Emergence stress and morphological constraints affect the species distribution and growth of subtropical intertidal seagrasses

Abstract

The effects of emergence stress and morphological constraints on the distribution and growth of 3 subtropical seagrass species, Cymodocea rotundata, C. serrulata and Thalassia hemprichii, were examined in a series of transplantation experiments and a laboratory desiccation experiment. C. rotundata and T. hemprichii occur in both the intertidal and subtidal zones off Ishigaki Island, southwest Japan, whereas C. serrulata is found only in the subtidal zone. Within the same species, intertidal shoots for both C. robundata and T. hemprichii are significantly smaller than subtidal shoots. A subtidal-to-intertidal transplantation experiment was conducted on 3 occasions: July and September 2001 and January 2002. In July and September, when the intertidal sites were exposed to air for a shorter period, shoot densities of the transplanted 3 species did not decrease. In contrast, the shoot densities of all 3 transplanted species decreased significantly in February, when the exposure to air was longer. The survival of C. serrulata (2% of the initial density) was much lower than that of C. rotundata (48%) and T. hemprichii (48%). In subtidal-to-intertidal transplants, the size of C. rotundata and T. hemprichii leaves decreased, approaching that of intertidal shoots, indicating high morphological plasticity. In situ observations revealed that transplanted seagrasses with large leaves were exposed to air for longer than were intertidal controls. In the desiccation experiment, T. hemprichii leaves had higher water contents than those of C. rotundata and C. serrulata. The morphological traits of C. rotundata and T. hemprichii and their ability to change shoot size appear to be related to the better survival of these species in the intertidal area as compared to C. serrulata. This is consistent with the observed variation in the species distribution in the intertidal zone.

Evaluation of various satellite sensors for waterline extraction in a coral reef environment: Majuro Atoll, Marshall Islands

“…This is also true at coral reef coasts, which have shallow, intertidal reef flats created by reef-building organisms (e.g., corals, calcareous algae, and foraminifera) and calcareous sand distributions on beaches and reef islands (Woodroffe, 2002). Previous studies have shown distinct zonal distributions of reef-dwelling organisms due to subaerial exposure, which is basically a function of surface morphology in intertidal areas (e.g., Stoddart, 1969;Yamano et al, 2001;Tanaka and Nakaoka, 2004). However, possible future rises in sea levels threaten to drown or inundate coral reefs and islands (Leatherman, 1997).…”

Interspecific variation in photosynthesis and respiration balance of three seagrasses in relation to light availability

“…This study was conducted at Shiraho on Ishigaki Island in the Ryukyu Islands group, southwestern Japan (24°21' N, 124°15' E; see Tanaka & Nakaoka 2004 for more detailed information on the study site). Sampling and experiments were performed on 2 occasions (July 2001 andFebruary 2002).…”

“…Generally, depth distributions vary among species, leading to specific zonation patterns from intertidal to subtidal areas (Mukai et al 1987, Lee Long et al 1993, Björk et al 1999, De Troch et al 2001, Tanaka & Nakaoka 2004, Tanaka & Kayanne 2007. For subtidal seagrass beds, light intensity is a major factor determining species' depth distributions (Duarte 1991).…”

Changes in temporal variance of rocky shore organism abundances in response to manipulation of mean intensity and temporal variability of aerial exposure

“…Prolonged periods of high barometric pressure and calm seas can push the sea level below the Mean Low Water Level (MLWL), exposing sessile organisms to air for long periods. Such conditions may affect the physiology (Silva et al 2005) and growth of organisms (Davison et al 1993, Tanaka & Nakaoka 2004, Dethier et al 2005, their tolerance to the impact of waves (Haring et al 2002) and grazing (Buschmann 1990, Harley 2003. In contrast, waves reduce drying out of intertidal organisms during low tides and can have positive effects on transport of nutrient particles to filter-feeders (Hawkins & Jones 1992).…”