Effects of heat waves and light deprivation on giant kelp juveniles (Macrocystis pyrifera, Laminariales, Paeophyceae

Due to climate change, the incidence of marine heat waves (MHWs) has increased, yet their effects on seaweeds are still not well understood. Adult sporophytes of Macrocystis pyrifera, the species forming the iconic giant kelp forests, can be negatively affected by thermal stress and associated environmental factors (e.g., nutrient depletion, light deprivation); however, little is known about the tolerance/vulnerability of juvenile sporophytes. Simultaneously to MHWs, juveniles can be subjected to light limitation for extended periods of time (days–weeks) due to factors causing turbidity, or even because of shading by understory canopyforming seaweeds. This study evaluated the effects of a simulated MHW (24°C, 7 d) in combination (or not) with light deprivation, on the hotosynthetic capacities, nutrient uptake, and tissue composition, as well as oxidative stress descriptors of M. pyrifera juvenile sporophytes (single blade stage, up to 20 cm length). Maximum quantum yield (Fv/Fm) decreased in juveniles under light at 24°C, likely reflecting some damage on the photosynthetic apparatus or dynamic photoinhibition; however, no other sign of physiological alteration was found in this treatment (i.e., pigments, nutrient reserves and uptake, oxidative stress). Photosynthetic capacities were maintained or even enhanced in plants under light deprivation, likely supported by photoacclimation (pigments increment); by contrast, nitrate uptake and internal storage of carbohydrates were strongly reduced, regardless of temperature. This study indicated that light limitation can be more detrimental to juvenile survival, and therefore recruitment success of M. pyrifera forests, than episodic thermal stress from MHWs.En prensa2,23

Vertical distribution and abundance of copepod nauplii and ichthyoplankton in northern Baja California during strong internal tidal forcing

11 pages, 3 tables, 4 figuresIn this study, we explored the changes in the vertical distribution and abundance of copepod nauplii and ichthyoplankton every hour in three different depth strata during a period of strong internal tides, which have been shown to accumulate and transport plankters. In the deeper stratum, the abundance of copepod nauplii was significantly greater, significantly increased during the cold phase of the internal tide, and was significantly correlated with both total and baroclinic current flows in the direction of internal tide propagation. On the other hand, ichthyoplankton abundance was generally low, with no stratification in vertical distribution, no significant changes across the two phases of the internal tide, and no correlation at any depth with any current flows. The cold phases of the internal tide were characterized by a shallow thermocline, a cooler water column, and a significant increase in the abundance of copepod nauplii in the bottom stratum. On the other hand, the warm phases of the internal tide were characterized by abrupt warming in surface waters, a depression of the thermocline, and a significant decrease of copepod nauplii in the bottom stratum. The depth distribution and buoyancy of the different groups of larvae may be responsible for the differences foundThis work was supported by CONACyT project (221662) awarded to LBL. LSV acknowledges the CONACyT Fronteras de la Ciencia (contract 2015-2-280) project for supportPeer reviewe