DOI: 10.1594/pangaea.876714
title: Seagrass meadows of Hervey Bay and the Great Sandy Strait, Queensland, derived from field surveys conducted 6-14 December, 1998

description: Approximately 2,362 ±289 km**2 of seagrass meadows were mapped in the waters of Hervey Bay and Great Sandy Strait between 6 and 14 December 1998. This was the first comprehensive survey of the Great Sandy region. The survey involved examination of 1,104 field validation points from Elliot Heads and Sandy Cape in the north to Tin Can Bay in the south, and identified 174 individual meadows. Seagrass extended from the intertidal and shallow subtidal waters to a depth of 32m. Seven species of seagrass were identified (Cymodocea serrulata, Halodule uninervis, Syringodium isoetifolium, Halophila decipiens, Halophila ovalis, Halophila spinulosa and Zostera muelleri) within 22 seagrass meadow/community types.Mapping survey methodologies followed standardised global seagrass research methods (McKenzie et al. 2001a, bit.ly/2t7U4M4) using both in situ and remote assessments. Within intertidal and shallow subtidal waters (2-10m depth), observers walked or free-dived to assess survey points. Seagrass habitat characteristics including visual estimates of above-ground percentage cover or biomass (3 replicates of a 50cm x 50cm quadrat) and species composition were recorded at each point according to standard methodologies (McKenzie et al. 2001b, bit.ly/2t5SWsK; McKenzie et al. 2014, bit.ly/2rN4EUN). Water depth and visual/tactile description of sediment were also recorded at each survey point. At each deep water point (&gt;10m) a real time video slaved to monitor on-board a vessel was used to record an image of bottom habitat for 4 to 6 minutes of time at drift speed (minimum 100m tow). Data on seagrass species presence and biomass, macro-algae, and sediment description was obtained from post processed video images as per Coles et al. (2009, bit.ly/2s28gXc). In conjunction with each camera tow a sled net and grab sample of the sediment were collected to confirm the taxonomy and sediment characterisation inferred from the video. A differential handheld global positioning system (GPS) was used to locate each survey point (accuracy ±5m). Seagrass meadow boundaries were determined based on the survey point positions and the presence of seagrass, coupled with depth contours and remote sensing (e.g., aerial photography) where available. The meadow boundary accuracy varied from 5m to 1,200m. The resulting polygon data of each seagrass meadow was saved as an ArcMap shapefile and projected to AGD94.Of the estimated 2,307 ±279 km**2 of seagrass in Hervey Bay, nearly half were large continuous deep-waters meadows of medium-high biomass Halophila spinulosa with Halophila ovalis/ Halophila decipiens in the southern section of the bay. The eastern section of the bay was generally barren substrate with isolated patches of H. spinulosa/ H. ovalis/ H. decipiens. The shallow subtidal banks were covered with low biomass H. spinulosa/ H. decipiens. On the intertidal sand banks, meadows were generally low biomass Zostera muelleri or Halodule uninervis, with H. ovalis. In the Great Sandy Strait, most of the 5,554 ±1,446 ha of seagrass were intertidal on large mud- and sand-banks, predominantly in the northern and central sections. Dense Z. muelleri with H. ovalis meadows dominated the intertidal banks, with the exception of Kauri Creek bank in the south, which was dominated by Cymodocea serrulata. Shallow subtidal meadows contributed only 5% to the total Great Sandy Strait seagrass. Subtidal meadows were dominated by Halophila species (H. spinulosa, H decipiens, H. ovalis) or Z. muelleri and occurred mostly in the northern and southern sections of the Strait in narrow bands along the edge of intertidal banks, or extending across the large subtidal banks. The meadows in Hervey Bay and the Great Sandy Strait are one of the largest single areas of seagrass resources on the eastern Australian seaboard. The meadows form part of significant internationally listed Great Sandy Strait Ramsar site and are within the Great Sandy Marine Park, providing critical habitat for dugong and turtle populations, shorebirds and productive fisheries.