First insights into the impacts of benthic cyanobacterial mats on fish herbivory functions on a nearshore coral reef

Benthic cyanobacterial mats (BCMs) are becoming increasingly common on coral reefs. In Fiji, blooms generally occur in nearshore areas during warm months but some are starting to prevail through cold months. Many fundamental knowledge gaps about BCM proliferation remain, including their composition and how they influence reef processes. This study examined a seasonal BCM bloom occurring in a 17-year-old no-take inshore reef area in Fiji. Surveys quantified the coverage of various BCM-types and estimated the biomass of key herbivorous fish functional groups. Using remote video observations, we compared fish herbivory (bite rates) on substrate covered primarily by BCMs (> 50%) to substrate lacking BCMs (< 10%) and looked for indications of fish (opportunistically) consuming BCMs. Samples of different BCM-types were analysed by microscopy and next-generation amplicon sequencing (16S rRNA). In total, BCMs covered 51 ± 4% (mean ± s.e.m) of the benthos. Herbivorous fish biomass was relatively high (212 ± 36 kg/ha) with good representation across functional groups. Bite rates were significantly reduced on BCM-dominated substratum, and no fish were unambiguously observed consuming BCMs. Seven different BCM-types were identified, with most containing a complex consortium of cyanobacteria. These results provide insight into BCM composition and impacts on inshore Pacific reefs.

BROADCAST SPAWNING PATTERN AND PELAGIC LARVAE DURATION OF ACROPORA CYTHEREA AND A. CLATHRATA FROM INSHORE REEF AREA IN KUANTAN COASTAL REGION

Acropora sp. is the second-most abundant among the coral genera in the Kuantan coastal region (KCR) located on the east coast of Peninsular Malaysia. This study investigated the timing of coral spawning of two Acropora species; Acropora cytherea and Acropora clathrata through dissection and histological analyses of coral fragments that were collected during predicted spawning months (March until May 2018) from Balok reef, Kuantan. Histological results showed the presence of mature oocytes from a sample collected in April and May 2018, which indicate an extended gamete release pattern for these species within KCR. The gamete maturity coincided with the peak sea surface temperature within KCR from April until May. Both Acropora species spawned between 10-11 nights after the full moon. Present results also indicated that both Acropora species have optimal pelagic larvae duration (PLD) between 6 – 8 days after spawning. This study contributed to the limited knowledge of coral reproductive biology on the east coast of Peninsular Malaysia. In addition, the timing of coral spawning provides valuable data for population connectivity modelling.

HYDRODYNAMIC MODELLING IN INSHORE REEF AREA WITHIN KUANTAN COASTAL REGION

Current circulation provides major transport mechanism especially for benthic organism in the ocean. The present study described current circulation in inshore reef area within Kuantan coastal region by applying a numerical modelling of MIKE 21 Flow Model FM software. Model simulation produced good outcomes when compared with field data measurement with root mean square error (RMSE) for surface elevation, current speed and direction were below 20. Results also clearly indicated that current speed in inshore reef area was highly correlated with local tidal pattern in which higher flow speed were observed during high tides compared to low tide. Contrary to previous belief, our results clearly show the prevalence of tidal forcing in shaping current flow pattern in the study area since the impact of wind forcing was minimal during different monsoon seasons. This study gave new insight into how local tidal properties can regulate hydrodynamic pattern especially in fine-scale inshore reef area.

Assessment Assessment of benthic and coral community structure in an inshore reef in Balok, Pahang, Malaysia

Hanapiah MFM, Saad S, Ahmad Z, Yusof MH, Khodzori MFA. Assessment of benthic and coral community structure in an inshore reef in Balok, Pahang, Malaysia. Biodiversitas 20: 872-877. Inshore water reef closer to human activities are often neglected since they are not protected by marine park management. Little is known on how this reef responses to challenging environment in terms of abundance, diversity and benthic community composition. This study provides a quantitative assessment on the benthic community composition at 5 reef sites in Balok, Pahang, Malaysia and observed the ecological adaptation in the reef community towards turbid water environment. Balok reef has 39% overall coral cover with very low macroalgae abundance (4%). A total of 28 coral genera from 12 families have been recorded with Porites the most dominant genus in the coral assemblages. Most reef sites in Balok are categorized under conservation class 1 (CC1), which indicated that resilient and survival of the reef rely on stress-tolerators taxa. The data presented here showed that Balok reef is highly resilient towards constant exposure to high sedimentation and wave action.

Measuring niche overlap between co-occurring Plectropomus spp. using acoustic telemetry and stable isotopes

Investigating niche overlap in exploited fish species can reveal behavioural information necessary to improve conservation and fisheries management at a species level. The present study examined spatial and dietary overlap between two co-occurring reef fish, namely Plectropomus leopardus and P. maculatus, at an inshore reef in the Great Barrier Reef Marine Park using acoustic telemetry and stable isotopes. Movements of tagged fish within an acoustic array of 19 receivers deployed along a narrow reef portion of Orpheus Island were monitored for up to 3 years. Although space use was similar between species, spatial overlap was rare and P. maculatus (n=30) was consistently deeper than P. leopardus (n=32). Dietary overlap between species was high based on overlapping δ15N and δ13C isotopic niches in muscle tissue (n=20). The complementary stable isotope and acoustic telemetry data revealed these species had similar isotopic niches but distinct space use patterns, which may be a product of competition for resources. These findings show species-specific behaviours within a genus commonly managed or reported as a single entity, and provide new information on partitioning of resources by Plectropomus spp. in inshore reef environments.

Mobula kuhlii cleaning station identified at an inshore reef in southern Mozambique

Cleaning interactions between the short fin devil ray, Mobula kuhlii, and the blue streaked cleaner wrasse, Labroides dimidiatus, were observed at two sites on a single reef in southern Mozambique. Cleaning interactions were filmed and described, with the number and location of interactions recorded and subsequently binned into six distinct body patches. Cleaners preferentially foraged within certain ray body patches, and this was found to vary between the two sites, possibly signifying that variations in a habitats composition can influence cleaning. Mobula kuhlii were not found to clean sympatrically with their close relatives in the Manta genus, implying their cleaning requires a distinct habitat or that niche partitioning is required to stem competition for host cleaner fishes attention. In total, 15 individuals were observed interacting with cleaners, and they never arrived alone, suggesting they may travel to cleaning areas in an aggregative manner.

Mobula kuhlii cleaning station identified at an inshore reef in southern Mozambique

Cleaning interactions between the short fin devil ray, Mobula kuhlii, and the blue streaked cleaner wrasse, Labroides dimidiatus, were observed at two sites on a single reef in southern Mozambique. Cleaning interactions were filmed and described, with the number and location of interactions recorded and subsequently binned into six distinct body patches. Cleaners preferentially foraged within certain ray body patches, and this was found to vary between the two sites, possibly signifying that variations in a habitats composition can influence cleaning. Mobula kuhlii were not found to clean sympatrically with their close relatives in the Manta genus, implying their cleaning requires a distinct habitat or that niche partitioning is required to stem competition for host cleaner fishes attention. In total, 15 individuals were observed interacting with cleaners, and they never arrived alone, suggesting they may travel to cleaning areas in an aggregative manner.