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Northwest Australia reveals its unique marine ecosystem

01 May 2017

Mangrove Jack (AIMS)

While unusually warm sea temperatures in the Kimberley region threaten to cause further coral bleaching between April and May, researchers have joined with the Bardi-Jawi Land and Sea Rangers to provide the first detailed look into the process of fish and coral replenishment and the importance of marine plants in the ecosystem.

By the end of the Western Australian Marine Science Institution’s Kimberley Marine Research Program (KMRP) project a team of researchers from five separate institutions will have answered some important questions about this unique environment such as: When do young corals and fish move from the open ocean back into shallow coastal waters? Where do they go? Are there important “nursery” habitats or areas that need protection? Who is responsible for eating the majority of plant material? How much do they eat?

Scientists from the Australian Institute of Marine Science (AIMS), CSIRO, Department of Parks and Wildlife WA (Parks and Wildlife), The University of Western Australia (UWA), Department of Fisheries (DoF) and Western Australian Museum (WA Museum) are working in partnership with the Bardi Jawi Land and Sea Rangers, Traditional Owners (TO’s) and the Kimberley Marine Research Station to provide the first quantitative estimates of coral and fish recruitment and herbivory in the Cygnet Bay / Sunday Island group of the southern Kimberley region.

Study area (Kimberley region)

The core goal of the project is not only to provide primary information on these processes but a blueprint on the appropriate techniques needed to continue to learn what is ‘normal’ in this environment.

“This is one of the first studies in which recruitment has been measured during each month of the year, rather than focusing on one or two months following predicted periods of coral spawning,” AIMS Coral Researcher Dr James Gilmour said. “We have therefore captured periods of spawning outside of those predicted, and also the recruitment of ‘brooded’ larvae - those produced following the fertilisation and development of larvae within the coral’s polyp.

“Initial results indicate that patterns of reproduction at the inshore Kimberley reefs are similar to those offshore, but with more recruitment occurring in some winter and summer months. This is a likely consequence of spawning by some corals, such as the massive Porites bommies, outside of the mass-spawning period in autumn, and also indicates that brooding corals that release larvae throughout much of the year are a significant component of the Kimberley reefs.

“The effect of the mass-bleaching was obvious, dramatically reducing rates of coral recruitment below those expected. These data also provide a useful baseline with which to assess the recovery of coral recruitment in coming years,” Dr Gilmour said.

 

Isopora (left) and Porites (right) coral recruits on terracotta settlement plates. (AIMS)

 

Project leader Dr Martial Depczynski (AIMS) looked at fish recuitment and found generally, recruitment was stronger during the wet season, consistent with other Western Australian ecosystems.

“Although this seasonal pattern was consistent among habitats, each habitat consisted of a unique assemblage of fishes which also varied widely in abundance,” Dr Depczynski said.

“Mangroves uniquely provided a nursery habitat for some very important species such as the snappers Mangrove jack (Lutjanus argentimaculatus – Maarrarn) and Moses perch (Lutjanus russellii).

“Similarly for seagrasses, the Golden-lined rabbitfish (Siganus lineatus - Barrbal) that provide an important source of food were found almost exclusively in seagrass habitats,” Dr Depczynski said.

The research team recorded rates of grazing on seagrass that were higher in the southern Kimberley than anywhere else in the world.

“Average consumption of the seagrass Thalassia hemprichii, otherwise known as turtlegrass, actually outstripped growth in some areas, demonstrating how important seagrass is as a food source,” CSIRO’s Dr Mat Vanderklift said.

 

Grazed turtle grass (Thalassia hemprichii). Turtle grass is a fast grower but in some places grazing by herbivores exceeded estimates of production. (Mat Vanderklift, CSIRO)

 

“What we’ve been able to confirm so far is that differences in species groups vary greatly between habitats meaning that all habitat types in at least the southern Kimberley are equally important,” Dr Depczynski said.

“Also, fish diversity overall was surprisingly low and well below expectations considering its closer proximity to the equator and global centre of fish diversity prompting further questions about the influence of the Kimberley’s unique characteristics and how they affect recruitment processes,” Dr Depczynski said.

The final report is due to be completed mid-2017.

More information can be found on the WAMSI KMRP Key Ecological Processes project Page:  www.wamsi.org.au/key-ecological-processes

 

Graphical representation summarizing findings from juvenile fish stereo RUV surveys during the wet (top panel) and dry (bottom panel) seasons across five habitat types (mangrove, seagrass, algae, coral and inter-tidal pools; separated by dashed lines). Habitats portrayed from left to right follow a typical Kimberley habitat profile from inter-tidal mangroves to adjacent seagrass meadows and algal fields to elevated rocky inter-tidal pools and submerged coral reefs. Colour shades in the background of each habitat represent groupings based on observed statistical differences in fish assemblages among habitats (brown-mangroves, green-seagrass, and pink- algae, coral and inter-tidal pools). Each fish diagram represents a different juvenile species; key to right shows scientific and Bardi Jawi names. Only the ten most abundant and highly influential species distinguishing between fish assemblages are presented. The number of fish in each panel is equivalent to the average number of juvenile fish per RUV replicate (e.g. MaxN = 5 in mangrove habitat during the wet season).

 

Key Ecological Processes project page: www.wamsi.org.au/key-ecological-processes

 

The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government's Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley.

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Kimberley Marine Research Program