Temperate Reef Communities Research Articles

Effect of marine heatwaves and warming on kelp microbiota influence trophic interactions.

The range-expansion of tropical herbivores due to ocean warming can profoundly alter temperate reef communities by overgrazing the seaweed forests that underpin them. Such ecological interactions may be mediated by changes to seaweed-associated microbiota in response to warming, but empirical evidence demonstrating this is rare. We experimentally simulated ocean warming and marine heatwaves (MHWs) to quantify effects on two dominant temperate seaweed species and their microbiota, as well as grazing by a tropical herbivore. The kelp Ecklonia radiata's microbiota in sustained warming and MHW treatments was enriched with microorganisms associated with seaweed disease and tissue degradation. In contrast, the fucoid Sargassum linearifolium's microbiota was unaffected by temperature. Consumption by the tropical sea-urchin Tripneustes gratilla was greater on Ecklonia where the microbiota had been altered by higher temperatures, while Sargassum's consumption was unaffected. Elemental traits (carbon, nitrogen), chemical defences (phenolics) and tissue bleaching of both seaweeds were generally unaffected by temperature. Effects of warming and MHWs on seaweed holobionts (host plus its microbiota) are likely species-specific. The effect of increased temperature on Ecklonia's microbiota and subsequent increased consumption suggest that changes to kelp microbiota may underpin kelp-herbivore interactions, providing novel insights into potential mechanisms driving change in species' interactions in warming oceans.

Warming signals in temperate reef communities following more than a decade of ecological stability.

Ecosystem structure and function are increasingly threatened by changing climate, with profound effects observed globally in recent decades. Based on standardized visual censuses of reef biodiversity, we describe 27 years of community-level change for fishes, mobile macroinvertebrates and macroalgae in the Tasmanian ocean-warming hotspot. Significant ecological change was observed across 94 reef sites (5-10 m depth range) spanning four coastal regions between three periods (1992-95, 2006-07, 2017-19), which occurred against a background of pronounced sea temperature rise (+0.80°C on average). Overall, fish biomass increased, macroinvertebrate species richness and abundance decreased and macroalgal cover decreased, particularly during the most recent decade. While reef communities were relatively stable and warming was slight between the 1990s and mid-2000s (+0.12°C mean temperature rise), increased abundances of warm affinity fishes and invertebrates accompanied warming during the most recent decade (+0.68°C rise). However, significant rises in the community temperature index (CTI) were only found for fishes, invertebrates and macroalgae in some regions. Coastal warming was associated with increased fish biomass of non-targeted species in fished zones but had little effect on reef communities within marine reserves. Higher abundances of larger fishes and lobsters inside reserves appeared to negate impacts of 'thermophilization'.

On the ecology of Cystophora spp. forests.

Cystophora is the second largest genus of fucoids worldwide and, like many other forest-forming macroalgae, is increasingly threatened by a range of anthropogenic impacts including ocean warming. Yet, limited ecological information is available from the warm portion of their range (SW Western Australia), where severe range contractions are predicted to occur. Here, we provide the first insights on the abundance, diversity, productivity, and stand structure of Cystophora forests in this region. Forests were ubiquitous over more than 800 km of coastline and dominated sheltered and moderately-exposed reefs. Stand biomass and productivity were similar or greater than that of kelp forests in the temperate reef communities examined, suggesting that Cystophora spp. play a similarly important ecological role. The stand structure of Cystophora forests was, however, different than those of kelp forests, with most stands featuring an abundant bank of sub-canopy juveniles and only a few plants forming the canopy layer. Stand productivity followed an opposite seasonal pattern than that of kelps, with maximal growth in late autumn through early winter and net biomass loss in summer. Annually, stands contributed between 2.2 and 5.7 kg · m-2 (fresh biomass) to reef productivity depending on the dominant stand species. We propose that Cystophora forests play an important and unique role in supporting subtidal temperate diversity and productivity throughout temperate Australia, and urge a better understanding of their ecology and responses to anthropogenic threats.

Desalination Discharge Influences the Composition of Reef Invertebrate and Fish Assemblages

Large-scale desalination is used increasingly to address growing freshwater demands and climate uncertainty. Discharge of hypersaline brine from desalination operations has the potential to impact marine ecosystems. Here, we used a 7-year Multiple-Before-After-Control-Impact experiment to test the hypothesis that hypersaline discharge from reverse osmosis desalination alters temperate reef communities. Using replicated, video-based, timed searches at eight sites, we sampled fish and invertebrate assemblages before, during, and after the discharge of hypersaline brine. We found that the composition of fish assemblages was significantly altered out to 55 m while the composition of invertebrate assemblages was altered out to 125 m from the outlet during hypersaline discharge. Fish richness and functional diversity increased around the outlet, while the invertebrate assemblages were no less diverse than those on reference reefs. Differences in faunal assemblages between outlet and reference sites during discharging included changes in the frequency of occurrence of both common and rare reef biota. Overall, we found the influence of hypersaline discharge on temperate reef biota to be spatially localized, with the reefs around the outlet continuing to support rich and diverse faunal communities. In some cases, therefore, the marine environmental consequences of large-scale, well-designed, desalination operations may be appropriately balanced against the positive benefits of improved water security.

Differential vulnerability to climate change yields novel deep-reef communities

The effects of climate-driven ocean change on reef habitat-forming species are diverse1,2 and can be deleterious to the structure and functioning of seafloor communities3–5. Although responses of shallow coral- or seaweed-based reef communities to environmental changes are a focus of ecological research in the coastal zone1,4–6, the ecology of habitat-forming organisms on deeper mesophotic reefs remains poorly known. These reefs are typically highly biodiverse7,8 and productive as a result of massive nutrient recycling9. Based on seafloor imagery obtained from an autonomous underwater vehicle8, we related change in community composition on deep reefs (30–90 m) across a latitudinal gradient (25–45° S) in southeastern Australia to high-resolution environmental and oceanographic data, and predicted future changes using downscaled climate change projections for the 2060s10–12. This region is recognized as a global hotspot for ocean warming13. The models show an overall tropicalization trend in these deep temperate reef communities, but different functional groups associate differentially to environmental drivers and display a diversity of responses to projected ocean change. We predict the emergence of novel deep-reef assemblages by the 2060s that have no counterpart on reefs today, which is likely to underpin shifts in biodiversity and ecosystem functioning. Deep reefs and their inhabitants are diverse, but environmental change, in particular warming, will cause these reefs found along southeastern Australia to tropicalize with different responses across functional groups, resulting in novel communities by the 2060s.

Facilitation of Australia’s southernmost reef-building coral by sea urchin herbivory

Competition for space between corals and macroalgae represents a key threatening process for coral reefs, yet the influence of climate change on this competitive interaction is poorly understood, particularly at the poleward margins of coral distribution. Here we describe the discovery of Australia’s southernmost hermatypic corals and explore novel dynamics facilitating the presence and extent of high-latitude coral communities. Examination of 607 shallow reef sites across temperate Australia revealed hard corals to be negatively associated with increasing kelp bed cover, but positively associated with increasing sea surface temperature, herbivorous fishes, grazing sea urchins, and increasing cover of turf algae, which proliferates in the absence of kelp. However, the nature of these effects varied across different regions of temperate Australia consistent with regional variability in the presence/absence of key functional groups for temperate reefs, such as guilds of subtropical herbivorous fishes and/or prevalence of overgrazing sea urchins. For the southernmost coral communities, in eastern Bass Strait Tasmania, the dominant reef-building coral Plesiastrea versipora was negatively associated with kelp and positively associated with the southward range-extending diadematid sea urchin Centrostephanus rodgersii, which has caused extensive kelp bed overgrazing since first locally reported in 1974. Facilitation of coral establishment was strongest on overgrazed barrens where urchin density was relatively low, but sufficient to maintain the reef kelp-free, while corals were less frequent at high urchin densities and completely absent from barrens colonised by intensively grazing limpets. In contrast to tropical Australian coral reefs and other temperate regions (e.g. Western Australia), assays of herbivory confirmed sea urchin grazing, not herbivorous fishes, as chiefly responsible for kelp consumption within this high-latitude system. Size structure of P. versipora in eastern Bass Strait was dominated by small colonies (~ 20 cm2), suggesting an expanding population at the poleward edge of the species’ range. Nevertheless, colonies up to a maximum area of 500 cm2 were observed, which are likely > 40 yrs old based on growth rates established in warmer waters. This research highlights novel patterns and processes structuring the interface between subtropical and temperate reef communities under climate change and specifically highlights the role of herbivores in releasing corals from competition with kelp under warming ocean regimes.

Biological interactions both facilitate and resist climate-related functional change in temperate reef communities.

Shifts in the abundance and location of species are restructuring life on the Earth, presenting the need to build resilience into our natural systems. Here, we tested if protection from fishing promotes community resilience in temperate reef communities undergoing rapid warming in Tasmania. Regardless of protection status, we detected a signature of warming in the brown macroalgae, invertebrates and fishes, through increases in the local richness and abundance of warm-affinity species. Even so, responses in protected communities diverged from exploited communities. At the local scale, the number of cool-affinity fishes and canopy-forming algal species increased following protection, even though the observation window fell within a period of warming. At the same time, exploited communities gained turf algal and sessile invertebrate species. We further found that the recovery of predator populations following protection leads to marked declines in mobile invertebrates-this trend could be incorrectly attributed to warming without contextual data quantifying community change across trophic levels. By comparing long-term change in exploited and protected reefs, we empirically demonstrate the role of biological interactions in both facilitating and resisting climate-related biodiversity change. We further highlight the potential for trophic interactions to alter the progression of both range expansions and contractions.

Climate-driven regime shift of a temperate marine ecosystem.

Ecosystem reconfigurations arising from climate-driven changes in species distributions are expected to have profound ecological, social, and economic implications. Here we reveal a rapid climate-driven regime shift of Australian temperate reef communities, which lost their defining kelp forests and became dominated by persistent seaweed turfs. After decades of ocean warming, extreme marine heat waves forced a 100-kilometer range contraction of extensive kelp forests and saw temperate species replaced by seaweeds, invertebrates, corals, and fishes characteristic of subtropical and tropical waters. This community-wide tropicalization fundamentally altered key ecological processes, suppressing the recovery of kelp forests.

The role of habitat complexity in shaping the size structure of a temperate reef fish community

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 532:197-211 (2015) - DOI: https://doi.org/10.3354/meps11330 The role of habitat complexity in shaping the size structure of a temperate reef fish community Rowan Trebilco1,2,*, Nicholas K. Dulvy1, Hannah Stewart3, Anne K. Salomon4,* 1Earth to Ocean Research Group, Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6 2Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart, TAS 7001 Australia 3West Vancouver Labs, Fisheries and Oceans Canada, 4160 Marine Drive, West Vancouver, BC, Canada V7V 1N6 4School of Resource and Environmental Management, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6 *‑Corresponding authors: rowan.trebilco@acecrc.org.au, anne.salomon@sfu.ca ABSTRACT: Understanding how habitat complexity shapes fish communities is necessary to predict the consequences of future habitat change. On temperate rocky reefs, the presence and characteristics of canopy-forming kelps and the architectural complexity, or rugosity, of the underlying rocky substratum are foundational elements of habitat complexity. However, it is not yet clear how these factors shape the size structure of rocky-reef-associated fish communities. Here, we use biomass spectrum models to evaluate how fish community size structure in high-latitude rocky-reef kelp forests is shaped by substratum rugosity and the degree of closure and density of the kelp canopy. We found that the presence of a closed kelp canopy was associated with an average 75% increase in overall fish biomass compared to open-canopy reefs. Furthermore, on the highest-rugosity reefs, the biomass of small fishes (32-64 g) was 800% higher than on the lowest-rugosity reefs, while large fish (1-2 kg) biomass was 60% lower. Consequently, biomass was more evenly distributed across body-size classes on high-rugosity reefs. By decomposing the biomass spectrum into total biomass and mean individual body mass, we found that higher kelp stipe densities also tended to be associated with larger fishes, but this effect was outweighed by the tendency for more small-bodied fishes with increasing rugosity. This study demonstrates how size-based analyses can give new insights into the ecology of temperate reef communities, and may be useful for tracking changes in kelp-associated assemblages in the coming decades with the maturation of marine protected areas, the recovery of sea otter populations, and changing climate. KEY WORDS: Biomass size spectra · Community ecology · Coral reef · Ecosystem baseline · Energy flow · Foundation species Full text in pdf format Supplementary material PreviousNextCite this article as: Trebilco R, Dulvy NK, Stewart H, Salomon AK (2015) The role of habitat complexity in shaping the size structure of a temperate reef fish community. Mar Ecol Prog Ser 532:197-211. https://doi.org/10.3354/meps11330 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 532. Online publication date: July 21, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Stability in temperate reef communities over a decadal time scale despite concurrent ocean warming

AbstractDespite increasing scientific and public concerns on the potential impacts of global ocean warming on marine biodiversity, very few empirical data on community‐level responses to rising water temperatures are available other than for coral reefs. This study describes changes in temperate subtidal reef communities over decadal and regional scales in a location that has undergone considerable warming in recent decades and is forecast to be a ‘hotspot’ for future warming.Plant and animal communities at 136 rocky reef sites around Tasmania (south‐east Australia) were censused between 1992 and 1995, and again in 2006 and 2007. Despite evidence of major ecological changes before the period of study, reef communities appeared to remain relatively stable over the past decade. Multivariate analyses and univariate metrics of biotic communities revealed few changes with time, although some species‐level responses could be interpreted as symptomatic of ocean warming. These included fishes detected in Tasmania only in recent surveys and several species with warmer water affinities that appeared to extend their distributions further south. The most statistically significant changes observed in species abundances, however, were not related to their biogeographical affinities. The majority of species with changing abundance possessed lower to mid‐range abundances rather than being common, raising questions for biodiversity monitoring and management. We suggest that our study encompassed a relatively stable period following more abrupt change, and that community responses to ocean warming may follow nonlinear, step‐like trajectories.

Biological and fishery characteristics of rubberlip morwong Nemadactylus douglasii (Hector, 1875) in eastern Australia

Rubberlip morwong Nemadactylus douglasii are important members of temperate reef communities off south-eastern Australia where they are targeted by offshore commercial and recreational fisheries. Macroscopic gonad staging and gonadosomatic indices demonstrated that N. douglasii have a distinct autumn/winter spawning period. Males and females attained sexual maturity at approximately 24 cm fork length, corresponding to an age of approximately 3 years old. During the spawning period male gonadosomatic index values were of an order of magnitude smaller than those for females, suggesting that N. douglasii may belong to the group of cheilodactylids that are not group spawners. The method of counting opaque zones in sectioned otoliths to estimate age was validated using marginal increment analysis. The results showed that opaque zones in the otoliths of N. douglasii were similar to other cheilodactylids in this region and formed once each year during spring/early summer. Males grew at a similar rate to females until approximately 2 years of age, after which males grew faster and attained larger sizes. The longest and oldest fish observed during the study were 52.4 cm fork length and 22 years, respectively. N. douglasii were fully recruited to the commercial fishery by 4 years of age and the fishery was dominated (>93%) by fish between 3 and 15 years of age. The age composition in landings showed evidence of variable recruitment through time. The total instantaneous mortality rate was estimated using catch curve analysis and ranged between 0.27 and 0.37 yr −1. Natural mortality was estimated as 0.14 yr −1 based on the maximum observed age. Steady declines during the past three decades in the quantities and average sizes of N. douglasii in landings suggest that the stock has been substantially depleted.

50 Can the effects of ocean warming on temperate reef communities be accurately predicted? lessons from a large scale, long term field experiment in central California

One of the most commonly predicted effects of global ocean warming on marine communities is a poleward shift in the distribution of species with an associated replacement of cold‐water species by warm‐water species. Such predictions are imprecise and based largely on broad correlations in uncontrolled studies that examine changes in species composition and abundance relative to seawater temperature. Before‐After‐Control‐Impact (BACI) analyses of the effects of a large thermal discharge shows that an induced 3.4 deg. C rise in seawater temperature over 10 years along 2 km of rocky coastline resulted in significant community‐wide changes in 150 species of algae and invertebrates relative to controls. Contrary to predictions from biogeographic models, there was no trend towards warm‐water species with southern geographic affinities replacing cold‐species with northern affinities. Instead, communities were greatly altered in apparently cascading responses to changes in abundance of several habitat‐forming taxa, particularly subtidal kelps (e.g. Pterygophora californica) and intertidal foliose red algae (e.g. Mazzaella flaccida). Many temperature sensitive algae decreased greatly in abundance, whereas many invertebrate grazers increased. The results indicate that the responses of temperate reef communities to ocean warming can be strongly coupled to direct effects on habitat‐forming taxa and indirect effects operating through ecological interactions. Given our understanding of temperate reef ecology and its local variability, the results also suggest that accurate predictions of the effects of global ocean warming will be difficult to make.