Grazing on Giant Kelp Microscopic Phases and the Recruitment Success of Annual Populations of Macrocystis Pyrifera (Laminariales, Phaeophyta) in Southern Chile1

Abstract

The giant kelp Macrocystis pyrifera (L.) C. Agardh is widely distributed in the Northern Hemisphere and Southern Hemisphere, yet it exhibits distinct population dynamics at local to regional spatial scales. Giant kelp populations are typically perennial with the potential for year-round reproduction and recruitment. In southern Chile, however, annual giant kelp populations exist and often persist entirely on secondary substrata (e.g., shells of the slipper limpet Crepipatella fecunda [Gastropoda, Calyptraeidae]) that can cover up to 90% of the rocky bottom. In these populations, the macroscopic sporophyte phase disappears annually during winter and early spring, leaving a 3-4 month period in which a persistent microscopic phase remains to support the subsequent year's recruitment. We tested the effects of a suite of grazers on the recruitment success of this critical microscopic phase at two sites in southern Chile. Field experiments indicated that the snail Tegula atra negatively impacted M. pyrifera sporophyte recruitment, but that recruitment was highest in the presence of sessile female limpets, C. fecunda. Conversely, small male C. fecunda (biofilm grazers) did not regulate kelp recruitment. Laboratory observations showed that C. fecunda males only grazed on microscopic kelp gametophytes and small (<250 μm) sporophytes, rejecting larger sporophytes, whereas T. atra grazed on all the kelp stages. Recruitment to the C. fecunda treatments far exceeded that to bare rock in the absence of grazers but was not due to the physical presence of C. fecunda shells. We concluded that the key to M. pyrifera recruitment success in southern Chile is its capacity to colonize secondary substrates provided by the slipper limpet C. fecunda.

Ecophysiological plasticity of annual populations of giant kelp (Macrocystis pyrifera) in a seasonally variable coastal environment in the Northern Patagonian Inner Seas of Southern Chile

“…Asterisk data was not recorded for that time studies of population dynamics and growth rate in variable environments. In the case of these annual kelp populations, this is especially crucial as the coupling of alternating sporophytic generations require a close match of growth, reproduction, recruitment, and the development of the microscopic stages Henríquez et al 2011). This study shows that annual giant kelp populations responded physiologically to enhance its response for surviving and maintaining populations in regions such as NPIS.…”

“…In many regions, light and nutrients can be present well above limiting levels throughout the year (e.g., Central California and Central Chile) thereby permitting continuously high M. pyrifera sporophyte productivity (Jackson 1987;van Tüssenbroek 1989;Vega et al 2005). On the other hand, in the NPIS, annual M. pyrifera populations have microscopic stages are essential for spanning the 4-5 month gap between successive sporophyte cohorts (Henríquez et al 2011). Recruitment occurs in late winter and early growth is key for re-establishing successfully a new sporophytic cohort.…”

Effect of grazing on distribution and recovery of harvested stands of Lessonia berteroana kelp in northern Chile

“…Two reasons could explain this pattern: (1) the strong consequences of grazer abundance and identity on the intertidal landscape (see Poore et al 2012Poore et al , 2014 and (2) some biogenic habitats (e.g. calcareous algae, empty limpet shells) can provide protection from severe grazing for sporelings of macroalgae (see Camus 1994, Henríquez et al 2011. Since impacts can scale with grazer body and population size (Sala & Graham 2002) moderate grazer densities may enhance the abundance of kelp recruits.…”

“…For example, on the southern coast of Chile, the presence of different grazers (e.g. mollusks and echinoderms) increased the abundance of early stages of kelp Macrocystis pyrifera in comparison to treatments with low densities and/or total exclusion of herbivores (Henríquez et al 2011). Two reasons could explain this pattern: (1) the strong consequences of grazer abundance and identity on the intertidal landscape (see Poore et al 2012Poore et al , 2014 and (2) some biogenic habitats (e.g.…”

“…crevices, pits) and/or biogenic heterogeneity (e.g. calcareous algae; Camus 1994, Sala & Graham 2002, Steneck et al 2002, Graham 2004, Henríquez et al 2011, Sala & Dayton 2011, Okamoto et al 2013. The former can reduce the density of propagules and juvenile plants and the latter acts as a spatial refuge for sporophyte survival and/or settlement facilitation (Santelices 1990).…”