Oceanographical processes, such as upwelling, induce variations in nutrient availability in marine ecosystems, and evidence indicates that nutrient input can strongly influence the physiological activities, structure, and dynamics of marine communities. Intertidal organisms have long been considered ideal study units in which to quantify the relationship of physical variations and differential energy allocations in specimens that undergo environmental variations, such as observed with nutrient availability. In habitats with differential nutrient input (upwelling versus non-upwelling), both food availability (algae abundance) and seasonal gonadal and foot weight variations were determined in the keyhole limpet Fissurella crassa. Gonadal weight is used as a measure of reproduction allocation whereas foot weight is an indirect indicator of energy allocation towards survival. RNA:DNA ratio in limpets was used as an indicator of biosynthetic capability. Our results indicate that, in general, algae abundance, muscular foot weight, and gonadal weight were higher in upwelling sites during all seasons studied. The same result was found for RNA:DNA ratios. Energetic allocation in animals that inhabit intertidal upwelling habitats supported a constant allocation towards reproduction and soft tissues. In contrast, animals that inhabit non-upwelling habitats showed important energetic restrictions associated with higher water temperature and lower food availability. Our results clearly show that in the keyhole limpet F. crassa food availability is a more important determinant of an individual's condition than a physical variation such as environment temperature.

Intertidal organisms have long been considered an ideal system to quantify how physical variations determine differential energy allocations in specimens inhabiting environmental gradients such as exposure to wave action. In habitats with differential intertidal wave exposure (sheltered, Sh; and exposed, E) seasonal gonadal and foot weight variations and their associations with exposure and food availability (algae abundance) were determined in the keyhole limpet Fissurella crassa. Gonadal weight is used as a measure of reproduction allocation whereas foot weight is an indirect indicator of energy allocation to survival. RNA:DNA ratio in limpets obtained from Sh and E habitats during the two different seasons was used as an indicator of biosynthetic capability. Our results indicate that algae abundance in E sites was higher in summer and lower in winter compared to Sh sites. In E sites the muscular foot weight of limpet was higher in summer in contrast to Sh sites where F. crassa muscular foot weight of limpet was higher in winter. Gonadal weight in Sh sites was higher in summer and remained constant in winter; whereas in E sites gonadal weight was lower in summer and higher in winter. RNA:DNA ratios indicate that regardless of intertidal wave exposure, F. crassa showed higher biosynthetic capability in summer. Energetic allocation in animals that inhabit sheltered intertidal habitats would support constant allocation towards reproduction. In contrast, animals that inhabit exposed habitats may favour seasonally reproduction allocation at expense of survival.