Digestion of natural food by larval and post-larval turbot Scophthalmus maximus

Hlgher abundances of copepods with external damage or in various states of internal decay have been found in shallow waters over banks, ridges and seamounts than in the surrounding waters. The increase occurred in 3 of 5 sets of multiple opening-closing net tows taken at Fieberling Guyot, Northeast Bank and Sixtymile Bank, west of San Diego, California, USA. Large numbers of copepod carcasses were also found above the summit of Jasper Seamount. The carcasses are attributed to higher levels of predation over shallow topographic features due to resident organisms that ascend above the summits at night to feed. At Fieberling Guyot (summit depth of about 500 m), this migration was at least 400 m above the summit. Carcasses identical to those collected in the net tows were produced in the laboratory by euphausiids feeding on copepods.

Section: Discussionmentioning

confidence: 99%

Copepod carcasses in the ocean. I. Over seamounts

Haury¹,

C²,

Gal³

et al. 1995

“…euphausiids) eat the internal tissues of their prey and release or egest partly empty exoskeletons (Ponomareva 1954, Ohman 1984, Beyer 1992. Partly digested crustacean prey were also reported for cnidarians (Sebens & Koehl 1984, Lewis 1992, fish larvae (Rosenthal & Hempel 1970, Chitty 1981, Checkley 1982, Conway et al 1993, and adult fish (Redden & Daborn 1991, Flinkman et al 1994. Lewis (1992), for example, found partly digested items on the surface of the gastrozoids of a cnidarian hydrocoral and Conway et al (1993) reported egestion of intact copepod exoskeletons by fish larvae.…”

Section: Introductionmentioning

confidence: 99%

Copepod carcasses in the ocean. II. Near coral reefs

Genin¹,

Gal²,

Haury³

1995

Copepod carcasses containing httle or no internal tissue, but bearing undamaged setae and appendages, dominated zooplankton samples collected near the coral reef of Eilat, Israel. The proportions of carcasses to total copepods (livlng plus dead) increased from open offshore waters (22 %) to the reef (65'5,). Proportions across a sandy shore without a reef were low (<25 X), with no significant changes with respect to distance from shore. Calanoid copepods exhibited higher proportions of carcasses than cyclopoids. Carcasses similar to those found in our plankton samples were egested in aquaria by freshly collected post-settling fish larvae and crinoids. High proportions (~80%) of carcasses CO-occurred with extrenlcly low ( < l 0 0 m-") abundances of zooplankton, further corroborating a relationship between predation and carcass abundance Since the nutritional value of carcasses is substantially less than that of l~ving individuals, d~fferentiating between llve copepods and carcasses should be critical for planktivores inhabiting reefs, as well as for investigations of trophic dynamics in such habitats.

“…Copepod egg membranes are considered to be largely composed of chitin (Marshal1 & Orr 1954), which is not, at least substantially, digested by larval fish (Conway et al 1993). As the egg membranes form an unbroken barrier, enzyme penetration must depend on enzymatic or mechanical disruption.…”

mentioning

confidence: 99%

“…Eggs can form on average 29% of the dry weight biomass of adult female Eurytemora velox (Conway et al 1993) and 13 to 53 % for E. herdmanni (Crawford & Daborn 1986) so non-digestion of eggs can represent a considerable loss of potentially valuable food. Fish larvae which cannot digest the eggs of ingested eggcarrying copepods will still obtain nutrition from the copepod.…”

mentioning

confidence: 99%

“…This study is the first to investigate the ability of a larval fish species, the turbot, to digest the subitaneous eggs of a selection of egg-carrying copepod species of both estuarine/coastal and open sea distrib-utions, including species which are only known to produce subitaneous eggs. Turbot larvae are particularly suited to this type of study as they package their faeces in a thin membrane (Conway et al 1993), so output of faecal material can be monitored.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Digestion of copepod eggs by larval turbot Scophthalmus maximus and egg viability following gut passage

Conway¹,

McFadzen²,

Tranter³

1994

Self Cite

Between 20.5 and 93.6'% of the subitaneous eggs of 6 species of egg-carrying copepods passed undigested through the digestive tracts of larval and early postlarval turbot Scophthalnius maximus. Viability of the eggs of Euryternora affinis, E. velox and Euterpina acutifrons remained high on egestion (67.0 to 91.7%), Pseudocalanus elonqatus and Oncaea venusta eggs had low viability (1.1 to 1.5 %l, while all Corycaeus anglicus eggs were rendered inviable. The indigest~bility of the eggs denies the turbot larvae a potentially valuable food resource, while retention of high egg viability in certain species reduces the effect of predation KEY WORDS: Scophthalmus maximus larvae . Copepod eggs .