Seasonal variation in floating persistence of detached Durvillaea antarctica (Chamisso) Hariot thalli

Abstract

Several large kelp species are capable of longdistance dispersal via rafting. However, seasonal changes in environmental conditions at the sea surface may variably affect the physiological status of the floating thalli; challenging conditions during summer may accelerate disintegration and cause rapid sinking. We used the bull kelp Durvillaea antarctica from northern-central Chile (30 ° S) to test seasonal variation in floating persistence. Experiments with tethered specimens were conducted in all seasons to assess how variable environmental conditions influence the morphology and photosynthetic characteristics of floating D. antarctica . Floating specimens stayed afloat at the surface for more than 1 month during moderate environmental conditions that prevailed in winter, spring, and fall. However, higher water temperatures and intense solar radiation in summer resulted in significant biomass losses and rapid disintegration of the floating kelps; consequently, they sank within < 1 month. These strong seasonal effects were reflected in decreasing maximal quantum yield as well as in maximum relative electron transport rates of photosynthesis. Understanding physiological responses of floating algae is important because increasing global temperatures and shifts in solar radiation may strongly affect the survival of floating algae, potentially reducing the distances and frequencies of rafting dispersal.

Latitudinal and seasonal effects on short-term acclimation of floating kelp species from the South-East Pacific

“…Deleterious combinations of high light and temperature at the sea surface affect the tissue integrity causing biomass losses at low latitudes (Coquimbo), regardless of the season. Similar results have been described for in situ (Graiff et al, 2013) and mesocosm experiments (Rothäusler et al, 2009(Rothäusler et al, , 2011c with D. antarctica and M. pyrifera, respectively.…”

“…Samples for pigments, soluble phlorotannins and antioxidant capacity were frozen in liquid nitrogen, stored at −80°C, and then sent on dry ice to the central analysis laboratory at Universidad Católica del Norte in Coquimbo. All analyses were done in similar ways as in previous studies with floating Macrocystis (Rothäusler et al, 2011a(Rothäusler et al, , 2011c and Durvillaea (Graiff et al, 2013;Tala et al, 2013) and are briefly described below.…”

“…However, during their voyage biotic factors, including grazing (by snails, urchins, crustaceans), fouling (by bryozoans, stalked barnacles, epiphytic algae) (Thiel and Gutow, 2005;Rothäusler et al, 2009;Gutow et al, 2012), and abiotic factors such as high water temperatures, intense solar radiation and nutrient depletion negatively affect the floating seaweeds, limiting their persistence at the sea surface (Hobday, 2000;Karsten et al, 2001;Vandendriessche et al, 2007;Graiff et al, 2013). Even though initial physiological acclimation can occur, the decline in growth and reproductive capacity are the main changes suppressing the colonization potential of floating kelps (Hobday, 2000;Macaya et al, 2005;Hernández-Carmona et al, 2006;Vandendriessche et al, 2007;Rothäusler et al, 2009.…”

“…In summer, high temperature and solar radiation may affect the photosynthetic efficiency and pigment concentration and cause an increase in tissue degradation, thereby contributing to the sinking of floating kelps (Rothäusler et al, 2009(Rothäusler et al, , 2011cGraiff et al, 2013). In contrast, during winter the conditions at the sea surface are more moderate and floating kelps can persist for longer time periods (Graiff et al, 2013;Tala et al, 2013). Solar radiation shows a general gradient decreasing from the equator towards the poles with greater seasonal changes at higher latitudes than at low latitudes (Kain, 1989).…”

“…Current knowledge on the growth and physiology of floating seaweeds and the environmental factors influencing their persistence at the sea surface is mainly limited to mid and low latitudes (b40°S) and experimental conditions (e.g. Vandendriessche et al, 2007;Rothäusler et al, 2009Rothäusler et al, , 2011aRothäusler et al, , 2011cGraiff et al, 2013). Considering that floating seaweeds are abundant at higher latitudes (N40°S) (Smith, 2002;Hinojosa et al, 2010Hinojosa et al, , 2011Rothäusler et al, 2012;Wichmann et al, 2012), long-distance rafting appears most relevant at these latitudes (Fraser et al, 2009;Macaya and Zuccarello, 2010a;Fraser et al, 2011;Cumming et al, 2014).…”