Underwater microscopy for in situ studies of benthic ecosystems

Abstract

Microscopic-scale processes significantly influence benthic marine ecosystems such as coral reefs and kelp forests. Due to the ocean's complex and dynamic nature, it is most informative to study these processes in the natural environment yet it is inherently difficult. Here we present a system capable of non-invasively imaging seafloor environments and organisms in situ at nearly micrometre resolution. We overcome the challenges of underwater microscopy through the use of a long working distance microscopic objective, an electrically tunable lens and focused reflectance illumination. The diver-deployed instrument permits studies of both spatial and temporal processes such as the algal colonization and overgrowth of bleaching corals, as well as coral polyp behaviour and interspecific competition. By enabling in situ observations at previously unattainable scales, this instrument can provide important new insights into micro-scale processes in benthic ecosystems that shape observed patterns at much larger scales.

Large-Scale Permanent Slide Imaging and Image Analysis for Diatom Morphometrics

“…Imaging and image processing methods have been developed and spread rapidly for marine research in the recent years [19][20][21][22]. In contrast to many of these techniques, our approach is conducted ex situ on oxidized material, as has been the common practice in diatom research for nearly 200 years.…”

In vivo imaging of coral tissue and skeleton with optical coherence tomography

“…For instance, mesenterial filaments can be expelled from the polyp stomach and extruded to the coral surface in response to temperature stress [21] and space competition with neighbouring corals and predators [38]. A recently developed underwater microscope was able to record mesenterial filament extrusion at high spatial and temporal resolution [25]. Likewise, OCT was capable of following and visualizing the extrusion of such filaments through temporary openings with microscale spatial resolution (figure 2h-i).…”

“…Although corals appear to be static on the macroscale, coral tissues are flexible on the micrometre to centimetre scale, where coral tissues can re-arrange on the scale of seconds due to, for example, physical force, behavioural control or illumination [25]. Massive thick-tissued corals respond to excess illumination via tissue contraction [18], which can increase tissue surface reflectivity and affect the internal tissue light microenvironment [17].…”

“…Microscopic imaging of live intact corals has also been realized in the laboratory [23,24] and in situ [25] but information about internal tissue organization is limited to early developmental stages, tissue explants or corals with thin tissue layers without pronounced calcified structures. Depth resolution and contrast in light microscopy is hampered by the absorption and scattering of visible light in the tissueskeleton matrix, and the same effects limit the depth resolution of confocal laser scanning microscopy on coral tissue to the outermost 100-200 mm using high numerical aperture objective lenses with a small field of view [26].…”

Stereo In-Line Holographic Digital Microscope

“…Observing plankton movement is important because disturbances in normal plankton predatory-prey behavior have been implicated as a factor in the production of harmful algal blooms [11]. Capturing plankton swimming has been achieved with video microscopes [12] and multiple exposures with a holographic microscope [13]. Many of the in situ microscopes are designed to be submerged, requiring a high pressure housing which greatly increases the cost.…”