Seagrass distribution throughout the region is most likely influenced by shelter, sediment characteristics, water turbidity and tidal exposure. The most extensive seagrass meadows in the SEQ region occur in the intertidal zone. Large seagrass meadows occur in areas of wide intertidal flats while small but dense seagrass meadows are found in association with narrow or confined channels. Seagrass do not occur on exposed oceanic shores in the Gold Coast region, but do occur in small intertidal areas within some rivers and creeks flowing directly into the ocean.

Between August 1987 and December 1987 a detailed survey documented the broad extent of seagrass distribution in SEQ¹². Hyland et al¹² identified seven species of seagrass, and estimated approximately 14,170 ha of seagrass meadows (light to dense) and 12,500 ha of sparse or patchy seagrass areas between Coolangatta and Noosa.

In January 1997, McLennan and Sumpton¹⁴ mapped the species composition and distribution of seagrass in The Broadwater and compared their findings with historical records. They identified three species of seagrass (Z. capricorni, H. ovalis and H. spinulosa) and reported the meadows were more widely distributed than in a previous studies. The total area of seagrass in the study area was approximately 304 ha, with 110 ha being classified as dense (> 50% cover), 137 ha as light (10 to 50% cover), 52 ha as sparse (< 10% cover) and five hectares as patchy. Nearly all seagrass was subtidal, although small amounts of intertidal seagrass were observed.

The distribution, species composition and abundance of seagrass meadows differ in each of the main regions of SEQ depending on levels of exposure (waves and tidal), sediment characteristics, water turbidity and seabed topography.

The most southern presence of seagrass in Queensland was reported as a few intertidal patches of Z. capricorni with H. ovalis in Currumbin Creek in 2007 (seagrasswatch.org). Prior to 2007, the most southern presence of seagrass in Queensland was reported from Tallebudgera Creek¹². Seagrass has also not been documented from the Nerang River upstream of the Broadwater. In 1987, a dense community dominated by Z. capricorni in association with H. spinulosa, H. ovalis and C. serrulata occurred along South Stradbroke Island¹². Mixed species communities of Z. capricorni/H. ovalis and monospecific communities of either Z. capricorni or H. ovalis also occurred as patches in association with many of the sand banks of the Broadwater¹².

Seagrass decline in the Broadwater has been reported and attributed to increased water current velocity, increased sand movement and reduced water quality as a result of foreshore modifications¹³.

In January 1997, McLennan and Sumpton¹⁴ mapped Z. capricorni, H. ovalis and H. spinulosa in The Broadwater. Z. capricorni and H. ovalis predominated, usually as mixed stands. Small patches of H. spinulosa intermingled with H. ovalis were observed at Carters Bank (north of Wave Break Island)¹⁴. Z. capricorni was present in extended meadows or as dense patches (0.5 to 3m diameter) throughout much of the study area. H. ovalis occurred as extensive meadows adjoining patches of Z. capricorni. H. ovalis generally had a greater depth range than Z. capricorni. Nearly all seagrass was subtidal, although small amounts of intertidal seagrass were observed on Carters Bank and on the western banks of South Stradbroke Island.

The areal coverage of seagrass in The Broadwater in 1997 (304 hectares)¹⁴ was greater than in 1987 (180 hectares)¹². However the 1997 survey reported a clear reduction in seagrass cover. This was possibly a consequence of a species change from Z. capricorni to H. ovalis in many meadows.

More recently, several seagrass surveys have been conducted as part of an Environmental Impact Statement (EIS) for the original Gold Coast Marine Development Project¹⁵. WBM conducted surveys in 2003 and 2004, reporting three species of seagrass within the southern Broadwater: Z. capricorni, H. ovalis and H. spinulosa (WBM Oceanics Australia 2003, 2004)¹⁶. Seagrass occurred as small (<0.5 ha), highly fragmented and apparently ephemeral patches, which were restricted largely to the steep slopes of channels and occasionally, on protected gradually sloping sand banks (i.e. Z. capricorni). Seagrass communities were often found to have a patchy distribution, particularly on the western foreshore of the Broadwater. Sparse H. ovalis was often found beyond the Z. capricorni in deeper waters, but did not form distinct meadows (WBM Oceanics Australia 2003, 2004)¹⁶.

A benthic survey of the Gold Coast Broadwater, Seaway and Marine Stadium areas was undertaken between 27 March and 8 April 2006 by GHD¹⁵. They identified a total of six seagrass species within the Seaway and Broadwater: Z. capricorni was generally found in intertidal or shallow subtidal areas often at the top of sand banks on either side of channel areas within the Broadwater; C. serrulata; H. uninervis; H. ovalis were generally found in deeper water areas, such as adjacent to the shoreline east of Wave Break Island; H. spinulosa, also found in deeper water; H. minor, a very small and uncommon species was identified in shallow water south of Wave Break Island (this species has not been previously identified in the region as it’s taxonomy remains under review¹¹. The most common species identified were Z. capricorni and H. ovalis. Dense meadows were located in areas generally north of Wave Break Island and a dense meadow of H. ovalis and H. spinulosa was identified adjacent to the eastern shoreline of Wave Break Island. Seagrass meadows within the Marine Stadium area, and banks of the southern channel, tended to be patchy and restricted to areas of less than 5 square metres. These patches of seagrass were dominated by Z. capricorni and located in intertidal or very shallow subtidal areas. The distribution of seagrass was generally located on western facing shorelines of sandbanks and on the eastern foreshores of Southport and Labrador. The total area of seagrass identified within the Broadwater was approximately 96 ha¹⁵.

In comparison with seagrass surveys undertaken during 2003 and 2004¹⁶ some distinct differences were noted. Prior to the 2006 surveys, only four species were identified. H. uninervis and H. minor were not reported in the 1980’s by Hyland et al.¹² or 1990’s by McLennan and Sumpton¹⁴. The presence of C. serrulata appears to have increased throughout the area, particularly in the Wavebreak Island area. The dense Z. capricorni meadows located on Labrador foreshore between Loders Creek and Biggera Creek are now intermixed with H. ovalis, H. uninervis and H. minor. Seagrass meadows composed of Z. capricorni and H. ovalis located within the Marine Stadium area appear to have dramatically reduced in their distribution and abundance since 2004.