Environmental DNA Biomonitoring Reveals Seasonal Patterns in Coral Reef Fish Community Structure

Coral reef fish populations are declining due to multiple factors including habitat destruction, overfishing, and climate change. While these can include seasonal impact, seasonal changes can also be a confounding factor, so that seasonal monitoring is essential for detecting true temporal changes in fish community abundance and composition. However, seasonal monitoring is rarely implemented. The aim of this study was to detect the seasonal patterns of coral reef fish community structure around Tidung Kecil Island, Indonesia, using eDNA metabarcoding (eDNA) and underwater visual census (UVC). The UVC identified 32 species belonging to 10 families in the rainy season and 29 species belonging to 7 families in the dry seasons. The eDNA metabarcoding identified 209 species belonging to 56 families and 27 species belonging to 17 families in the rainy and dry seasons, respectively. Based on eDNA metabarcoding data, coral reef fish abundance and community composition differed significantly between seasons (Mann Whitney, p<0.01), while the UVC method did not detect these seasonal differences (Mann Whitney, p>0.05). UVC and eDNA data both showed a predominance of omnivorous fishes in the rainy season and carnivorous fishes in the dry season. Ecological indices did not differ significantly between seasons for either method, although the species making the highest contributions to the similarity (SIMPER) analysis differed between methods. Overall, this study confirms the premise that eDNA metabarcoding can be an effective tool for monitoring seasonal variation in coral reef fish communities.

Reef fish community structure in the islands of Paraja Bay, Pandeglang District, Banten, Indonesia

Mujiyanto, Sugianti Y, Afandy YA, Rahayu R, Bidikusuma RA, Nasriri AS, Syam AR, Purnaningtyas SE. 2021. Reef fish community structure in the islands of Paraja Bay, Pandeglang District, Banten, Indonesia. Biodiversitas 22: 4402-4413. Paraja Bay waters have five small islands that coexist with Ujung Kulon National Marine Park and act as a buffer zone for the diversity of fishery resources. This study aimed to assess the reef fishes community structure at small islands in Paraja Bay. Observations were made in 20 locations during August and September 2019 in the five small islands. Reef fishes community structure showed 106 species as included major group (54 species), indicator group (24 species) and target group (28 species), among five small islands, i.e. Badul, Mangir, Oar, Sumur and Umang Islands. The highest reef fishes abundance was founded in Umang Island waters. Several target fish species recorded during the study were mature fish (such as those targeted by fishermen). Only a small proportion were juveniles. Reef fish community structure was categorized as stress community to stable community with its indication was low diversity value, high evenness index, and low dominance. The low diversity index value illustrates that the level of uniformity of reef fish species in Paraja Bay waters is high. This condition is evidenced by each coral fish group's evenness index included in the main species group around 0.93 to 0.98. The target species is 0.88 to 0.99.

Reef fish community structure along the southeastern US Atlantic continental shelf break and upper slope appears resistant to increasing lionfish (Pterois volitans/miles) density

Temperate reefs host diverse fish communities along the southeast United States Atlantic coast (SEUS), yet the sustainable management of reef fishes faces myriad challenges. One challenge has been the introduction of Indo-Pacific lionfish (Pterois volitans/miles; hereafter “lionfish”), which have spread quickly throughout the SEUS since their introduction in the late 1900s. We analyzed long-term (2001–2019) video data along the continental shelf break and upper slope (45–125 m deep) of the SEUS to assess changes in lionfish densities over time, characterize reef fish community structure, and determine if native reef fish community structure has changed due to lionfish. Lionfish densities increased substantially during the study, from zero individuals observed in 2001 to approximately 1.2 individuals observed per 100 m3 (and present in all included transects) by 2019, yet no fish community metrics were negatively related to lionfish density. Demersal habitat influenced fish community structure more than any other variable examined, with more individuals and different fish communities occurring on high-relief compared to low-relief hardbottom habitats. The effects of latitude, depth, and bottom temperature on reef fish community structure were generally weak or nonexistent. Although previous empirical work has found that lionfish negatively affect native fishes at small scales (<30 km2), it is unclear why we did not find similar results in our larger-scale study. It may be related to vagaries of the spatial scale of observation, lionfish effects being primarily limited to high-relief habitats, time lags, or lionfish densities not being high enough yet to cause observable ecological effects.