Biomass variation and reproductive phenology of Gracilaria gracilis in a Patagonian natural bed (Chubut, Argentina)

Abstract

The biomass variation and the reproduction of the natural Gracilaria gracilis bed in Bahía Bustamante (Patagonia, Argentina) were analyzed for 2 years, with the aim of determining the present situation of the population for an updated status overview; establishing the relevant features of the temporal variation in both biomass and reproductive states in relation to environmental factors, epiphytes and associated algae; and assessing carpospore availability for future spore-culture development. Field measurements and sampling were performed monthly between March 2006 and February 2008. In both years, G. gracilis biomass presented marked seasonal variations, with a minimum in winter and a maximum in late spring and in summer. During both years, coexistence of the three life-cycle phases was found, with dominance of tetrasporophytes. Two data sets from individuals originated from sexual reproduction (tetraspores and carpospores) and from asexual reproduction by thallus fragmentation were analyzed separately. In the fragmentation fraction, tetrasporophyte frequencies remained higher than those for gametophytes. However, in the spore-originated fraction, a generation ratio close to 0.5 was observed. Female gametophytes bearing cystocarps were always present, with a maximum in summer and autumn. Biological data were related to environmental factors by means of canonical correspondence analysis (CCA). The first year was characterized by higher biomass values of G. gracilis and Undaria pinnatifida, lower epiphytism, larger Gracilaria thalli and greater proportion of mature tetrasporophytes and gametophytes. The second year was characterized by a high proportion of Gracilaria vegetative thalli and high epiphyte density. The best time to obtain spores from cystocarpic thalli would be in summer and early autumn.

Responses of the haploid-to-diploid ratio of isomorphic biphasic life cycles to time instability

“…Such were the cases of Gracilaria verrucosa [4], Chondrus crispus [24], Chondracanthus chamissoi [10], Gelidium sesquipedale [20], Mazzaella cornucopiae [22], Sarcothalia crispata [15], Pterocladiella capillacea [27], Mazzaella splendens [5], Gelidium pusillum [17], Gracilaria gracilis [13] and Grateloupia turuturu [1], showing that the H:D time variability is worldwide. The H:D of Mazzaella flaccida observed at Piedras Blancas and Vandenberg (Pacific Coast of North America) with a fine temporal resolution [28] exhibited oscillations mismatching the seasonal cycle.…”

Food and habitat choice in the spider crab <em>Leucippa pentagona</em> (Majoidea: Epialtidae) in Bahía Bustamante, Patagonia, Argentina

“…The feeding preferences of L. pentagona may be beneficial for G. gracilis and could have important implications for the subtidal community of Bahía Bustamante. The annual production of G. gracilis has dropped significantly in the last few years (Martin et al 2011). This decrease could be related to the high abundance of epiphytes and their negative effects on the host (Martin et al 2013).…”

“…The bay has a semidiurnal tidal regime, with average amplitude of 4.2 m. There are dense patches of the economically important red alga Gracilaria gracilis. In recent years, the alien alga Undaria pinnatifida have been found in coastal areas of the bay (Martin et al 2011).…”

“…In Argentine Patagonia, G. gracilis forms large and dense beds at some wave-protected sites of Golfo San Jorge (Bahía Bustamante, Puerto Melo and Bahía Arredondo) and Golfo Nuevo. Beds in Bahía Bustamante are the most important in terms of extension and biomass (Martin et al 2011). However, these beds have significant biomass variation that could be attributed to higher abundance of epiphytes and epiphyte-imposed stress (Martin et al 2013).…”

Reproductive biology of the spider crab Leucippa pentagona (Decapoda: Epialtidae), in Bustamante Bay, Argentina

“…1) where a well established population of Leucippa pentagona was found. It is an enclosed bay with dense beds of the economically important red alga Gracilaria gracilis (Stackhouse) Steentoft, Irvine & Farnham growing in the subtidal environment (Martin et al, 2010). The area is influenced by coldtemperate waters of the Patagonian Current and, occasionally, by warmer waters of the Brazil Current during summer.…”