Yohei Nakamura

The tropicalization of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts

Climate-driven changes in biotic interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to ‘barrens’ when temperate urchin grazing increases. Here, we propose a novel phase-shift away from macroalgal dominance caused by tropical herbivores extending their range into temperate regions. We argue that this phase shift is facilitated by poleward-flowing boundary currents that are creating ocean warming hotspots around the globe, enabling the range expansion of tropical species and increasing their grazing rates in temperate areas. Overgrazing of temperate macroalgae by tropical herbivorous fishes has already occurred in Japan and the Mediterranean. Emerging evidence suggests similar phenomena are occurring in other temperate regions, with increasing occurrence of tropical fishes on temperate reefs.

Global human footprint on the linkage between biodiversity and ecosystem functioning in reef fishes.

A global survey of reef fishes shows that the consequences of biodiversity loss are greater than previously anticipated as ecosystem functioning remained unsaturated with the addition of new species. Additionally, reefs worldwide, particularly those most diverse, are highly vulnerable to human impacts that are widespread and likely to worsen due to ongoing coastal overpopulation.

Food habits of fishes in a seagrass bed on a fringing coral reef at Iriomote Island, southern Japan

Abstract To clarify the feeding habits of fishes in tropical seagrass beds on coral reefs, the gut contents of 53 fish species, collected in an Enhauls acoroides-dominated bed at Iriomote Island, southern Japan, were examined. Ontogenetic changes in food preference were recognized in 9 species, including lethrinids, mullids, pomacentrids, labrids, and scarids. Cluster analysis based on dietary overlaps showed that the seagrass fish assemblage comprised seven feeding guilds (small-crustacean, large-crustacean, plant, detritus, hard-shelled mollusc, fish, and planktonic-animal feeders). Of these, small-crustacean feeders were the most abundantly represented. On the other hand, planktonic-animal and hard-shelled mollusc feeders were each represented by only two species. Compared with previous studies on the feeding habits of temperate seagrass fishes, the present fish assemblage was characterized by larger species numbers of detritivores, herbivores, and piscivores and fewer planktonic-animal feeders.

Comparison of invertebrate abundance in a seagrass bed and adjacent coral and sand areas at Amitori Bay, Iriomote Island, Japan

To examine whether or not reef-associated seagrass beds harbor abundant food resources for resident and visiting fishes, the invertebrate density and biomass in a seagrass bed were compared with those in adjacent coral and sand areas at Amitori Bay, Iriomote Island, Japan, in June 2002. The vegetation within the bed was dominated by Enhalus acoroides, the coral area comprising primarily Acropora spp. Epifaunal density was greater on the seagrass than on the corals. whereas biomass was greater on the latter. Tanaids, chironomid larvae, errant polychaetes, and gammaridean amphipods were dominant taxa on the seagrass; larger crustaceans, such as crabs and shrimps, being abundant on the corals. The density of infauna was greatest in the seagrass bed, followed by the coral and sand areas, whereas biomass was greatest in the coral area, followed by the seagrass bed and sand area. Each of the three habitats was dominated by harpacticoid copepods and errant polychaetes, although the density of each taxonomic group differed among the habitats. Important food items of seagrass bed fishes, such as harpacticoid copepods, gammaridean amphipods, errant polychaetes, and tanaids, were abundant in the seagrass bed, the density of each being greater than in the other two habitats.

Habitat use patterns of fishes across the mangrove-seagrass-coral reef seascape at Ishigaki Island, southern Japan

To clarify seascape-scale habitat use patterns of fishes in the Ryukyu Islands (southern Japan), visual censuses were conducted in the mangrove estuary, sand area, seagrass bed, coral rubble area, branching coral area on the reef flat, and tabular coral area on the outer reef slope at Ishigaki Island in August and November 2004, and May, August and November 2005. During the study period a total of 319 species were observed. Species richness and abundance were highest in the branching and tabular coral areas, followed in order by the seagrass bed and mangrove estuary, and coral rubble and sand areas, in each month. Cluster analysis resulted in a clear grouping of assemblage structures by habitat type rather than by census month. SIMPER analysis showed that fish assemblages in the tabular coral area were mainly characterized by Acanthurus nigrofuscus, Pomacentrus lepidogenys, P. philippinus and P. vaiuli, the branching coral area by Chromis viridis and Pomacentrus moluccensis, the coral rubble area by Amblyeleotris steinitzi and Ctenogobiops pomastictus, the seagrass bed by Cheilio inermis, Lethrinus atkinsoni and Stethojulis strigiventer, the sand area by Valenciennea longipinnis, and the mangrove estuary by Gerres oyena, Lutjanus fulvus and Yongeichthys criniger. Moreover, fishes exhibited two habitat use strategies, inhabiting either a single or several specific habitats throughout their benthic life history stages, or having a possible ontogenetic habitat shift from the mangrove estuary or seagrass bed to coral-dominated habitats (e.g., Lethrinus atkinsoni, Lethrinus obsoletus, Lutjanus fulviflamma, Lutjanus fulvus, Lutjanus gibbus, Lutjanus monostigma and Parupeneus barberinus), suggesting that the mangrove estuary and seagrass bed have a nursery function.

Habitat Use by Fishes in Coral Reefs, Seagrass Beds and Mangrove Habitats in the Philippines

Understanding the interconnectivity of organisms among different habitats is a key requirement for generating effective management plans in coastal ecosystems, particularly when determining component habitat structures in marine protected areas. To elucidate the patterns of habitat use by fishes among coral, seagrass, and mangrove habitats, and between natural and transplanted mangroves, visual censuses were conducted semiannually at two sites in the Philippines during September and March 2010–2012. In total, 265 species and 15,930 individuals were recorded. Species richness and abundance of fishes were significantly higher in coral reefs (234 species, 12,306 individuals) than in seagrass (38 species, 1,198 individuals) and mangrove (47 species, 2,426 individuals) habitats. Similarity tests revealed a highly significant difference among the three habitats. Fishes exhibited two different strategies for habitat use, inhabiting either a single (85.6% of recorded species) or several habitats (14.4%). Some fish that utilized multiple habitats, such as Lutjanus monostigma and Parupeneus barberinus, showed possible ontogenetic habitat shifts from mangroves and/or seagrass habitats to coral reefs. Moreover, over 20% of commercial fish species used multiple habitats, highlighting the importance of including different habitat types within marine protected areas to achieve efficient and effective resource management. Neither species richness nor abundance of fishes significantly differed between natural and transplanted mangroves. In addition, 14 fish species were recorded in a 20-year-old transplanted mangrove area, and over 90% of these species used multiple habitats, further demonstrating the key role of transplanted mangroves as a reef fish habitat in this region.

New perspectives on aquarium fish trade

Since the 1990s, the international market for importing aquarium fish is suspicious of stock coming from South-East Asia. Fish catches are still executed with cyanide-based toxic products. In the present paper, the potential of the French Polynesian Islands to develop a marine aquarium fish business with a new approach is explored. Coral reef fish are captured at the larval stage with crest nets, then larvae are reared in aquaria before being put on the world ornamental fish market. This approach offers several advantages: (i) larvae are captured with a passive system placed on the reef crest (crest net) that does not destroy the environment and limits the stress on collected larvae; (ii) larvae are then put into farmed basins that allow them to be controlled sanitarily; and (iii) larvae are weaned at the farm and fed rapidly with artificial food. This method increases survival rates as it eliminates the food acclimatization problem of fish captured at adult stage (main cause of fish mortality in aquaria). Overall, reared larvae will constitute a new product in terms of species, sizes and quality of ornamental fish on the aquarium market.

Tropical Fishes Dominate Temperate Reef Fish Communities within Western Japan

Climate change is resulting in rapid poleward shifts in the geographical distribution of tropical and subtropical fish species. We can expect that such range shifts are likely to be limited by species-specific resource requirements, with temperate rocky reefs potentially lacking a range of settlement substrates or specific dietary components important in structuring the settlement and success of tropical and subtropical fish species. We examined the importance of resource use in structuring the distribution patterns of range shifting tropical and subtropical fishes, comparing this with resident temperate fish species within western Japan (Tosa Bay); the abundance, diversity, size class, functional structure and latitudinal range of reef fishes utilizing both coral reef and adjacent rocky reef habitat were quantified over a 2 year period (2008–2010). This region has undergone rapid poleward expansion of reef-building corals in response to increasing coastal water temperatures, and forms one of the global hotspots for rapid coastal changes. Despite the temperate latitude surveyed (33°N, 133°E) the fish assemblage was both numerically, and in terms of richness, dominated by tropical fishes. Such tropical faunal dominance was apparent within both coral, and rocky reef habitats. The size structure of the assemblage suggested that a relatively large number of tropical species are overwintering within both coral and rocky habitats, with a subset of these species being potentially reproductively active. The relatively high abundance and richness of tropical species with obligate associations with live coral resources (i.e., obligate corallivores) shows that this region holds the most well developed temperate-located tropical fish fauna globally. We argue that future tropicalisation of the fish fauna in western Japan, associated with increasing coral habitat development and reported increasing shifts in coastal water temperatures, may have considerable positive economic impacts to the local tourism industry and bring qualitative changes to both local and regional fisheries resources.

Comparison between community structures of fishes in Enhalus acoroides-and Thalassia hemprichii-dominated seagrass beds on fringing coral reefs in the Ryukyu Islands, Japan

To clarify differences in community structures and habitat utilization patterns of fishes in Enhalus acoroides- and Thalassia hemprichii-dominated seagrass beds on fringing coral reefs, visual censuses were conducted at Iriomote and Ishigaki islands, southern Japan. The numbers of fish species and individuals were significantly higher in the E. acoroides bed than in the T. hemprichii bed, although the 15 most dominant fishes in each seagrass bed were similar. Cluster and ordination analyses based on the number of individuals of each fish species also demonstrated that fish community structures were similar in the two seagrass beds. Species and individual numbers of coral reef fishes which utilized the seagrass beds numbered less than about 15% of whole coral reef fish numbers, although they comprised about half of the seagrass bed fishes. Of the 15 most dominant species, 5 occurred only in the two seagrass beds, including seagrass feeders. Ten other species were reef species, their habitat utilization patterns not differing greatly between the two seagrass beds. Some reef species, such as Lethrinus atkinsoni and L. obsoletus, showed ontogenetic habitat shifts with growth, from the seagrass beds to the coral areas. These results indicate that community structures and habitat utilization patterns of fishes were similar between E. acoroides- and T. hemprichii-dominated seagrass beds, whereas many coral reef fishes hardly utilized the seagrass beds.

Relationship between pelagic larval duration and abundance of tropical fishes on temperate coasts of Japan

The influence of pelagic larval duration (PLD) and egg type dispersal capabilities of 35 demersal and pelagic-spawning tropical fish species is examined in relation to their abundance on the temperate coasts of Japan. The PLDs of pelagic spawners were significantly longer than those of demersal spawners, and a high occurrence of pelagic spawners on the temperate coasts suggests that these fishes are more easily transported to temperate coasts than demersal spawners. For demersal spawners, the common species on the temperate coasts had significantly longer PLDs than the rare species; this suggests that PLD is a major factor influencing the distribution patterns of tropical demersal spawners on temperate coasts. Moreover, a negative correlation between PLD and the abundance of some species of pelagic and demersal spawners suggests the presence of reproductively active fishes in northern subtropical and even in temperate waters.