Genetic patterns in Montipora capitata across an environmental mosaic in Kāne’ohe Bay

Abstract

Spatial genetic structure (SGS) is important to a population's ability to adapt to environmental change. For species that reproduce both sexually and asexually, the relative contribution of each reproductive mode has important ecological and evolutionary implications because asexual reproduction can have a strong effect on SGS. Reef building corals reproduce sexually, but many species also propagate asexually under certain conditions. In order to understand SGS and the relative importance of reproductive mode across environmental gradients, we evaluated genetic relatedness in almost 600 colonies of Montipora capitata across 30 environmentally characterized sites in Kaneohe Bay, Oahu, Hawaii using low-depth restriction digest associated sequencing. Clonal colonies were relatively rare overall but influenced SGS. Clones were located significantly closer to one another spatially than average colonies and were more frequent on sites where wave energy was relatively high, suggesting a strong role of mechanical breakage in their formation. Excluding clones, we found no evidence of isolation by distance within sites or across the bay. Several environmental characteristics were significant predictors of the underlying genetic variation (including degree heating weeks, time spent above 30°C, depth, sedimentation rate and wave height); however, they only explained 5% of this genetic variation. Our results show that colony fragmentation contributes to the ecology of M. capitata at local scales and that genetic diversity is maintained despite strong environmental gradients in a highly impacted ecosystem, suggesting potential for broad adaptation or acclimatization in this population.

Community composition of coral-associated Symbiodiniaceae is driven by fine-scale environmental gradients

“…Montipora capitata colonies were tagged and collected under Special Activity Permit 2018-03 to HIMB from Hawai'i Department of Aquatic Resources. Details of the sampling design and block delimitation have been described in (Caruso et al, 2021). In summary we performed stratified random sampling of sites by first dividing the bay into five blocks, based on the water flow regimes and water residence time (Lowe, Falter, Monismith, & Atkinson, 2009b, 2009a.…”

Coral environmental history is primary driver of algal symbiont composition, despite a mass bleaching event

“…Montipora capitata colonies were tagged on 30 patch reefs in Kāne‘ohe Bay, O’ahu, Hawai‘i, under SAP permit 2018-03 and SAP 2019-16 to HIMB from Hawai‘i Department of Aquatic Resources. Kāne‘ohe Bay was divided into 5 ‘blocks’ based on modeled water flow regimes and water residence times (88) and six sites (86) were selected in each block using stratified random sampling within habitats designated as patch reefs ( Figure 1 ). Site IDs consist of the digit corresponding to the block in which the site is contained, followed by the site number (e.g., 1_10, with six sites per block, but not necessarily in consecutive order).…”

“…Sediment traps were also deployed at the center of the block and exchanged every 1-2 months, and the weight of sediment was used to estimate the sedimentation rate in each site following (96). See (86) and (81) for details on site selection, host genetic sampling, and environmental data collection and analysis.…”

“…All analyses were completed in R 2021.09.0+351 version (R Core Team, 2020). We calculated a variety of summary statistics from the temperature time series for each site (86): mean daily temperature, average daily range, mean daily standard deviation, global mean, maximum and minimum temperature at each site. We calculated Degree heating weeks (DHW) per site as the accumulated time when temperature was above the bleaching threshold, set as 28.5°C given a MMM of 27.5 o C (42, 101).…”

“…Kāne'ohe Bay, the largest protected embayment in the Hawaiian Islands, has among the highest coral cover in Hawaiʻi (82,83). The bay is environmentally and biologically heterogeneous (84)(85)(86), with the northern extents experiencing higher circulation and lower mean residence times than the southern portion of the bay (87,88). Interestingly, because Kāneʻohe Bay is relatively shallow and has high productivity and long residence times, the fluctuations in pCO2 and temperature are increased relative to open coastal reefs.…”