Organisms fundamentally have four options in response to a changing environment: tolerate, move, adapt, or die, but what is less clear is how the importance of these options vary across taxa and among realms. I will present research on the relative importance of these mechanisms across marine ectotherms along with comparisons and contrasts with the experience on land. Physiological data and ecological surveys suggest that, in the ocean, organisms have narrow thermal tolerances and that many organisms cannot tolerate much warming in place. However, marine animals are also characterized by extensive dispersal of offspring across wide geographic areas, which favors colonization and range shift as a key mechanism by which they respond to environmental change. Marine species distributions are shifting rapidly and often quite predictably. Finally, large population sizes and extensive dispersal create large standing genetic variation in many marine species that creates the potential for rapid evolution.

Japanese sardine is known to undergo drastic and multi-decadal stock fluctuations. Large catches of Japanese sardine were observed in the 1930s and 1940s as well as in the 1980s. Recent peak was 4.49 million tons recorded in 1988; in contrast, the catch in the 2000s has been <1% of this amount. The drastic fluctuation had a serious impact on Japanese fishery industry.

The fluctuation has been pointed out to be under the influence of the climate change for 30 years. I’ll talk about the recent studies, which show the basis of climate change hypothesis and explain the mechanism of the stock fluctuation. These studies suggest that the Japanese sardine life history and stock fluctuation is strongly linked to a western boundary current, Kuroshio.

Interest of the past studies about fish stock fluctuation was usually to find the primary driver of the stock fluctuation. However, of course a single drive, such as the climate change, cannot explain the stock fluctuation perfectly. Considering the increasing need of stock availability forecast, I introduce other possible drivers for the stock fluctuation. Also, I’ll remark on some related issues; the species replacement between sardine and anchovy, the relationship with other sardine species, and the influence of global warming.

Global and local degradation of coral reefs and macroalgal beds can have ecosystem-wide impacts on biodiversity and ecological functioning. However, recently reported community shifts from temperate macroalgae to tropical corals offer conservation potential for corals at the expense of macroalgae under climate warming. Although such community shifts are sporadically reported across the world, our understanding of the patterns and driving processes behind these shifts is still limited. Here, we reconstruct long-term climate-driven range shifts for 45 species of macroalgae, corals and herbivorous fishes from over 60 years-records, stretching across the Japanese archipelago. We found that tropical corals and herbivorous fishes are expanding into existing temperate Japanese macroalgae communities, which in turn are contracting faster than they are expanding. Further, we present novel evidence that the macroalgal-to-coral shifts are facilitated by ocean warming, aided by the dominant poleward-flowing current system. The contrasting range dynamics for corals and herbivorous fishes suggest that ocean warming is promoting macroalgal-to-coral shifts both directly by increased competition from the expansion of tropical corals into the contracting temperate macroalgae, and indirectly via deforestation by the expansion of tropical herbivorous fish. Beyond individual species’ effects, our results provide novel evidence on the important role of the interaction between climate warming and ocean currents in shaping community-level responses, with concomitant changes to ecosystem structure and functioning.

Estimating population size is a fundamental component of wildlife management and stock assessment. Close-kin mark-recapture (CKMR) is a recently developed method that uses information about relatedness in a sample, made possible by recent advances in genetic methods for kinship determination. The rationale is that the presence of a kinship pair in the sample is analogous to the recapture of a marked individual in the traditional mark-recapture method. Kinship pairs in the sample are less likely to be found in larger populations; thus, the number of kinship pairs may reflect adult abundance.

In this talk, first, I will briefly review the current CKMR method with applications to marine species (southern bluefin tuna and white shark), which relies on parent—offspring (PO) or cross-cohort half-sibling (ccHS) relationships. Second, I will explore the availability of within-cohort half-sibling (wcHS) relationship, which is applicable to semelparous species. The wcHS relationship is strongly affected by family-correlated survivorship in the population thus provides information about the degree of overdispersed reproduction. Third, I will present a new statistics that tests overdispersion in a species offspring number based on PO and wcHS relationships. Taken together, finally, I will discuss the usefulness of analyzing wcHS relationship and conclude that the series of results can greatly widen the scope of the CKMR method.

Marine populations are generally well connected through larval exchange, and juvenile and adult migration. Genetic differentiation and movement scales of marine species can be influenced by various physical factors including geographic distance, topography, and oceanographic features. We postulated that genetic isolation by distance (IBD) patterns and movement scales of marine species vary between different geographic features. Using 30 highly polymorphic microsatellite loci, we estimated the genetic isolation by distance pattern, effective density, and movement scale of a coastal flatfish (Pseudopleuronectes yokohamae) collected along a semi-enclosed Tokyo Bay and semi-enclosed but strong tidal governed Seto inland sea, Japan. F-statistics indicated a clear genetic differentiation between populations collected within and outside Tokyo Bay, while a relatively homogeneous genetic structure of populations along Seto Inland Sea. Genetic IBD patterns showed the slope of correlation was much higher in Tokyo Bay (2.19×10-4) than in Seto Inland Sea (1.19×10−5), indicating higher genetic isolation with increasing distance in the former. The linkage disequilibrium method suggested that average effective densities were 16.09 and 21.85 adults/km in Tokyo Bay and Seto Inland Sea, respectively. Applying these effective densities with isolation by distance theory estimated that the average movement distances were 5.96 km in Tokyo Bay and 21.98 km in Seto Inland Sea. We consider that stronger tidal currents along Seto Inland Sea may contribute to longer dispersal distance of the larvae, eventually leading to the homogeneous genetic structure and larger movement scales of the populations compared to those of the Tokyo Bay populations.

In 2D systems, ecosystem size, or spatial scale, has been considered a general predictor of various ecological properties. An outstanding example is the spatial scaling of metapopulation stability: theory predicts that metapopulation stability should increase with ecosystem size, because larger ecosystems will harbor more diverse subpopulations with more stable aggregate dynamics. However, scale-invariant complexity of ecosystems – an underappreciated, but widespread feature of ecosystems – can also serve as the physical template that underpins diversity of population dynamics in a metapopulation. Here, I combine theory and analyses of a unique long-term dataset to show that a scale-invariant characteristic of fractal river networks, branching complexity, stabilizes watershed metapopulations. Theory predicted that the stabilizing effect of branching complexity can be a consequence of purely stochastic processes. Contrary to current theories developed in 2D systems, metapopulation size had vague effects on metapopulation stability. These theoretical predictions were supported by 18-y observations of fish populations across 31 watersheds. Our cross-watershed comparisons revealed consistent stabilizing effects of branching complexity on metapopulations of very different riverine fishes. A strong association between branching complexity and metapopulation stability is likely to be a pervasive feature of branching networks that strongly affects species persistence.

Management efforts to improve water quality have been made in eutrophic lakes, but the recovery of submerged macrophytes is sometimes interfered by overabundance of water chestnuts, an annual floating-leaved plant. We develop and analyze a spatially-implicit patch occupancy model to understand an underlying mechanism for the dominance of the floating-leaved plant and its effects on lake dynamics. The model assumed that submerged plants, algae and the floating-leaved plant compete for the occupation of habitats at each patch and accumulated organic sludge derived from algal carcass favors the establishment of the floating-leaved plant. The model showed that the occurrence of the floating-leaved plant always increases the likelihood and strength of hysteresis, hampering the restoration of submerged plants. This outcome occurs when the loss rate of organic sludge is low, implying that anthropogenic disturbances such as levee revetment and water level manipulation attenuate the restorability of submerged vegetation. We also found that decreasing nutrient supplies can reduce lake restorability, suggesting the necessity of additional management actions such as removals of overgrowing water chestnuts and accumulated organic sludge. Our results highlight the importance of not only water quality but also bottom surface conditions for better understanding and restoration of eutrophic lakes.