Research Study 1

Fig. 1.  Overlap of environmental DNA signals (numbers shown) between the three sites.  Each tidepool has its own complement of unique DNA, varying from 21 - 30% of the total depending upon tidepool, and extents of overlap are indicated

A person could be forgiven for thinking that tidepools separated by just a few tens of meters would have similar if not the same environmental DNA signatures.  But this has been shown by two Stanford University researchers not to be true for three tidepools in San Mateo County, CA.  The tidepools are within 40m separation distance, and are isolated from one another during low tides, but interconnected at high tides. The researchers sample water from each tidepool at even intervals over a single 5.5h low-tide tide period and analyse for DNA residuals.  Results show the presence of 415 species across 28 phyla with significant differences in species numbers and DNA representation between all three sites (Fig. 1), indicating incomplete mixing between the sites during tidal immersion.  What this means for the average beach walker is unclear, but overall the authors intimate that data so derived can be useful for monitoring changes in community composition during impending climate change.

NOTE  genetic material shed from organisms, in the form of skin, cells, exuvia, mucus, and so on, that has accumulated in the environment, whether it be water, soil, air, or other.  It is useful for tracking presence of hard-to-see organisms, ones that have been present and then recently left, and for biodiversity estimates.  Molecular evidence of this sort may persist for days or hours, depending upon water flow, organismal movements, type of tissue, and many other factors.  As crabs and hermit crabs seem to be among the more abundant organisms common to all three tidepools,  the publication is included in this section of the ODYSSEY

Research Study 2

Fig. 1.  Comparative distributions of saxitoxin concentrations in commercially harvested Dungeness crabs Metacarcinus magister in the Kodiak and Southeast regions of Alaska over three decades from 1993 - 2023.  Other data presented by the authors show that Tanner crabs Chionoecetes spp. harvested in Alaska may be even more severely affected, with up to 100% of individuals containing saxitoxins

When one thinks of Paralytic Shellfish Poisoning (PSP) it is mostly  clams that come to mind, but it may surprise you to know that crabs, notably Dungeness crabs Metacarcinus magister in Alaska are commonly afflicted with the condition.  The crabs prey on bivalves such as clams, mussels, and oysters that contain saxitoxins sequestered from their microalgal Alexandrium catenella-containng foodstuffs, and store them in their own viscera.  The first recorded case of poisoning in humans from eating a crab was in 1992 but, based upon the rate of spread of PSP over the past decades, there is growing risk.  Researchers from a variety of coastal research centres and health laboratories in Alaska and North Carolina write about the disease prevalence in Alaska and note that presently (2025) there is a 60% chance that a Dungeness crab purchased in the Kodiak area of Alaska will contain toxic levels of PSP.  The toxins concentrate in the crabs' viscera, most notably in digestive gland and gonads, and there has been a move by the Alaska Department of Fish and Game in the Kodiak and southeast regions of the state (Fig. 1) to allow sale only of eviscerated crabs.  The authors do not comment on what seems to be particularly intense infestation of saxitoxins in Alaska populations of crabs in comparison with populations elsewhere along the coast.

NOTE  the same applies to other commercially important decapods such as King Paralithodes and Snow (tanner) crabs

NOTE  for crab connoisseurs who consider the tangy and flavourful preparation of mainly digestive gland and gonads of a crab known as "crab butter" to be a favourable taste sensation, this restriction borders on sacrilege.  For a crabophile sitting around a campfire eating fresh crab meat as hors d'oeuvres, it is the next pasta course that would be most anticipated were it to contain a sauce made from the crab's visera.  The taste is unique, delicious, and highly sought after by crab aficionados