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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

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.


Mesco Point and its environments.a) Perspective photography (photo Regione Liguria) of the coastal tract between Mesco Point and the town of Monterosso-al-Mare, with the main nearshore geomorphological and ecological features. b) The beach of Monterosso-al-Mare viewed from the heights of Mesco Point (photo A. Peirano).The distance between Mesco Reef and the embankment is about 1400 m. Note the change in the structure of the embankment between the early 1990s (photo in b) and 2008 (photo in a).
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pone.0118581.g002: Mesco Point and its environments.a) Perspective photography (photo Regione Liguria) of the coastal tract between Mesco Point and the town of Monterosso-al-Mare, with the main nearshore geomorphological and ecological features. b) The beach of Monterosso-al-Mare viewed from the heights of Mesco Point (photo A. Peirano).The distance between Mesco Reef and the embankment is about 1400 m. Note the change in the structure of the embankment between the early 1990s (photo in b) and 2008 (photo in a).

Mentions: Important environmental changes have occurred in the study area during the last decades (S1 Fig.). Since the 1970s, shelf waters have been warming, with a temperature increase of 1.1°C between the surface and 50 m depth and an acceleration during the 1990s [27]. A regime shift has been shown to occur at the end of the 1980s [28]. In addition to these large-scale climatic effects, which had important influence on the composition of the marine biota in the Ligurian Sea [29], also local human pressures increased in roughly the same decades. In the 1960s a small marina was built at the western extremity of the beach of Monterosso-al-Mare (about 1 km from Mesco Reef), whereas between 1963 and 1974 an embankment 150 m long and 90 m wide was created in the middle of the beach (Fig. 2), to serve as a car park during summer [30]. The beach underwent erosion since the construction of the embankment, which was reinforced with revetments in the 1980s and again in the 1990s; other static coastal defences (groynes, breakwaters, and seawalls) were also built [31]. Major beach replenishments have been done in the 2000s [32]. Coastal works have probably been responsible of the increased water turbidity in the area: water transparency (Secchi disk) passed from 23.8 m (± 1.3 se) in the 1950s to 11.8 m (± 0.9 se) in the 1990s [29] and to 12.7 m (± 0.3 se) in the 2000s [33]. Resident population decreased from 2000 inhabitants in 1960 to 1556 inhabitants in 2008 (data from the Italian Statistical Institute); on the contrary, tourism increased steadily to the current accommodation capacity of about 1200 people (data from the National Observatory of Tourism), which causes the population to nearly double during the summer. Since 1997, Mesco Point and Mesco Reef have been included in the “Cinque Terre” Marine Protected Area (MPA): as a consequence, fishing has been banned and diving strictly regulated.


Ecological Change, Sliding Baselines and the Importance of Historical Data: Lessons from Combing Observational and Quantitative Data on a Temperate Reef Over 70 Years
Mesco Point and its environments.a) Perspective photography (photo Regione Liguria) of the coastal tract between Mesco Point and the town of Monterosso-al-Mare, with the main nearshore geomorphological and ecological features. b) The beach of Monterosso-al-Mare viewed from the heights of Mesco Point (photo A. Peirano).The distance between Mesco Reef and the embankment is about 1400 m. Note the change in the structure of the embankment between the early 1990s (photo in b) and 2008 (photo in a).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0118581.g002: Mesco Point and its environments.a) Perspective photography (photo Regione Liguria) of the coastal tract between Mesco Point and the town of Monterosso-al-Mare, with the main nearshore geomorphological and ecological features. b) The beach of Monterosso-al-Mare viewed from the heights of Mesco Point (photo A. Peirano).The distance between Mesco Reef and the embankment is about 1400 m. Note the change in the structure of the embankment between the early 1990s (photo in b) and 2008 (photo in a).
Mentions: Important environmental changes have occurred in the study area during the last decades (S1 Fig.). Since the 1970s, shelf waters have been warming, with a temperature increase of 1.1°C between the surface and 50 m depth and an acceleration during the 1990s [27]. A regime shift has been shown to occur at the end of the 1980s [28]. In addition to these large-scale climatic effects, which had important influence on the composition of the marine biota in the Ligurian Sea [29], also local human pressures increased in roughly the same decades. In the 1960s a small marina was built at the western extremity of the beach of Monterosso-al-Mare (about 1 km from Mesco Reef), whereas between 1963 and 1974 an embankment 150 m long and 90 m wide was created in the middle of the beach (Fig. 2), to serve as a car park during summer [30]. The beach underwent erosion since the construction of the embankment, which was reinforced with revetments in the 1980s and again in the 1990s; other static coastal defences (groynes, breakwaters, and seawalls) were also built [31]. Major beach replenishments have been done in the 2000s [32]. Coastal works have probably been responsible of the increased water turbidity in the area: water transparency (Secchi disk) passed from 23.8 m (± 1.3 se) in the 1950s to 11.8 m (± 0.9 se) in the 1990s [29] and to 12.7 m (± 0.3 se) in the 2000s [33]. Resident population decreased from 2000 inhabitants in 1960 to 1556 inhabitants in 2008 (data from the Italian Statistical Institute); on the contrary, tourism increased steadily to the current accommodation capacity of about 1200 people (data from the National Observatory of Tourism), which causes the population to nearly double during the summer. Since 1997, Mesco Point and Mesco Reef have been included in the “Cinque Terre” Marine Protected Area (MPA): as a consequence, fishing has been banned and diving strictly regulated.

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.