Predator control of marine communities increases with temperature across 115 degrees of latitude.

Early naturalists suggested that predation intensity increases toward the tropics, affecting fundamental ecological and evolutionary processes by latitude, but empirical support is still limited. Several studies have measured consumption rates across latitude at large scales, with variable results. Moreover, how predation affects prey community composition at such geographic scales remains unknown. Using standardized experiments that spanned 115° of latitude, at 36 nearshore sites along both coasts of the Americas, we found that marine predators have both higher consumption rates and consistently stronger impacts on biomass and species composition of marine invertebrate communities in warmer tropical waters, likely owing to fish predators. Our results provide robust support for a temperature-dependent gradient in interaction strength and have potential implications for how marine ecosystems will respond to ocean warming.

Solar Radiation as an Isolated Environmental Factor in an Experimental Mesocosm Approach for Studying Photosynthetic Acclimation of Macrocystis pyrifera (Ochrophyta).

Solar radiation effects on the ecophysiology and biochemical responses of the brown macroalga Macrocystis pyrifera (L.) C. Agardh were evaluated using a mesocosm approach in Southern Chile. Treatments with different radiation attenuations were simulated with three vertical attenuation coefficients: (1) total (Kd = 0.8 m-1), (2) attenuated (Kd = 1.2 m-1), and (3) low (Kd = 1.6 m-1) radiation levels. Nutrient concentration and temperature did not show differences under the three light conditions. Photosynthetic activity was estimated by in vivo chlorophyll a (Chla) fluorescence under the three light treatments as an isolated physical factor in both in situ solar radiation in the field. This was achieved using a pulse amplitude-modulated (PAM) fluorometera-Diving PAM (in situ). Photosynthetic activity and biochemical composition were measured in winter during two daily cycles (1DC and 2DC) in different parts of the thalli of the plant: (1) canopy zone, (2) middle zone, and (3) down zone, associated with different depths in the mesocosm system. Nevertheless, the in situ electron transport rate (ETR in situ ) was higher in the exposed thalli of the canopy zone, independent of the light treatment conditions. The concentration of phenolic compounds (PC) increases in the down zone in the first daily cycle, and it was higher in the middle zone in the second daily cycle. The Chla increased in the morning time under total and attenuated radiation in the first daily cycle. Solar radiation increasing at midday prompted the photoinhibition of photosynthesis in the canopy zone but also an increase in productivity and phenol content. Therefore, light attenuation in the water column drove key differences in the photo-physiological responses of M. pyrifera, with the highest productivity occurring in thalli positioned in the canopy zone when exposed to solar irradiance.

GRAZING ON GIANT KELP MICROSCOPIC PHASES AND THE RECRUITMENT SUCCESS OF ANNUAL POPULATIONS OF MACROCYSTIS PYRIFERA (LAMINARIALES, PHAEOPHYTA) IN SOUTHERN CHILE(1).

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.