Importance of various marine coastal habitats during the life cycle ofSpratelloides delicatulusin Con Dao, the oldest MPA in Vietnam

Abstract

1. Marine protected areas (MPAs) are set up to conserve biodiversity, but their design is not always based on strictly scientific considerations. Ideally, an MPA should protect all key habitats necessary for a marine species to complete its life cycle. The identification of these key habitats is complex, especially during the early life of marine fishes.2. A widely distributed tropical and important low trophic-level fish species, Spratelloides delicatulus (Clupeidae), was used to evaluate the significance of various coastal habitats for its larvae and juveniles in the Con Dao Archipelago MPA in Vietnam. Early stages (larvae and juveniles) were sampled monthly over one year (June 2016 to May 2017) using light traps in three main habitats (seagrass beds, coral reefs and harbour). The species was identified using morphometry and DNA barcoding. Age and growth variables were estimated using otolith daily growth increments.3. A total of 3,581 fish were caught. The species was not found in captures between January and February, directly linked to the decrease in seawater temperature and was most abundant from April to June. For a subsample of 248 fish (7-38 mm standard length), ages ranged from 7 to 108 days.4. Captures and back-calculated birthdates using otolith daily increments showed that S. delicatulus spawns during the period of high seawater temperature, from March to October. The species colonizes all three habitats during the early stages (0-26 days old), with growth rate lowest on the seagrass beds. Nevertheless, the species occupies seagrass beds exclusively during the older stages.5. The conservation of seagrass beds in the Con Dao archipelago is essential for protection of juvenile stages of this species but this habitat is presently not included in the MPA patches. Establishment of a continuum of protected areas linking habitats, rather than the existing patches is needed to conserve the complete life cycle of this species in the Con Dao MPA.

Spatial and temporal diversity of fish captured by light traps in various habitats in coastal waters in the oldest marine protected area in Vietnam and its implications for conservation

“…cf. delicatulus has already been demonstrated by its life history in Con Son Bay (Pham et al, 2020).…”

“…The importance of coral reef and seagrass connectivity for blue sprat S. cf. delicatulus has already been demonstrated by its life history in Con Son Bay (Pham et al, 2020).…”

“…As documented by Doherty (1987), Thorrold (1992) and Brogan (1994) in other areas, the present study confirmed that light traps are a useful tool to attract a large number of individuals and species in different habitats of the coastal region of Con Son Island. It was shown that light traps captured not only larvae and juveniles of different species, but also adults of small‐sized species, such as Spratelloides (Pham et al, 2020) and many crypto‐benthic species belonging to different fish families including Gobiidae, Tripterygiidae and Blenniidae (Pham et al, 2022). According to Costello et al (2017), light traps are effective for investigating some understudied components of marine biodiversity because they attract organisms in their young stages, which are generally difficult to catch using conventional gear.…”

“…For example, Pham et al (2020) reported a peak hatching period of S. delicatulus in March in Con Son Bay. Among the 15 most abundant fish species, the Clupeidae family dominated during both the dry and the wet seasons, corresponding to small‐sized and short‐lived pelagic species with a protracted seasonal spawning period (Milton & Blaber, 1991; Ghosh et al, 2013; Rivera et al, 2017; Pham et al, 2020; Hunnam, 2021). The composition of the remaining most prevalent species varied between the two seasons.…”

“…The harbour could thus play a role in the early development of certain species in Con Son. Pham et al (2020) showed that the blue sprat S. delicatulus spent part of its life in this environment and thrived in Con Son harbour. Similarly, Mercader et al (2017) demonstrated that a Mediterranean harbour could support young fish due to the complexity of the habitat.…”