No abstract

There is concern about historical and continuing loss of canopy-forming algae across the world's temperate coastline. In South Australia, the sparse cover of canopy-forming algae on the Adelaide metropolitan coast has been of public concern with continuous years of anecdotal evidence culminating in 2 competing views. One view considers that current patterns existed before the onset of urbanisation, whereas the alternate view is that they developed after urbanisation. We tested hypotheses to distinguish between these 2 models, each centred on the reconstruction of historical covers of canopies on the metropolitan coast. Historically, the metropolitan sites were indistinguishable from contemporary populations of reference sites across 70 km (i.e. Gulf St. Vincent), and could also represent a random subset of exposed coastal sites across 2100 km of the greater biogeographic province. Thus there was nothing 'special' about the metropolitan sites historically, but today they stand out because they have sparser covers of canopies compared to equivalent locations and times in the gulf and the greater province. This is evidence of wholesale loss of canopy-forming algae (up to 70%) on parts of the Adelaide metropolitan coast since major urbanisation. These findings not only set a research agenda based on the magnitude of loss, but they also bring into question the logic that smaller metropolitan populations of humans create impacts that are trivial relative to that of larger metropolitan centres. Instead, we highlight a need to recognise the ecological context that makes some coastal systems more vulnerable or resistant to increasing human-domination of the world's coastlines. We discuss challenges to this kind of research that receive little ecological discussion, particularly better leadership and administration, recognising that the systems we study out-live the life spans of individual research groups and operate on spatial scales that exceed the capacity of single research providers.

Five species of abalone occur along the southern Australian coastline; of these three species, Haliotis laevigata Donovan, Haliotis roei Gray, and Haliotis ruber Leach, are of commercial importance; the other two species are Haliotis cyclobates Peron and Haliotis scalaris Leach. The habitat, movement, feeding behaviour, food, and ecological relationships with predators were studied for each species at three study sites. Each species of abalone occupies a distinctive microhabitat. H. cyclobates lives in calm-water places associated with communities of the seagrass Posidonia australis and the razor shell Pinna dolobrata; H. laevigata lives on open rock adjacent to sand in moderate to rough water localities; H. ruber prefers caves in calm- to rough-water localities; H. roei occurs in narrow crevices in the upper sublittoral on rough-water coasts ; H. scalaris is an under-boulder or crevice-living species. All species are sedentary, but may make local movements in search of food. Several species may occur in a given habitat but there is little microhabitat overlap. The seasonal variation in food eaten by each species is described. All species show preference for red algae and reject most species of brown algae, subsisting predominantly on red algae and seagrasses according to the possibilities of the habitat. H. laevigata feeds mainly on algal drift and H. roei is substantially a grazing species. The other species feed on algal drift or graze opportunistically. Water movement is an important environmental factor affecting the feeding of those species which feed on algal drift. H. laevigata and H. ruber feed best in conditions of moderate water movement but poorly if the water is too calm or too rough. Water movement elicits a characteristic feeding response in these species. The predators of abalone include fish, crabs, molluscs, and starfish; their interaction with abalone is discussed. Crevices, caves, and cavities under boulders provide a refuge in space from predators for H. roei, H. ruber, and H. scalaris and juveniles of other species, which appear to be confined to these places, except for nocturnal feeding excursions, by the activity of their predators. The adults of the different species differ from each other in their dependence on water movement, their preference for open or cryptic sites such as crevices or caves for resting, their size and their methods of feeding. These differences between the species, taken together, ensure that there will be very little overlap between them in the sorts of places that they seek to live in or their behaviour in seeking food; in those cases where food-seeking behaviour is similar, interspecific competition would seem to be negligible because food is abundant. Predation would seem to have been more important than interspecific competition as the selective pressure that established and maintains these differences between the species.

This paper concerns the conservation of abalone stocks in a genetic and fisheries sense. We review genetic and ecological information relating to the differentiation of abalone stocks in South Australia and propose that metapopulation theory provides an apt framework in which to develop the concept of an abalone stock. We consider what is a minimum viable population for abalone and illustrate our discussion with a case study of an abalone population that declined through a combination of fishing, recruitment failure, and inadequate protection by a refugium. Refugia can play an important role in abalone conservation by maintaining egg production and genetic diversity and by preserving populations for scientific study.

Evidence is accumulating that species' responses to climate changes are best predicted by modelling the interaction of physiological limits, biotic processes and the effects of dispersal-limitation. Using commercially harvested blacklip (Haliotis rubra) and greenlip abalone (Haliotis laevigata) as case studies, we determine the relative importance of accounting for interactions among physiology, metapopulation dynamics and exploitation in predictions of range (geographical occupancy) and abundance (spatially explicit density) under various climate change scenarios. Traditional correlative ecological niche models (ENM) predict that climate change will benefit the commercial exploitation of abalone by promoting increased abundances without any reduction in range size. However, models that account simultaneously for demographic processes and physiological responses to climate-related factors result in future (and present) estimates of area of occupancy (AOO) and abundance that differ from those generated by ENMs alone. Range expansion and population growth are unlikely for blacklip abalone because of important interactions between climate-dependent mortality and metapopulation processes; in contrast, greenlip abalone should increase in abundance despite a contraction in AOO. The strongly non-linear relationship between abalone population size and AOO has important ramifications for the use of ENM predictions that rely on metrics describing change in habitat area as proxies for extinction risk. These results show that predicting species' responses to climate change often require physiological information to understand climatic range determinants, and a metapopulation model that can make full use of this data to more realistically account for processes such as local extirpation, demographic rescue, source-sink dynamics and dispersal-limitation.