Seascape Configuration and Fine-Scale Habitat Complexity Shape Parrotfish Distribution and Function across a Coral Reef Lagoon

Structural complexity spanning fine to broad spatial scales can influence the distribution and activity of key organisms within marine ecosystems. However, the relative importance of hard (e.g., corals) and/or soft (e.g., macroalgae) structural complexity for marine organisms is often unclear. This study shows how both broad-scale (seascape configuration of coral structure) and fine-scale habitat complexity (structure height, number of holes, and presence of macroalgae) can influence the abundance and spatial ecology of reef fish. Underwater visual census of fish, surveys of habitats, remote underwater videos, and behavioral observations by following individual fish were used to quantify fine-scale habitat characteristics (e.g., complexity, coral structure height, macroalgae presence) and the abundance, size structure, and behavior (rates of herbivory, tortuosity ratios and total distance travelled) of abundant parrotfish. Both seascape configuration and macroalgae influenced the patterns of fish abundance and rates of herbivory. However, these relationships varied with trophic groups and ontogenetic stages. Abundance of adult and intermediate-phase parrotfishes was positively influenced by densely aggregated coral structures, whereas juvenile abundance was positively influenced by the presence of macroalgae. Foraging path and bite rates of an abundant parrotfish, Chlorurus spilurus, were not influenced by coral structure configuration or height, but the presence of macroalgae increased the bite rates of all juvenile parrotfish. Our results suggest that a combination of seascape configuration, fine-scale habitat complexity, and microhabitat selectivity influence reef fish community structure and foraging behavior, thus altering herbivory. However, these relationships can differ among functional groups of fish and life-history stages. Information on these fish-habitat interactions is critical for identifying habitats that facilitate ecological functions and ensures the successful management and conservation of essential habitats

Seascape Configuration and Fine-Scale Habitat Complexity Shape Parrotfish Distribution and Function across a Coral Reef Lagoon

Structural complexity spanning fine to broad spatial scales can influence the distribution and activity of key organisms within marine ecosystems. However, the relative importance of hard (e.g., corals) and/or soft (e.g., macroalgae) structural complexity for marine organisms is often unclear. This study shows how both broad-scale (seascape configuration of coral structure) and fine-scale habitat complexity (structure height, number of holes, and presence of macroalgae) can influence the abundance and spatial ecology of reef fish. Underwater visual census of fish, surveys of habitats, remote underwater videos, and behavioral observations by following individual fish were used to quantify fine-scale habitat characteristics (e.g., complexity, coral structure height, macroalgae presence) and the abundance, size structure, and behavior (rates of herbivory, tortuosity ratios and total distance travelled) of abundant parrotfish. Both seascape configuration and macroalgae influenced the patterns of fish abundance and rates of herbivory. However, these relationships varied with trophic groups and ontogenetic stages. Abundance of adult and intermediate-phase parrotfishes was positively influenced by densely aggregated coral structures, whereas juvenile abundance was positively influenced by the presence of macroalgae. Foraging path and bite rates of an abundant parrotfish, Chlorurus spilurus, were not influenced by coral structure configuration or height, but the presence of macroalgae increased the bite rates of all juvenile parrotfish. Our results suggest that a combination of seascape configuration, fine-scale habitat complexity, and microhabitat selectivity influence reef fish community structure and foraging behavior, thus altering herbivory. However, these relationships can differ among functional groups of fish and life-history stages. Information on these fish–habitat interactions is critical for identifying habitats that facilitate ecological functions and ensures the successful management and conservation of essential habitats.This research was funded by the Swedish Research Council (Grant numbers 2015-05848, 2015-01257, E0344801)

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

Ecological Responses of Seascape Heterogeneity

A core aim of landscape ecologists as well as conservation and management practices has been to understand how processes that structure communities vary as a function of landscape context. Landscape heterogeneity (i.e. landscape composition, configuration) and fine-scale habitat characteristics can influence ecological interactions across habitat patches at a range of scales. Therefore, the main objective of this work is to apply a landscape ecology perspective to understand how seascape heterogeneity can influence demographic rates, community patterns, and ecological processes. To accomplish this overall goal, I conducted a literature review on oyster reefs from a seascape ecology perspective (Chapter 1) and I carried out three independent research studies (Chapters 2-4) using observational and experimental approaches. In Chapter 2, I assessed demographic rates of oysters in reefs adjacent to various habitat types in a transition zone. In northeast Florida, the dominant coastal habitat transitions from Smooth Cordgrass (Sporobolus alterniflorus; temperate species) to Black Mangroves (Avicennia germinans; tropical species). These two foundation species may affect the demographic rates of the Eastern Oyster (Crassostrea virginica), another foundation species commonly located adjacent to them. Therefore, I deployed juvenile oysters in cage experiments comprising three levels of predator exposure on (a) oyster reefs bordering Smooth Cordgrass, (b) reefs bordering Black Mangroves, and (c) isolated oyster bars, to quantify survival and growth rates north and south in the Guana Tolomato Matanzas National Estuarine Research Reserve. Additionally, I analyzed three datasets with information on the abundances of oysters, associated organisms, potential predators, and other biotic (e.g., chlorophyll a) and abiotic factors (e.g., salinity, dissolved oxygen) across the seascape. The results of this chapter indicated that neighboring habitats and regional variation in the seascape may influence demographic rates of oysters. Although oyster demographic rates across intertidal zones have been examined in oyster reefs at higher latitudes, far less is known about them at subtropical locations where desiccation stress is expected to be greater due to higher temperature. Furthermore, little is known about oyster demographic rates when in association with a macrophyte intertidal habitat, which may reduce desiccation stress and positively influence oysters at higher intertidal zones. In Chapter 3, I measured demographic rates of oysters along intertidal zones on oyster reefs and on oyster clusters associated to Red Mangrove prop roots in Tampa Bay, Florida. This study addressed: (a) how do demographic rates of the Eastern Oyster vary along intertidal zones (bottom, middle, and top) on oyster reefs and on prop roots and (b) whether the association of oysters with mangroves may reduce desiccation stress, thus positively influencing oysters at higher intertidal zones. I found oysters on prop roots to be at higher densities and had higher survival. Consistent with density and survival, water loss (a proxy for desiccation stress) was lower on the prop roots, suggesting that the mangrove canopy may have provided a positive effect on oysters. This chapter contributes to our understanding of fine-scale zonation patterns on two biogenic habitats that exist in close association. In tropical seascapes, beds of benthic macroalgae occur naturally interspersed within or nearby other habitats, but it is unclear what roles they play to support marine fauna. Even less is known about how the introduction of non-native macroalgal habitats (e.g., macroalgal farms) into tropical seascapes may affect ecological processes that influence ecosystem function and its comparison to seascapes with natural macroalgal beds. To address this knowledge gap, in Chapter 4, I surveyed fish assemblages and deployed macroalgal assays to quantify herbivory within naturally-occurring macroalgal habitats, macroalgal farms, as well as at varying distances in the seascape near Mafia Island, Tanzania. The results showed that macroalgal beds had a higher species richness of fish and lower herbivory, while higher herbivory occurred in farmed seascapes likely to the farms attracting herbivores. This chapter advances our understanding of the effects that alteration of tropical seascapes (due to the introduction of farms) may have on patterns of community assembly and ecological processes. Overall, the findings of this dissertation suggested that neighboring habitat patches can influence demographic characteristics of organisms, but the responses may be contextual upon location in the seascape due to variation in regional factors. Moreover, fine-scale variation in biotic and abiotic factors in intertidal habitats can affect demographic rates of organisms and the presence of other foundation species may influence these patterns. Lastly, seascape alterations can influence patterns of community assembly and ecological processes thus affecting ecosystem structure and function. As seascapes continue to be altered due to climate change (e.g., poleward movement of foundation species) and anthropogenic activities (e.g., farming practices), studies that assess the ecological responses of such changes will improve our understanding on the cascading effects within ecosystems and the services they provide

Population Dynamics of Pinfish in the Eastern Gulf of Mexico (1998-2016)

Forage fishes play an important role in marine ecosystems by transferring energy and nutrients through the food web. The population dynamics of forage species can therefore have cascading effects across multiple trophic levels. Here, we analyzed a 19-year dataset on Pinfish (Lagodon rhomboides) across four eastern Gulf of Mexico estuaries to investigate population dynamics, inter- and intra-annual synchrony, metapopulation portfolio effects, growth, and habitat effects. Young-of-year growth rates did not differ among estuaries. The population dynamics of these four systems were stable in the long-term, but highly dynamic inter-annually. Intra-annual dynamics were stable and predictable despite variation in long-term means. Some estuaries exhibited positive inter-annual synchrony, and all four estuaries were synchronous intra-annually. There was evidence for stronger portfolio effects for the entire four-estuary metapopulation, as well as for the two northern estuaries while the southern estuaries appeared to act as a single population. Submerged aquatic vegetation was by far the most important predictor for both presence and abundance of Pinfish. It is important to understand the factors driving forage fish population fluctuations to better predict ecosystem effects, including those to species of economic and ecological importance. These predictors can be useful for the implementation of ecosystem-based management decisions

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

Canopy‐forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life‐history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta‐analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal‐associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life‐history stage. Major overlap (40%-43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal‐associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal‐associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal‐associated fish and fisheries.Support was provided by The Australian National University (National Institutes Grant—Research School of Biology), WA Department of Biodiversity, Conservation & Attractions, Australian Institute of Marine Science, the Environment Conservation Fund of the Government of Hong Kong SAR (ECF15/2015 to PTYL and PKSL), the Philippine Department of Science and Technology Grants-in-Aid Program (to RAA and AAB), the Australian Research Council (DE130100688 to ASH), the Royal Society (UF140691 fellowship to NAJG), and the Swedish Research Council (2015-01257, E0344801). We thank Sofia Wikström and three anonymous peer reviewers for constructive comments on earlier drafts

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

Canopy-forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life-history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta-analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal-associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life-history stage. Major overlap (40%-43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal-associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal-associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal-associated fish and fisheries

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