R Leaper

Changes in the Range of Some Common Rocky Shore Species in Britain – A Response to Climate Change?

Since the 1990s there has been a period of rapid climate warming in Europe. Long-term broad scale datasets coupled with time series at specific locations for rocky intertidal species dating back to the 1950s have been collected in Britain and Ireland. Resurveys of the original locations in 2001–2003 have been undertaken to identify changes in the biogeographical range and abundance of these species. The results show that some ‘southern’ species including Osilinus lineatus da Costa and Gibbula umbilicalis da Costa have undergone north and north-eastern range extensions. Populations have increased in abundance and adult size has decreased since the previous surveys were conducted. These changes have been synchronous throughout Britain, strongly suggesting that climate is responsible. The use of intertidal species as indicators of climate change is proposed.

Using historical data to detect temporal changes in the abundances of intertidal species on Irish shores

An historical data set, collected in 1958 by Southward and Crisp, was used as a baseline for detecting change in the abundances of species in the rocky intertidal of Ireland. In 2003, the abundances of each of 27 species was assessed using the same methodologies (ACFOR [which stands for the categories: abundant, common, frequent, occasional and rare] abundance scales) at 63 shores examined in the historical study. Comparison of the ACFOR data over a 45-year period, between the historical survey and re-survey,showed statistically signi¢cant changes in the abundances of 12 of the 27 species examined. Two species(one classed as northern and one introduced) increased signi¢cantly in abundance while ten species (¢ve classed as northern, one classed as southern and four broadly distributed) decreased in abundance. The possible reasons for the changes in species abundances were assessed not only in the context of anthropogenic eiects, such as climate change and commercial exploitation, but also of operator error. The error or diierences recorded among operators (i.e. research scientists) when assessing species abundance using ACFOR categories was quanti¢ed on four shores. Signi¢cant change detected in three of the 12 species fell within the margin of operator error. This eiect of operator may have also contributed to the results of no change in the other 15 species between the two census periods. It was not possible to determine the eiect of operator on our results, which can increase the occurrence of a false positive (Type 1) or of a false negative (Type 2) outcome.

Changes in the Antarctic sea ice ecosystem: potential effects on krill and baleen whales

The annual formation and loss of some 15 million km2 of sea ice around the Antarctic significantly affects global ocean circulation, particularly through the formation of dense bottom water. As one of the most profound seasonal changes on Earth, the formation and decay of sea ice plays a major role in climate processes. It is also likely to be impacted by climate change, potentially changing the productivity of the Antarctic region. The sea ice zone supports much wildlife, particularly large vertebrates such as seals, seabirds and whales, some exploited to near extinction. Cetacean species in the Southern Ocean will be directly impacted by changes in sea ice patterns as well as indirectly by changes in their principal prey, Antarctic krill, affected by modifications to their own environment through climate change. Understanding how climate change will affect species at all trophic levels in the Southern Ocean requires new approaches and integrated research programs. This review focuses on the current state of knowledge of the sea ice zone and examines the potential for climatic and ecological change in the region. In the context of changes already documented for seals and seabirds, it discusses potential effects on the most conspicuous vertebrate of the region, baleen whales.

Spatial scales of variance in abundance of intertidal species: effects of region, dispersal mode, and trophic level.

Determination of the pattern of variation in population abundance among spatial scales offers much insight into the potential regulating factors. Here we offer a method of quantifying spatial variance on a range of scales derived by sampling of irregularly spaced sites along complex coastlines. We use it to determine whether the nature of spatial variance depends on the trophic level or the mode of dispersal of the species involved and the role of the complexity of the underlying habitat. A least-cost distance model was used to determine distances by sea between all pairs of sites. Ordination of this distance matrix using multidimensional scaling allowed estimation of variance components with hierarchical ANOVA at nested spatial scales using spatial windows. By repeatedly moving these spatial windows and using a second set of spatial scales, average variance scale functions were derived for 50+ species in the UK rocky intertidal. Variance spectra for most species were well described by the inverse power law (1/fbeta) for noise spectra, with values for the exponent ranging from 0 to 1.1. At higher trophic levels (herbivores and carnivores), those species with planktonic dispersal had significantly higher beta values, indicating greater large- than small-scale variability, as did those on simpler coastlines (southwestern England and Wales vs. western Scotland). Average abundance and proportional incidence of species had the strongest influence on p values, with those of intermediate abundance and incidence having much greater large-scale variance (beta approximately 0.5) than rare or ubiquitous species (beta approximately 0).

Management of Antarctic baleen whales amid past exploitation, current threats and complex marine ecosystems

Abstract As baleen whales recover from severe exploitation, they are probably subject to a wide variety of threats within the Antarctic marine ecosystem, including directed take. Here we review both the management and current status of Antarctic baleen whales and consider those threats likely to impact on them. Threats range from global problems - marine pollution and climate change - to localized issues including shipping, habitat disturbance, unregulated wildlife tourism and fishery activities. We identify the most pressing anthropogenic threats to baleen whales including scientific whaling and climate change. It is unclear whether current management approaches will be able to effectively encompass all these threats while also accounting both for the differing levels of scientific understanding and for the differing recovery rates of the whale species. For management we recommend the following: 1) incorporation of both ecosystem considerations and the suite of identified threats not limited to direct take, 2) identification of measurable indicators of changes in whales that allow more certainty in monitoring of populations and the environment, and 3) recognition of significant relationships between baleen whales and habitat features to provide information on distribution and use.

Predictions of beta diversity for reef macroalgae across southeastern Australia

We analyzed and predicted spatial patterns of turnover in macroalgal community composition (beta diversity) that accounted for broad-scale environmental gradients using two contrasting community modelling methods, Generalised Dissimilarity Modelling (GDM) and Gradient Forest Modelling (GFM). Percentage cover data from underwater macroalgal surveys of subtidal rocky reefs along the southeastern coastline of continental Australia and northern coastline of Tasmania were combined with 0.018-resolution gridded environmental variables, to develop statistical models of beta diversity. GDM, a statistical approach based on a matrix regression, and GFM, a machine learning approach based on ensemble tree based methods, were used to fit models and generate predictions of beta diversity within unsurveyed areas across the region of interest. Patterns of macroalgal beta diversity predicted by both methods were remarkably congruent and showed a similar and striking change in community composition from eastern South Australia to western Victoria and northern Tasmania. Macroalgal communities differed markedly in predicted composition between the open coast and inshore locations. A distinct algal community was predicted for the enclosed Port Philip Bay in Victoria. Sea surface temperature standard deviation and average contributed most to changes in beta diversity for both the GDM and GFM models; changes in wave exposure and oxygen also influenced beta diversity in the GDM model, while salinity and exposure contributed substantially to the GFM model. The GDM and GFM analyses allowed us to model and predict spatial patterns of beta diversity in macroalgal communities comprising .180 species over 6600 km of coastline. These outputs advance regional-scale conservation management by allowing planners to interpolate from point source ecological data to assess the distribution of biodiversity across their full domain of interest. The congruence betweenmethods suggests that strong environmental gradients related to temperature and exposure are the common drivers of community change in this region.

Congruence in demersal fish, macroinvertebrate, and macroalgal community turnover on shallow temperate reefs.

To support coastal planning through improved understanding of patterns of biotic and abiotic surrogacy at broad scales, we used gradient forest modeling (GFM) to analyze and predict spatial patterns of compositional turnover of demersal fishes, macroinvertebrates, and macroalgae on shallow, temperate Australian reefs. Predictive models were first developed using environmental surrogates with estimates of prediction uncertainty, and then the efficacy of the three assemblages as biosurrogates for each other was assessed. Data from underwater visual surveys of subtidal rocky reefs were collected from the southeastern coastline of continental Australia (including South Australia and Victoria) and the northern coastline of Tasmania. These data were combined with 0.01 degree-resolution gridded environmental variables to develop statistical models of compositional turnover (beta diversity) using GFM. GFM extends the machine learning, ensemble tree-based method of random forests (RF), to allow the simultaneous modeling of multiple taxa. The models were used to generate predictions of compositional turnover for each of the three assemblages within unsurveyed areas across the 6600 km of coastline in the region of interest. The most important predictor for all three assemblages was variability in sea surface temperature (measured as standard deviation from measures taken interannually). Spatial predictions of compositional turnover within unsurveyed areas across the region of interest were remarkably congruent across the three taxa. However, the greatest uncertainty in these predictions varied in location among the different assemblages. Pairwise congruency comparisons of observed and predicted turnover among the three assemblages showed that invertebrate and macroalgal biodiversity were most similar, followed by fishes and macroalgae, and lastly fishes and invertebrate biodiversity, suggesting that of the three assemblages, macroalgae would make the best biosurrogate for both invertebrate and fish compositional turnover.

Do communities exist? Complex patterns of overlapping marine species distributions

Understanding the way in which species are associated in communities is a fundamental question in ecology. Yet there remains a tension between communities as highly structured units or as coincidental collections of individualistic species. We explored these ideas using a new statistical approach that clusters species based on their environmental response: a species archetype, rather than clustering sites based on their species composition. We found groups of species that are consistently highly correlated, but that these groups are not unique to any set of locations and overlap spatially. The species present at a single site are a realization of species from the (multiple) archetype groups that are likely to be present at that location based on their response to the environment.

Present and Future Conservation Management of Antarctic Baleen Whales

The massive reduction of whales as a result of commercial whaling is one of the single largest human impacts to the Antarctic marine ecosystem. Systematic hunting of over 1.3 million whales, in only 70 years, almost eliminated an entire group from the marine ecosystem. While the setting of catch limits to zero for conservation and management purposes (the moratorium) has saved many heavily exploited populations from extinction, at the same time there has been a dramatic expansion of ‘Special Permit’ (scientific) whaling, conducted both within and outside of designated whale sanctuaries. Here we discuss a number of future management scenarios that include an expanding conservation agenda, a continuation of ‘Special Permit’ whaling, a cessation in whaling and resumption of commercial whaling. To conclude, we briefly speculate on a number of potential threatening processes associated with growing levels of commercial, governmental and private human activity that may not only impact whales but Antarctica as a whole.