Physiological energetics and gross biochemical composition of the ascidian Styela clava cultured in suspension in a temperate bay of Korea

Abstract

The ascidian Styela clava has recently become a common species for suspended aquaculture in Korea. Because of the ecological and commercial importance of this species, it is important to understand seasonal variations in its physiological energetics and gross biochemical composition. The purpose of this study was to determine fundamental biological traits for the cultivation of S. clava. Physiological processes (food consumption, feces production, ammonia excretion and respiration), and gross biochemical composition (protein, lipids, and carbohydrates) of the ascidian were measured monthly from April 2008 to April 2009 under in situ environmental conditions in a mariculture region on the temperate coast of Jindong Bay, Korea. Changes in the physiology and somatic growth of S. clava were largely influenced by seasonal variation in water temperatures. The reduced importance of food availability in explaining their physiological adjustments seems to be due to low seston concentrations in water column of the bay. Seasonal variations in the ingestion and respiration rates of the ascidians were mismatched, resulting in an energy imbalance (i.e. an increased metabolic energy cost and lowered ingestion rate; and vice versa). This mismatched activity resulted in negative scope for growth (SFG) values during spring–summer, followed by rapid exhaustion of energy reserves and flesh weight loss. Weight loss during this period was also related to spring spawning. During autumn–winter, the ascidians had a positive SFG as a result of decreased oxygen consumption and elevated ingestion rates, showing accumulation of nutrient reserves and weight gain. The ascidians showed positive SFG, even in cold conditions below 12 °C in the present study. In this respect, an autumn–winter culturing period is recommended to maximize ascidian production in long-line suspended culture under the natural environmental conditions occurring in the study area.