Growth and Persistence of Diverse Intertidal Crusts: Survival of the Slow in a Fast-Paced World

Encrusting algae are conspicuous components of hard-substratum benthic communities in the photic zone despite being poor competitors and slow growers. Little is known about their growth rates or about mechanisms controlling key processes such as wound healing and surviving overgrowth. We manipulated 12 crustose species (including red and brown algae and a lichen) from the intertidal zone of Washington, USA, studying their varying responses to identical experimental conditions. Three of 8 crust species tested showed increased growth rates with size. Species healed from standardized wounds at different rates and using different mechanisms (e.g. lateral vs vertical regeneration) as seen in cross-sections. Three species showed altered growth rates at unwounded margins of wounded crusts, suggesting intrathallus communication. Year-long experiments involving simulated overgrowth showed that some species can maintain healthy tissue in a covered area, and one (the coralline Lithothamnion phymatodeum) even grew new tissue there. Other species gradually lost color, thickness, and area in covered areas. Hildenbrandia occidentalis survived remarkably well when covered, possibly due to its very slow growth and low metabolic demand. One suggested mechanism underlying the high variation in responses among crusts is the degree to which their thalli may be anatomically integrated by features such as cell fusions; physiological work testing translocation via these features is needed. Other mechanisms allowing persistence include rapid wound healing and frequent recruitment.

Physiological Responses to Environmental Variation in Intertidal Red Algae: Does Thallus Morphology Matter?

Morphological variation within and among many species of algae show correlated life history traits. The trade-offs of Life history traits among different morphs are presumed to be determined by morphology. Form-function hypotheses also predict that algae of different morphological groups exhibit different tolerances to physiological stress, whereas algae within a morphological group respond similarly to stress. We tested this hypothesis by comparing photosynthetic and respiratory responses to variation in season, light, temperature, desiccation and freezing among the morphologically similar fronds of Chondrus crispus and Mastocarpus stellatus and the alternate stage crust of M. stellatus. Physiological differences between fronds of the 2 species and crusts and fronds were consistent with their patterns of distribution and abundance in the intertidal zone. However, there was no clear relationship between algal morphology and physiological response to environmental variation. These results suggest that among macroalgae the correlation between Life history traits and morphology is not always causal. Rather, the link between life history traits and morphology is constrained by the extent to which physiological characteristics codetermine these features.

Extension and Partitioning in an Oblique Subduction Zone, New Zealand: Constraints from Three-Dimensional Numerical Modeling

Contraction, strike slip, and extension displacements along the Hikurangi margin northeast of the North Island of New Zealand coincide with large lateral gradients in material properties. We use a finite- difference code utilizing elastic and elastic-plastic rheologies to build large- scale, three-dimensional numerical models which investigate the influence of material properties on velocity partitioning within oblique subduction zones. Rheological variation in the oblique models is constrained by seismic velocity and attenuation information available for the Hikurangi margin. We compare the effect of weakly versus strongly coupled subduction interfaces on the development of extension and the partitioning of velocity components for orthogonal and oblique convergence and include the effect of ponded sediments beneath the Raukumara Peninsula. Extension and velocity partitioning occur if the subduction interface is weak, but neither develops if the subduction interface is strong. The simple mechanical model incorporating rheological variation based on seismic observations produces kinematics that closely match those published from the Hikurangi margin. These include extension within the Taupo Volcanic Zone, uplift over ponded sediments, and dextral contraction to the south.

Age, Growth and Population Structure of Jumbo Flying Squid, Dosidicus Gigas, Based on Statolith Microstructure Off the Exclusive Economic Zone of Chilean Waters

The jumbo flying squid, Dosidicus gigas, support an important squid fishery off the Exclusive Economic Zone of Chilean waters. However, we only have limited information about their biology. In this study, age, growth and population structure of D. gigas were studied using statoliths from 333 specimens (386 females and 147 males) randomly sampled in the Chinese squid jigging surveys from 2007 to 2008 off the Exclusive Economic Zone of Chile. Mantle lengths (MLs) of the sample ranged from 206 to 702 mm, and their ages were estimated from 150 to 307 days for females and from 127 to 302 days for males. At least two spawning groups were identified, the main spawning peak tended to occur between August and November (austral spring group), and the secondary peak appeared during March to June (austral autumn group). The ML-age relationship was best modelled by a linear function for the austral spring group and a power function for the austral autumn group, and the body weight (BW)-age relationship was best described by an exponential function for both the groups. Instantaneous relative growth rates and absolute growth rates for ML and BW did not differ significantly between the two groups. The growth rate of D. gigas tended to be high at young stages, and then decreased after the sub-adult stage (>180 days old). This study suggests large spatial and temporal variability in key life history parameters of D. gigas, calling for the collection of more data with fine spatial and temporal scales to further improve our understanding of the fishery biology of D. gigas.