Effects of Macroalgal Habitats on the Community and Population Structure of Temperate Reef Fishes

Two families of brown macroalgae that occur in sympatry dominate temperate subtidal rocky coasts: the Laminareales, and the Fucales. Both of these families are habitat-forming species for a wide variety of invertebrates and fishes. Variation in the presence, density, and composition of brown macroalgae can have large influences on the evolution and ecology of associated organisms. Here, using a series of observational and experimental studies, I evaluated the effects of heterogeneity in the composition of brown macroalgal stands at the population and community levels for reef fishes. A central ecological challenge is the description of patterns that occur at local scales, and how these are manifested at larger ones. I conducted further sampling across a set of sites nested within locations over three regions, Juan Fernandez Islands (Chile), Northern New Zealand, and Tasmania (Australia), to evaluate patterns of variation in the diversity and composition of fish assemblages. Specifically, I explored spatial variation in fish assemblages as a function of rocky reef habitats (dominated by brown-macroalgae) and other sources of variation (abiotic and biotic factors) that potentially mediate the relationship between fishes and reef habitats. Analyses suggest that spatial variation in diversity (e.g., species and trophic) may be explained by spatial variation in depth, temperature, and composition of macroalgal habitats. At each location, only 2-3 families dominated the composition of fish assemblages, but species identities varied among locations. In a subsequent study, I assessed the fish-habitat associations from sites within the Juan Fernandez Islands, an isolated eastern Pacific Island that lack large brown macroalgae. I found that, despite the close proximity of these Islands to the South American continent, fish assemblages were mostly composed of endemic representatives from families that dominate the fish assemblages in New Zealand and Australia. Spatial variation in depth and temperature did not contribute to the observed variation in fish abundance. Instead, I found that benthic habitat-forming species (particularly foliose brown macroalgae) appeared to limit the abundance of some reef fishes. These results suggest that a mixture of large-scale (e.g., stochastic recruitment) and small-scale processes (i.e., relating to habitat heterogeneity) influence the diversity, composition and abundance of fish assemblages. Subsequently, I evaluated relationships between reef fishes and macroalgae composition across multiple sites, surveyed repeatedly over four seasons. I found that fishes were associated with different components of heterogeneity in macroalgal habitats, potentially indicating interspecific partitioning of resources that may arise from differential feeding habits and sizesusceptibility to predation. Seasonal variation in the fish-habitat associations was detected, and site differences in macroalgal composition explained significant variation in the local diversity of fishes. Using a series of small-scale lab and field-based manipulative experiments, I determined the demographic and behavioural responses of reefassociated fishes to heterogeneity in the composition of brown macroalgal habitats. I found that (i) different fish species distinguished between monospecific macroalgae stands (macroalgal identity affected the abundance of 7 of 15 reef fish species); (ii) there is within-species variation in the response of fishes to macroalgal composition (suggesting ontogenetic habitat shifts); and (iii) the abundance of 5 of 7 reef fish species, and the overall structure of the local fish assemblage, varied with the composition of mixed-species macroalgal stands. Lastly, I evaluated the potential for fishes to provision demographic feedbacks to macroalgae. Specifically, I conducted a mesocosm experiment to evaluate the effects of fishes on grazing amphipods, and therefore, the potential indirect-effects of fishes on large-brown macroalgae. I found that only one of the two fish species studied reduced grazer abundance. Although the second fish species did not consume grazing amphipods, its presence altered amphipod behaviour to significantly reduce grazing efficiency on the macroalgal-host. This study illustrates how density and trait-mediated indirect interactions can have similar effects on primary producers. Overall, my observational and experimental components of this thesis emphasize the influence of heterogeneity in macroalgal structures on the breadth of habitat use for reef fishes at multiple locations. I found strong behaviourally mediated linkages between the abundance of reef fishes and composition of macroalgal stand. I also provide some evidence that mutualistic relationships may exist between kelp and associated fishes

A New Species of Chromis (Teleostei: Pomacentridae) from Mesophotic Coral Ecosystems of Rapa Nui (Easter Island) and Salas y Gomez, Chile

A new species of Chromis (Teleostei: Pomacentridae) is described from three specimens collected at 90 m depth in a mesophotic coral ecosystem at Rapa Nui, Chile. Chromis mamatapara, new species, can be distinguished from its congeners by the following combination of characters: dorsal-fin rays XIV,13–14; pectoral-fin rays 18–19, third from top of fin longest; tubed lateral-line scales 18; total gill rakers on first arch 30–32; vertebrae 11þ15; and by coloration of living specimens, especially the presence of a single, pronounced, white spot, roughly the same diameter as the orbit, located where the posterior base of the dorsal fin intersects the caudal peduncle. The most similar DNA barcode (mitochondrial COI gene), among those available, is Chromis tingting from Japan (3.5% uncorrected divergence); however, C. mamatapara, new species, also superficially resembles other species for which sequences are unavailable for comparisons, including C. okamurai from Japan and C. struhsakeri from Hawaii. Due to the high geographic isolation and consequently high endemism in the Rapa Nui region, we believe that C. mamatapara, new species, is endemic to mesophotic ecosystems of Rapa Nui, Isla Salas y Gomez, and nearby seamounts, a discovery that contributes to the high endemism of the region and thus the need for conservation efforts

The contribution of macroalgae-associated fishes to small-scale tropical reef fisheries

Macroalgae-dominated reefs are a prominent habitat in tropical seascapes that support a diversity of fishes, including fishery target species. To what extent, then, do macroalgal habitats contribute to small-scale tropical reef fisheries? To address this question we: (1) Quantified the macroalgae-associated fish component in catches from 133 small-scale fisheries, (2) Compared life-history traits relevant to fishing (e.g. growth, longevity) in macroalgal and coral-associated fishes, (3) Examined how macroalgae-associated species can influence catch diversity, trophic level and vulnerability and (4) Explored how tropical fisheries change with the expansion of macroalgal habitats using a case study of fishery-independent data for Seychelles. Fish that utilised macroalgal habitats comprise 24% of the catch, but very few fished species relied entirely on macroalgal or coral habitats post-settlement. Macroalgal and coral-associated fishes had similar life-history traits, although vulnerability to fishing declined with increasing contribution of macroalgae association to the catch, whilst mean trophic level and diversity peaked when macroalgal-associated fish accounted for 20%-30% of catches. The Seychelles case study revealed similar total fish biomass on macroalgal and coral reefs, although the biomass of primary target species increased as macroalgae cover expanded. Our findings reinforce that multiple habitat types are needed to support tropical fishery stability and sustainability. Whilst coral habitats have been the focus of tropical fisheries management, we show the potential for macroalgae-associated fish to support catch size and diversity in ways that reduce vulnerability to overfishing. This is pertinent to seascapes where repeated disturbances are facilitating the replacement of coral reef with macroalgal habitats

Effects of Macroalgal Habitats on the Community and Population Structure of Temperate Reef Fishes

Two families of brown macroalgae that occur in sympatry dominate temperate subtidal rocky coasts: the Laminareales, and the Fucales. Both of these families are habitat-forming species for a wide variety of invertebrates and fishes. Variation in the presence, density, and composition of brown macroalgae can have large influences on the evolution and ecology of associated organisms. Here, using a series of observational and experimental studies, I evaluated the effects of heterogeneity in the composition of brown macroalgal stands at the population and community levels for reef fishes. A central ecological challenge is the description of patterns that occur at local scales, and how these are manifested at larger ones. I conducted further sampling across a set of sites nested within locations over three regions, Juan Fernandez Islands (Chile), Northern New Zealand, and Tasmania (Australia), to evaluate patterns of variation in the diversity and composition of fish assemblages. Specifically, I explored spatial variation in fish assemblages as a function of rocky reef habitats (dominated by brown-macroalgae) and other sources of variation (abiotic and biotic factors) that potentially mediate the relationship between fishes and reef habitats. Analyses suggest that spatial variation in diversity (e.g., species and trophic) may be explained by spatial variation in depth, temperature, and composition of macroalgal habitats. At each location, only 2-3 families dominated the composition of fish assemblages, but species identities varied among locations. In a subsequent study, I assessed the fish-habitat associations from sites within the Juan Fernandez Islands, an isolated eastern Pacific Island that lack large brown macroalgae. I found that, despite the close proximity of these Islands to the South American continent, fish assemblages were mostly composed of endemic representatives from families that dominate the fish assemblages in New Zealand and Australia. Spatial variation in depth and temperature did not contribute to the observed variation in fish abundance. Instead, I found that benthic habitat-forming species (particularly foliose brown macroalgae) appeared to limit the abundance of some reef fishes. These results suggest that a mixture of large-scale (e.g., stochastic recruitment) and small-scale processes (i.e., relating to habitat heterogeneity) influence the diversity, composition and abundance of fish assemblages. Subsequently, I evaluated relationships between reef fishes and macroalgae composition across multiple sites, surveyed repeatedly over four seasons. I found that fishes were associated with different components of heterogeneity in macroalgal habitats, potentially indicating interspecific partitioning of resources that may arise from differential feeding habits and sizesusceptibility to predation. Seasonal variation in the fish-habitat associations was detected, and site differences in macroalgal composition explained significant variation in the local diversity of fishes. Using a series of small-scale lab and field-based manipulative experiments, I determined the demographic and behavioural responses of reefassociated fishes to heterogeneity in the composition of brown macroalgal habitats. I found that (i) different fish species distinguished between monospecific macroalgae stands (macroalgal identity affected the abundance of 7 of 15 reef fish species); (ii) there is within-species variation in the response of fishes to macroalgal composition (suggesting ontogenetic habitat shifts); and (iii) the abundance of 5 of 7 reef fish species, and the overall structure of the local fish assemblage, varied with the composition of mixed-species macroalgal stands. Lastly, I evaluated the potential for fishes to provision demographic feedbacks to macroalgae. Specifically, I conducted a mesocosm experiment to evaluate the effects of fishes on grazing amphipods, and therefore, the potential indirect-effects of fishes on large-brown macroalgae. I found that only one of the two fish species studied reduced grazer abundance. Although the second fish species did not consume grazing amphipods, its presence altered amphipod behaviour to significantly reduce grazing efficiency on the macroalgal-host. This study illustrates how density and trait-mediated indirect interactions can have similar effects on primary producers. Overall, my observational and experimental components of this thesis emphasize the influence of heterogeneity in macroalgal structures on the breadth of habitat use for reef fishes at multiple locations. I found strong behaviourally mediated linkages between the abundance of reef fishes and composition of macroalgal stand. I also provide some evidence that mutualistic relationships may exist between kelp and associated fishes

JEMBE 50994_Data

The entire file is the data associated to the manuscript. The first sheet (Fish and Kelp Abundance) is the census data from two different sampling seasons in 4 sites (transects 50 m long). The second sheet is size over algae in which was counted the size of fish along with different kelp habitat use (in holdfast, baldes or outside). The third sheet is the epiphyte presence/absence from the digested tissue by herbivorous fish. The fourth sheet is the sporophytes count from digested and undigested tissue. The fish and last sheet is the data presented in the supplementary information

Applying an ecosystem service approach to unravel links between ecosystems and society in the coast of central Chile

Ecosystem-based management implies understanding feedbacks between ecosystems and society. Such understanding can be approached with the Drivers–Pressures–State change–Impacts–Response framework (DPSIR), incorporating stakeholders\u27 preferences for ecosystem services to assess impacts on society. This framework was adapted to six locations in the central coast of Chile, where artisanal fisheries coexist with an increasing influx of tourists, and a set of fisheries management areas alternate with open access areas and a no-take Marine Protected Area (MPA). The ecosystem services in the study area were quantified using biomass and species richness in intertidal and subtidal areas as biological indicators. The demand for ecosystem services was elicited by interviews to the principal groups of users. Our results evidenced decreasing landings and a negative perception of fishermen on temporal trends of catches. The occurrence of recreational fishing was negligible, although the consumption of seafood by tourists was relatively high. Nevertheless, the consumption of organisms associated to the study system was low, which could be linked, amongst other factors, to decreasing catches. The comparison of biological indicators between management regimens provided variable results, but a positive effect of management areas and the MPA on some of the metrics was observed. The prioritising of ecosystem attributes by tourists was highly homogenous across the six locations, with “scenic beauty” consistently selected as the preferred attribute, followed by “diversity”. The DPSIR framework illustrated the complex interactions existing in these locations, with weak linkages between society\u27s priorities, existing management objectives and the state of biological communities. Overall, this work improved our knowledge on relations between components of coastal areas in central Chile, of paramount importance to advance towards an ecosystem-based management in the area