Growth patterns of Western Mediterranean seagrasses:species-specific responses to seasonal forcing

Abstract

ABSTRACT. The seasonal growth pattern of the 4 seagrass species occurring in the NW Mediterranean (i.e. Cymodocea nodosa, Zostera noltii, 2. marina, Posidonla oceanica) was studied in populat~ons growing in the same locality (Cala Jonquet, Girona, NE Spain), and thus experiencing the same seasonal (i.e. temperature and light) forcing, to evaluate the contnbution of species-specific responses to seagrass growth seasonality. C. nodosa, 2. noltij, and Z marina showed comparable growth patterns as indicated by significant correlations of growth across species (cross correlation, r > 0.54, p < 0 05) This result provlded evidence of a similarity in the response of these species to seasonal forcing. The seasonal pattern of P. oceanica resembled that of the other species in shoot weight, shoot elongat~on, and ramet recruitment, whereas it differed in internode weight and rhizome elongation. Despite some similarities in seasonal growth patterns, the patterns were lagged by 1 to 2 mo across species, and the magnitude of seasonal growth fluctuations was species-dependent. Species-specific responses of seagrasses to climate forcing should be related to differences in the capacity of the plants to store resources and to the extent of ramet integration among species, both processes being closely related to plant size. Large seagrasses (e g. oceanica), with thick and long-living rhizomes, should be able to store more photoassimilates and to transport them over longer distances than small plants (e.g. C. nodosa), with thinner and shorter-11v1ng riuzomes. Large species should, therefore, be able to grow more independently of env~ronmental conditions than small ones. Moreover, C. nodosa showed the greatest response to temperature fluctuat~ons whereas 2, marina growth was strongly coupled to seasonal l~g h t conditions, indicating d~fferent plant sensitivity to climate fluctuations among species. This study confirms the great var~ability In seagrass seasonality possible under similar seasonal forcing, and demonstrates that seagrass seasonality has both an extrinsic component, dependent on seasonal forcing of light and temperature, and an intrinsic component. The intnnsic component of seagrass seasonality likely involves a differential capacity of the species to regulate the internal resource economy which may buffer, or amplify, the external seasonal forcing.

Scaling of processes shaping the clonal dynamics and genetic mosaic of seagrasses through temporal genetic monitoring

“…Independent of longer-term meadow stability, the dynamics of Z. marina meadows are punctuated by annual variations in density, with a rather synchronized peak of recruitment of new ramets in early spring, filling gaps left by an annual winter drop in density (Marba et al, 1996). Spring increase in density can be caused by the local clonal spread of genets that have persisted through winter, or new waves of recruits through ramet and seedling dispersal/settlement over broader spatial scales.…”

Direct measurements of root growth and productivity in the seagrasses Posidonia australis and P. sinuosa

“…The nature of the experimental conditions in this study (removal of roots prior to planting, culture in standardized medium in pots) means that root-growth values are not typical of plants growing in a meadow situation and are likely to be close to the maximum potential growth rates. If growth rates for the transplants of P. australis and P. sinuosa are scaled up to a unit area of meadow, then increases in root length (2-5 m root m 22 d 21 ) would be similar to estimates for a meadow of the small, fast-growing Mediterranean seagrass Cymodocea nodosa during summer and considerably higher than root-growth values of Posidonia oceanica derived from annual rhizome growth (historical rhizome reconstruction) or from tagging rhizomes and estimating root growth between two points (Duarte et al 1998;Marbá and Duarte 2001; Table 5). Similarly, annual root productivities in P. australis and P. Fig.…”

“…Studies that included changes in root biomass (Marbá et al 1996), root productivity, and linear root length over time (Cebrián et al. 1997;Marbá and Duarte 2001) showed more root production during summer months, reflecting speciesspecific seasonal patterns in shoot production.…”

“…Studies that included changes in root biomass (Marbá et al 1996), root productivity, and linear root length over time (Cebrián et al 1997;Marbá and Duarte 2001) showed more root production during summer months, reflecting speciesspecific seasonal patterns in shoot production. A study on root initiation in Posidonia oceanica transplants showed faster root formation for autumn and winter plantings than summer plantings (Balestri and Lardicci 2006), but subsequent root growth was not investigated.…”

Patch dynamics and response to disturbance of the seagrass Zostera novazelandica on intertidal platforms in southern New Zealand

“…Overall environmental conditions can be severe during winter and early spring when there is a large influx of fresh water run-off due to rain over these intertidal platforms, coupled with reduced irradiance and water temperature (cf. Marba et al 1996b) and occasional storm waves several metres high. Wind stress is more likely to occur at low tide during summer when warm winds occur almost daily.…”