Many marine fish and invertebrates show a dual life history where settled adults produce dispersing larvae. The planktonic nature of the early larval stages suggests a passive dispersal model where ocean currents would quickly cause panmixis over large spatial scales and prevent isolation of populations, a prerequisite for speciation. However, high biodiversity and species abundance in coral reefs contradict this panmixis hypothesis. Although ocean currents are a major force in larval dispersal, recent studies show far greater retention than predicted by advection models. We investigated the role of animal behavior in retention and homing of coral reef fish larvae resulting in two important discoveries: (i) Settling larvae are capable of olfactory discrimination and prefer the odor of their home reef, thereby demonstrating to us that nearby reefs smell different. (ii) Whereas one species showed panmixis as predicted from our advection model, another species showed significant genetic population substructure suggestive of strong homing. Thus, the smell of reefs could allow larvae to choose currents that return them to reefs in general and natal reefs in particular. As a consequence, reef populations can develop genetic differences that might lead to reproductive isolation.coral reef ͉ olfaction ͉ population genetics

Human activities are releasing gigatonnes of carbon to the Earth's atmosphere annually. Direct consequences of cumulative post-industrial emissions include increasing global temperature, perturbed regional weather patterns, rising sea levels, acidifying oceans, changed nutrient loads and altered ocean circulation. These and other physical consequences are affecting marine biological processes from genes to ecosystems, over scales from rock pools to ocean basins, impacting ecosystem services and threatening human food security. The rates of physical change are unprecedented in some cases. Biological change is likely to be commensurately quick, although the resistance and resilience of organisms and ecosystems is highly variable. Biological changes founded in physiological response manifest as species range-changes, invasions and extinctions, and ecosystem regime shifts. Given the essential roles that oceans play in planetary function and provision of human sustenance, the grand challenge is to intervene before more tipping points are passed and marine ecosystems follow less-buffered terrestrial systems further down a spiral of decline. Although ocean bioengineering may alleviate change, this is not without risk. The principal brake to climate change remains reduced CO(2) emissions that marine scientists and custodians of the marine environment can lobby for and contribute to. This review describes present-day climate change, setting it in context with historical change, considers consequences of climate change for marine biological processes now and in to the future, and discusses contributions that marine systems could play in mitigating the impacts of global climate change.

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While evidence is mounting that larval reef fish are active participants in the process of dispersal and settlement, the sensory and behavioural mechanisms by which these fishes disperse and return from their oceanic phase to the reefs remain unknown. On One Tree Island (Great Barrier Reef, Australia), we tested freshly collected animals in a large choice-flume on the shore. Here, we present the first evidence that larval reef fish (primarily apogonids) approaching the time of settlement are capable of detecting differences between ocean and lagoon water and prefer lagoon water. We also demonstrate that they sniff actively with well-innervated noses and that attraction to lagoon water was not affected by warmer or colder temperatures. We conclude that they used chemical signals to orient toward lagoon water. Finally, we describe ebb tide plumes of lagoon water that extend many kilometers from reefs. Such plumes could provide chemosensory cues for dispersal and settlement stages of reef fish as they develop swimming efficiency. We argue that fishes may imprint to reef odour as embryos and/or early larvae and that this could facilitate both retention near the natal reef and navigation toward reefs from greater distances.

Shallow subtidal areas of rocky reefs in central and southernNew South H 'ales may best be described as a mosaic of habitats, the distributions of which are seemingly related to depth, wave exposure and a number of biological processes, particularly herbivory. The Eringe habitat is generally found only in the most shaltow waters. Eorests of the laminarian alga Ecklonia radiata are often found at intermediate depths.In deeper, or more sheltered water, sponges, ascidians and red algae are more abundant and the abundances of sea urchins and other invertebrate grazers decline. Overtying this broadbrush pattern are patches of crustose coraltine atgae (the Barrens habitat), the distributions of which are not clearly related to depth. Invertebrate herbivores, and sea urchins in particular, are abundant in the Barrens habitat. The Barrens habitat was most represented at the more southern locations. At the two most northern locations, reefs were shorter in length and dominated by aseidians (Tyura species).

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The elemental fingerprints or composition of otoliths of fish may provide a natural tag of the 'nursery' habitat of juvenile fish. The natural tag could then be used to determine the 'nursery' habitat of adult fish found on coastal reefs. We collected juvenile Pelates sexlineatus from 2 to 5 sites within each of 7 estuaries to determine whether elemental composition of otoliths differed among estuaries and among sites within estuaries. In addition, fish were collected in 2 successive years to determine whether temporal differences may be found in elemental fingerprints that could then confound subsequent assignment of adults to 'nursery' estuaries. Significant differences in elemental fingerprints (Sr, Ba and Mn) were found within and among estuaries, but there was often an interaction with time suggesting that there were differences among estuaries/sites but the difference varied between times. Quadratic discriminant functions (QDFs) generated to discriminate among estuaries suggested that the QDFs calculated from a single year class were more successful at assigning fish to the correct estuary than either (1) QDFs based on both years combined or (2) using the QDFs generated from the first year class to classify the second year class. Small-scale variability among sites within an estuary suggested that for an estuarine fishery we may be able to classify fish to their site of origin; this warrants further investigation. Adult fish from a coastal fishery can now be assigned to their 'nursery' estuary by analysing the juvenile region of their otoliths, provided that discriminant functions are generated from the appropriate year class of recruits. KEY WORDS: Estuarine nursery area · Otolith microchemistry · Trace elementsResale or republication not permitted without written consent of the publisher

ABSTRACT. Estuaries and associated seagrass habitats are thought to be important nursery areas for many fishes. There is, however, no direct evidence for movement of fish from estuaries to reefs. The alm of this study was to determine if populations of Achoerodus viridis (Labridae) on rocky reefs were sustained by (1) recruitment to estuarine seagrass habitat followed by m o \ i e~~~c n t to rocky reefs, (2) direct recruitment to rocky reefs, or (3) a combination of the two. Recruits were collected from estuarine seagrass and rocky reef habitats and elements in their otoliths analysed by inductively coupled plasmamass spectrometry (ICP-MS) to determine if d~fferent 'elemental fingerprints' could be found. Higher concentrations of Zn, AI, Pb, Mn, Ba and CO were found in otoliths of recruits from estuar~ne seagrass habitat than In otoliths of recruits from coastal reefs, the latter 3 elements showing sign~ficant differences. Strontium occurred in significantly h~g h e r concentrations in otoliths of recruits from coastal reefs. Differences in concentrations of some elements In the otoliths of recruits allo\ved fish from the 2 env~ronments to be dlstinyuished 1~1 t h a high degree of dccuracy, enabling the contribution of estuarine recruitment to sustaining reef populations to be determined. Elemental composition of the juvenile core of otoliths from adults on reefs was related to the composition of otoliths of recruits from each environment to identify historical recruitment environments. Discriminant function analysis showed that 41 % of adults had recruited to estuaries and 59%) had recruited to reefs, but these figures may be overestimated because adults must be assigned to 1 of the 2 groups. There was evidence to suggest that some adults may form a third intermediate group. Further validation (e.g. comparison w~t h laser or probe based methods and tagging techniques) of our a p p r o~~c h is warranted. Elemental techniques may have great potential for resolving fisheries problems and identifying broader scale effects of environmental degradation.