Causes of decoupling between larval supply and settlement and consequences for understanding recruitment and population connectivity

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Experimental Marine Biology and Ecology 392 (2010): 9-21, doi:10.1016/j.jembe.2010.04.008.Marine broadcast spawners have two-phase life cycles, with pelagic larvae and benthic adults. Larval supply and settlement link these two phases and are crucial for the persistence of marine populations. Mainly due to the complexity in sampling larval supply accurately, many researchers use settlement as a proxy for larval supply. Larval supply is a constraining variable for settlement because, without larval supply, there is no settlement. Larval supply and settlement may not be well correlated, however, and settlement may not consistently estimate larval supply. This paper explores the argument that larval supply (i.e., larval abundance near settlement sites) may not relate linearly to settlement. We review the relationship between larval supply and settlement, from estimates and biases in larval supply sampling, to non-behavioral and behavioral components, including small-scale hydrodynamics, competency, gregarious behavior, intensification of settlement, lunar periodicity, predation and cannibalism. Physical and structural processes coupled with behavior, such as small-scale hydrodynamics and intensification of settlement, sometimes result in under- or overestimation of larval supply, where it is predicted from a linear relationship with settlement. Although settlement is a function of larval supply, spatial and temporal processes interact with larval behavior to distort the relationship between larval supply and settlement, and when these distortions act consistently in time and space, they cause biased estimates of larval supply from settlement data. Most of the examples discussed here suggest that behavior is the main source of the decoupling between larval supply and settlement because larval behavior affects the vertical distribution of larvae, the response of larvae to hydrodynamics, intensification of settlement, gregariousness, predation and cannibalism. Thus, larval behavior seems to limit broad generalizations on the regulation of settlement by larval supply. Knowledge of the relationship is further hindered by the lack of a well founded theoretical relationship between the two variables. The larval supply- settlement transition may have strong general consequences for population connectivity, since larval supply is a result of larval transport, and settlement constrains recruitment. Thus, measuring larval supply and settlement effectively allows more accurate quantification and understanding of larval transport, recruitment and population connectivity.JP would like to thank WHOI Ocean Life Institute for partial funding. FP’s contribution is based upon research supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation

Cyanobacterial diversity and bioactivity of inland hypersaline microbial mats from a desert stream in the Sultanate of Oman

The cyanobacterial layer (1-3 mm) of microbial mats of Wadi Muqshin, Sultanate of Oman, in hypersaline continental pools near the Empty Quarter desert were analyzed for cyanobacterial diversity, pigments composition and antibacterial and quorum sensing inhibition activities at the microbial community level. The salinity of the ponds reached up to 75 ‰, the temperature was around 49 °C and the salt composition was similar to seawater. Cyanobacteria in pools containing coccoid and filamentous forms similar to those normally found in salt ponds and in intertidal flats were found. Among the observed taxa were Microcoleus chthonoplastes, Spirulina subsalsa, Johannesbaptistia pellucida, Chroococcidiopsis sp., Aphanocapsa sp., Chroococcus sp., Gloeocapsa sp., Schizothrix sp. and Leptolyngbya sp. Using high performance liquid chromatography (HPLC), the pigments chlorophyll a, scytonemin, chlorophyllid a, β-carotene and fucoxanthin were detected, with the highest concentrations obtained for the ultra-violet (UV) sunscreen pigment scytonemin. The chemical extracts of the microorganisms in the mats cyanobacterial layer exhibited antibacterial activity against 3 out of 9 tested pathogenic bacterial strains and showed quorum sensing inhibition activity against the reporters Agrobacterium tumefaciens NTL4 (pZLR4) and Salmonella enterica S235 but not Chromobacterium violaceum CV017. We conclude that the studied inland hypersaline microbial mats harbor similar diversity to their counterparts in intertidal flats and evaporation ponds and could produce chemical compounds that are of biotechnological significance