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Ecological Change, Sliding Baselines and the Importance of Historical Data: Lessons from Combing Observational and Quantitative Data on a Temperate Reef Over 70 Years

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ABSTRACT

Understanding the effects of environmental change on ecosystems requires the identification of baselines that may act as reference conditions. However, the continuous change of these references challenges our ability to define the true natural status of ecosystems. The so-called sliding baseline syndrome can be overcome through the analysis of quantitative time series, which are, however, extremely rare. Here we show how combining historical quantitative data with descriptive ‘naturalistic’ information arranged in a chronological chain allows highlighting long-term trends and can be used to inform present conservation schemes. We analysed the long-term change of a coralligenous reef, a marine habitat endemic to the Mediterranean Sea. The coralligenous assemblages of Mesco Reef (Ligurian Sea, NW Mediterranean) have been studied, although discontinuously, since 1937 thus making available both detailed descriptive information and scanty quantitative data: while the former was useful to understand the natural history of the ecosystem, the analysis of the latter was of paramount importance to provide a formal measure of change over time. Epibenthic assemblages remained comparatively stable until the 1990s, when species replacement, invasion by alien algae, and biotic homogenisation occurred within few years, leading to a new and completely different ecosystem state. The shift experienced by the coralligenous assemblages of Mesco Reef was probably induced by a combination of seawater warming and local human pressures, the latter mainly resulting in increased water turbidity; in turn, cumulative stress may have favoured the establishment of alien species. This study showed that the combined analysis of quantitative and descriptive historical data represent a precious knowledge to understand ecosystem trends over time and provide help to identify baselines for ecological management.

No MeSH data available.


Quantitative historical analysis.a) Kite diagrams of the change in cover over time (as estimated from photoquadrats) of four categories of species: winners, losers, commuters, constants (see text). b) Average (± se) Euclidean distance among photoquadrats and their coefficient of variability from 1961 to 2008.
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pone.0118581.g004: Quantitative historical analysis.a) Kite diagrams of the change in cover over time (as estimated from photoquadrats) of four categories of species: winners, losers, commuters, constants (see text). b) Average (± se) Euclidean distance among photoquadrats and their coefficient of variability from 1961 to 2008.

Mentions: Based on their change in cover with time, 14 species were labelled as winners. Some of them (e.g., Leptogorgia sarmentosa) were already present in the photoquadrats of 1961–62, but most winners (e.g., Womersleyella setacea, Spirastrella cunctatrix, and Eunicella verrucosa) appeared for the first time in the photoquadrats of 1996 (S3 Fig.); Caulerpa racemosa was first observed in 2008: scarce within photoquadrats, this alien alga showed nevertheless already abundant in the area (S2 Fig.). Losers included 11 species, most of which disappeared (e.g. Alcyonium coralloides, Savalia savaglia, and Cellaria fistulosa) or reduced their cover (e.g., Axinella damicornis and Lithophyllum stictaeforme) in 1990 or 1996 (S3 Fig.). Commuters, whose cover underwent major change in1990 and/or 1996 (S3 Fig.), included 12 species (e.g., Flabellia petiolata, large hydroids, Pentapora fascialis, Salmacina dysteri, and Sarcotragus foetidus). Finally, 16 species showed constant, i.e., exhibited little of no change in cover on photoquadrats between 1961–62 and 2008 (Fig. 4A).


Ecological Change, Sliding Baselines and the Importance of Historical Data: Lessons from Combing Observational and Quantitative Data on a Temperate Reef Over 70 Years
Quantitative historical analysis.a) Kite diagrams of the change in cover over time (as estimated from photoquadrats) of four categories of species: winners, losers, commuters, constants (see text). b) Average (± se) Euclidean distance among photoquadrats and their coefficient of variability from 1961 to 2008.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4340909&req=5

pone.0118581.g004: Quantitative historical analysis.a) Kite diagrams of the change in cover over time (as estimated from photoquadrats) of four categories of species: winners, losers, commuters, constants (see text). b) Average (± se) Euclidean distance among photoquadrats and their coefficient of variability from 1961 to 2008.
Mentions: Based on their change in cover with time, 14 species were labelled as winners. Some of them (e.g., Leptogorgia sarmentosa) were already present in the photoquadrats of 1961–62, but most winners (e.g., Womersleyella setacea, Spirastrella cunctatrix, and Eunicella verrucosa) appeared for the first time in the photoquadrats of 1996 (S3 Fig.); Caulerpa racemosa was first observed in 2008: scarce within photoquadrats, this alien alga showed nevertheless already abundant in the area (S2 Fig.). Losers included 11 species, most of which disappeared (e.g. Alcyonium coralloides, Savalia savaglia, and Cellaria fistulosa) or reduced their cover (e.g., Axinella damicornis and Lithophyllum stictaeforme) in 1990 or 1996 (S3 Fig.). Commuters, whose cover underwent major change in1990 and/or 1996 (S3 Fig.), included 12 species (e.g., Flabellia petiolata, large hydroids, Pentapora fascialis, Salmacina dysteri, and Sarcotragus foetidus). Finally, 16 species showed constant, i.e., exhibited little of no change in cover on photoquadrats between 1961–62 and 2008 (Fig. 4A).

View Article: PubMed Central - PubMed

ABSTRACT

Understanding the effects of environmental change on ecosystems requires the identification of baselines that may act as reference conditions. However, the continuous change of these references challenges our ability to define the true natural status of ecosystems. The so-called sliding baseline syndrome can be overcome through the analysis of quantitative time series, which are, however, extremely rare. Here we show how combining historical quantitative data with descriptive ‘naturalistic’ information arranged in a chronological chain allows highlighting long-term trends and can be used to inform present conservation schemes. We analysed the long-term change of a coralligenous reef, a marine habitat endemic to the Mediterranean Sea. The coralligenous assemblages of Mesco Reef (Ligurian Sea, NW Mediterranean) have been studied, although discontinuously, since 1937 thus making available both detailed descriptive information and scanty quantitative data: while the former was useful to understand the natural history of the ecosystem, the analysis of the latter was of paramount importance to provide a formal measure of change over time. Epibenthic assemblages remained comparatively stable until the 1990s, when species replacement, invasion by alien algae, and biotic homogenisation occurred within few years, leading to a new and completely different ecosystem state. The shift experienced by the coralligenous assemblages of Mesco Reef was probably induced by a combination of seawater warming and local human pressures, the latter mainly resulting in increased water turbidity; in turn, cumulative stress may have favoured the establishment of alien species. This study showed that the combined analysis of quantitative and descriptive historical data represent a precious knowledge to understand ecosystem trends over time and provide help to identify baselines for ecological management.

No MeSH data available.