Diverse habitat preferences of two sea cucumber species and the seasonal change in a coral reef area

Different sea cucumbers have different preferred habitats and seasonal changes,which is still lack of detailed research.This study selects two common tropical sea cucumbers(Holothuria edulis and Stichopus chloronotus) to explore the reasons that affect their habitat selection and seasonal changes,so as to provide support for the spatial planning of sea cucumbers reserve in coral reef area.The study area is a compound distribution area of living coral reefs and sandy bottom in the north of Wuzhizhou Island.The survey time is January,April-September,2019.Three fixed transects(G,H,and Q) were selected to reveal the population ecological characteristics of them in the typical dry season(January,April,May,and June) and rainy season(July,August,and September).The variation range of density for H.edulis and S.chloronotus were 2.0-8.9 inds./10 m~2 and 0.2-0.7 inds./10 m~2,respectively.The population density in rainy season was significantly higher than that in dry season(P<0.05).H.edulis tends to be distributed in deeper water.The distribution of H.edulis was significant positively correlated with the sand coverage and sand continuity in G transect(P<0.05),and significant negatively correlated with live coral coverage in three transects(P<0.01).The shift from dry season to rainy season is a key factor affecting their habitat preference.In dry season,the preferred habitats of S.chloronotus are small rock(SR),sand(S), and small coral reef(SCR),while the H.edulis is S,SR,and dead coral rubbles(DCR).In rainy season,the preferred habitats of S.chloronotus are shift to SCR and SR,while the H.edulis is SCR,DCR,and sand.