Examples of effects on predator populations include: • Coral trout numbers continue to occur in lower densities on reefs open to fishing compared to similar reefs closed to fishing (see Section 2.4.8).140 • Of the four highest ecological risk predatory fishes taken in the East Coast Inshore Fin Fish Fishery141, two (king threadfin and barred javelin) have an undefined stock status and the other two (black jewfish and giant queenfish) were not assessed in the 2012 Queensland stock assessment.122 • The Queensland shark control program has targeted predators such as tiger sharks since its inception in 1962. • Many sharks are incidentally caught in commercial fisheries.138,142 • There are declining populations of some seabird populations (see Section 2.4.13) and suspected declines in some dolphin species (see Section 2.4.16). The partial recovery of crocodile and loggerhead turtle populations will have increased predation by those species.
Symbiosis is the interdependence of different organisms that benefits one or both participants. There are a wide range of symbiotic relationships in the Great Barrier Reef including those that are mutually beneficial (mutualism); beneficial for one organism without affecting the other (commensalism); and beneficial for one organism to the detriment of another (parasitism).
Symbiotic relationships are likely to have deteriorated in the southern two-thirds of the Region.
One of the most important symbioses in the Region is between corals and microscopic algae.143 This symbiosis is an example of mutualism. The algae photosynthesise like other green plants, however up to 95 per cent of the nutrients produced are used by the coral host organism.143,144 In return the coral provides the algae with a safe habitat. An example of commensalism is the association between the Chelonibia barnacle and its marine turtle hosts.145 Isopod crustaceans gaining shelter and food by living on the gills of many reef fishes is an example of parasitism.146 High numbers of parasites can be an indicator of poor environmental conditions.147 Very little is known about the condition and trend of most symbiotic relationships in the Region. Based on the overall condition of the ecosystem, it is likely they are in good condition in the northern third of the Region. The poorer overall condition of the ecosystem in the southern two-thirds of the Region148 may have affected symbiotic processes. The extent of the effect would depend on the individual species involved. In particular, the coral–algal symbiosis will have been significantly affected by the decline in hard coral cover (see Section 2.3.5) and thermal stress events (resulting in coral bleaching) (Section 3.2.6).149,150,151,152,153