BIOMASS AND DYNAMICS OF GROWTH OF ULVA SPECIES IN PALMONES RIVER ESTUARY¹

Abstract

During the last decade, the Palmones River estualy has undergone severe eutrophication followed by a green tide episode; two species ofUlva, rotundata Blid. and Ulva curvata (Kutz.) De Toni, were the main macroalgae responsible for this bloom. From November 1993 to December 1994, we followed the biomass, the growth dynamics, and tissue elemental composition (C:N:P) of Ulva species, as well as some physicochemical variables in the estualy. Maximum biomass (up to 375 g dly wt.m-2 in some spots, corresponding to a thallus area index of nearly 17 m2 Ulva m-2 sediment) were observed in June and December. However, the biomass vaned among the sampling stations. Water nitrate, ammonia, and phosphate showed high concentrations throughout the year, with extremely high transient pulses, sustaining the high growth rates obseroed. Growth rates were estimated directly i n the field. The rates were generally higher i n Ulva discs maintained in net cages than those estimated by changes in biomass standing stock between two consecutive samplings. The dqerence between both estimates was used to quantijj the importance of the processes causing loss of biomass, which were attrib utable to grazing, exported biomass, and thallus decomposition under anaerobic conditions resulting from extreme selfshading. Maximum chlor@hyll content was found in winter, whereas the minimum was in spring. Atomic N:P ratios were generally higher in the algae than in the water, However, the absolute concentrations of tissue N and P were always higher than the cn'tical h e l s for maximum growth, which suggests that growth was not limited by inorganic N or P availability. The results suggested that the increase in nutrient loading in the river may have triggered the massive development of green algae and that light limitation and temperature stress in summer seem to be the main factors controlling the abundance of Ulva in the estualy. I n addition to light availability and thermal stress, the different loss processes may have a decisive role in the dynamics of Ulva biomass. K q index words: eutrophication; growth; primaly p r e duction; Ulva Local proliferations of masses of green algae are often found in estuaries and coastal waters of areas undergoing eutrophication (Geertz-Hansen et al.

Regulation of spatial and seasonal variation of macroalgal biomass in a brackish, eutrophic lake

“…Bird grazing takes place mainly during the late summer and autumn when the difference between sites is already evident; thus we assume that grazing was also not responsible for the observed difference. Several authors have suggested the importance of wind and currents as important factors for transport of free-floating macroalgae Hernández et al 1997;Salomonsen et al 1997). In the Veerse Meer, transport from the more exposed site at Kwistenburg may be more important as a loss factor than at Middelplaten.…”

“…weekly to biweekly) it can be assessed whether growth or loss processes determine spatial variation in macroalgal distribution and how growth in its turn correlates to environmental parameters (Sfriso 1995;Hernández et al 1997). Thus far, only few studies have addressed spatial variation in this way (Geertz-Hansen et al 1993;Hernández et al 1997;Sfriso and Marcomini 1997;Barthelemy et al 2001).…”

Allelopathic growth inhibition ofProrocentrum micans(Dinophyta) byUlva pertusaandUlva linza(Chlorophyta) in laboratory cultures

“…Blooms of green macroalgae have been reported to have a harmful impact on intertidal marine ecosystems in a variety of ways, including changes in ecosystem structure (Raffaelli et al, 1998;Taylor, 1999;Nelson & Lee, 2001) and reduction of biodiversity (Valiela et al, 1997;Raffaelli et al, 1998;Taylor, 1999). Moreover, green tides may also have a deleterious effect on local fisheries and aquaculture industries and may contribute to a decrease in tourism revenue due to the presence of aesthetically displeasing and noxious-smelling deposits of drift weed on shorelines (Hernandez et al, 1997;Taylor, 1999). 'Red tides' (caused by blooms of harmful microalgae) are also occurring with increasing frequency in coastal waters worldwide and cause disastrous damage to the fishery and aquaculture industries of many countries (Qi et al, 1993;Horner et al, 1997;Kim, 1997).…”

“…Because of the severe ecological and economic problems that result from coastal algal blooms, many investigations have sought the mechanisms that enable these bloom-forming algae to outcompete other coastal primary producers and establish dominant populations. Understanding the mechanisms may be helpful in developing strategies for the control of such harmful algal blooms (Hernandez et al, 1997;Smayda, 1997;Valiela et al, 1997;Taylor et al, 2001).…”

“…Ulva pertusa and Ulva linza (previously Enteromorpha linza; Hayden et al, 2003) are two of the most common macroalgae contributing to the phenomenon known as green tides (Fletcher et al, 1990;Hernandez et al, 1997;Lotze & Schramm, 2000;Taylor et al, 2001), while Prorocentrum micans is one of the most harmful microalgae responsible for red tides (Adams et al, 1968;Qi et al, 1993;Zhu et al, 1997). The present study investigates the potential algicidal effects of U. pertusa and U. linza on cultures of P. micans.…”