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Three species of the intertidal pulmonate limpet genus Siphonaria are sympatric on the south coast of South Africa and all lay gelatinous benthic egg masses. Siphonaria capensis and S. concinna hatch as planktonic larvae, whereas S. serrata has direct-developing larvae. Intertidal zonation of these species contradicts a model predicting direct development in species that occupy the high shore of the intertidal, and planktonic development in species that inhabit the low shore. Siphonaria concinna and S. serrata reach maximum densities on the middle to high shores, often co-existing in the same microhabitats. Siphonaria capensis is most abundant higher in the intertidal, especially in shallow pools where it lays its egg masses. Adults of both S. concinna and S. serrata are usually found on bare rock, though they deposit egg masses in other microhabitats. Whereas Siphonaria serrata uses microhabitats where desiccation is reduced, S. concinna is, in addition, able to use harsher habitats. Laboratory desiccation and field translocation experiments indicated that spawning where low-tide desiccation is reduced enhances embryonic survival. In various microhabitats, embryonic survival reflects interspecific differences in egg mass physical structure and egg capsule size that result in trade-offs between respiratory gas diffusion and desiccation. The relationship between mode of larval developmental and intertidal zonation is complex. While there may be no direct relationship between larval development and the intertidal height occupied by adults, the physical structure of egg masses and the microhabitats used for spawning are adaptive and complementary in terms of desiccation. In the absence of a capacity to migrate vertically to spawn, populations can be reproductively successful only by occupying intertidal heights with microhabitats suitable for the survival of egg masses. [ABSTRACT FROM AUTHOR]

The recruitment of intertidal benthic organisms that have planktonic larvae is influenced by hydrodynamics at multiple nested spatial scales, ranging from tens of centimetres to kilometres. Intertidal mussel populations on the south coast of South Africa are known to exhibit higher cover within bays than on open-coast shorelines. This study tested the hypothesis that topographically driven differences in hydrodynamics will result in comparatively higher recruitment within bays. Specifically, we estimated recruitment rates of the native brown mussel Perna perna and the invasive Mediterranean mussel Mytilus galloprovincialis (family Mytilidae) over five spring tidal cycles at bay and open-coast sites at both Algoa Bay and St Francis Bay, and the data were then correlated with upwelling indices derived from wind data. We recorded 3 313 P. perna and 2 485 M. galloprovincialis recruits individually and found that mussel recruitment within bays was as much as two orders of magnitude higher than on open coast. The relationship between recruit numbers and upwelling indices was positive, although non-significant, and markedly stronger for the open-coast sites (where r2 values were 0.51–0.59). These results indicate that better mussel cover within bays can be at least partially explained by higher recruitment rates. [ABSTRACT FROM AUTHOR]

The Endangered northern rockhopper penguin Eudyptes moseleyi, like all penguins, is monomorphic, making sex determination of individuals in the field challenging. We examined the degree of sexual size dimorphism of adult birds across the species’ breeding range in the Atlantic Ocean and developed discriminant functions (DF) to predict individuals’ sex using morphometric measurements. We found significant site-specific differences in both bill length and bill depth, with males being the larger sex on each island. Across all islands, bill length contributed 78% to dissimilarity between sexes. Penguins on Gough Island had significantly longer bills, whilst those from Tristan da Cunha had the deepest. Island-specific DFs correctly classified 82-94% of individuals, and all functions performed significantly better than chance. The model for Nightingale Island correctly classified the greatest proportion of individuals (94-95%), while that for Tristan da Cunha performed the poorest (80-82%). A discriminant function derived from all sites accurately sexed 86-88% of northern rockhopper penguins achieving similar accuracy to island-specific functions. While molecular techniques conclusively determine an individual’s sex, morphometric measurements can provide a reliable estimate with close to 90% accuracy using a method that is less invasive and requires little technical expertise. Sexing is an important tool for meaningful interpretation of ecological data. Consideration of sex-specific differences in future studies will aid investigation of a potential sex-dependent vulnerability in this Endangered species.

Environmental temperature affects ectotherm performance and fitness because physiological performance increases up to a sublethal optimum temperature; this is not fixed, but depends on the species and individual history. We explored the influence of species identity, size and thermal history on thermal tolerance in four species of littorinid snails in South Africa. As expected, heat coma temperature (HCT) was lower than the lethal temperatures (LT50), and was greater for juveniles, while LT50 was greater for adults. The ranking by both metrics was Echinolittorina natalensis > Littoraria glabrata > Afrolittorina africana > A. knysnaensis, reflecting their biogeographical distributions. No species showed an effect of laboratory acclimation for 14 days at temperatures from 20 to 35 °C, though HCT was lower for field fresh individuals than for all other treatments. Nor was there acclimatisation of LT50 between seasons. Bioregion is a proxy for lifetime acclimatisation yet the Afrolittorina species showed nonsignificant differences between conspecifics from different regions. The effect of size differed between the two metrics, and field fresh individuals showed lower HCT values than laboratory-treated individuals—which taken together indicates the need for care when interpreting the results of lab work. The thermal tolerances of these species reflect their biogeography and appear fixed with little or no plasticity, rendering these littorinids vulnerable to future climate warming. [ABSTRACT FROM AUTHOR]