Fears over coral health in latest Harbour report card
THE health of coral, seagrass, mangroves and mud crabs have given the Gladstone Healthy Harbour Partnership cause for concern in its 2018 Gladstone Harbour report card.
Graded on a scale from A to E, coral scored an E, seagrass a D, mangroves a C and mud crabs a D.
Mangroves were a new addition this year under the Habitat section after mud crabs were added in the 2017 report card.
Partnership chair of the Independent Science Panel and CQUniversity professor John Rolfe said coral health was concerning.
"The things that are disappointing for us are corals and that seems to be something that's not just a Gladstone thing - it's a Southern Great Barrier Reef thing and we're getting the same stories from the Keppels," Mr Rolfe said.
"We don't understand for sure why they're remaining so low but we think it's something to do with turbidity - not enough sunlight getting through the water at times - and we think it might have something to do with higher nutrient levels.
"Higher nutrient levels are increasing the amount of algae over the coral formations, which stops the coral from increasing further."
Mr Rolfe said mud crab health was assessed in three ways.
"First we asses the red spots - the visual disease, second we measure the abundance - we check how quickly we can catch mud crabs in a controlled environment and the third thing we look at is the ratio of males to females," he said.
"The good news is on the red spot side we've got a very good result with a very small proportion (affected), but on the abundance and female to male ratios we scored more poorly this year.
"That suggests the mud crab population might have diminished a little bit and the male/female ratio gives an indication of fishing pressure."
The addition of mangroves helped boost the overall environment score.
"Mangroves scored more healthy than coral and seagrass so it pushed up the environmental score a little bit (and) it pushed up the habitat score a little bit, but the overall grade for environment remained a a 'C' - a pass - it didn't make a huge difference because there's so many components to the environment score," Mr Rolfe said.
Habitats have been particularly slow in showing signs of recovery.
"What we're learning is it's very slow to get changes and improvements. What we do know is with the biodiversity things - fish and mud crabs - those things vary a lot from year to year," Mr Rolfe said.
"Now we are starting to get enough data together to be able to explain things."
Mr Rolfe said measuring seagrass health was more complicated to measure.
"It gets eaten by turtles and dugongs so just because we're getting poor biomass from seagrass doesn't mean it's not supporting lots of other biodiversity," he said.
"Over time we are starting to understand that a little bit better."
Overall, last year's results were similar to those reported in 2017. Environmental health overall received a C, social and economic health both received Bs and cultural health received a C.
"The Harbour is quite stable at the moment so we're not seeing a lot of change from year to year. That's to be expected because we haven't had huge weather events," Mr Rolfe said.
"Environment has been pretty stable, water quality and sediment quality remain really good and has been consistent for a few years.
"The habitats area, which is corals, seagrass and mangroves, they are still fairly poor particularly corals and seagrass so it's been a really slow recovery from the big floods in 2011 and 2013.
"Fish and mud crabs, fish is much the same, but mud crabs have stood back a little bit this year with slightly worse results and again that's just something to do with the local conditions."