Reproductive Phenology of Pterocladiella capillacea (Rhodophyta: Gelidiales) from Southern Baja California, Mexico

Abstract

The abundance of vegetative and reproductive fronds of Pterocladiella capillacea (Gelidiaceae) from an intertidal population at Lobos Point, on the Pacific coast of southern Baja California, Mexico, was measured bimonthly between March 1998 and January 1999. Fronds with tetrasporic sori occurred throughout the year, although in low percentages with respect to the total amount of fronds: monthly means ranged between 0.5% (May) and 6.0% (July). Fronds with cystocarps and fronds with spermatangia were found only in January, with even lower percentages: 0.15% and 0.10%, respectively. The overall predominance of reproductive tetrasporophytic fronds over reproductive gametophytic fronds is common in natural populations of the Gelidiaceae. Reproductive phenology, however, varies widely within this family, even within the same species, as is the case for P. capillacea. Little is known about factors affecting the reproductive phenology of this cosmopolitan alga; field and laboratory studies are needed to provide a reliable predictive framework.

Most red seaweeds (Rhodophyta) have a triphasic life history, involving an alternation of gametophytes, carposporophytes, and tetrasporophytes (Graham and Wilcox 2000). Only gametophytes and tetrasporophytes constitute free-living individuals; carposporophytes occur within female gametophytes. This kind of life history does not occur in animals or vascular plants, so an increasing number of ecological and evolutionary studies are being done on it (e.g., Hughes and Otto 1999, Scrosati and DeWreede 1999). A primary step in life-history studies is assessing the abundance of reproductive phases in natural populations. Species of the family Gelidiaceae (Gelidiales) are common on several coasts around the world, so their reproductive characteristics have been studied by several researchers. For this family, gametophytes and tetrasporophytes are isomorphic and tetrasporophytic fronds generally predominate over gametophytic fronds in natural populations (Akatsuka 1986, Santelices 1988).

Pterocladiella capillacea (S. G. Gmelin) Santelices & Hommersand is a common species of the Gelidiaceae in several warm-temperate and tropical coasts from the Atlantic and Pacific Oceans and adjacent seas (Stewart 1968, Lawson and John 1987, Ramírez and Santelices 1991, Felicini and Perrone 1994, González-González et al. 1996, Silva et al. 1996, Santelices and Hommersand 1997, Coll and Oliveira 1999, Littler and Littler 2000, Neto 2000). Thus, studies on the geographic variation of its reproductive phenology may help to understand ecological and evolutionary factors affecting seaweed life-history traits. Phenological studies on P. capillacea have been done for a number of sites worldwide (see Discussion). In this paper we describe the reproductive phenology of P. capillacea from southern Baja California, Mexico. This species has already been reported from the Mexican Pacific coast (González-González et al. 1996), but no studies on its reproductive phenology have been done for this area. Because populations of the Gelidiaceae are generally dominated by those with tetrasporophytic fronds, this pattern was also expected for P. capillacea from southern Baja California. However, its reproductive phenology was impossible to predict because this may depend on species, latitude, local conditions, or year for the Gelidiaceae (Akatsuka 1986, Santelices 1988).

Materials and Methods

The thallus of Pterocladiella capillacea consists of branched prostrate stolons and several upright fronds (see a picture of fronds from the study site in Scrosati 2002). We studied an intertidal population of P. capillacea from Lobos Point (23° 25´ N, 110° 14´ W), on the west (Pacific) coast of the Baja California Peninsula, Mexico, between March 1998 and January 1999. At this site, the highest tidal amplitude is about 2 m. Pterocladiella capillacea is the dominant species between about 0.3 and 1.5 m above mean lower low water on vertical rocky walls directly exposed to waves, although its upper limit may be higher in some places due to topography and wave action. We could not make subtidal observations because waves were usually large at this site, but the lowest tides allowed us to see the rocky substrate a few tens of centimeters below the 0.3-m mark, where no P. capillacea was visible. Seawater temperature at Lobos Point varied between 18°C (winter) and 29°C (summer) between March 1998 and March 1999 (R.S...