Who is Sleeping in a Bed of Seagrass?
  • Last updated:
  • 16 Aug 2018

Article by Michele Jackson, Senior Project Officer, Sunshine Coast Council 

Seagrass is naturally constructed from rhizome, root, sheath and leaf. It’s foundation is made from a sandy mattress, intertidal substrate and surrounded by shallow saline water. Resistant to the elements, its robust leaf blades and veins, cushion wave and current energy, usefully trap sediment too. Seagrass reproduce either asexually through rhizome growth, or sexually via seeds from flowers fertilised by water-borne pollen. These primary producers of our beautiful Pumicestone Passage exploit the sun rays and grow into a community of meadows which enable better water quality and prevent algal growth.

Seagrasses, such as those found in the Pumicestone Passage, are important breeding and feeding grounds for large numbers of fish and invertebrate species. It provides a critical food source for threatened species such as dugongs (Nature Conservation Act: Vulnerable) and green turtles Chelonia mydas (QLD: Vulnerable), black swans that frequent our Pumicestone Passage, as well as habitat for numerous fish species of commercial significance.

The Passage is recognised as having national significance and as such council was requested by the state and federal government to map seagrass communities since 2011. Over 23 hectares of mapped seagrass distribution dominates the Pumicestone Passage to date.

Seagrass leaves support an array of tiny filter-feeding animals, such as the pictured Eurypegasus draconis, commonly referred to as little dragon fish or sea moth. It was caught and released unharmed in the Pumicestone Passage, sheltering in the seagrass beds. It is hard to imagine a fish that measures less than 3mm in length. It’s food includes isopods, copepods, goby eggs, nematodes, shrimps and molluscs (Herold and Clark 1993). Our tiny, benthic sea moth loves to be tucked in and sleeping within his bed of seagrass.

Halophila ovalis in our mixed meadows of the Pumicestone Passage

Last year I wrote about Zostera muelleri, which is the most dense, dominant in intertidal and shallow subtidal areas, while Halophila ovalis (see image below) was only seen in our annual surveys in subtidal areas.

H. ovalis, commonly referred to as paddle weed or dugong grass, tends to occur in mixed meadows with Z. muelleri, in the shallow subtidal and was seen in monospecific stands in deeper waters. H. ovalis is widespread and is impacted by anthropogenic threats locally, but recovers quickly if the threats are removed. Population trends are stable or increasing in many parts of its range, including our Pumicestone Passage.

H. ovalis is listed as Least Concern of the Threatened Species IUCN Red List 2018, however currently under further investigation.
                
Another seagrass survey will be completed in 2018 and I look forward to sharing a video with you next time.