Roles of transport and mixing processes in kelp forest ecology

Abstract

where B, D, I and E are the number of births, deaths, immigrants and emigrants, respectively. The biology of canopy-forming kelps like Macrocystis is such that there are multiple avenues by which physical processes influence terms on the right-hand side of Eqn 1. Among the most obvious are those affecting immigration and emigration rates, although all four parameters may be impacted. Kelps [i.e. brown algae of the order Laminariales (Abbott and Hollenberg, 1976)] produce reproductive propagules (microscopic spores) that serve as the primary agent of dispersal and have little capacity for swimming. Therefore, hydrodynamics dictate how far spores are carried, whether they exit their population of origin, and rates at which they enter adjacent populations. Properties of spore transport interact with other life history features as well. Most canopy-forming kelps have specific depth and substrate requirements, which confine them to locations where there is adequate light for growth and rocky seafloor for attachment. Especially for taxa that inhabit deeper, subtidal waters (5-30m depth), these constraints encourage discontinuities in distribution, with populations growing as disjunct forests separated by expanses Accepted 13 September 2011 Summary Fluid-dynamic transport and mixing processes affect birth, death, immigration and emigration rates in kelp forests, and can modulate broader community interactions. In the most highly studied canopy-forming kelp, Macrocystis pyrifera (the giant kelp), models of hydrodynamic and oceanographic phenomena influencing spore movement provide bounds on reproduction, quantify patterns of local and regional propagule supply, identify scales of population connectivity, and establish context for agents of early life mortality. Other analyses yield insight into flow-mediated species interactions within kelp forests. In each case, advances emerge from the use of ecomechanical approaches that propagate physical-biological connections at the scale of the individual to higher levels of ecological organization. In systems where physical factors strongly influence population, community or ecosystem properties, such mechanics-based methods promote crucial progress but are just beginning to realize their full potential.

Diffusion Boundary Layers Ameliorate the Negative Effects of Ocean Acidification on the Temperate Coralline Macroalga Arthrocardia corymbosa

“…However, further research is required to fully examine the role of kelp canopies on understorey organisms. For example, the flow rates in our slow flow treatment were zero for over four hours, and while velocity can reach zero within seaweed canopies [89], the temporal dynamics will be a function of seaweed density, size and bulk seawater velocity, which is usually greater than zero [20], [89], [92], [93]. Future research should examine what protective role the DBL could play at a greater range of seawater velocities, and for a greater range of species, than those used here.…”

Assessing vertebrate biodiversity in a kelp forest ecosystem using environmental DNA

“…Our results support the latter hypothesis, although the detection probability in this study system may be high due to local oceanography at the time of sampling, the retentive properties of kelp forests (Gaylord et al . 2012), or both. We note, too, that differences in community composition and taxon abundance between the open water vs. nearshore habitats may also be due to depth as open water samples were collected at the surface while all other habitat samples were collected 1 m from the bottom.…”

Sea urchin barrens as alternative stable states of collapsed kelp ecosystems

“…In widespread barrens, the urchin-dominated state may be further stabilized by a lack of reproductive source populations of kelp that provide spores for recruitment (Keats 1991). Kelp spores are short-lived and typically settle within 5 to 10 m of the parent plant (Norton 1992, Gaylord et al 2012), although maximum dispersal distances of up to 5 km have been measured for some species (e.g. Laminaria hyperborea, Norton 1992; Macrocystis pyrifera, Gaylord et al 2006).…”