Search for: All records

Abstract Multiple-use conflicts of the marine benthos (“bottom-use conflicts”) are increasing as humans expand use of the coastal zone. These conflicts necessitate balanced policies that consider the economic and ecological benefits of different bottom uses. In the Virginia coastal lagoons on the US east coast, there is a potential bottom-use conflict between hard clam (Mercenaria mercenaria) aquaculture and seagrass (Zostera marina) meadows. We leveraged two decades (2001–2021) of aerial imagery and environmental data to quantify historic trends in bottom use, assess the realized niche of seagrass and clam aquaculture across depth, sand fraction, root mean square (RMS) velocity, fetch, and sea surface temperature (SST) anomaly, and used random forest models to predict the potential extent of seagrass, clam aquaculture, and bottom-use conflict. We found growth in the coverage of both seagrass (+ 3373%) and clam aquaculture (+ 140%) over the past 20 years with a corresponding increase in bottom-use conflict (+ 2579%), though conflict area remained relatively minor. Seagrass occurred in deeper areas with higher fetch, a higher frequency of SST anomalies, lower sand fraction, and similar RMS velocities to areas containing clam aquaculture. Our random forest models predicted potential for the expansion of seagrass (+ 62%) and clam aquaculture (+ 263.9%) with a relatively small area of predicted spatial overlap (12.3%) under current conditions. These results illustrate how species distribution models can help us understand the spatial impacts of aquaculture on natural ecosystems and inform managers and policy makers to create objective policies that balance socioeconomic and ecologic needs. 

Coastal marine heatwaves have destructive and lasting impacts on foundational species 13 and are increasing in frequency, duration, and magnitude. High atmospheric temperatures are 14 often associated with marine heatwaves (MHW) which are defined as 5-days of water 15 temperatures above a seasonally varying 90th percentile threshold. In this study we consider the 16 prevalence of MHW propagation into surficial sediments to cause sediment heatwaves (SHW). 17 Within a shallow, subtidal seagrass meadow in Virginia, USA, sediment temperature was 18 measured at hourly intervals at a depth of 5 cm between June 2020-October 2022 at the meadow 19 edge and central meadow interior. The observed sediment temperature, along with a 29-year 20 record of water temperature and water level was used to develop a sediment temperature model 21 for each location. Modeled sediment temperatures were used to identify sediment heatwaves that 22 may thermally stress belowground seagrass. At both meadow locations, sediment heatwave 23 frequency increased at a rate twice that of MHWs in the average global open ocean, coinciding 24 with a 172% increase in the annual number of SHW days, from 11 to 30 days year-1 between 25 1994-2022. Sediment heatwaves at both meadow locations co-occurred with a MHW 79-81% of 26 the time, with nearly all SHWs having a zero day lag. The top 10% most extreme MHWs and 27 SHWs occurred between November and April when thermal stress to seagrass was unlikely. In 28 June 2015 a SHW co-occurred with an anomalously long duration MHW that was associated 29 with a 90% decline in seagrass from this system, suggesting that SHWs may have contributed to 30 the observed seagrass loss. These results document heatwave propagation across the pelagic-31 sediment interface which likely occur broadly in shallow systems with impacts to critical coastal 32 ecosystem processes and species dynamics. 

Coastal landscapes are naturally shifting mosaics of distinct ecosystems that are rapidly migratingwith sealevel rise. Previous work illustrates that transitions among individual ecosystems have disproportionate impacts on the global carbon cycle, but this cannot address nonlinear interactions between multiple ecosystems that potentially cascade across the coastal landscape. Here, we synthesize carbon stocks, accumulation rates, and regional land cover data over 36 years (1984 and 2020) for a variety of ecosystems across a large portion of the rapidly transgressing mid-Atlantic coast. The coastal landscape of the Virginia Eastern Shore consists of temperate forest, salt marsh, seagrass beds, barrier islands, and coastal lagoons. We found that rapid losses and gains within individual ecosystems largely offset each other, which resulted in relatively stable areas for the different ecosystems, and a 4% (196.9 Gg C) reduction in regional carbon storage. However, new metrics of carbon replacement times indicated that it would take only 7 years of carbon accumulation in surviving ecosystems to compensate this loss. Our findings reveal unique compensatory mechanisms at the scale of entire landscapes that quickly absorb losses and facilitate increased regional carbon storage in the face of historical and contemporary sea-level rise. However, the strength of these compensatory mechanisms may diminish as climate change exacerbates the magnitude of carbon losses.