coastal and marine natural values of the kimberley - wwf - Australia

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36. Coastal and Marine Natural Values of the Kimberley6.MARINE ANDCOASTALCOMMUNITIES6.1 GENERAL NORTH-WESTSHELF COMMUNITIESMuch of what is known about the shelfbiota is from fisheries investigations.Large areas of the shelf have also beeninvestigated by the petroleum industry,however very little of this information isin the public domain.Taiwanese pair-trawl fishing in the early1980s indicated differences in fish faunaacross the shelf between the Broome,Cape Londonderry and shelf break(offshore) sectors. The Broome regionhad higher catch rates of small snappers(Lutjanidae), emporers (Lethrinidae),goatfish (Mullidae), threadfin breams(Nemipteridae), bigeyes (Priacanthidae)and cods (Serranidae). The easternKimberley region had higher catch ratesof large red snappers (Lutjanidae) andsweetlips (Haemulidae). The deep slopebottom near the shelf break had higherabundances of jobfish (Pristipomoides).Inshore of 30 m depth, traps and drop-linesindicate a carnivore dominance of catfishArius spp., black jewfish Protonibeadiacanthus and golden snapper Lutjanusjohnii (Department of Fisheries, 2004).Although many shelf fishes occurthroughout the shelf range, they areusually predominant in particular habitattypes, which may vary between life stages.The red emperor Lutjanus sebae juvenilesare common in the nearshore turbidwaters on coastal and offshore reefs. Thesubadults and adults are distributed acrossthe continental shelf to 180 m depth,associated with coral reefs, epibenthiccommunities, limestone sand flats andgravel patches. Juvenile goldband snapperPristipomoides multidens are found onsedimentary habitats with no relief withadults forming schools in 60-245 mdepth near reefs, shoals and epibenthos.The scarlet perch Lutjanus malagaricusjuveniles are solitary in nearshore waters,often in seagrass. Adults are dispersedacross the continental shelf to 140 mdepth, associated with reefs, shoals,flatbottom with epibenthos and habitatswith vertical relief.Several prawn species have coastaljuvenile phases with wider adult dispersalonto the shelf, including brown tigerprawn Penaeus esculentus (sand andsandy mud seabed) and various coralprawns (soft and hard bottoms).6.2 SEDIMENT BEDCOMMUNITIESAreas of sandy habitat support ‘spongegardens’ of large erect sponges,gorgonian corals and sea whip corals.These communities are prevalent in thesandier mid-shelf 50-100 m habitats. Thediversity of sponges in these communitiesis considered to be high (> 600 species;Wassenberg & Cook, 2002).Considerable portions of this communitywere initially affected by the Taiwanesepair-trail fishing, which involveddemersal (bottom) trawling with heavygear. The catches and catch compositionchanged considerably between 1980and 1990, partially reflecting changesin the sponge habitat and the associatedfish species (Sainsbury et al., 1993).Subsequent Australian otter trawling wasalso considered to impact this habitat. Therecovery rate is thought to be in excessof 20 years, so habitat distribution andspecies composition is only considered toreflect historical disturbances, rather thanactual distribution (Fulton et al., 2006).The sediment sponge communities(large epibenthos) support particularcommunities of fishes, particularlysnappers and emporers (Moran &Stephenson, 2000). Bare sedimentcommunities have a greater dominanceof lizardfish (Synodontidae) andthreadfin bream (Nemipteridae; Moran& Stephenson, 2000). The demersalcrustacean fauna of the Northwest Shelfis particularly species rich, with 308species in 40-80 m depth, including crabs,penaeid prawns and carid shrimps. The
Coastal and Marine Natural Values of the Kimberley37.infauna is also extremely diverse, beingdominated by polychaetes (Poore, 1995).Infaunal species richness is an indicationof important soft sediment processes thatdrive the food chain, even in the pelagicsystem. Banana prawns feed on softsediment invertebrates and where theyform dense aggregations, often visible atthe surface, is indicative of areas of highbiodiversity value at the seabed. Suchareas are of particular importance for theecology of the Kimberley and dependentcommercial fisheries.6.3 SHELF ‘STRUCTURE’COMMUNITIESThe Northern Demersal ScalefishFishery targets species that are widelydistributed across the continental shelfbut concentrated in abundance inspecific habitats. These habitats includeareas with hard bottom, vertical reliefand large epibenthos (Department ofFisheries, 2004). The distribution ofsuch communities, as evidenced bythe distribution of fishing effort, ispredominantly along the old continentalshelf coastline in approximately 100mof water, but also occurs in other areasof the shelf from 60 to 150m depth(Figure 14). Fishes of these ‘structure’communities include families of the reeffish snappers (Lutjanidae), cods andgroupers (Serranidae) and the emperors(Lethrinidae). The predominant fishedspecies are: the goldband snappersPristipomoides multidens, P. typus andP. fi lamentosus; the red emperor snapperLutjanus sebae; cods such as Epinephelusmultinotatus and E. bleekeri; and theemperors, such as the spangled emperorLethrinus nebulosus.Other, non-commercial, carnivorousfishes in these areas include trigger fishspecies (Abalistes stellaris, Sufflamenfraenatus, Abalistes sp), longfinbannerfish Heniochus acuminatus,Myripristis murdjan, red lionfish Pteroisvolitans, red squirrelfish SargocentronFigure 14: Distribution of trapping effort for the Northern Demersal ScalefishFishery (Department of Fisheries, 2004).rubrum (Department of Fisheries, 2004).As discussed above, fisheries data is themain source of knowledge but becausethe fishery uses traps and baited droplines,only generalist carnivores aredocumented. The number of fish familiescharacterising these habitats will begreater than indicated here.6.4 SHELF SLOPECOMMUNITIESThe deeper continental slope habitatsfrom 150 to 400m differ in fish faunafrom the shelf and offshore shoalhabitats. The fauna is diverse but alsoof commercial interest and thereforein considerable abundance. It includesdeepwater snappers Etelis carbunculus,E. coruscans, E. radiosus, Lipocheiluscarnolabrum, Paracaesio kusakarii,Paracaesio stonei, Pristipomoidesargyrogrammicus, P. zonatus, P. auricillaand Aphareus rutilans; the deepwatersparid Dentex tumifrons, the deepwateremperor Wattsia mossambica; and thedeepwater cods Epinephelus morrhua,Epinephelus radiatus and Epinephelusoctofasciatus. The crustacean Australianscampi Metanephrops sp is also presenton the slope.Bioregionalisation of the demersal shelffishes indicated a province from Broometo Melville Island, with indicator speciesbeing Bembrops nelsoni, Bythaelurussp., Halicmetus sp., Malthopsis spp,Neobythites australiensis, Neobythitesbimaculatus, Neobythites macrops,Neobythites soelae, Parapterygotriglasp., Physiculus roseus (Last et al., 2005).This province has 418 known fish specieswith 64 of these being endemic.The value of these ecosystems may beunderestimated. As discussed in section6.8.5, the presence of megafauna such asbeaked whales is an indication of highbiodiversity value. Evidence that theseanimals are benthic feeders (Woodside etal., 2006) is even greater indication thatthe ecosystem processes at the seafloor aresignificant. This is not a reason to suspecthowever, that these areas are equally richthroughout. As discussed in section 5.1,marine ecosystems exhibit a high degreeof variability in terms of the quality ofresources available to marine fauna.
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