Microchemical analyses of fish otoliths have revolutionized fisheries science. Molecules deposited within otoliths may originate from ambient water and diet, with molecular concentrations being subject to subsequent physiological alteration after exposure. Analyses of otolith microstructure and incorporation of inorganic elements have led to major advances in stock assessment and fisheries ecology. However, the use of otoliths for microchemical analyses has drawbacks. Specifically, otolith removal from live specimens requires specimen sacrifice, which may be forbidden in the case of protected species. In addition, otoliths rarely contain sufficient concentrations of organic matter to allow reconstruction of food-web relationships via multiple stable isotopes, and otolith microstructure can be difficult to interpret in some species. Here, we review alternatives to otoliths that can provide microchemical analytes for life-history studies in fishes. Our focus is to describe advantages and disadvantages to the use of each alternative structure, with particular attention paid to trace-element analysis for inorganic matrices and stable-isotope analysis for organic ones. In general, the chronological analysis of elemental and isotopic values within each structure depends on the inert nature (or lack of molecular turnover) of the tissue. Structures with high turnover rates or those that are metabolically active will not effectively record elemental or isotopic compositions over time. Here, we provide an assessment of the use of bony endoskeleton, fin spines, fin rays, scales, and eye lenses as alternatives or complements to fish otolith analysis.

The perennial red macroalga Gracilaria vermiculophylla (Ohmi) Papenfuss has recently been introduced to the Baltic Sea and is a potential competitor to Fucus vesiculosus, the most common native perennial alga in large parts of the Baltic Sea. Gracilaria might interfere with Fucus through direct competition for resources. In addition, Gracilaria is a favoured refuge for mesograzers, which prefer to feed on Fucus. Mesocosm-experiments were conducted over one year in the Kiel Fjord in order to test the direct and indirect effects of Gracilaria on Fucus. Fucus was incubated with Gracilaria at three different densities and grazers in high or low abundances. High densities of Gracilaria inhibited the growth of Fucus adults and also reduced the half-life-time of Fucus germlings. Associated grazers also had a negative effect on Fucus adults. Our results suggest that Gracilaria is able to influence Fucus in the Baltic Sea through direct competition for resources and by exposing it to higher grazer pressure.

The effects of infrequent disturbance events on marine fishes are often difficult to determine, due largely to lack of sufficient pre-and post-disturbance event data. In January 2010, subtropical southwestern Florida (USA) experienced extreme cold for 13 days, which caused extensive mortality of many fish species. The effect of this severe cold event on common snook (Centropomus undecimalis), an economically important gamefish, was assessed using three years (2007)(2008)(2009)) of pre-event and one year (2010) of post-event data from a tag-recapture program conducted over 28 km of Gulf of Mexico barrier islands of Florida. All metrics pointed to a significant effect of the severe cold event: post-disturbance apparent survival of marked fish was 96-97% lower than pre-disturbance, and post-disturbance common snook abundance was 75.57% and 41.88% less than in 2008 and 2009, the two years immediately pre-event. Although severe cold events have impacted subtropical Florida in the past, these events are infrequent (the previous recorded event was >30 years prior), and documentation of the impacts on common snook have not previously been published.

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