Habitat structural complexity is a key factor shaping marine communities. However, accurate metho... more Habitat structural complexity is a key factor shaping marine communities. However, accurate methods for quantifying structural complexity underwater are currently lacking. Loss of structural complexity is linked to ecosystem declines in biodiversity and resilience. We developed new methods using underwater stereo-imagery spanning four years (2010-2013) to reconstruct 3D models of coral reef areas, and quantified both structural complexity at two spatial resolutions (2.5 and 25 cm) and benthic community composition to characterise changes after an unprecedented thermal anomaly on the west coast of Australia in 2011. Structural complexity increased at both resolutions in quadrats (4 m(2) ) that bleached, but not those that did not bleach. Changes in complexity were driven by species-specific responses to warming, highlighting the importance of identifying small-scale dynamics to disentangle ecological responses to disturbance. We demonstrate an effective, repeatable method for quantifying the relationship among community composition, structural complexity and ocean warming, improving predictions of the response of marine ecosystems to environmental change. This article is protected by copyright. All rights reserved.
ABSTRACT Since the 1970s, populations of the Australian White Ibis (Threskiornis molucca) have dr... more ABSTRACT Since the 1970s, populations of the Australian White Ibis (Threskiornis molucca) have dramatically increased in many Australian urban centres. Managers of ibis are currently focusing on limiting this bird’s reproductive success in order to reduce population sizes or at least halt further increases in urban areas. Here we use data on nesting success and survival for three populations of ibis around greater Sydney to develop an age-structured population model. The estimated growth rate for all populations combined was about 1.5 % per year and for individual sites were more variable at −1, −7, and 9 %. For all populations, growth rates were most sensitive (based on elasticity analyses) to the survival of adults and least sensitive to fecundity, especially of 3 year olds. Further exploration of the importance of fecundity rates, which are relatively poorly known for these populations, suggests that rates of <0.4 fledglings per nest per year is very likely to lead to a population decline (λ less than lower bound of 95 % CI). Conversely, positive population growth is nearly assured (λ greater than upper bound of 95 % CI) for fecundities of >0.7 fledgling per nest per year. The results suggest that ibis from other locations (probably their traditional breeding areas in inland Australia) have immigrated into urban environments as estimated growth rates cannot account for current population sizes. Management strategies must take these findings into account and also consider that ibis are declining in their traditional habitats to avoid exacerbating their decline at a regional scale.
ABSTRACT Offshore islands are often preferentially selected for marine sanctuaries (no take areas... more ABSTRACT Offshore islands are often preferentially selected for marine sanctuaries (no take areas) over inshore reefs on populated coasts because they support relatively unique marine communities and critical habitat for protected marine wildlife and are often less accessible to people. To evaluate whether marine sanctuaries around an offshore island with a large fur seal colony performed differently to inshore areas, we compared fish assemblages at 36 reef sites within marine sanctuaries and fished areas around an offshore Island and within inshore areas of the Batemans Marine Park in temperate southeastern Australia. In each site, we quantified fish assemblage structure using 3–4 replicate baited remote underwater video deployments. We also evaluated the role of fur seal activity, sea surface temperature and wave exposure in structuring fish assemblages on reefs inside and outside marine sanctuaries. Of these variables, only fur seal activity on shallow island reefs (∼10 m deep) was significantly related to fish assemblage structure with a negative relationship to fish richness and abundance. The fish assemblages in marine sanctuaries differed significantly from fished areas on deep reefs around Montague Island (30–40 m deep) and on shallow inshore reefs (∼10 m deep), with 119% and 45% more fish and 49% and 19% more species of fishes in marine sanctuaries in the two areas, respectively. There were also significantly more kyphosids, labrids, southern maori wrasse (Ophthalmolepis lineolatus) and silver sweep (Scorpis lineolata) in marine sanctuaries than in fished areas on deep reefs around Montague Island. Although there was, on average, 34% more fish on shallow reefs inside than outside marine sanctuaries around Montague Island, there were no significant differences in fish assemblages when the influence of fur seal activity was taken into account. Given that fur seals numbers are increasing and they eat reef fishes, marine sanctuaries on shallow reefs adjacent to seal colonies may not achieve some of the positive benefits associated with increased fish biomass (e.g. increased kelp cover) to same level as sanctuaries more distantly located. We suggest, therefore, that careful consideration of long-term conservation goals (e.g. conservation of fur seals or local enhancement of fish diversity) is needed before preferentially locating marine sanctuaries adjacent to fur seal colonies.
Proceedings. Biological sciences / The Royal Society, Jan 22, 2014
Climate-driven changes in biotic interactions can profoundly alter ecological communities, partic... more 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 sim...
Habitat structural complexity is a key factor shaping marine communities. However, accurate metho... more Habitat structural complexity is a key factor shaping marine communities. However, accurate methods for quantifying structural complexity underwater are currently lacking. Loss of structural complexity is linked to ecosystem declines in biodiversity and resilience. We developed new methods using underwater stereo-imagery spanning four years (2010-2013) to reconstruct 3D models of coral reef areas, and quantified both structural complexity at two spatial resolutions (2.5 and 25 cm) and benthic community composition to characterise changes after an unprecedented thermal anomaly on the west coast of Australia in 2011. Structural complexity increased at both resolutions in quadrats (4 m(2) ) that bleached, but not those that did not bleach. Changes in complexity were driven by species-specific responses to warming, highlighting the importance of identifying small-scale dynamics to disentangle ecological responses to disturbance. We demonstrate an effective, repeatable method for quantifying the relationship among community composition, structural complexity and ocean warming, improving predictions of the response of marine ecosystems to environmental change. This article is protected by copyright. All rights reserved.
ABSTRACT Since the 1970s, populations of the Australian White Ibis (Threskiornis molucca) have dr... more ABSTRACT Since the 1970s, populations of the Australian White Ibis (Threskiornis molucca) have dramatically increased in many Australian urban centres. Managers of ibis are currently focusing on limiting this bird’s reproductive success in order to reduce population sizes or at least halt further increases in urban areas. Here we use data on nesting success and survival for three populations of ibis around greater Sydney to develop an age-structured population model. The estimated growth rate for all populations combined was about 1.5 % per year and for individual sites were more variable at −1, −7, and 9 %. For all populations, growth rates were most sensitive (based on elasticity analyses) to the survival of adults and least sensitive to fecundity, especially of 3 year olds. Further exploration of the importance of fecundity rates, which are relatively poorly known for these populations, suggests that rates of <0.4 fledglings per nest per year is very likely to lead to a population decline (λ less than lower bound of 95 % CI). Conversely, positive population growth is nearly assured (λ greater than upper bound of 95 % CI) for fecundities of >0.7 fledgling per nest per year. The results suggest that ibis from other locations (probably their traditional breeding areas in inland Australia) have immigrated into urban environments as estimated growth rates cannot account for current population sizes. Management strategies must take these findings into account and also consider that ibis are declining in their traditional habitats to avoid exacerbating their decline at a regional scale.
ABSTRACT Offshore islands are often preferentially selected for marine sanctuaries (no take areas... more ABSTRACT Offshore islands are often preferentially selected for marine sanctuaries (no take areas) over inshore reefs on populated coasts because they support relatively unique marine communities and critical habitat for protected marine wildlife and are often less accessible to people. To evaluate whether marine sanctuaries around an offshore island with a large fur seal colony performed differently to inshore areas, we compared fish assemblages at 36 reef sites within marine sanctuaries and fished areas around an offshore Island and within inshore areas of the Batemans Marine Park in temperate southeastern Australia. In each site, we quantified fish assemblage structure using 3–4 replicate baited remote underwater video deployments. We also evaluated the role of fur seal activity, sea surface temperature and wave exposure in structuring fish assemblages on reefs inside and outside marine sanctuaries. Of these variables, only fur seal activity on shallow island reefs (∼10 m deep) was significantly related to fish assemblage structure with a negative relationship to fish richness and abundance. The fish assemblages in marine sanctuaries differed significantly from fished areas on deep reefs around Montague Island (30–40 m deep) and on shallow inshore reefs (∼10 m deep), with 119% and 45% more fish and 49% and 19% more species of fishes in marine sanctuaries in the two areas, respectively. There were also significantly more kyphosids, labrids, southern maori wrasse (Ophthalmolepis lineolatus) and silver sweep (Scorpis lineolata) in marine sanctuaries than in fished areas on deep reefs around Montague Island. Although there was, on average, 34% more fish on shallow reefs inside than outside marine sanctuaries around Montague Island, there were no significant differences in fish assemblages when the influence of fur seal activity was taken into account. Given that fur seals numbers are increasing and they eat reef fishes, marine sanctuaries on shallow reefs adjacent to seal colonies may not achieve some of the positive benefits associated with increased fish biomass (e.g. increased kelp cover) to same level as sanctuaries more distantly located. We suggest, therefore, that careful consideration of long-term conservation goals (e.g. conservation of fur seals or local enhancement of fish diversity) is needed before preferentially locating marine sanctuaries adjacent to fur seal colonies.
Proceedings. Biological sciences / The Royal Society, Jan 22, 2014
Climate-driven changes in biotic interactions can profoundly alter ecological communities, partic... more 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 sim...
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