ABSTRACT: Climate change is characterised by mul- tiple abiotic forcings acting simultaneously on biotic systems. In marine systems, temperature appears to drive much of the observed change in biotic commu- nities subject to climate change, but this may reflect the focus of most studies only on temperature without consideration of other environmental variables af- fected by climate change. The giant kelp Macrocystispyrifera was once abundant in eastern Tasmania, forming extensive habitats of ecological and economic importance, but recent extensive population decline has occurred. Southerly incursion of warm oligotro- phic East Australian Current (EAC) water has in- creased in frequency and intensity into this region, which has warmed ~4 times the global average, and the warming trend is predicted to continue. This study investigated the single and combined effects of tem- perature, light, and nitrate availability on the physiol- ogy of juvenile M. pyrifera sporophytes in a laboratory experiment. Determination of relative growth rate, photosystem II characteristics, pigments, elemental chemistry, and nucleic acid characteristics over 28 d showed that all experimental factors af fected sporel- ing physiology. Temperature and light drove much of the observed variation related to performance charac- teristics, and rapid deterioration of kelp tissue was a consequence of temperature stress (high tempera- ture), photoinhibition (high light), and low light, ac- companied by impaired photosynthetic efficiency and increased RNA concentration, presumably associated with production of photoprotective proteins. Surpris- ingly, higher relative growth rates were observed in low-nitrate treatments. These findings suggest that negative effects of temperature on M. pyrifera popu- lations will be mediated by local variation in light and nutrient conditions.
This study focuses on two ecologically important kelp species belonging to the order Laminariales, the giant M. pyrifera and the invasive kelp Undaria pinnatifida. Macrocystispyrifera is a dominant species in the Pacific Ocean coasts of northern and southern America and sub-Antarctic islands (Hay 1990a, Graham et al. 2007). Undaria pinnatifida (Harvey) Suringar is native to northeast Asia but has spread to coastal areas of Europe, Australia, New Zealand and America, where its populations are now well established (Pérez et al. 1981, Hay 1990b, Sanderson 1990, Minchin and Nunn 2014). In Europe, U. pinnatifida is listed as one of the top 10 invasive species (Gallardo 2014), colonizing artificial substrates in harbours along southern coast of England (Arenas et al. 2006). In New Zealand, M. pyrifera is a native species and co-habits with U. pinnatifida in coastal areas in the South and North Islands (Pérez et al. 1981, Hay et al. 1985, Hay 1990a, 1990b, Sanderson 1990, Minchin and Nunn 2014). Invasive macroalgal species have been thought to have negative effects on local communities by displacing native macroalgal species (Bax et al. 2003, Schaffelke and Hewitt 2007, Williams and Smith 2007). For example, U. pinnatifida has been reported to decrease macroalgal richness by displacing native species such as M. pyrifera populations in Argentina (Raffo et al. 2009). However, in New Zealand, U. pinnatifida appears to have only a slightly negative effect on native intertidal macroalgal communities, and positively affected
Seaweed meals have been used as food additives for several aquatic organisms to promote growth and feed efficiency. In the white shrimp (Litopenaeus vannamei) inclusion of meal of Macrocystispyrifera (Cruz-Suárez et al., 2009) and Sargassum spp. (Casas-Valdez et al., 2002) at concentrations of 4% have been shown an increase in feed intake, growth rate and biomass production. The prawn Artemesia longinaris is a commercially important marine species that inhabits coastal waters of Argentina, Uruguay, and South Brazil, where temperatures range from 8 to 22ºC and salinities between 33 and 36 (Boschi & Gavio, 2005). Recently the interest in this shrimp has been increasing as a potential species for culture in temperate-zone. In the present study, we have analyzed water-soluble extracts of brown seaweeds Undaria pinnatifida and M. pyrifera, and their chemical characteristics and antioxidant properties in vitro. They were used as feed additives to A. longinaris, and the radical scavenging activity was investigated in midgut gland homogenates using electron paramagnetic spin resonance (EPR) spectroscopy.
The velocities and accelerations accompanying ocean waves can impose large hydrodynamic forces on marine organisms, including kelps (e.g. Denny, 1988; Seymour et al. 1989; Vogel, 1994; Friedland and Denny, 1995). A variety of mechanical strategies have been proposed by which organisms cope with these forces (Koehl, 1984, 1986; Denny, 1988; Johnson and Koehl, 1994; Friedland and Denny, 1995). Of particular importance are strategies pertaining to very large kelps. For example, Koehl and Wainwright (1977) suggest that the bull kelp Nereocystis luetkeana avoids the brunt of hydrodynamic forces by ‘going with the flow’, a strategy facilitated by this species’ flexibility and great length, and by the extensibility of its stipe material. Macrocystispyrifera, the giant kelp, is similar in size and flexibility to N. luetkeana and has similar materials properties; it may thus employ a similar strategy. This strategy gives no guarantee, however, that these plants will not be broken. Indeed, wave forces imposed during storms tear both N. luetkeana and M. pyrifera stipes from the rest of the plant and even dislodge entire holdfasts (Koehl and Wainwright, 1977; Seymour et al. 1989).
al. 2008). A brown alga (Phaeophyceae), the Macrocystis sporophyte is constructed of vegetative fronds anchored to the substrate by a holdfast and held upright in the water column through gas-filled pneumatocysts located at the base of each blade or laminae (Lobban 1978). This alga forms a complex habitat that is host to numerous species relationships between producers (e.g., red foliose algae, corallines, kelps and other brown algae) and consumers (e.g., predators, grazers, planktivores, and detritovores) (Graham et al. 2008). Studies of trophic interactions in kelp forests have traditionally involved macroscopic organisms (Pace et. al 1999, Graham 2004). Several researchers, however, have suggested a need for further scientific investigations into relationships that involve biological pathogens (North 1979, Kohlmeyer 1979, Schatz 1984, Hyde et al. 1998, Silliman and Newell 2003). Biological pathogens that affect kelp are regulated by environmental variability (North 1971), anthropogenic influences (Andrews 1976), and biotic agents such as fungi (Kohlmeyer 1969, Schatz 1984, Apt 1988), bacteria (Andrews 1976, Apt 1988) and endophytic algae (Andrews 1977, Yoshida and Akiyama 1979, Apt 1988). I investigated the existence, proliferation, and trophic relationship between marine fungi present on Macrocystispyrifera and an abundant grazer, the turban snail, within central California.
Several studies about marine ecological interrela- tionships have identified M. pyrifera as an important refuge environment from herbivory, for nurseries of invertebrates and fish (Macchiavello et al., 2010). These studies were conducted by various national researchers in different parts of continental Chile (Santelices et al., 1981; Moreno & Jaramillo, 1983; Ojeda & Santelices, 1984; Santelices & Ojeda, 1984a, 1984b; Dayton, 1985; Vásquez & Santelices, 1990; Lancellotti & Vásquez, 1999). Research regarding the social and economic importance of M. pyrifera has been carried out in Chile as well (Alveal, 1995; Vásquez, 2008; Westermeier et al., 2011). Experi- mental and ecological works, as well as an understanding of the reproductive strategies of this species, have permitted the determination of population dynamic aspects of M. pyrifera in southern Chile (Buschmann et al., 2006).
Nevertheless, several key issues regarding the Macrocystis life history remain to be resolved. Most importantly, Macrocystis microscopic life-history stages have not been observed in the field. Microphotometric techniques have recently been developed for identifying Macrocystis zoospores based on species-specific zoospore absorption spectra (Graham 1999, Graham & Mitchell 1999). Subsequent determination of Macrocystis zoospore concentrations from in situ plankton samples led to direct studies of Macrocystis zoospore planktonic processes (e.g., Graham 2003). However, upon settlement, Macrocystis zoospores germinate into gametophytes of variable cell number and pigment concentration, negating the use of microphotometric techniques for studying post- settlement processes (Graham 2000). Fluorescently labelled monoclonal antibodies have been developed for distinguishing between Macrocystis and Pterygophora gametophytes based on cell surface antigens (Hempel et al. 1989, Eardley et al. 1990). However, the effectiveness of these tags diminishes when applied to field samples, in which kelp cells are universally coated with bacteria (D.C. Reed, personal communication). Additionally, although Kinlan et al. (2003) observed plas- ticity in growth of laboratory-cultured Macrocystis embryonic sporophytes under realistic environ- mental conditions (light and nutrients), and thus the potential for arrested development in this stage, their experiments provided no evidence of arrested development of gametophytes. This study demonstrated (1) that delayed recruitment of Macrocystis post-settlement stages is possible and (2) the general lack of understanding of the physiological processes that regulate the growth, maturation and senescence of Macrocystis microscopic stages. For example, it is considered that kelp female gametophytes living under adequate environmental conditions will have only one or very few cells, one oogonium per gametophyte, and become reproductive
Abstract Macrocystis integrifolia and Lessonia trabecu- lata form vast kelp beds providing a three-dimensional habi- tat for a diverse invertebrate and Wsh fauna oV northern Chile. Habitat modiWcations caused by the El Niño Southern Oscillation (ENSO) are likely to alter the inhabiting commu- nities. The aim of this study was to reveal relationships between distinct habitat structures of a M. integrifolia kelp bed, a dense L. trabeculata kelp bed and L. trabeculata patches colonizing a barren ground, and the associated dom- inant macrobenthic key species. Seasonally 15 sampling units (10 m 2 each) of any of the three habitats were moni- tored by SCUBA divers, which counted sporophytes and macroinvertebrates living between the latter. Furthermore, samples of plants were analysed in the laboratory to measure the morphological variables: total plant length, maximal holdfast diameter, stipe number, number of dichotomies per stipe, frond width and total drained wet mass. Multivariate analysis showed that the L. trabeculata kelp bed is denser, with a higher number of dichotomies per stipe, whereas sporophytes of M. integrifolia are longer with more stipes and wider fronds. Sporophytes of L. trabeculata patchily