The Reef Coral Coscinaraea marshae Is Not a High-Latitude Endemic

The ‘temperate’ reef coral Coscinaraea marshae Wells, 1962, is reported from Siberut Island (West Sumatra, Indonesia), a near-equatorial locality, 3375 km away from its northernmost range limit in Western Australia, where it is considered a high-latitude endemic. This tropical record suggests that the latitudinal distributions of poorly recorded reef corals may not yet be fully understood, which might be relevant in the light of progressing seawater warming.

Environmental and Life-history Factors Influencing Juvenile Demography of a Temperate Reef Fish

<p>Realistic population models and effective conservation strategies require a thorough understanding of the processes that drive variation in individual growth and survival, particularly within life stages that are subject to high mortality. For fragmented marine populations it is also important to consider how processes driving variation performance may vary through space and time. In this study I assess the interaction of two primary factors driving juvenile demography: benthic habitat composition and larval history traits, in a temperate reef fish, Forsterygion lapillum (the common triplefin). It is well understood that juveniles of many marine organisms are closely associated with structured nearshore habitats as they provide resources (refuge and food sources) that are critical for juvenile growth and/or survival. Nursery habitats are often assessed using measures of fitness of juveniles inhabiting them (e.g. rates of growth). However individual fitness measures may not only be indicative of conditions experienced in the benthic phase, but also an individual's prior history. Recent evidence suggests that variation in larval traits at settlement (e.g., size and age at settlement, larval growth rate) can impact on subsequent ecological performance (e.g., feeding ability and/or predator avoidance) and therefore influence subsequent fitness (i.e. rates of growth and/or probabilities of survival). I used otolith microstructure to assess separate and joint effects of habitat composition and larval traits on the growth of young F. lapillum. Both macroalgal composition of habitat patches and larval traits affected juvenile growth rates, and results suggested that habitat composition may have the potential to mediate fitness-related advantages that may accrue to certain individuals as a result of paternal effects and/or larval dispersal history. Quantifying spatio-temporal variability in the post-settlement fitness of Individuals with that differ in larval traits is essential for effective spatial management of marine populations. I further explore the joint effects of macroalgal composition and larval traits, within the context of additional spatial and temporal environmental variation. Results provide direct evidence that habitat can mediate the strength of carryover effects, but that the impact of habitat was variable between local populations and settlement events through time. In chapter 4 of my thesis, I focus on how small-scale variation in macroalgal composition within a nursery habitat (while controlling for individual variation) can affect the strength of density dependent growth and survival rates of F. lapillum. Density-dependent survival is evident during the first 30 days after settlement, and the strength of density dependence varied as a function of macroalgal composition. Resulting variation in estimates of nursery value (i.e., the number of late-stage juveniles produced per area unit of habitat) highlight the importance of incorporating local scale variation in juvenile demography into assessments of nursery habitat. Lastly, I assess a potential strategy of fishes to persist in a wide range of benthic environments. The ability to adjust traits (i.e., phenotypic plasticity) may allow organisms that encounter a range of unpredictable environmental conditions to maximise fitness within a single generation. In chapter 5 I explore patterns of variation in morphology of juvenile F. lapillum from two different subpopulations and from different macroalgal habitats. I evaluate possible evidence for constraints on morphological variation arising from variation in growth rate prior to and following settlement. Results suggest that for organisms with complex life cycles, variation in growth rates experienced during dispersal may constrain plasticity in later stages.</p>

Environmental and Life-history Factors Influencing Juvenile Demography of a Temperate Reef Fish

<p>Realistic population models and effective conservation strategies require a thorough understanding of the processes that drive variation in individual growth and survival, particularly within life stages that are subject to high mortality. For fragmented marine populations it is also important to consider how processes driving variation performance may vary through space and time. In this study I assess the interaction of two primary factors driving juvenile demography: benthic habitat composition and larval history traits, in a temperate reef fish, Forsterygion lapillum (the common triplefin). It is well understood that juveniles of many marine organisms are closely associated with structured nearshore habitats as they provide resources (refuge and food sources) that are critical for juvenile growth and/or survival. Nursery habitats are often assessed using measures of fitness of juveniles inhabiting them (e.g. rates of growth). However individual fitness measures may not only be indicative of conditions experienced in the benthic phase, but also an individual's prior history. Recent evidence suggests that variation in larval traits at settlement (e.g., size and age at settlement, larval growth rate) can impact on subsequent ecological performance (e.g., feeding ability and/or predator avoidance) and therefore influence subsequent fitness (i.e. rates of growth and/or probabilities of survival). I used otolith microstructure to assess separate and joint effects of habitat composition and larval traits on the growth of young F. lapillum. Both macroalgal composition of habitat patches and larval traits affected juvenile growth rates, and results suggested that habitat composition may have the potential to mediate fitness-related advantages that may accrue to certain individuals as a result of paternal effects and/or larval dispersal history. Quantifying spatio-temporal variability in the post-settlement fitness of Individuals with that differ in larval traits is essential for effective spatial management of marine populations. I further explore the joint effects of macroalgal composition and larval traits, within the context of additional spatial and temporal environmental variation. Results provide direct evidence that habitat can mediate the strength of carryover effects, but that the impact of habitat was variable between local populations and settlement events through time. In chapter 4 of my thesis, I focus on how small-scale variation in macroalgal composition within a nursery habitat (while controlling for individual variation) can affect the strength of density dependent growth and survival rates of F. lapillum. Density-dependent survival is evident during the first 30 days after settlement, and the strength of density dependence varied as a function of macroalgal composition. Resulting variation in estimates of nursery value (i.e., the number of late-stage juveniles produced per area unit of habitat) highlight the importance of incorporating local scale variation in juvenile demography into assessments of nursery habitat. Lastly, I assess a potential strategy of fishes to persist in a wide range of benthic environments. The ability to adjust traits (i.e., phenotypic plasticity) may allow organisms that encounter a range of unpredictable environmental conditions to maximise fitness within a single generation. In chapter 5 I explore patterns of variation in morphology of juvenile F. lapillum from two different subpopulations and from different macroalgal habitats. I evaluate possible evidence for constraints on morphological variation arising from variation in growth rate prior to and following settlement. Results suggest that for organisms with complex life cycles, variation in growth rates experienced during dispersal may constrain plasticity in later stages.</p>

Rewilding of Protected Areas Enhances Resilience of Marine Ecosystems to Extreme Climatic Events

Marine protected areas (MPAs) are employed as tools to manage human impacts, especially fishing pressure. By excluding the most destructive activities MPAs can rewild degraded areas of seabed habitat. The potential for MPAs to increase ecosystem resilience from storms is, however, not understood, nor how such events impact seabed habitats. Extreme storm disturbance impact was studied in Lyme Bay MPA, Southwest United Kingdom, where the 2008 exclusion of bottom-towed fishing from the whole site allowed recovery of degraded temperate reef assemblages to a more complex community. Severe storm impacts in 2013–2014 resulted in major damage to the seabed so that assemblages in the MPA were more similar to sites where fishing continued than at any point since the designation of the MPA; the communities were not dominated by species resistant to physical disturbance. Nevertheless, annual surveys since 2014 have demonstrated that the initial recovery of MPA assemblages was much quicker than that seen following the cessation of chronic towed fishing impact in 2008. Likewise, General Additive Mixed Effect Models (GAMMs) showed that inside the MPA increases in diversity metrics post-Storm were greater and more consistent over time than post-Bottom-Towed Fishing. As extreme events are likely to become more common with climate change, wave exposure observations indicated that 29% of coastal reef MPAs around the United Kingdom may be exposed to comparable wave climate extremes, and may be similarly impacted. This paper therefore provides an insight into the likely extent and magnitude of ecological responses of seabed ecosystems to future extreme disturbance events.

Tropicalization of temperate reef fish communities depends on urchin herbivory and thermal response diversity

Global declines in structurally complex habitats are reshaping both land and seascapes in directions that affect biological communities’ responses to warming. Here, we test whether widespread loss of kelp habitats through sea urchin overgrazing systematically changes warming sensitivity of fish communities. Community thermal affinity shifts related to habitat were assessed by simulating and comparing fish communities from 2,271 surveys across 15 ecoregions. We find that fishes in kelp and urchin barrens differ in realized thermal affinities and range sizes, but only in regions where species pools have high variability in species’ thermal affinities. Barrens on warm-temperate reefs host relatively more warm-affinity fish species than neighbouring kelp beds, highlighting acceleration of tropicalization processes facilitated by urchin herbivory. By contrast, proportionally more cool-affinity fishes colonize barrens at high temperate latitudes, contributing to community lags with ocean warming in these regions. Our findings implicate urchins as drivers of ecological change, in part by affecting biological resilience to warming.

Optimal fishing effort benefits fisheries and conservation

The ecosystem effects of all commercial fishing methods need to be fully understood in order to manage our marine environments more effectively. The impacts associated with the most damaging mobile fishing methods are well documented leading to such methods being removed from some partially protected areas. In contrast, the impacts on the ecosystem from static fishing methods, such as pot fishing, are less well understood. Despite commercial pot fishing increasing within the UK, there are very few long term studies (> 1 year) that consider the effects of commercial pot fishing on temperate marine ecosystems. Here we present the results from a controlled field experiment where areas of temperate reef were exposed to a pot fishing density gradient over 4 years within a Marine Protected Area (MPA), simulating scenarios both above and below current levels of pot fishing effort. After 4 years we demonstrate for the first time negative effects associated with high levels of pot fishing effort both on reef building epibiota and commercially targeted species, contrary to existing evidence. Based on this new evidence we quantify a threshold for sustainable pot fishing demonstrating a significant step towards developing well-managed pot fisheries within partially protected temperate MPAs.