Characterization of phanerogam communities (Posidonia oceanica and Cymodocea nodosa) using side-scan-sonar images

Siljeström, Patricia; Rey, J.; Moreno, Adela

doi:10.1016/s0924-2716(96)00025-1

Cited by 18 publications

(9 citation statements)

References 7 publications

(8 reference statements)

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“…The best results in mapping seagrass meadows are achieved using the complementary approaches of indirect (instrumental) and direct (scuba) techniques (Cinelli et al, 1995;Piazzi et al, 2000). Among indirect techniques, side scan sonar (SSS) is one of the most used and powerful tools for largescale mapping of seagrass meadows in the Mediterranean Sea (Colantoni et al, 1982;Siljestrom et al, 1996;Pasqualini et al, 2000). On the other hand, underwater survey by scuba diving along line-transects is a visual method particularly useful when the extent of the study area is limited; it is also used for ground-truthing information from indirect mapping techniques and is the only method for collecting detailed data on the structure and morphology of P. oceanica meadows (Calvo et al, 1993;Peirano et al, 1995).…”

Section: Introductionmentioning

confidence: 99%

A new synthetic index and a protocol for monitoring the status ofPosidonia oceanica meadows: a case study at Sanremo (Ligurian Sea, NW Mediterranean)

Montefalcone

Albertelli

Bianchi

et al. 2005

Aquatic Conserv: Mar. Freshw. Ecosyst.

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ABSTRACT1. The status of a Posidonia oceanica meadow in front of the town of Sanremo, Italy, was studied through a combined use of benthic mapping and synthetic indices.2. Mapping was accomplished by integrating side scan sonar imagery and data collected by scuba diving along transects placed perpendicularly to the coastline. A thematic map (scale 1:5000) was produced. Extent of the meadow, occurrence of dead matte areas, and morphology of the lower limit (with new definition) are all described.3. Two synthetic environmental indices were applied to transect data in order to quantify the status of the meadow: the Conservation Index and the Substitution Index. The former is related to the proportion of dead matte; the latter is a novel index measuring the amount of replacement of the 'constructional' seagrass P. oceanica by the 'non-constructional' seagrass Cymodocea nodosa. The potential of a 'phase shift' in Ligurian Sea seagrass meadows is discussed.4. The approach here proposed, based on detailed mapping plus synthetic indices, may provide immediate information to evaluate the state of Mediterranean Posidonia oceanica for monitoring and management.

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Section: Introductionmentioning

confidence: 99%

A new synthetic index and a protocol for monitoring the status ofPosidonia oceanica meadows: a case study at Sanremo (Ligurian Sea, NW Mediterranean)

Montefalcone

Albertelli

Bianchi

et al. 2005

Aquatic Conserv: Mar. Freshw. Ecosyst.

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“…This monospeci c plant community presents a very strong acoustic response in 100 kHz, appearing as a dark area with a ne and homogeneous granular texture ( gure 3) with a high contrast against the soft sediment where it settles, which is characterized by a weak acoustic response. In contrast, the same vegetation is almost transparent using 500 kHz (Siljeströ m et al 1996). The extremely high acoustic response of this vegetation contrasts with the external morphology, as the plant presents spatially separated shoots on the surface, while the rhizomes and root system remains buried between 5 and 30 cm deep.…”

Section: Acoustic Interpretation Of the Imagesmentioning

confidence: 96%

Selectivity in the acoustic response of Cymodocea nodosa (Ucria) Ascherson

Siljeström¹,

Moreno²,

Carbó³

et al. 2002

International Journal of Remote Sensing

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The objective of this paper is to present a hypothesis to explain the selective response of Cymodocea nodosa in sonar images taken with frequencies of 100 and 500 kHz, as with the former frequency the communities present a very strong acoustic response, while with the second they appear almost transparent. The morphology and anatomy of the plant is analysed, and it is concluded that the air contained in the channels of leaves, rhizomes and roots, in relationship with the penetration in soft sediments of the frequencies used is the cause for the acoustic signature of the communities.

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“…In subtidal areas, a towed underwater video camera can be used, as described in Haag et al (2008) or in Kendall et al (2005). More recently, the use of acoustic sonar has been developed, since it usually permits covering wider areas in a shorter time (Komatsu et al, 2003 ;Pasqualini et al, 2000 ;Pasqualini et al, 1998 ;Siljeström et al, 1996). These various methods provide data which are set inside a geo-referenced space.…”

Section: Introductionmentioning

confidence: 99%

Long-term evolution (1988–2008) of Zostera spp. meadows in Arcachon Bay (Bay of Biscay)

Plus

Dalloyau

Trut

et al. 2010

Estuarine, Coastal and Shelf Science

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The spatial variability of seagrass meadows in Arcachon Bay, was studied between 1988 and 2008 using a combination of mapping techniques based on aerial photographs for intertidal dwarf-grass (Zostera noltii) beds and acoustic sonar for permanently submerged eelgrass (Zostera marina) populations. The results show a severe decline over the period for both species, as well as an acceleration of the decline since 2005 for Z. noltii. The total surface regression over the studied period is estimated to be 22.8 km 2 for Z. noltii and 2.7 km 2 for Z. marina, which represent declines of 33 and 74% respectively. Environmental data time series spanning the same period were investigated in order to seek the causes for such a decline. The calculated inter-annual trends for temperature, salinity, nitrate plus nitrite, ammonia, suspended sediment and chlorophyll a did not identify any clear environmental change capable of explaining the observed seagrass regression. For instance, no evident sign of eutrophication was observed over the study period. On the other hand, we suggest that the observed variations of ammonia in the inner part of the lagoon are a symptom of the seagrasses' disappearance and thus, a first sign indicating a change of the Arcachon Bay ecosystem towards more instability and vulnerability. Several hypotheses to explain the observed seagrass decay are proposed.

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Characterization of phanerogam communities (Posidonia oceanica and Cymodocea nodosa) using side-scan-sonar images

Cited by 18 publications

References 7 publications

A new synthetic index and a protocol for monitoring the status ofPosidonia oceanica meadows: a case study at Sanremo (Ligurian Sea, NW Mediterranean)

A new synthetic index and a protocol for monitoring the status ofPosidonia oceanica meadows: a case study at Sanremo (Ligurian Sea, NW Mediterranean)

Selectivity in the acoustic response of Cymodocea nodosa (Ucria) Ascherson

Long-term evolution (1988–2008) of Zostera spp. meadows in Arcachon Bay (Bay of Biscay)

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