Shifts in dominance of benthic communities along a gradient of water temperature and turbidity in tropical coastal ecosystems

Abstract

Tropical coastal benthic communities will change in species composition and relative dominance due to global (e.g., increasing water temperature) and local (e.g., increasing terrestrial influence due to land-based activity) stressors. This study aimed to gain insight into possible trajectories of coastal benthic assemblages in Raja Ampat, Indonesia, by studying coral reefs at varying distances from human activities and marine lakes with high turbidity in three temperature categories (<31 °C, 31–32 °C, and >32 °C). The benthic community diversity and relative coverage of major benthic groups were quantified via replicate photo transects. The composition of benthic assemblages varied significantly among the reef and marine lake habitats. The marine lakes <31 °C contained hard coral, crustose coralline algae (CCA), and turf algae with coverages similar to those found in the coral reefs (17.4–18.8% hard coral, 3.5–26.3% CCA, and 15–15.5% turf algae, respectively), while the higher temperature marine lakes (31–32 °C and >32 °C) did not harbor hard coral or CCA. Benthic composition in the reefs was significantly influenced by geographic distance among sites but not by human activity or depth. Benthic composition in the marine lakes appeared to be structured by temperature, salinity, and degree of connection to the adjacent sea. Our results suggest that beyond a certain temperature (>31 °C), benthic communities shift away from coral dominance, but new outcomes of assemblages can be highly distinct, with a possible varied dominance of macroalgae, benthic cyanobacterial mats, or filter feeders such as bivalves and tubeworms. This study illustrates the possible use of marine lake model systems to gain insight into shifts in the benthic community structure of tropical coastal ecosystems if hard corals are no longer dominant.

Stony Corals and Their Associated Fauna Residing in Marine Lakes under Extreme Environmental Conditions

“…Corals growing on mangrove roots is an uncommon feature, although there are reports from coastal areas in the Caribbean, such as in the U.S. Virgin Islands [27,28], Panama [29,30], and Florida [31], and also in the Indo-Pacific, such as the Great Barrier Reef [32,33]. The corals were mostly present at a depth range of 0.5-5 m. In four marine lakes (Papua11, Papua12, Papua15, and Papua24) hard corals represented 10-20% of the total benthic cover [23], resembling inshore and turbid reefs in the Indo-Pacific [24][25][26]. For comparison, the nearby reefs in Raja Ampat can range in coral cover from 10 to 86% [23] In some marine lakes, the corals formed small reefs (Figures 2d and 3c,d), while in others, corals occurred in patches (Figure 2c).…”

“…Environmental characteristics of 12 marine lakes with hard coral fauna in Raja Ampat, Indonesia. Code names for marine lakes follow those of earlier studies [21][22][23]. Averages (and ranges in brackets) of temperature, salinity, and pH are based on five sites within each marine lake.…”

“…Temperature ( The corals were mostly present at a depth range of 0.5-5 m. In four marine lakes (Papua11, Papua12, Papua15, and Papua24) hard corals represented 10-20% of the total benthic cover [23], resembling inshore and turbid reefs in the Indo-Pacific [24][25][26]. For comparison, the nearby reefs in Raja Ampat can range in coral cover from 10 to 86% [23] In some marine lakes, the corals formed small reefs (Figures 2d and 3c,d), while in others, corals occurred in patches (Figure 2c). Most corals exhibit massive and encrusting growth forms.…”