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RESEARCH ARTICLE |
Modelling the resilience of seagrass |
communities exposed to pulsed freshwater |
discharges: A seascape approach |
Clinton StipekID1 |
*, Rolando Santos2 |
, Elizabeth Babcock1 |
, Diego Lirman1 |
1 Marine Biology and Ecology Department, Rosenstiel School of Marine and Atmospheric Science, University |
of Miami, Miami, Florida, United States of America, 2 College of Arts, Sciences and Education, Florida |
International University, Miami, Florida, United States of America |
* Clinton.stipek@rsmas.miami.edu |
Abstract |
Submerged aquatic vegetation (SAV) communities display complex patch dynamics at seascape scales that are presently poorly understood as most studies of disturbance on SAV |
habitats have focused on changes in biomass at small, quadrat-level scales. In this study, |
analyses of remote sensing imagery and population modelling were applied to understand |
SAV patch dynamics and forecast the fate of these important communities in Biscayne Bay, |
Miami, Florida, US. We evaluated how the proximity of freshwater canals influences seagrass-dominated SAV patch dynamics and, in turn, how patch-size structure influences the |
stability of seagrass seascapes under different salinity scenarios. Seagrass fragmentation |
rates were higher in sites adjacent to freshwater canals compared to sites distant from the |
influences of freshwater deliveries. Furthermore, we documented a clear trend in patch mortality rates with respect to patch size, with the smallest patches (50 m2 |
) undergoing 57% |
annual mortality on average. The combination of higher fragmentation rates and the higher |
mortality of smaller seagrass patches in habitats exposed to pulses of low salinity raises |
concern for the long-term persistence of seagrass meadows in nearshore urban habitats of |
Biscayne Bay that are presently targets of Everglades restoration. Our model scenarios that |
simulated high fragmentation rates resulted in SAV population collapses, regardless of SAV |
recruitment rates. The combined remote sensing and population modelling approach used |
here provides evaluation and predictive tools that can be used by managers to track seagrass status and stress-response at seascape levels not available previously for the seagrasses of South Florida. |
Introduction |
Submerged aquatic vegetation (SAV) assemblages composed of seagrasses and macroalgae create productive ecosystems in shallow coastal environments around the world [1, 2]. These ecosystems provide a wide range of essential ecological and economic services valued at US $3.8 |
trillion per year [3, 4]. While serving as habitat to species such as green sea turtles and |
PLOS ONE | https://doi.org/10.1371/journal.pone.0229147 February 21, 2020 1 / 15 |
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OPEN ACCESS |
Citation: Stipek C, Santos R, Babcock E, Lirman D |
(2020) Modelling the resilience of seagrass |
communities exposed to pulsed freshwater |
discharges: A seascape approach. PLoS ONE 15 |
(2): e0229147. https://doi.org/10.1371/journal. |
pone.0229147 |
Editor: Silvia Mazzuca, Università della Calabria, |
ITALY |
Received: September 12, 2019 |
Accepted: January 30, 2020 |
Published: February 21, 2020 |
Copyright: © 2020 Stipek et al. This is an open |
access article distributed under the terms of the |
Creative Commons Attribution License, which |
permits unrestricted use, distribution, and |
reproduction in any medium, provided the original |
author and source are credited. |
Data Availability Statement: All relevant data are |
within the manuscript and its Supporting |
Information files. The data used to create data Figs |
3 and 4 are included as supplemental files (S1 and |
S2 Files) in excel format. |
Funding: This work received support from the US |
Army Corps of Engineers and the National Park |
Service through the Integrated Biscayne Bay |
Ecological Assessment and Monitoring (IBBEAM). |
Competing interests: The authors have declared |
that no competing interests exist. |
manatees, seagrass meadows also provide increasingly valuable ecosystem services such as carbon sequestration, coastal sedimentation stabilization, and improvement of water clarity [5, 6]. |
Furthermore, SAV facilitate trophic transfers to nearby habitats, such as marshes, mangroves, |
and coral reefs [7]. Seagrasses also provide the essential nursery habitat for fisheries species |
such as snappers, groupers, shrimp, and queen conch [8, 9]. |
Between 1980 and 2006, seagrasses have been disappearing at a rate of 110 km2 per year |
globally [10]. Seagrass declines have been magnified near populated coastlines due to coastal |
development [11, 12]. One example of coastal and watershed modifications impacting seagrass |
communities can be found in Florida Bay, Florida, US, from 1987–1990 and again in 2015, |
where mass mortality of the seagrass Thalassia testudinum resultedin the loss of > 4000 hectares of dense seagrass beds [13, 14]. Florida Bay is a shallow lagoon located downstream of the |
Florida Everglades, a watershed that has been drastically modified due to the installation of a |
water management canal system that has caused a reduction in the amount of freshwater |
reaching the bay [13]. In Florida Bay, seasonal periods of hypersalinity have been linked |
directly to the mass mortality of seagrasses [14]. |
Freshwater inputs and salinity patterns are also key drivers of seagrass abundance and distribution in Biscayne Bay, Florida. Biscayne Bay is a shallow coastal lagoon highly influenced |
by the quantity and timing of freshwater deliveries [15, 16]. From the early 1900s-1960s, canals |
were built for the drainage of agricultural and urban lands and flood prevention. While the historic salinity patterns were dominated by the slow discharge of fresh water through overland |
flows and groundwater, fresh water is presently primarily discharged into littoral habitats |
through pulsed releases from canals. This creates environments near canals that experience |
drastic drops in salinity (reaching 0 in some instances) over a matter of hours. These changes |
in the salinity regime have been linked to changes in the abundance and distribution of seagrasses and associated fauna [16–18]. In response to these significant impacts and the changes |
to the regional hydrology, the Comprehensive Everglades Restoration Plan (CERP) is presently |
being implemented to improve the quality and quantity of fresh water delivered into the |
coastal bays of South Florida. To document and predict the impacts of CERP, there is a pressing need to develop models and indicators that evaluate status and trends of key ecosystem |
indicators like seagrasses at multiple spatial and temporal scales. |
Historically, the impacts of human and natural disturbances on seagrass meadows have |
been commonly characterized at small, quadrat-level scales, with limited attention paid to the |
influence of the disturbance on seagrass seascape dynamics [19, 20]. With the documentation |
of widespread declines and reports of localized mass seagrass mortality, there is an increasing |
need to evaluate response patterns at scales beyond the quadrat level [21]. Seagrass patches |
vary widely in size from < 1 m2 to hectares of continuous seagrass cover. Because of their clear |
boundaries (seagrass patches are commonly surrounded by sediments or rubble), seagrass |
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