations. This pattern was captured as output of our simulated scenarios that
showed rapid population declines under high fragmentation scenarios. In Biscayne Bay, 94%
of the seagrass patches created by fragmentation were produced by the two largest size classes.
The stability in the cover of the seagrass meadows recorded over the 70-year period of record
by Santos et al. [23], even when fragmentation rates were high in some time periods, is likely
due to the fact that the larger patches were able to fragment and still remain within the large
size classes that provide a size refuge against mortality. Continued fragmentation would, eventually, lead to a reduction in the abundance of these large and stable patch sizes, resulting in
the population declines observed in our simulations. The persistence of the simulated seagrass
populations was directly related to the fragmentation rates that affected the proportion and
size distribution of patches. Under high fragmentation scenarios, the abundance of larger
patches declined quickly. Without the source of new small patches through fragmentation as
these larger patches decline, the populations disappeared within 50 years, regardless of recruitment rates. In contrast, under low fragmentation scenarios, the abundance of larger patches
remains stable or even increases over time, leading to the persistence of the population. Thus,

ADJ SC 0.95 N/A 1.03 1.01 0.98 0.96 0.96 0.95 0.97

DIS CK 1.03 1.03 0.93 0.95 1.03 1.00 0.96 0.93 0.98

DIS BL 1.02 1.00 0.91 1.02 0.92 1.16 0.98 1.15 1.02

ADJ BP 1.00 0.93 0.97 1.19 0.94 .96 1.14 0.97 1.01

ADJ CP 1.02 1.05 1.05 1.04 0.96 0.96 1.06 0.98 1.01

DIS TP 0.92 1.03 N/A 0.96 0.97 1.06 0.96 0.92 0.97

Average 0.99 1.00 0.98 1.03 0.97 1.02 1.01 0.97

Std. Dev. 0.044 0.047 0.061 0.086 0.04 0.077 0.076 0.092

ADJ: Adjacent to canals, DIS: Distant from canals.

https://doi.org/10.1371/journal.pone.0229147.t002

Resilience of seagrass communities exposed to pulsed freshwater discharges

PLOS ONE | https://doi.org/10.1371/journal.pone.0229147 February 21, 2020 9 / 15

was 1.07 (SD± = 0.08), recorded during the 1985–1991 time step. The lowest λ recorded for

adjacent sites was 0.95, displayed in 2003–2009. The lowest λ for distant sites was 0.92 recorded

from 1950–1963. No significant differences in average λ were found between distant (mean λ

= 0.99 (±0.07)) and adjacent sites (mean λ = 1.0 (±0.07)) (t-test, p>0.05).

The stable population proportions determined by the eigenvectors showed that size-3

patches composed the highest, on average, proportion of the population at 0.38 when all sites

are combined (Table 3). Size 1 had the next highest proportion at 0.23, with size 2 composing

0.21 of the population. Sizes 4 and 5 had the lowest proportions with values of 0.12 and 0.05

respectively.

Population projections and fragmentation scenarios

All scenarios were run over 17, 5-year intervals. Low fragmentation and high fragmentation

scenarios used a fragmentation rate of 0.8 and 10.2 patches created per existing patch, respectively. Low recruitment scenarios used a recruitment rate of 0.007 patches created per existing

patch, average recruitment was 0.15 patches created per existing patch, and high recruitment

was 0.6 patches created per existing patch. The stable size distribution for the high fragmentation/low recruitment scenario was 0.39, 0.43, 0.11, 0.01, and 0.06 for the respective size classes.

The stable size distribution for the low fragmentation/low recruitment scenario was 0.06, 0.32,

0.41, 0.11, and 0.10 for the respective size classes. The stable size distribution for the high fragmentation/average recruitment scenario was 0.55, 0.37, 0.01, 0.02, and 0.05 for the respective

size classes. The stable size distribution for the low fragmentation/average recruitment site was

0.21, 0.08, 0.33, 0.20, and 0.17 for the respective size classes. The stable size distribution for the

high fragmentation/high recruitment scenario was 0.66, 0.29, 0.01, 0.01, and 0.03 for the

respective size classes. The stable size distribution for the low fragmentation/high recruitment

scenario was 0.27, 0.04, 0.32, 0.18, and 0.19 for the respective size classes.

Scenarios were run with an initial population vector composed of 200 patches divided into

48 (size 1), 56 (size 2), 72 (size 3), 17 (size 4), and 7 (size 5) patches based on the average conditions recorded in this study. SAV population abundance declined to near zero in the high fragmentation scenarios regardless of recruitment rates (Fig 4). In contrast, seagrass populations

persisted under low fragmentation scenarios and abundances for the larger size classes (4 and

5) increased as recruitment increases (Fig 4).

Discussion

Seagrasses around the world have experienced multiple disturbances that have resulted in

accelerating rates of loss of these important coastal ecosystems [10, 34]. Within this worldwide

Table 3. Proportion of the population (i.e., eigenvectors) composed by each seagrass patch size class over time averaged across the six sites.

Time Step Size 1 Size 2 Size 3 Size 4 Size 5

1938–1944 0.11 0.20 0.45 0.17 0.06

1944–1953 0.27 0.20 0.37 0.12 0.05

1953–1963 0.23 0.20 0.42 0.10 0.07

1963–1973 0.22 0.19 0.42 0.10 0.07

1973–1985 0.16 0.24 0.36 0.17 0.07

1985–1991 0.31 0.23 0.33 0.09 0.04

1991–2003 0.31 0.21 0.38 0.07 0.03

2003–2008 0.25 0.23 0.32 0.17 0.04

Average (±STD) 0.23 (0.07) 0.21 (0.02) 0.38 (0.05) 0.12 (0.04) 0.05 (0.02)

https://doi.org/10.1371/journal.pone.0229147.t003

Resilience of seagrass communities exposed to pulsed freshwater discharges

PLOS ONE | https://doi.org/10.1371/journal.pone.0229147 February 21, 2020 10 / 15

context of degradation, nearshore habitats of Biscayne Bay have shown remarkable resilience,

having experienced, on average, only < 4% declines in SAV cover over 70 years [23]. This limited decline is also noteworthy considering that the nearshore habitats of Biscayne Bay have

been significantly modified over the past 5–6 decades by the construction of a canal system

Fig 4. SAV patch abundance patterns over time simulated under high fragmentation (left panels) and low fragmentation (right panels) for (A, D)

low recruitment, (B, E) average recruitment, and (C, F) high recruitment scenarios.

https://doi.org/10.1371/journal.pone.0229147.g004

Resilience of seagrass communities exposed to pulsed freshwater discharges

PLOS ONE | https://doi.org/10.1371/journal.pone.0229147 February 21, 2020 11 / 15

that has not only reduced the overall amount of fresh water reaching Biscayne Bay but also created large gradients in salinity [16, 35]. Our historical seascape and patch dynamic analyses

shows that seagrass stability has not been greatly affected by these changes and that seagrass

meadows appear to be both resistant and resilient to the modified salinity patterns. The fluctuation in lambda values documented, showing alternating periods of population decline with

periods of population growth due to variable disturbance regimes, are further evidence of SAV

resilience patterns in Biscayne Bay.

While the limited historical loss of seagrasses cover documented here and previously by

Santos et al. [23] is a positive result compared to the multiple reports of declines elsewhere, our

patch-based seagrass population model developed based on the historical imagery showed that

fluctuating salinity found near canals does have a negative impact through the fragmentation

of seagrass meadows. Thus, even if seagrass habitats in Biscayne Bay have retained areal coverage, they are showing signs of salinity-driven fragmentation. Reports from other systems have

shown that fragmented habitats are more susceptible to further disturbance and that they can

decline rapidly [36–38]. Our simulation scenarios suggest that, under persistent high rates of

fragmentation, seagrass populations may fall below a resistance threshold and decline rapidly

thereafter. While recruitment of new seagrass patches through sexual or asexual reproduction

may, to some extent, mitigate the impacts of high fragmentation, here we found that populations under simulated continuous high fragmentation scenarios can disappear within 50 years.

This study is the first to quantify the patch dynamics of seagrass communities in South Florida and our seascape approach has revealed key aspects of how seagrass populations respond

to differing environmental conditions. The mortality rate of seagrass patches was significantly

affected by patch size, with the mortality rate of the smallest patches (57%) being an order of

magnitude higher than that of the largest patches (< 5%). Similar size-based patterns of mortality were documented for corals and sponges, clonal/colonial taxa that also showed higher

mortality of the smaller size classes [28, 39]. Smaller seagrass patches have been shown in other

studies to have higher susceptibility to physical disturbances [25, 38]. The high mortality rate

of smaller patches could be due to their lower biomass-to-perimeter ratio that may limit their

anchoring capabilities as well as expose them to higher erosion rates along the patch perimeter

[23]. Larger patches may have a more extensive root system with higher storage of belowground biomass that can help increase their resilience and lead to lower mortality rates.

Considering the large difference in mortality rates among patch sizes, any shift in population structure that reduces mean patch size (e.g., fragmentation) would reduce the resilience of

seagrass populations. This pattern was captured as output of our simulated scenarios that

showed rapid population declines under high fragmentation scenarios. In Biscayne Bay, 94%

of the seagrass patches created by fragmentation were produced by the two largest size classes.

The stability in the cover of the seagrass meadows recorded over the 70-year period of record

by Santos et al. [23], even when fragmentation rates were high in some time periods, is likely

due to the fact that the larger patches were able to fragment and still remain within the large

size classes that provide a size refuge against mortality. Continued fragmentation would, eventually, lead to a reduction in the abundance of these large and stable patch sizes, resulting in

the population declines observed in our simulations. The persistence of the simulated seagrass

populations was directly related to the fragmentation rates that affected the proportion and

size distribution of patches. Under high fragmentation scenarios, the abundance of larger

patches declined quickly. Without the source of new small patches through fragmentation as

these larger patches decline, the populations disappeared within 50 years, regardless of recruitment rates. In contrast, under low fragmentation scenarios, the abundance of larger patches

remains stable or even increases over time, leading to the persistence of the population. Thus,