Openness of Fish Habitat Matters: Lake Pelagic Fish Community Starts Very Close to the Shore

Fish communities differ significantly between the littoral and the pelagic habitats. This paper attempts to define the shift in communities between the two habitats based on the European standard gillnet catch. We sampled the benthic and pelagic habitats from shore to shore in Lake Most and Římov Reservoir (Czech Republic). The 3 m deep pelagic nets were spanned across the water body at equal distances from two boundary points, where the depth was 3.5 m. The benthic community contained more fish, more species, and smaller individuals. The mild sloped littoral with a soft bottom attracted more fish than the sloping bank with a hard bottom and less benthos and large Daphnia. The catch of the pelagic nets was dominated by eurytopic fish—rudd (Scardinius erythrophthalmus) and roach (Rutilus rutilus) in Most and bleak (Alburnus alburnus) in Římov. With the exception of one case where overgrown macrophytes extended the structured habitat, the largest shift from the benthic to the pelagic community was observed only in the first pelagic gillnet above the bottom depth of 3.5 m. Open water catches were relatively constant with small signs of decline towards the middle of the lake. The results indicate that the benthic gillnet catch is representative of a very limited area and volume, while most of the volume is dominated by the pelagic community. This has important consequences for the assessment of the community parameters of the whole lake following the European standards for gillnet sampling design.

The Role of Sea-Whip Coral (Leptogorgia sp.) as Habitat of Temperate Near-Shore Fish of Gulf of Mexico Jetties

Many fish species use intercoastal jetties throughout their life cycle to migrate to and from the ocean into bays and estuaries. During migration, fish may encounter rock, algae, sand, sea-grass, and coral. Anecdotal information indicates that some migrating fish of intercoastal jetties preferentially select colonies of gorgonian coral (Leptogorgia spp.) vs. any other habitat when encountering a predator.  Since very little information exists regarding Leptogorgia, we focused our study in determining the importance of such coral as fish habitat.  Stationary field sampling was conducted seasonally to determine the abundance of these coral, the type of migrating fish, and the habitat they associated with.  Mesocosm studies were then conducted to determine whether Leptogorgia habitats are important to fish in the presence or absence of a predator.  Five different habitats were compared (rock, algae, sand, Leptogorgia, and seagrass) and 6 species of fish (sergeant major, pinfish, mangrove snapper, spotfin mojarra, pigfish, and red drum). In the field study component, more than 600 colonies of Leptogorgia were observed and 17 different fish species.  The most commonly observed fish were sergeant major, pinfish, mangrove snapper, and spotfin mojarra, however, sergeant majors were the most abundant species using coral as habitat.  The use of mesocosms showed that all fish species significantly selected for structured habitat over non-structured habitat (e.g. sand), but that the fish commonly called ‘sergeant major’ significantly (ANOVA; p ≤ 0.001) selected for Leptogorgia.

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

<p>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.</p>

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

<p>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.</p>

Morphometric characteristics of mungkus fish (Sicyopterus sp.) from several rivers in Bengkulu Province, Indonesia

Mungkus fish (Sicyopterus sp) is one of the freshwater fish that is caught by many people in Bengkulu Province. The mungkus fish are amphidromous and live in rocky rivers and fast-flowing rivers. This fish has a ventral sucker for sticking to rocks. The aim of this research was to determine the types of mungkus fish that can be found in Bengkulu Province waters based on morphometric characters. The research was conducted on 8 major rivers in 5 districts in Bengkulu Province including Argamakmur, Muko-Muko, Seluma, Manna, and Kaur. Based on the results, showed that the mungkus fish were characterized based on morphometric, there were 3 types of fish including Sicyopterus squamosissimus, Sicyopterus cynocephalus, and Sicyopterus lagocephalus. Mungkus fish found in the northern Bengkulu region tend to be smaller in size, have almost the same color pattern and darker body color than the fish found in the South Bengkulu region. The most common species found in Bengkulu is Sicyopterus squamosissimus. The Sicyopterus lagocephalus species can also only be found in rivers in the South Bengkulu region. The fish morphometric characteristics shows that differences in fish habitat will affect the growth of fish and the existence of living species in nature.