Spectral reflectance of Thalassia testudinum (Hydrocharitaceae) seagrass: low salinity effects

Abstract

Massive anthropogenic changes in estuarine salinities, from manipulations of freshwater flows, are again occurring through governmental projects “correcting” past freshwater alterations. The downstream effects of increased freshwater on seagrass meadows, a major fisheries and ecosystem habitat, are not clear. Spectral responses to low salinities were quantitatively delimited for the important habitat seagrass Thalassia testudinum utilizing spectral reflectance measurements for the first time (non‐invasive sampling). Over a range of salinities (32–16 parts per thousand sea salts [ppt] for 24 h) and spectra (308–1138 nm), Thalassia specimens showed statistically significant differences in spectral values (P < 0.05) between treatments at normal (32 ppt) and 50% reduced (16 ppt) seawater. Mature blades yellowed at low salinities. Reflectance changes at 525 nm and 650–680 nm at low salinities suggested changes in xanthophylls and chlorophylls. Four indices were also used to characterize the reflectance spectra to delineate the effect of the salinity changes: (1) The normalized difference vegetation index (NDVI) for mature blades reduced at 16 ppt from that at 32 ppt. (2) The chlorophyll normalized difference index (Chl NDI) suggested chlorophyll content decreases in response to reduced salinity. (3) The structure independent pigment index (SIPI), higher in mature blades at 16 ppt than new blades, indicates a higher carotenoid : chlorophyll ratio in mature blades. (4) The photochemical reflectance index (PRI) suggested a lower photochemical efficiency at lower salinities. The main low‐salinity effect on Thalassia physiology delineated herein is likely through changes in pigmentation (decreases in chlorophyll and changes in xanthophyll cycle epoxidation).

KARAKTERISASI RESPON SPEKTRAL SPESIES LAMUN Enhalus acoroides DAN Cymodocea rotundata DI PULAU KARIMUNJAWA

“…Pantulan pada saluran NIR juga tidak setinggi pada daun Ea tanpa epifit. Temuan serupa juga diperoleh oleh Thorhaug et al (2002;2003;2006) Pada daun Ea yang rusak, respon spektral hampir mirip dengan daun Ea ber-epifit, dimana puncak pantulan bergeser pada panjang gelombang yang lebih panjang yaitu 590 nm dan puncak yang lebih rendah pada 656 nm. Namun, perbedaannya adalah kenaikan respon spektral terjadi pada semua saluran tampak.…”

“…Hasil penelitian ini dapat dibandingkan dengan penelitian yang telah dilakukan sebelumnya, antara lain oleh Fyfe (2003), Thorhaug et al (2002;2003;2006;2007 Thorhaug et al (2002;2003) menemukan bahwa ada pergeseran lokasi red-edge pada Thalassia sp. dan spesies lamun lain saat mengalami stres dan penuaan, dimana keduanya berhubungan dengan berkurangnya kandungan klorofil dalam daun.…”

“…dan spesies lamun lain saat mengalami stres dan penuaan, dimana keduanya berhubungan dengan berkurangnya kandungan klorofil dalam daun. Lebih lanjut, Thorhaug et al (2006) menganalisis pantulan spektral spesies Thalassia sp. pada berbagai kondisi salinitas perairan dan menemukan bahwa ada pergeseran lokasi red-edge pada daun Thalassia sp.…”

Supervised Classification of Benthic Reflectance in Shallow Subtropical Waters Using a Generalized Pixel-Based Classifier across a Time Series

“…Despite their environmental and economic significance, seagrass populations are threatened worldwide by coastal development and eutrophication and may be nearing a crisis with respect to global sustainability [7]. The land-water interaction along coasts is influenced by freshwater networks where hydrologic impacts to seagrass ecosystems include increases in nutrients such as nitrogen and phosphorus occurring from industrial or agricultural sources [8], sediment discharge from watershed deforestation and mangrove clearing [8], and disruption of the natural salinity regime [2,9]. Without appropriate management, widespread loss of seagrass habitats is predicted to continue [10], especially given continued development of coastal lands.…”

Estimation of ginkgo leaf necrosis induced by Typhoon 0613 with spectral reflectance

“…Under water stress, and the change of plant spectral reflectance in the near-infrared range has been reported in some other researches (Holben et al, 1983;Jackson et al 1985;Moran et al, 1989;Yamamoto et al, 1995;Penuelas et al , 1999). Thorhaug et al (2006) stated that browning and necrosis resulted in a clear change in the shape of the reflectance spectra of Thalassia blades and suggested that the reflectance spectra at 750 nm might be a suitable stress index. Riedell et al (1995) noted that crop canopy chlorosis and necrosis in small grain fields infested with greenbugs, etc.…”