Phyllospadix

Abstract: Allochthonous subsidies of organic material can profoundly influence population and community structure; however, the role of consumers in the processing of these inputs is less understood but may be closely linked to community and ecosystem function. Inputs of drift macrophytes subsidize sandy beach communities and food webs in many regions. We estimated feeding rates of dominant sandy beach consumers, the talitrid amphipods (Megalorchestia corniculata, in southern California, USA, and Talitrus saltator, in southern Galicia, Spain), and their impacts on drift macrophyte subsidies in field and laboratory experiments. Feeding rate varied with macrophyte type and, for T. saltator, air temperature. Size-specific feeding rates of talitrid amphipods were greatest on brown macroalgae (Macrocystis, Egregia, Saccorhiza and Fucus). Rates for large individuals of both species ranged from ∼40 mg wet wt individual−112 h−1 on brown macroalgae to negligible feeding by M. corniculata on a vascular plant (surfgrass). Amphipod growth rates were also greatest on Macrocystis and lowest on surfgrass, Phyllospadix. For a Californian beach with substantial inputs of macrophyte wrack (>70 kg wet wt m−1 month−1 in summer), we estimated that the population of talitrid amphipods could process an average of 55% of the palatable Macrocystis input. Our results indicate that talitrid amphipod populations can have a significant impact on drift macrophyte processing and fate and that the quantity and composition of drift macrophytes could, in turn, limit populations of beach consumers.

Abstract: Near Santa Barbara, California (USA), the large laminarian kelp Egregia laevigata (Setchell) occurred from the lower intertidal zone to subtidal depths. In the intertidal zone there was a large recruitment of E. laevigata in the spring. The kelp were largely excluded from a zone in the lowest intertidal zone where the surf grass Phyllospadix sp, grew, but were abundant on all other rock surfaces. Experiments demonstrated that, while neither grazers nor sessile organisms significantly reduced recruitment, E. laevigata of the previous year-class did so. There were also interactions among E. laevigata of the same year-class, expressed as a density-dependent mortality of very small algae, and as faster growth rates and greater number of branches of kelp at low densities. These processes tended to make both numbers and biomass of E. laevigata uniform. The mortality rates of large E. laevigata were so high that, in some locations, no kelp survived for more than 8 months. E. laevigata was, therefore, essentially an annual and opportunistic species in the intertidal zone.

Abstract: Previous taxonomic treatments of the family Zosteraceae in Australia/New Zealand have recognized Heter- ozostera tasmanica (monotypic) and four Zostera species all belonging to subgenus Zosterella: Z. capricorni, Z. muelleri, Z. mucronata, Z. novazelandica. Zostera has always been taxonomically problematic in Australia, where researchers have expressed difficulty with species recognition due to vague or inconsistent morphological characters. There also has been a lack of agreement on generic (notably the distinctness of Heterozostera) and subgeneric delimitation. Recent anatomical, develop- mental, and molecular studies urge a reevaluation of relationships in the family. To clarify the taxonomy of Zosteraceae, we investigated interspecific phylogenetic relationships focusing on Australian species of subgenus Zosterella. We examined material comprising all genera of Zosteraceae (Heterozostera, Nanozostera, Phyllospadix, Zostera), six/seven species of Zostera subgenus Zosterella (including all Australian/New Zealand species), and one of four species of Zostera subgenus Zostera .W e conducted phylogenetic analyses of morphological data and DNA sequences from nuclear (ITS) and plastid (trnK intron, rbcL) genomes. Our results indicate two major clades (highly divergent at both morphological and molecular levels) and two subclades (with low morphological and molecular divergence) within Zosteraceae. Little morphological and molecular variation was observed among representatives within the clade of Australian/New Zealand members of subgenus Zosterella, and none provided cladistic support for taxa recognized formerly as separate species. We recommend that Zosteraceae comprise two genera (Phyllospadix, Zostera) with the latter subdivided into three subgenera (Zostera, Zosterella, Heterozostera). Furthermore, Australian/New Zealand representatives of Zostera subgenus Zosterella should be merged within a single species (Z. capricorni) to reflect the inability of morphological or molecular data to effectively delimit additional species in this group.

Abstract: The fate of subtidally drifting macrophytal detritus after its deposition ashore was stud- ied based on short-term mass loss effects and species composition of beach-cast detritus. Different species of macroalgae and seagrass varied in both physical and microbial decay, as well as faunal decomposition rates. Their preferred status as food for detritivorous amphipods also varied. Thus, beach-cast detritus changed in species composition during detritus aging. Estimated turnover rates, based on daily input rates and mass loss rates, ranged from <1 d for Nereocystis luetkeana, Macro- cystis integrifolia and Ulva spp. to roughly 30 d for Fucus spp. and Phyllospadix spp. Thus, the dynamics of nutrient fluxes within the marine-terrestrial ecotone depends not only on the spatial distribution and amount of beach-cast detritus, but also on its species composition.