Impact of mooring activities on carbon stocks in seagrass meadows

Abstract

Boating activities are one of the causes that threaten seagrass meadows and the ecosystem services they provide. Mechanical destruction of seagrass habitats may also trigger the erosion of sedimentary organic carbon (Corg) stocks, which may contribute to increasing atmospheric CO2. This study presents the first estimates of loss of Corg stocks in seagrass meadows due to mooring activities in Rottnest Island, Western Australia. Sediment cores were sampled from seagrass meadows and from bare but previously vegetated sediments underneath moorings. The Corg stores have been compromised by the mooring deployment from 1930s onwards, which involved both the erosion of existing sedimentary Corg stores and the lack of further accumulation of Corg. On average, undisturbed meadows had accumulated ~6.4 Kg Corg m−2 in the upper 50 cm-thick deposits at a rate of 34 g Corg m−2 yr−1. The comparison of Corg stores between meadows and mooring scars allows us to estimate a loss of 4.8 kg Corg m−2 in the 50 cm-thick deposits accumulated over ca. 200 yr as a result of mooring deployments. These results provide key data for the implementation of Corg storage credit offset policies to avoid the conversion of seagrass ecosystems and contribute to their preservation.

Rocking the Boat: Damage to Eelgrass by Swinging Boat Moorings

“…No change in density or canopy height after 10 m. Zostera marina Wales (United Kingdom)A comparison of the impact of “seagrass-friendly” boat mooring systems on Posidonia australis Demers et al, 2013Peer reviewedSwing moorings led to a 9 m radius bar patch in seagrass, screw moorings had little impact. Scar size was 254 m 2 . Posidonia australis Jervis Bay in New South WalesEstimating losses of Posidonia australis due to boat moorings in Lake Macquarie, Port Stephens and Wallis LakeGlasby and West, 2015GrayAmount of damage increases with depth and is typically greater in beds of P. australis than Z. capricorni Posidonia australis and Zostera capricorni Lake Macquarie, Port Stephens and Wallis LakeLosses and recovery of organic carbon from a seagrass ecosystem following disturbanceMacreadie et al, 2015Peer reviewedFifty years after disturbance from moorings limited recovery present Posidonia australis New South WalesImpact of mooring activities on carbon stocks in seagrass meadowsSerrano et al, 2016Peer reviewed1.3 and 0.9 ha of seagrass lost at two different sites due to moorings. Organic carbon stores have been compromised due to these moorings.…”

Reviews and syntheses: <sup>210</sup>Pb-derived sediment and carbon accumulation rates in vegetated coastal ecosystems: setting the record straight

“…The C org stocks over the last 100 yr were 20% and 5% lower in seagrass and in mangrove/tidal marsh sediments, respectively, compared to the corresponding 'ideal' profile under non-eroded conditions. Part of this is likely related to the fact that the concentration of C org is not changed, which in reality may actually change since fine sediments, where C org is more efficiently adsorbed, are more easily eroded and OM is remineralized when exposed to oxic conditions during 20 resuspension (Burdige, 2007;Lovelock et al, 2017a;Serrano et al, 2016a) (see simulations 3.2.4 and 3.2.5). Consequently, losses could be significantly larger, as shown in some papers (Macreadie et al, 2013(Macreadie et al, , 2015Marbà et al, 2015;Serrano et al, 2016a).…”

“…The continuous line in Type VII represents the excess 210 Pb concentration profile at a reference undisturbed site. Type II (Cearreta et al, 2002;Gardner et al, 1987;Haslett et al, 2003;Swales and Bentley, 2015;Mazarrasa et al, 2017);Type III (Church et al, 1981;Sanders et al, 5 2010aSanders et al, 5 , 2010bSerrano et al, 2016a;Sharma et al, 1987;Smoak and Patchineelam, 1999); Type IV (Chen and Twilley, 1999;Greiner et al, 2013;Mudd et al, 2009;Sanders et al, 2010b;Serrano et al, 2016c;Smoak et al, 2013;Yeager et al, 2012); Type V (Alongi et al, 2005;Chanton et al, 1983;Kirchner and Ehlers, 1998;Serrano et al, 2016c;Smoak and Patchineelam, 1999); Type VI (Greiner et al, 2013;Serrano et al, 2016c;2016d); Type VII Ravens et al, 2009 ; MAR = 0.3 g cm -2 yr -1 ; C org = 8%). Bar charts illustrate the deficits in excess 210 Pb inventories and C org stocks after erosion events.…”

“…Similarly to type III, these profile types can be caused by mixing processes in vegetated coastal ecosystems (Sanders et al, 2010a;Serrano et al, 2016a;Yeager et al, 2012). However, they could also be produced by an acceleration of the sedimentation rate, as interpreted by Greiner et al (2013), Smoak et al (2013) and Bellucci et al (2007) in seagrass, mangrove and tidal marsh, respectively, or by the decay of OM, as modeled by Chen and 15 Twilley (1999) and Mudd et al (2009), and observed by Church et al (1981) in tidal marsh sediments containing > 30% OM in top layers.…”

Impact of anthropogenically created canopy gaps on wave attenuation in a Posidonia oceanica seagrass meadow

“…Moorings using anchors (anchoring) and fixed weights moorings (mooring) are one of the main causes of anthropogenic disturbances within seagrass meadows (Walker et al 1989, Hastings et al 1995, Montefalcone et al 2008, Boudouresque et al 2012, Demers et al 2013, Giakoumi et al 2015. Gaps caused by trawling and the anchoring of large boats have been found along the Mediterranean coast (Francour et al 1999, Leriche et al 2006) and nearshore mooring scars can increase the loss of sedimentary organic carbon stores (Serrano et al 2016). The resulting habitat patchiness, where large stretches of habitat are removed or damaged, influences ecosystem integrity to the point that ecological function may be compromised (Larsen et al 2008).…”