Preliminary Study Of Foraging Behavior And Reproductive Biology Of The Sea Star Asterias Amurensis

This paper was concerned with the feeding behavior and reproduction cycle ofthe North Pacific sea star （Asterias amurensis）. The size and species selection feedingby sea star on the oysters （Crassostrea gigas）, mussels （Mytilus edulis） and clams（Ruditapes philippinarum）, the behavioural and metabolic responses of the sea star todifferent concentration of food signals （5single amino acid and3bivalve tissuehomogenate） and the reproductive biology were investigated in this paper. Theseresults will help for the provision of protective refuges for species of interest releasedonto the sea bed, such as in population enhancement operations and bottomaquaculture. The most results are summarized as follow:1. The size-selective feeding behavior by sea star （weight:73.51±3.12g, radiuslength:7.82±0.20cm） on the juvenile oysters, mussels and clams were studied in thispaper. The prey selection indexes, predation rates, daily average feeding rate of seastar on smaller length of the clams （29³2mm） were nonsignificantly higher thanother length groups, which respectively were29.25%,0.27ind/d,0.36%. While thesea star significantly selected the minimum length （21²6mm） of oysters and musselsmost, and the prey selection indexes, predation rates, daily average feeding rate weredecreased with the increasing of shell length.2. Experiments were carried out to investigate the effect of prey density onpredation, prey selection and component behaviors which were examined bypresenting individual sea star with combination of three bivalves （oysters, musselsand clams） in various proportions （5:5:5,5:10:10,5:20:20,20:5:5） with six replicates.Predator and prey behaviors （searching and handling prey） were observed throughoutthe experiment and the proportion of time for each foraging behavior was calculated as total duration of the behavior. We quantified prey selection indexes, predation rates,daily average feeding rate, and proportion of time spent searching and handling preyand prey characteristics （shell length, energy content per prey） to indentifymechanisms underlying predation patterns and selection of prey. Daily averagefeeding rates of sea stars showed that sea stars predated clams most, significantlyhigher than oysters and mussels, while selected oysters least, which was not changedwith the prey relative abundance. Examination of behaviors indicated that time spentsearching prey by A. amurensis was not changed significantly among experimentalgroups, but time spent handling prey was decreased along with the increase of preydensity.3. The behavioural and metabolic responses of the sea star to differentconcentration of food signals （5single amino acid and3bivalve tissue homogenate）were examined. Stimulus concentration increase elicited a rise in both the percentageof reacting animals and in the reaction intensity at the amino acid concentration of10^-410-10mol/L except for tyrosine. At low stimulus concentration, A. amurensisreaction consisted of tube foot waving, and only high concentrations initiated acomplicated sequence of several types of behaviour. However, fright reactions wereobserved in high concentrations (10^-310^-2mol/L) of amino acid except for glutamicacid. Differences were found among the impact of different type of stimuli on thebehavior response by A. amurensis exposed to them. Glutamic acid, glycine and clamRuditapes philippinarum homogenates were the strongest attractant for experimentsea stars. For eight tested stimuli, a dependance between stimulus concentration andthe oxygen consumption rate （OCR） was observed, with the increase in stimulusstrength causing the increase in the metabolic rate. For the tissue homogenates groups,the OCR was significantly higher than the control. However, statistically significantdifferences from the control were only found in sea stars exposed to highconcentration of glycine, glutamic acid and aspartic acid. No significant differenceswere observed among different concentration of tyrosine. 4. Sea stars A. amurensis were collected from Qingdao Fushan Bay, and theanatomic features of gonads were studied. A. amurensis was dioecious and theanatomic features of ovary and testis were similar. Ovary and testis comprise fivepairs, and each ray has one pair. The gonads were racemose branched and located onboth sides of the base of each ray in interambulacral area. There were no matingorgans, and no other accessory glands. Each gonad has gonoduct, with small poreopening to the aboral surface between two rays. The gonads were closely linked to thegenital sinus, aboral ring sinus and aboral nervous system. Ovaries and testes volumechange with the seasons, which gonads are generally small in the non-breedingseasons with few branches. Distinction between male and female cannot usually bemade by external appearance alone. As the gonads mature, the gonad cysts are welldeveloped with the largest ones nearest the base of the ray. At this time, the gonads ofeither sex are easily distinguished by the color; the ovaries become yellowish orangeand the testes yellowish white.5. The sea stars were sampled from Qingdao Fushan Bay, from June2011toMarch2012. The reproductive cycle was studied by gonad indices （GI） andhistological examination of ovaries and testes. No significant differences wereobserved relative to the1:1sex ratio. Sexual maturity of females and males occurredin August and September, when the water temperature began to decrease. Spawningoccurred during October and January next year. Seawater temperature and day lengthwere considered to be two factors affecting reproduction of sea star. Six maturitystages were used to describe the histological development of the gonad. There weredifferent stage of oocytes and spermatozoa in different development periods. The GIand pyloric caeca index （PCI） tended to have an inverse relationship, suggesting thatpyloric caeca provided nutrients for the gonads growing.