Anthropogenic threats to benthic habitats do not pose an equal risk, nor are they uniformly distributed over the broad depth range of marine habitats. Deep sea benthic environments have, by and large, not been heavily exploited and most are in relatively good condition. In contrast, shelf and coastal habitats, and deep ocean pelagic fisheries, have been exploited extensively and human impacts here are locally severe. A critical point is that anthropogenic threats do not act in isolation; rather, they are cumulative and the impacts are compounded for every affected habitat. In general, the impacts of humans on benthic habitats is poorly understood. Habitat mapping provides condition assessments and establishes baselines against which changes can be measured. GeoHab scientists ranked the impacts on benthic habitats from fishing as the greatest threat, followed by pollution and litter, aggregate mining, oil and gas, coastal development, tourism, cables, shipping, invasive species, climate change and construction of wind farms. The majority of authors (84%) reported that monitoring changes in habitat condition over time was a planned or likely outcome of the work carried out. In this chapter the main anthropogenic threats to benthic habitats are reviewed in relation to their potential impacts on benthic environments.

This introductory chapter provides an overview of the book's contents and definitions of key concepts including benthic habitat, potential habitat and seafloor geomorphology. The chapter concludes with a summary of commonly used habitat mapping technologies. Benthic (seafloor) habitats are physically distinct areas of seabed that are associated with particular species, communities or assemblages that consistently occur together. Benthic habitat maps are spatial representations of physically distinct areas of seabed that are associated with particular groups of plants and animals. Habitat maps can illustrate the nature, distribution and extent of distinct physical environments present and importantly they can predict the distribution of the associated species and communities.

Demands are being made of the marine environment that threaten to erode the natural, social and economic benefits that human society derives from the oceans. Expanding populations ensure a continuing increase in the variety and complexity of marine based activities - fishing, power generation, tourism, mineral extraction, shipping etc. The two most commonly acknowledged purposes for habitat mapping in the case studies contained in this book are to support government spatial marine planning, management and decision-making and to support and underpin the design of marine protected areas (MPAs; see Ch. 64).

This chapter presents a broad synthesis and overview based on the 57 case studies included in Part 2 of this book, and on questionnaires completed by the authors. The case studies covered areas of seafloor ranging from 0.15 to over 1,000,000 km2 (average of 26,600 km2) and a broad range of geomorphic feature types. The mean depths of the study areas ranged from 8 to 2,375 m, with about half of the studies on the shelf (depth <120 m) and half on the slope and at greater depths. Mapping resolution ranged from 0.1 to 170 m (mean of 13 m). There is a relatively equal distribution of studies among the four naturalness categories: near-pristine (n=17), largely unmodified (n = 16), modified (n=13) and extensively modified (n=10). In terms of threats to habitats, most authors identified fishing (n=46) as the most significant threat, followed by pollution (n=12), oil and gas development (n=7) and aggregate mining (n=7). Anthropogenic climate change was viewed as an immediate threat to benthic habitats by only three authors (n=3). Water depth was found to be the most useful surrogate for benthic communities in the most studies (n=17), followed by substrate/sediment type (n=14), acoustic backscatter (n=12), wave-current exposure (n=10), grain size (n=10), seabed rugosity (n=9) and BPI/TPI (n=8). Water properties (temperature, salinity) and seabed slope are less useful surrogates. A range of analytical methods were used to identify surrogates, with ARC GIS being by far the most popular method (23 out of 44 studies that specified a methodology).

This study presents compelling evidence for a diverse and abundant seabed community which has developed over the course of the Holocene beneath the Amery Ice Shelf in East Antarctica. Fossil analysis of a 47 cm long sediment core reveals a rich modern fauna, dominated by filter feeders (sponges and bryozoans), with an abundant infauna predominantly of polychaetes. The down-core assemblage reveals a succession in the colonisation of this site. The lower portion of the core (prior to ~9600 yr BP) is completely devoid of preserved fauna. The first colonisers of the site after this time were the mobile benthic organisms. Their occurrence in the core is matched by the first appearance of planktonic taxa, indicating a retreat of the ice shelf following the last glaciation to within sufficient distance to advect planktonic particles via bottom currents. The benthic infauna and filter feeders emerged during the peak abundance of the planktonic organisms, indicating their dependence on this advected food supply which is brought via bottom currents flowing from the open shelf waters of Prydz Bay. Understanding patterns of species succession in this environment has important implications for determining the potential significance of future global change. The collapse of Antarctic ice shelves, as has happened in recent times, would significantly change the organic supply regime, and therefore the nature of these sub-ice shelf benthic communities.

In order to protect the diversity of marine life in Australia's Exclusive Economic Zone (EEZ), the federal parliament has passed the Environmental Protection and Biodiversity Conservation (EPBC) Act 1999. The Act is being implemented through the design of a national representative system of marine protected areas (MPAs) that will place under protection a representative portion of Australia's EEZ by 2012. A total of 13 MPAs have already been nominated for the southeast region in 2006. Limited biological data in Australia's EEZ has resulted in biophysical information compiled by Geoscience Australia being used as a proxy for seabed biodiversity in support of marine conservation planning. Information we use to characterise the seabed includes bathymetry, geomorphology, acoustic properties, sediment properties, slope and sediment mobilisation due to waves and tides. To better characterise habitats on the Australian continental shelf, Geoscience Australia is creating 'seascape' maps (similar to geological facies maps) that integrate these multiple layers of spatial data, and are useful for the prediction of the distribution of biodiversity in Australia's EEZ. This information provides 100% spatial coverage based on objective, multivariate statistical methods and offers certainty for managers and stakeholders including the oil and gas industry, who are involved with designing Australia's national MPA system. Certainty for industries operating in the EEZ is enhanced by a reproducible, science-based approach for identifying conservation priorities and the classification of seafloor types within multiple use areas.

Dense coral-sponge communities on the upper continental slope at 570 - 950 m off George V Land have been identified as a Vulnerable Marine Ecosystem in the Antarctic. The challenge is now to understand their likely distribution. Based on results from the Collaborative East Antarctic Marine Census survey of 2007/2008, we propose some hypotheses to explain their distribution. Icebergs scour to 500 m in this region and the lack of such disturbance is probably a factor allowing growth of rich benthic ecosystems. In addition, the richest communities are found in the heads of canyons. Two possible oceanographic mechanisms may link abundant filter feeder communities and canyon heads. The canyons in which they occur receive descending plumes of Antarctic Bottom Water formed on the George V shelf and these water masses could entrain abundant food for the benthos. Another possibility is that the canyons harbouring rich benthos are those that cut the shelf break. Such canyons are known sites of high productivity in other areas because of a number of oceanographic factors, including strong current flow and increased mixing with shelf waters, and the abrupt, complex topography. These hypotheses provide a framework for the identification of areas where there is a higher likelihood of encountering these Vulnerable Marine Ecosystems.

Explaining spatial variation and habitat complexity of benthic habitats from underwater video through the use of maps. Different methodologies currently used to process and analyse percent cover of benthic organisms from underwater video will be addressed and reviewed.

Understanding and predicting the bio-physical relationships between seabed habitats, biological assemblages, and marine biodiversity is critical to managing marine systems. Species distributions and assemblage structure of infauna were examined on the oceanic shelf surrounding Lord Howe Island (LHI) relative to seabed complexity within and adjacent to a newly discovered relict coral reef. High resolution multibeam sonar was used to map the shelf, and identified an extensive relict reef in the middle of the shelf, which separated an inner drowned lagoon from the outer shelf. Shelf sediments and infauna were sampled using a Smith McIntyre grab. The three geomorphic zones (drowned lagoon, relict reef and outer shelf) were strong predictors or surrogates of the physical structure and sediment composition of the LHI shelf and its infaunal assemblage. Infaunal assemblages were highly diverse with many new and endemic species recorded. Each zone supported characteristic assemblages and feeding guilds, with higher abundance and diversity offshore.

Crinoids, and especially comatulids as Anthometra adriani, are well represented among the macrofauna from the continental shelf offshore from Terre Adélie and George V Land, East Antarctica. These animals are suspension feeders that depend on the local current regime to feed. Nearly 500 specimens from this species were sampled during the Collaborative East Antarctic Marine Census (CEAMARC) expedition onboard the RV Aurora Australis (December 2007 to January 2008), from 46 of the 87 stations over a 400 km² area. Abiotic environmental factors (such as depth, temperature, salinity, oxygen) were measured at each site. The ecological niche of Anthometra adriani was described using Ecological Niche Factor Analysis (ENFA) and Mahalanobis Distances Factor Analysis (MADIFA). An Environmental Suitability Map (ESM) was developed for this species on the CEAMARC study area. The results show that A. adriani seems to prefer relatively cold and well-oxygenated waters in moderately deep areas. The ESM shows four optimal regions for this species: the eastern side of the George V Basin, the western part of the Mertz Bank, the southern side of the Adélie Bank, and the coastal area between the Astrolabe and Mertz Glaciers.