Addition of species abundance and performance predicts community primary production of macroalgae

Abstract

Understory plant assemblages are important sources of primary production in both terrestrial and marine environments, and they may exhibit different dynamics than their overstory counterparts. For example, production within dense upper canopies is typically light-limited by shading, whereas such canopy architecture effects are likely unimportant in low-light environments, such as those inhabited by sparser understory assemblages. In these assemblages, light saturation of understory production may be common as species become limited by their photosynthetic capacity, which is adapted to low-light levels. Here we show that a simple model relating species-specific light use relationships measured in the laboratory to biomass and light levels measured in nature accurately predicts community gross primary production (GPP) in a marine understory algal community. We validate the model by comparing GPP measured in situ in enclosed chambers with model estimates for the same incubations. Model estimates of GPP explained 70% of the variation in the measured estimates. The results show that GPP was accurately estimated by simple addition of the photosynthetic capacity of each species in the community based on their biomass and the available light. The difference between modeled and measured GPP did not show any relationship with community biomass or diversity, and the results suggest that diversity does not significantly affect productivity in this system. This type of model should be applicable in other environments where canopy architecture does not play a significant role in limiting photosynthesis.

Species insurance trumps spatial insurance in stabilizing biomass of a marine macroalgal metacommunity

“…Although we know most of these species are physiologically diverse (Miller et al. , Harrer et al. ), their functional traits and ability to use complementary resources remain mostly unknown.…”

“…Other factors such as nutrient supply, suspended sediments, and water flow are also considered important in explaining the biomass dynamics of understory macroalgae (Schiel and Foster 2015), and contrasting responses to such environmental variables as well as competitive interactions may have contributed to complementarity in their biomass dynamics. Although we know most of these species are physiologically diverse (Miller et al 2012, Harrer et al 2013, their functional traits and ability to use complementary resources remain mostly unknown.…”

Effects of five southern California macroalgal diets on consumption, growth, and gonad weight, in the purple sea urchin Strongylocentrotus purpuratus

“…Our results focus on the four species of algae that collectively comprised > 75% of the biomass in kelp forests off Santa Barbara (Miller, Harrer & Reed 2012) and elucidate the effects of these algae on performance of purple sea urchins, which may have implications for urchin populations in the wild. First, the ability to switch between diets, namely diets of Chondracanthus and Macrocystis (the urchin's preferred food), with little or no cost to growth and reproduction suggests that Chondracanthus could serve as an important alternative food source when Macrocystis is disproportionately removed by large waves (Dayton & Tegner 1984;Dayton et al 1999;Gaylord, Denny & Koehl 2008).…”

“…Upon the removal of Macrocystis, understory algae such as Chondracanthus become more abundant (Arkema, Reed & Schroeter 2009;Miller, Reed & Brzezinski 2011) and may serve as a suitable food that can sustain urchin populations and promote high growth and reproduction. Chondracanthus' relatively low rate of primary production (Miller, Harrer & Reed 2012), however, indicate it might not be a long-term sustainable food source. Additionally our results suggest that in the context of the four abundant algae we tested, algal assemblage diversity may not be as important as the availability of one or two high quality food sources.…”

“…These four species were chosen because they represented a large proportion (> 75%) of the algal biomass in our study region in southern California (Miller, Harrer & Reed 2012) and are consumed by Strongylocentrotus in the field (Byrnes, Cardinale & Reed 2013). Thus, changes in the performance of purple sea urchins resulting from changes in the availability of these four species of macroalgae could have large implications for the structure of subtidal reef communities.…”