The supporting components outlined below are considered to be important or noteworthy in the context of maintaining the character of the site, but are not considered to represent critical components in the context of the considerations outlined in section 3.1.1 of this report. In this context:
The supporting components are not, in isolation, thought to fundamentally underpin the identified critical services/benefits. However, supporting components may, in combination with other critical and supporting components, underpin critical services/benefits.
Some supporting components are already partially covered by other critical components, processes or services/benefits.
The supporting components, while not critical, are important to wetland functioning and are noteworthy in this regard.
There are no empirical data describing variability in seagrass-meadows cover over time, nor are their data describing seagrass extent prior to the Ramsar site declarations.
As discussed in section 2.4.1, a one-off snap-shot of seagrass coverage of the site (and surrounding areas) was undertaken by Roelofs et al. (2005). This survey was undertaken post-Ramsar declaration. It is unknown whether the seagrass extent mapped by Roelofs et al. (2005) was representative of conditions the time of listing (that is, Stage II 1989). However, in qualitative terms it is known that tropical seagrasses can show great changes over time in response to disturbance by waves and flooding (for example, Preen et al. 1995, Kendrick et al. 1999, Campbell and McKenzie 2004). The dominant seagrass species within the site are pioneer species that can rapidly recolonise following disturbance (Bridges et al. 1981; Birch and Birch 1984). Consequently, when considering natural variability in seagrass extent over time, episodic changes must be taken into account.
3.4.2Monsoon Rainforests and Riparian Vegetation
Some but not all monsoon rainforests patches can be associated with seeps, which constitute a type of wetland. Riparian vegetation has been included in this component due to the overlaps in spatial distribution and species composition between these two habitat types. However, it is to be noted that certain riparian communities would also be classified as Component 4 (Melaleuca forests). Monsoon rainforests and/or riparian vegetation communities are associated with Wetland Types M, N and Y (refer Section 2.4.2).
There are no broad-scale empirical data describing variability over time in extent of riparian and/or monsoon rainforest supported by springs within the Ramsar site (refer section 2.4.2). Banfai and Bowman (2006) examined aerial photography to document changes at 50 rainforest patches over time, which incorporated both riparian vegetation as well as ‘non-wetland-dependent’ vegetation patches. Four time periods were selected: 1964 (pre-listing), 1984, 1994 and 2004.
Banfai and Bowman (2006) found that rainforest boundaries were highly dynamic at the decadal scale, with a landscape-wide expansion of rainforest boundaries exhibited between 1964 and 2004 (Figure 3 -31). Rainforest patch size increased by an average of 15 percent between 1964 and 1984, around seven percent between 1984 and 1994 and about six percent between 1994 and 2004. This suggests a relatively constant average rate of increase over decadal scales, both before and after site listing. This expansion was attributed to global environmental change phenomena such as increases in rainfall and atmospheric carbon dioxide (Banfai and Bowman 2007). It is to be noted that it is unknown whether, or what proportion of, the particular patches of rainforest that were investigated as part of the study were supported by springs (that is, wetland type Y) or were riparian vegetation (that is, wetland types M and N).
Figure 3 31 Changes in area of monsoon rainforest within Kakadu National Park (source: Banfai and Bowman 2006)
3.4.3Other Wetland Habitats
As outlined throughout this document, wetland habitats are an exceptionally important feature of the Ramsar site that supports a variety of natural and cultural values. All wetland types present within the site have been described in Section 2.4 (with further details provided in Section 3.3 for wetland types that are seen as ‘critical’ in the context of this ECD).
As previously mentioned, terrestrial habitats comprise large expanses of the Ramsar site. Specifically, the greater part of Kakadu National Park is savannah of Eucalypt-dominated open forest and woodland formations, typically with tall grassy understoreys (Russell-Smith 1995). Additionally, areas of heath are present and the plateau features scattered hardy shrubs and spinifex grasses (Russell-Smith 1995). The terrestrial habitats support a variety of fauna species, many of which use resources from a combination of terrestrial and wetland habitats (refer Section 2.5.5). Terrestrial flora and fauna species are an integral part of the wetland ecosystems, contributing significantly to wetland functions and processes such as energy and nutrient cycles (Finlayson et al. 2006).
Kakadu National Park supports highly diverse and abundant aquatic invertebrate populations (Outridge 1987; Finlayson et al. 1990). Aquatic invertebrates are consumers that have a vital role in the decomposition and uptake of nutrients in aquatic ecosystems, such that nutrients are processed and available for higher consumers (that is species that prey on aquatic invertebrates). As discussed in Section 3.5.5, some aquatic invertebrate species such as shrimp can have a particularly strong influence on benthic foodwebs by influencing/processing benthic sediments, detritus and algal communities.
In terms of aquatic invertebrates providing a valuable prey resource, almost half of the wetland bird species eat swimming or bottom-dwelling aquatic invertebrates (Cowie et al. 2000). These food resources are shared between species on the basis of foraging zones, foraging techniques and prey size. A significant feature of the freshwater fish communities is that they typically lack specialist herbivorous species and most fish species are largely carnivorous (Section 3.2.6) on aquatic invertebrates as a significant feature of the freshwater fish communities is that they typically lack specialist herbivorous species (Cowie et al. 2000). MacFarlane (1996) analysed community-based data and found that predation by fish is non-selective of macroinvertebrate taxa. Invertebrates also provide food for aquatic reptiles, with crustaceans in particular comprising a significant proportion of the diets of freshwater and saltwater crocodiles (Section 3.3.7) and pig-nosed turtle (Section 3.2.10).
Aquatic invertebrate fauna can display vast seasonal differences, with species diversity and distribution typically greatest during the wet season (Finlayson et al. 1990). Finlayson et al. (2006) state that the major aquatic invertebrate families of Kakadu National Park have a high year-to-year constancy compared with other regions of Australia, which is most likely related to the relatively low degree of inter-annual variability in stream flow. Note that endemic aquatic invertebrates are discussed in Critical Component 11 (refer Section 3.2.11).
3.4.6Regionally Endemic Species
In addition to the local endemic invertebrate species, which represent critical components (see Section 3.2.11), the site contains several regionally endemic species (see also Section 2.5.5). The following aquatic species are considered regionally endemic, meaning they occur exclusively within the Timor Sea Drainage Division):
Endemic species of Leptophlebiidae mayfly Tillyardophlebia dostinei, which has been recorded from a single freshwater stream within the site (Rockhole Mine Creek, Dean and Suter 2004). Dean and Suter (2004) suggest that this species is likely to be more widely distributed, with a possible conspecific recorded at Manning Gorge in north Western Australia (Timor Sea Drainage Division).
Seven of the nine species of the mayfly family Leptophlebiidae recorded in the Ramsar site are thought to be restricted to the Timor Sea Drainage Division (Finlayson et al. 2006).
Magela hardyhead Craterocephalus marianae – This species has a highly restricted geographic range, occurring within the South Alligator River and East Alligator River within the Ramsar site, as well as the Mann River in nearby Arnhem Land (Allen et al. 2003). Allen et al. (2003) indicates that this species is abundant within its limited range, forming large schools in fast flowing, shallow creeks with sand or gravel beds.
Midgley’s grunter Pingalla midgleyi – This species has a restricted distribution that incorporates the East Alligator River and South Alligator River within the Ramsar site, as well as the upper reaches of the Katherine River (Allen et al. 2003). It occurs in well shaded rocky pools in clear, flowing creeks with a sandy bed. It is thought to be common where it occurs (Allen et al. 2003).
Exquisite rainbowfish Melanotaenia exquisita – This species has a disjunct distribution, and is thought to be restricted to the South Alligator and Katherine Rivers within the Ramsar site, and upland tributaries of the Edith River (Northern Territory) and the King George River (Western Australia). This species typically inhabits small, clear, swift-flowing streams, often congregating in rock pools at the base of small waterfalls such as Jim Jim Falls in the South Alligator system, Seventeen Mile Falls in the Katherine system (located outside Kakadu National Park), and King George Falls in Western Australia.
Sharp-nose grunter Syncomistes butleri – This species is restricted to the Timor Sea Drainage Division between the Drysdale River (Western Australia) and the Liverpool River (Northern Territory) (Allen et al. 2003). It is described as reasonably common in the upper reaches of the large river systems in which it occurs, and is found in slow or fast moving water of lagoons and streams, typically in deeper waters (Allen et al. 2003).
Bambusa arnhemica (Poaceae) – A bamboo species that is endemic to the high-rainfall north-western areas of the Northern territory. The species is locally abundant in riparian vegetation, but has a patchy distribution that includes the South Alligator River in Kakadu National Park, and other major watercourses such as the Adelaide, Mary, Finniss and lower Daly Rivers (Franklin and Bowman 2004).
Hygrochloa aquatica (Poaceae) – An aquatic grass species that floats from emerged tufts. This species is endemic to the Top End, occurring from the Daly River to the East Alligator River, and grows on the shallow margins of permanent and seasonal swamps, billabongs and floodplains (Cowie et al. 2000).
Nymphoides spongiosa (Menyanthaceae) – An aquatic herb with floating leaves. The species grows in still shallow, freshwater swamps, floodplains and lagoons in Kakadu National Park and neighbouring regions (for example, Mary River, Howard River).
Nymphoides subacuta (Menyanthaceae) – An aquatic herb with floating leaves. The species grows in shallow freshwater swamps and lagoons in Kakadu National Park and the Darwin region.