Marine broadcast spawners have two-phase life cycles, with pelagic larvae and benthic adults. 2 Larval supply and settlement link these two phases and are crucial for the persistence of marine 3 populations. Mainly due to the complexity in sampling larval supply accurately, many 4 researchers use settlement as a proxy for larval supply. Larval supply is a constraining variable 5 for settlement because, without larval supply, there is no settlement. Larval supply and 6 settlement may not be well correlated, however, and settlement may not consistently estimate 7 larval supply. 8This paper explores the argument that larval supply (i.e., larval abundance near settlement sites) 9 may not relate linearly to settlement. We review the relationship between larval supply and 10 settlement, from estimates and biases in larval supply sampling, to non-behavioral and 11 behavioral components, including small-scale hydrodynamics, competency, gregarious behavior, 12 intensification of settlement, lunar periodicity, predation and cannibalism. Physical and structural 13 processes coupled with behavior, such as small-scale hydrodynamics and intensification of 14 settlement, sometimes result in under-or overestimation of larval supply, where it is predicted 15 from a linear relationship with settlement. Although settlement is a function of larval supply, 16 spatial and temporal processes interact with larval behavior to distort the relationship between 17 larval supply and settlement, and when these distortions act consistently in time and space, they 18 cause biased estimates of larval supply from settlement data. 19Most of the examples discussed here suggest that behavior is the main source of the decoupling 20 between larval supply and settlement because larval behavior affects the vertical distribution of 21 3 larvae, the response of larvae to hydrodynamics, intensification of settlement, gregariousness, 1 predation and cannibalism. Thus, larval behavior seems to limit broad generalizations on the 2 regulation of settlement by larval supply. Knowledge of the relationship is further hindered by 3 the lack of a well founded theoretical relationship between the two variables. 4The larval supply-settlement transition may have strong general consequences for population 5 connectivity, since larval supply is a result of larval transport, and settlement constrains 6 recruitment. Thus, measuring larval supply and settlement effectively allows more accurate 7 quantification and understanding of larval transport, recruitment and population connectivity. 8 9 4

Aim Topographic complexity is widely accepted as a key driver of biodiversity, but at the patch‐scale, complexity–biodiversity relationships may vary spatially and temporally according to the environmental stressors complexity mitigates, and the species richness and identity of potential colonists. Using a manipulative experiment, we assessed spatial variation in patch‐scale effects of complexity on intertidal biodiversity. Location 27 sites within 14 estuaries/bays distributed globally. Time period 2015–2017. Major taxa studied Functional groups of algae, sessile and mobile invertebrates. Methods Concrete tiles of differing complexity (flat; 2.5‐cm or 5‐cm complex) were affixed at low–high intertidal elevation on coastal defence structures, and the richness and abundance of the colonizing taxa were quantified after 12 months. Results The patch‐scale effects of complexity varied spatially and among functional groups. Complexity had neutral to positive effects on total, invertebrate and algal taxa richness, and invertebrate abundances. However, effects on the abundance of algae ranged from positive to negative, depending on location and functional group. The tidal elevation at which tiles were placed accounted for some variation. The total and invertebrate richness were greater at low or mid than at high intertidal elevations. Latitude was also an important source of spatial variation, with the effects of complexity on total richness and mobile mollusc abundance greatest at lower latitudes, whilst the cover of sessile invertebrates and sessile molluscs responded most strongly to complexity at higher latitudes. Conclusions After 12 months, patch‐scale relationships between biodiversity and habitat complexity were not universally positive. Instead, the relationship varied among functional groups and according to local abiotic and biotic conditions. This result challenges the assumption that effects of complexity on biodiversity are universally positive. The variable effect of complexity has ramifications for community and applied ecology, including eco‐engineering and restoration that seek to bolster biodiversity through the addition of complexity.

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We examined larval availability and settlement of the intertidal mussel Perna perna simultaneously at different spatial and temporal scales using a nested design at 2 sites, 3 km apart on the south coast of South Africa. Each site had 3 locations (300 m apart) where 5 artificial settler collectors were placed about 20 cm apart. Collectors were replaced on temporal scales varying from fortnightly (for 16 mo) to daily (2 series of 15 to 20 d). Each intertidal location was paired with an inshore location (these too were 300 m apart) within 500 m of the shore, where larval availability was measured by 3 vertical plankton hauls collected on the same dates as for settler sampling. There was strong temporal variation in abundances of larvae and settlers, and no correlation (r always < 0.14) was found between the two. Larvae were abundant only at the start of sampling and rare for the rest of the study, while distinct peaks in settler numbers occurred later. No spatial effect was detected for larval availability, while there was strong spatial variation in settlement at the location level. These results indicate that, on scales of 100s of m to km, delivery of larvae from the nearshore water column onto the shore is strongly differential, with some locations consistently receiving more settlers than others. We conclude that, at these sites, the patchiness in settlement observed on scales of 100s of m depends on differential delivery, rather than differential offshore distribution of larvae. We suggest that differential delivery is due to the effect of nearshore bottom topography on local hydrodynamics.