Seagrasses In World Heritage Site Have Not Recovered Years After Heat Wave

2017-04-10T12:08:39+00:00 April 10, 2017|
(Credit: NOAA)

(Click to enlarge) (Credit: NOAA)

Massive seagrass beds in Western Australia’s Shark Bay — a UNESCO World Heritage Site — haven’t recovered much from the devastating heat wave of 2011, according to a new study demonstrating how certain vital ecosystems may change drastically in a warming climate.

(From Science Daily) — The peer-reviewed study, published recently in Marine Ecology Progress Series, was led by Dr. Rob Nowicki, a Mote Marine Laboratory Postdoctoral Research Fellow who conducted the fieldwork while earning his doctorate from Florida International University (FIU). Dr. Michael Heithaus, Dean of FIU’s College of Arts & Sciences, and colleagues from multiple institutions have studied Shark Bay’s ecosystem for more than 20 years. The current study included partners from FIU, Deakin University in Australia and Nova Southeastern University in Fort Lauderdale, Florida.

Shark Bay earned its World Heritage status, in part, because of its 1,853 square miles (4,800 square kilometers) of seagrass beds, which UNESCO’s website calls the “richest in the world.” This vast, subtropical ecosystem hosts thousands of large sharks, other fish, sea turtles, bottlenose dolphins and a critical population of dugongs, plant-eating mammals related to manatees.

“We were studying a relatively pristine ecosystem, but in summer 2011 we had the hottest water temperatures on record at the time, and we saw 70-90 percent losses of seagrasses at our study sites; no one expected it to be that bad,” Nowicki said. “After our colleagues documented the losses, we wanted to know how much the ecosystem might recover over a few years. If you take a punch and get up quickly, you’re ready for the next punch. But our study has suggested this system took a punch, and in the short term, it has not gotten back up.”

The researchers surveyed 63 sites in Shark Bay four times between 2012 and 2014 to assess seagrass recovery and changes. Before the heat wave, many sites were dominated by the temperate seagrass known as “wireweed” (Amphibolis antarctica), whose dense and tall thickets provide ample food and shelter for numerous species. The heat wave drastically thinned many wireweed beds, and in many places their rhizomes (underground stems) blackened and died, leaving bare sand.

The new study showed that surviving A. antarctica beds appeared stable but didn’t reclaim much turf. Instead, the tropical seagrass Halodule uninervis, a close relative of the shoalgrass native to Florida, began filling the gaps. H. uninvervis was spotted at 2 percent of sites in 2012, but had expanded to almost 30 percent of them by 2014.

“The seagrass hit hard was the most common species — and was dense like a mini forest,” said Heithaus, doctoral advisor to Nowicki and co-author of the study. “Losing that cover is really huge; it’s like going from a bushland in Africa to a well-mowed lawn.

Read the full article here: https://www.sciencedaily.com/releases/2017/04/170405144222.htm