Geomorphic Gradients in Shallow Seagrass Carbon Stocks

Seagrass meadows are important sinks of organic carbon (Corg), in particular the near-surface Corg pool (≤ 15 cm) compared to deeper sediments. Near-surface carbon is highly susceptible to disturbance and loss to the atmosphere, however, inadequate accounting for variability in this pool of carbon limits their uptake into carbon accounting frameworks. We therefore investigated the spatial variability in seagrass near-surface Corg and biomass Corg across different geomorphic (estuary, lagoonal and reef-associated) and community typologies (pioneer and persistent). Near-surface Corg stock in vegetated areas (25.78 Mg Corg ha−1 ± 26.64) was twice that from unvegetated areas (14.27 Mg Corg ha−1 ± 15.86), reinforcing the paradigm that the presence of seagrass enhances carbon stocks. Lagoonal and reef-associated meadows showed similar Corg stocks (p \u3e 0.05), which were substantially higher (p \u3c 0.05) than estuary meadows. Likewise, persistent seagrass communities (Cymodocea dominance) stored higher (p \u3c 0.05) stocks of Corg than pioneer communities (Halophila and Halodule dominance). Linear regression models showed significant but weak relationships between seagrass cover, shoot density and standing biomass with near-surface Corg stocks, whereas significant and strong relationships were observed for organic matter, dry bulk density and median grain size. The results highlight the need for higher resolution carbon assessments to better understand local and regional variability, in order to better inform carbon accounting and conservation policy

Mass coral bleaching in 2010 in the southern Caribbean.

Ocean temperatures are increasing globally and the Caribbean is no exception. An extreme ocean warming event in 2010 placed Tobago's coral reefs under severe stress resulting in widespread coral bleaching and threatening the livelihoods that rely on them. The bleaching response of four reef building taxa was monitored over a six month period across three major reefs systems in Tobago. By identifying taxa resilient to bleaching we propose to assist local coral reef managers in the decision making process to cope with mass bleaching events. The bleaching signal (length of exposure to high ocean temperatures) varied widely between the Atlantic and Caribbean reefs, but regardless of this variation most taxa bleached. Colpophyllia natans, Montastraea faveolata and Siderastrea siderea were considered the most bleaching vulnerable taxa. Interestingly, reefs with the highest coral cover showed the greatest decline reef building taxa, and conversely, reefs with the lowest coral cover showed the most bleaching but lowest change in coral cover with little algal overgrowth post-bleaching

Percent change in hard coral and macroalgal cover at Buccoo, Culloden and Speyside one year and two years post 2010 mass bleaching.

<p>The same superscript indicate significant pairwise comparisons (p<0.05) for reef taxa (bold print).</p

Averaged monthly sea surface temperatures (SST) for Tobago derived from the 50 km night time NOAA Coral Reef Watch Product.

<p>Averaged monthly sea surface temperatures (SST) for Tobago derived from the 50 km night time NOAA Coral Reef Watch Product.</p

Average daily <i>in situ</i> (10 m) temperatures at Buccoo, Culloden and Speyside reefs during the 2010 mass bleaching event (September 2010 to March 2011).

<p>Average daily <i>in situ</i> (10 m) temperatures at Buccoo, Culloden and Speyside reefs during the 2010 mass bleaching event (September 2010 to March 2011).</p

Percent bleaching mortality of four framework building taxa at Buccoo, Culloden and Speyside following the onset of the bleaching event (October 2010).

<p>Bars represent standard error.</p

Mass Coral Bleaching in 2010 in the Southern Caribbean

<div><p>Ocean temperatures are increasing globally and the Caribbean is no exception. An extreme ocean warming event in 2010 placed Tobago's coral reefs under severe stress resulting in widespread coral bleaching and threatening the livelihoods that rely on them. The bleaching response of four reef building taxa was monitored over a six month period across three major reefs systems in Tobago. By identifying taxa resilient to bleaching we propose to assist local coral reef managers in the decision making process to cope with mass bleaching events. The bleaching signal (length of exposure to high ocean temperatures) varied widely between the Atlantic and Caribbean reefs, but regardless of this variation most taxa bleached. <i>Colpophyllia natans</i>, <i>Montastraea faveolata</i> and <i>Siderastrea siderea</i> were considered the most bleaching vulnerable taxa. Interestingly, reefs with the highest coral cover showed the greatest decline reef building taxa, and conversely, reefs with the lowest coral cover showed the most bleaching but lowest change in coral cover with little algal overgrowth post-bleaching.</p></div

Map of Tobago showing the locations of sampling sites (black stars) with inset of Trinidad and Tobago.

<p>Map of Tobago showing the locations of sampling sites (black stars) with inset of Trinidad and Tobago.</p

Mean percent coral bleaching and new mortality per month at Buccoo, Culloden and Speyside during the 2010 mass bleaching event (October 2010 to March 2011).

<p>Bars represent standard error. O = October 2010, N = November 2010, D = December 2010, J = January 2011, F = February 2011 and M = March 2011.</p