Discriminating between food and space imitation in benthic suspension feeders using self-thinning relationships

Abstract

Growth and survival have been shown to be density-dependent in many populations of benthic suspension feeders, but it is generally difficult to determine whether food or space is the limiting factor. The study of biomass-density relationships (B-N diagram) in self-thinning situations may provide an additional criterion for such a purpose. It is shown here that the slope of B-N diagrams may vary significantly depending on whether food or space is the Limiting factor When food is Limiting, it varies as a function of the exponent relating respiration to individual biomass. When space is limiting, the slope varies as a function of the length-weight relationship, roughness of the substrate at scales significant to the organisms, and the relationship between individual size and maximum population density. Testing the slopes of B-N relationships may, therefore, provide evidence concerning the nature of the limiting factor. Further, when food is the Limiting factor, the intercept of B-N diagrams is an index of site quality. An example of the use of the B-N diagram for purposes of managing bivalve aquaculture is provided for mussels cultivated on bouchots (intertidal stakes). It is shown that in this particular case, space and food probably alternated seasonally as limiting factors. In addition, under the hypothesis that the entire population is completely harvested on a single occasion, analysis of the B-N diagram provides an estimate of the optimal sowing density in order to minimize competition and avoid subsequent thinning operations. These results illustrate the utllity of managing cultivated populations in terms of biomass and density jointly.

Evaluation of self‐thinning models and estimation methods in multilayered sessile animal populations

“…Accordingly, they associated the ST phenomenon with the metabolic rate of the population (MR, measured as the respiration rate of individuals [ml O 2 /h]), which itself is related to the mean individual mass (MR } Nm 3/4 ) and the environmental conditions (MR } F, where F is the overall energy flow through the population), leading to an exponent of b ¼ À1/3 (and c ¼ À4/3) under constant resource supply per unit area (Begon et al 1986, Bohlin et al 1994, Enquist et al 1998, Belgrano et al 2002, Brown et al 2004). The majority of ST studies have focused on the determination of the factor regulating competition (space/food) in a given population, based on comparison between observed and these theoretical ST exponents (Fréchette and Lefaivre 1990).…”

“…When ST models were applied to sessile animals such as mussels, it was recognized that their multilayered packing, which increases the surface area available to the organisms, and allometric growth could introduce bias in the model and cause a deviation of the theoretical SST exponent (White 1981, Westoby 1984, Weller 1987b, Hughes and Griffiths 1988and Norberg 1988a. These deviations have been included in more recent mussel selfthinning analysis (Fréchette and Lefaivre 1990, Guiñez and Castilla 1999, Guiñez et al 2005. Particularly, Guiñez and Castilla (1999) proposed to incorporate the number of layers in the model and defined the tridimensional ST model as…”

“…It is well known that the highly dense multilayered disposition of mussels can lead to space and food limitations (Okamura 1986, Fréchette et al 1992, Alvarado and Castilla 1996 and to self-thinning as the individuals grow (Hughes and Griffiths 1988, Fréchette and Lefaivre 1990, Fréchette and Lefaivre 1995, Petraitis 1995, Guiñez and Castilla 1999, Guiñez et al 2005. However, despite that several authors have analyzed ST in mussel populations (Hughes and Griffiths 1988, Fréchette and Lefaivre 1990, Petraitis 1995, Fréchette et al 1996, Guiñez and Castilla 1999, Alunno-Bruscia et al 2000, Alunno-Brusciaet al 2001, Filgueira et al 2008) some aspects of the biomass/massdensity relationships need to be revised.…”

“…However, despite that several authors have analyzed ST in mussel populations (Hughes and Griffiths 1988, Fréchette and Lefaivre 1990, Petraitis 1995, Fréchette et al 1996, Guiñez and Castilla 1999, Alunno-Bruscia et al 2000, Alunno-Brusciaet al 2001, Filgueira et al 2008) some aspects of the biomass/massdensity relationships need to be revised. Firstly, the main goal of self-thinning analysis has been to determine the competition limiting factor by comparing theoretical and observed exponents.…”

Production efficiency of mussel bottom culture

“…The slope of the axis after four weeks was -0.41 with`95% CI: [-0.23,-0.71] and at the end of the experiment after 12 weeks it was -0.36 with 95% CI: [-0.19,-0.68]. According to the self-thinning theory, there is no evidence that the population was regulated through or moving towards either classical food regulated self-thinning (FST, expected slope towards -3/2) or space regulated self-thinning (SST, expected slope towards -4/3), as the slope did not decrease over time and was well above -1 (Hughes & Griffiths 1988, Fréchette & Lefaivre 1990, Fréchette & Bacher 1998. However, we observed density-dependent loss rates (d -1 ) in this experiment, with the highest loss rates observed within the first four weeks.…”