Temperature effects on reproduction and early life-history traits in the brachyuran crab Cancer setosus in the Humboldt Current System

Abstract

The cold Humboldt Current (HC) allows for a wide distribution range of the crab Cancer setosus MOLINA, 1782 along the Pacific Coast of Peru and Chile (~2 degrees S to 46 degrees S). Life of this cold-water adapted brachyuran crab in the HC is challenged by high interannual temperature variability influenced by El Nino Southern Oscillation (ENSO). Early life-history stages may be particularly sensitive to abrupt changes in temperature and may thus represent physiological bottlenecks in species distribution. The present study aims at identifying the effects and limits of latitudinal and ENSO temperature variation on reproduction and early life history traits of C. setosus. The number of annual ovipositions was calculated from monthly frequencies of ovigerous females and the temperature dependent duration of egg development (65 days at 12 degrees C to 23 days at 22 degrees C). In Ancud, Chile (41 degrees S) one annual clutch is laid in late winter, while in Concepcion (36 degrees S), slightly higher winter temperatures (12 degrees C vs. 10 degrees C in Ancud) enable for reproduction throughout the year (~3.6 clutches per year). However, towards the species northern range the annual number of clutches decreases to ~2 in Coquimbo (29 degrees S) and ~1 in Casma (9 degrees S), which is attributed to an increase in metabolic costs of life under warmer conditions. Temperature dependent changes in the reproductive cycle were confirmed by observations on crabs reared in aquaria in Antofagasta (23 degrees S, 16-22 degrees C) and in Puerto Montt (41 degrees S, 12, 16 and 19 degrees C) for up to 10 and 5 months, respectively. The decreasing interbrood periods at higher temperatures are accompanied by a decrease in the energetic investment per offspring. Eggs laid at low temperatures in Puerto Montt (~11 degrees C) contained 32% more energy, measured as dry mass, carbon, nitrogen, and fatty acid content and volume, than eggs of equal sized females produced at ~19 degrees C in Antofagasta. However, when exposed to warmer temperatures, seasonally in the field and under aquaria conditions, females in Puerto Montt went on to produce smaller eggs in subsequent egg masses. The larger investment per offspring at lower pre-oviposition temperature is discussed to be adaptive by providing the hatching larvae with a higher amount of energy needed for their prolonged development at lower temperatures. Female investment in egg traits is not carried over 1:1 into larval traits. Throughout egg development almost twice as much of the total of fatty acids was used for metabolism in eggs incubated at 12 degrees C compared to 19 degrees C (-1.12 and -0.62 microgram/egg, respectively). The observed high degree of reproductive plasticity is discussed as a key to the species' wide distributional range and to sustaining exploitable populations under conditions of high and unpredictable environmental stochasticity. However, the current level of uncontrolled fishing pressure and the low enforcement of the minimum legal size of 120 mm carapace width (CW) have caused Chilean C. setosus catches to decline for more than a decade. Next to a strict enforcement of the minimum CW, the creation of no-fishing areas is recommended, for (i) allowing recovery of the stock and maintaining larval supply, (ii) studying population dynamics and the ecological role of this benthic predator in the absence of fisheries mortality, and (iii) preventing likely long-term effects of size selective extraction of large, fast-growing specimens on the populations gene-pool ('fisheries-induced evolution').