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Energy and ash contents of sandy beach macrofauna from the West Coast of South Africa

Keywords: Energy , ash , sandy beach , macrofauna , West Coast of South Africa , amphipod urothoe grimaldii

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ENGLISH ABSTRACT: The energy values and ash contents of 15 species of macrofauna found on three exposed sandy beaches on the west coast of South Africa were examined over an 18-month period. The values obtained ranged from a mean of 26,65 kJ.g-' ash-free dry weight (AFDW) in the haustoriid amphipod Urothoe grimaldii to 19,83 kJ.gˉ1 for the bivalve Donax serra and the values obtained are applied to biomass data for the three beaches. A pattern of decreasing energy content with increasing mean body weight was observed. No patterns of seasonal or regional variation were detected in either energy values or ash contents. Ash contents depended on taxonomic group (owing to morphological effects) and the mean size of the species; in the case of the Crustacea increasing with size within a given taxonomic grouping. The mean energy value for the 15 species was 23,81 kJ.gˉ1, higher than the 23,09 kJ.gˉ1 conversion factor obtained by Brey, Rumohr & Ankar (1988) for aquatic macrobenthic invertebrates in general, and in accordance with the suggestion by Slobodkin & Richman (1961) that energy contents are affected by the extent of storage for adverse conditions. ************* AFRIKAANSE OPSOMMING: Die energiewaardese n asinhoud van 15 spesies van makrofauna gevind op drie blootgestelde sanderige strande aan die weskus van Suid Afrika is oor'n tydperk van 18 maande bestudeer. Die bevindinge wissel van 'n gemiddelde waarde van 26,65 kJ.gˉ1 as vrye dro gewig (ADG) in die haustoriede amfipood Urothoe grimaldii tot 19,83 kJ.gˉ1 ADG vir die tweekleppige Donax serra, en die bevindinge word toegepas op die biomassa-data van die bogenoemde drie strande. 'n Tendens van afnemende energie-inhoud met toenemende gemiddelde liggaamsgewig was waarneembaar. Geen seisoensgebonde- of streeksvariasies was waarneembaar in die energiewaardes of in die asinhoud nie. Asinhoud is afhanklik van die taksonomiese groep (as gevolg van morfologiese effekte) en die gemiddelde grootte van die spesies, en in die geval van die Crustacea is dear 'n toename in grootte binne 'n gegewe taksonomiese groepering. Die gemiddelde energiewaarde vir die 15 spesies was 23,81k J.gˉ1 ADG, ho r as die 23,09 kJ.gˉ1 wisselfaktor wat deur Brey, Rumohr & Ankar (1988) voorgestel word vir akwatiese makrobentiese Invertebrata oor die algemeen en dit is in ooreenstemming met die voorstel van Slobodkin & Richman (1961) dat energie-inhoud ho r is hoe ongunstiger die heersende toestande is .

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