Growth and sediment disturbances of Caulerpa spp. (Chlorophyta) in a submarine canyon

Abstract

Growth rates of 7 species of Caulerpa were measured in sifu at depths of 20 m in Salt River canyon, St. Croix, US Virgin Islands. Mean stolon elongation rate for all species of Caulerpa studied was approximately 1 cm d-l. Dry biomass accumulated in this new growth was less than 10 mg d-', and specific growth rates were less than 10 % d-'; these values are low compared to rates of many benthic macroalgae. Macrofauna (conchs, ghost shrimp, hermit crabs, urchins, rays) were observed disturbing sediment. Plants were uprooted or buried by animals that foraged, burrowed, and made excavations or sediment mounds. Plants experimentally uprooted or burled to simulate effects of animal activities had significantly lower stolon elongation, biomass accumulation, and specific growth rates than control plants. We hypothesize that the productivity of these algae is limited in part by animal-mediated sediment disturbances.

Production, decomposition, and heterotrophic utilization of the seagrass Halophila decipiens in a submarine canyon

“…Thereafter the rates fluctuated but remained consistently higher in the surface bags. d-l), the dominant rhizophytic algae in the Canyon (Williams et al 1985).…”

“…Halophila decipiens, allochthonous seagrass detritus, and macroalgae are the major sources of primary production, organic matter and vegetated habitat in the Salt River Canyon (Table 1) (Josselyn et al 1983, Josselyn et al 1986, Williams et al 1985 However, the turnover tlme for H. decipiens is faster. On the average, a new leaf pair emerged about every 1.7 d, whereas most other seagrasses have leaf emergence rates on the order of 9 to 16 d (Patriquin 1973, Zieman & Wetzel 1980, Thayer et al 1984a, Fonseca et al 1987).…”

“…Disturbance and burial of plant material on the Canyon floor is a dynamic and important mechanism influencing the distribution of Halophila decipiens and the disposition of organic matter (Williams et al 1985, Josselyn et al 1986. Two important sources of disturbance are wave surge accompanied by sand movement, and burrowing and bottom feeding activities of macrofauna which uproot and frequently bury H. decipiens (Williams et al 1985).…”

“…Two important sources of disturbance are wave surge accompanied by sand movement, and burrowing and bottom feeding activities of macrofauna which uproot and frequently bury H. decipiens (Williams et al 1985). Burial of plant material is important for at least 2 reasons.…”

“…Frequent disturbance by burrowing and foraging animals and wave surge continually uproot or bury entire plants (Williams et al 1985, Josselyn et al 1986). The buried plant material forms organic detritus that decomposes in the sediment while material on the sediment surface decomposes in place or is transported down the Canyon (Josselyn et al 1983).…”