Nutrition of the Sea Urchin, Strongylocentrotus Purpuratus

-1). Low C:N ratios of feces obtained from grazing C. fragile (8.5) or encrusted kelp (11.4), compared to clean kelp (30.7), suggest that feces from invaded assemblages are a higher quality food source for microbes and detritivores. To compare dispersal characteristics of feces from each diet, we measured pellet shape, size, density, and settling and critical erosion velocities. Using a wave model, we estimated the depth at which feces would be deposited under seasonally varying wave conditions. We found that pellets of C. fragile are likely deposited at the greatest depths (33 to 55 m), pellets of clean kelp at intermediate depths (28 to 47 m), and pellets of encrusted kelp at the shallowest depths (22 to 40 m). Our findings suggest a smaller amount of higher quality feces enters the detrital food web at greater depths from Codium meadows than from native kelp beds.

Section: Defecation Rate and Absorption Efficiencymentioning

confidence: 99%

Fecal production by sea urchins in native and invaded algal beds

Sauchyn¹,

Scheibling²

2009

“…The importance of this process in echinoids is still unknown, but it may be high (Miller & Mann 1973), and thus contribute to the overestimation of actual absorption rates. Second, in echinoids, absorption rates are affected by the microflora associated with the gut (Lasker & Giese 1954, Fong & Mann 1980. During long-term monospecific feeding experiment this microflora may become more and more adapted to digest the offered food.…”

Section: Absorptionmentioning

confidence: 99%

“…This dependence results from the poor musculature associated with the gut of echinoids (De Ridder & Jangoux 1982), thus enhancing the importance of water and newly ingested material in materials progressing through the gut. This explains why starving echinoids have a much longer gut residence time than continuously feeding echinoids (Lasker & Giese 1954, Bedford & Moore 1985. It is assumed that gut residence time and absorption rates of benthic primary consumers are positively correlated (Lopez & Levinton 1987).…”

Section: Absorptionmentioning

confidence: 99%

Ingestion, absorption, and growth rates of Paracentrotus lividus (Echinodermata: Echinoidea) fed different macrophytes

Frantzis¹,

Grémare²

1993

We recorded ingestion, absorption, total and gonadal growth rates of Paracentrotus lividus fed unlimited rations of 12 macrophytes (Rissoella verruculosa, Corallina elongata, Asparagopsjs armata, Cystose~ra mediterranea, Stypocaulon scoparium, Padina pavonica, Cystoseira compressa, Colpomenia dnuosa, Dilophus spiralis, Ulva rfg~da, Posidon~a oceanica and Codium vermilara) over a 6 mo period. Macrophytes seemed to affect ingestion, absorption, total and gonadal growth rates. This effect was altered by changes in echinoid size and temperature during the length of the experiment. The highest ingestion, total growth and gonadal production were obtained with R. verruculosa whereas the lowest rates were obtained with A armata and D. spiralis. There was no gonadal growth below a minimal ingestion rate of 3 g organic matter per 6 mo. Above this ingestion rate threshold, the allocation of energy between somatic and gonadal growth was not affected by the offered macrophyte. The highest absorption rates were recorded for A. armata. The lowest absorption rates were recorded for C. elongata and S. scoparium. Ingestion and absorption rates correlated negatively. Overall, individual growth rates positively correlated with rates of ingested organic matter, and even more so for the total time interval of the growth experiment, with absorbed organic matter. Individual monthly growth rates were better correlated with amounts of ingested organic matter than with ingested volume, wet weight, dry weight, or even energy, proteins and essential amino acids. Probably due to high individual variability, coefficients of determination were not significantly higher when using absorbed amounts of organic matter, dry weight, energy and proteins.

“…Fong & Mann (1980) showed that the gut microflora of a sea urchin, Strongylocentrotus droebachiensis, was capable of uptake of 14C-labelled glucose, and that the label from bacterial protein was subsequently incorporated into the tissues of the urchin. Mann (1982) also cites results of work in which 14C-label in cellulose was incorporated into bacterial protein and subsequently appeared in the proteins of the urchins (see also Lasker & Giese 1954. Prim & Lawrence 1975.…”

Section: Introductionmentioning

confidence: 99%

Exploitation of phytoplankton as a food resource by the kelp bed ascidian Pyura stolonifera

Seiderer¹,

Newell²

1988

The ascidian Pyura stolonifera (Heller) is an important component of the filter-feeding community off the coast of South Africa. Scanning electron microscopy of the inhalant siphon, pharyngeal basket and gut contents of freshly-collected ascidians suggests that the food supply comprises a muted resource of phytoplankton cells of 3 to 5pm diameter, particulate detritus and diatoms. There is a progressive concentration of cells of 3 to 5 km diameter during passage through the pharynx, and these form a dominant component of the material taken into, and lysed in the gut. Some diatoms and detritus are also ingested, but to a large extent pass through the gut undigested. Digestive enzyme activity in the endostyle was negligible, but protease, chitinase, laminarinase and cu-amylase were of importance in the gut. Very little cellulase activity occurred in the gut, and there was no evidence of significant bacterial involvement in the decomposition of complex polysaccharides. This indicates that phytoplankton is likely to be of more significance in the diet of P. stolonifera than the refractory components in the water column. The relatively high specific activity of carbohydrases in the gut results in a large energetic gain relative to estimated carbon losses through respiration. P. stolonifera thus appears to be well-adapted to exploit the eplsodic phytoplankton availability which characterises the southern Benguela upwelling system, and in this respect resembles the mussel Chorornytilus meridionalis which, together with P. stolonifera, forms the major suspension-feeding component in the kelp beds off the west coast of the Cape Peninsula. It therefore seems likely that the particulate matter which dominates the water column in kelp beds enters the decomposer pathway and does not represent a nutritional resource which is exploited directly by the filter-feeding community.