Epibiosis between the sand crab Emerita analoga and the mussel Semimytilus algosus

Coastal zones of the Humboldt Current Upwelling System (HCUS) are composed both of rocky and sandy beaches inhabited by macrozoobenthic communities. These show oscillating changes in the dominance of species; the abundance of the sand crab Emerita analoga is linked to phases of the El Niño Southern Oscillation (ENSO). The biogenic surfaces of these crabs serve as substrate for opportunistic colonizers. This study is the first record of an epibiosis between E. analoga and the rock mussel Semimytilus algosus, detected at a southern Peruvian sandy beach. Mussels fouled a wide size-range of adult E. analoga (7.3%) but they themselves belonged to small-size classes. The largest S. algosus was 17.4 mm in length. Highest permanence of epibionts was found on larger sand crabs (maximum between 24 and 27 mm). Significantly more mussels were found on the ventral surface (39.4%) compared to 10 other surface areas of the sand crab. Possible benefits and disadvantages of the observed epibiosis for both the basibiont and the epibiont are discussed.

Breeding success and traits of equal and unequal pairs of little penguins (Eudyptula minor) on Phillip Island during 2001-2008

According to life-history theory, individuals optimize their decisions in order to maximize their fitness. This raises a conflict between parents, which need to cooperate to ensure the propagation of their genes but at the same time need to minimize the associated costs. Trading-off between benefits and costs of a reproduction is one of the major forces driving demographic trends and has shaped several different parental care strategies. Using little penguins (Eudyptula minor) as a model, we investigated whether individuals of a pair provide equal parental effort when raising offspring and whether their behavior was consistent over 8 years of contrasting resource availability. Using an automated identification system, we found that 72% of little penguin pairs exhibited unforced (i.e., that did not result from desertion of 1 parent) unequal partnership through the postguard stage. This proportion was lower in favorable years. Although being an equal pair appeared to be a better strategy, it was nonetheless the least often observed. Individuals that contributed less than their partner were not less experienced (measured by age), and gender did not explain differences between partners. Furthermore, birds that contributed little or that contributed a lot tended to be consistent in their level of contribution across years. We suggest that unequal effort during breeding may reflect differences in individual quality, and we encourage future studies on parental care to consider this consistent low and high contributor behavior when investigating differences in pair investment into its offspring. Key words: attendance patterns, individual quality, meal size, parental care, reproductive costs, seabirds.